DK THE ECOLOGY BOOK

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ECOSYSTEMS 149

The rebirth of
Krakatau

Ecologists also studied the diversity Central Park in Manhattan, New York In 1883, volcanic eruptions
of beetles and flies in nine parks of City, is an “island” in an urban setting. devastated the Indonesian
different sizes in Cincinnati, Ohio. Its checklist includes 134 bird species, island of Krakatau, wiping out
Area was the best predictor of 197 insect, 9 mammal, 5 reptile, 59 flora and fauna on the island
species richness, but when the fungi, and 441 plant species. and nearby Sertung and
ecologists coupled their findings Panjang. By 1886, mosses,
with data on population sizes, they activity, the island theory has also algae, flowering plants, and
calculated that an increased size of encouraged the creation of wildlife ferns had returned to Krakatau,
parkland acts primarily to reduce corridors. These link areas of borne either on the wind or as
extinction rates rather than to suitable habitat, which helps seeds on the surf. The first
provide habitats for new species. maintain ecological processes—for young trees emerged in 1887;
example, allowing animal movement various insect species, and a
Conservation practices and enabling viable populations to single lizard, were discovered
Soon after the island biogeography survive—without requiring a great in 1889. Recent research shows
theory was developed, ecologists expansion of protected areas. ■ that the level of immigration
began to apply it to conservation. to Krakatau and its neighbors
Nature reserves and national parks I will argue that every peaked during the period of
were seen as “islands” in landscapes scrap of biological forest formation, from 1908 to
altered by human activity. When 1921, but extinctions were at
first creating protected areas, diversity is priceless … their height when the dense
ecologists debated the optimum Edward O. Wilson tree canopy prevented sunlight
size: was one big reserve better than from reaching the forest floor,
several smaller ones? As the island between 1921–33. Although
theory shows, biodiversity depends the immigration of land birds
on a number of factors, and different and reptiles has almost
species benefit in different settings. stopped, new species of land
A sizable mammal will not survive mollusk and many insect
in a small reserve, but many small groups are still arriving from
organisms will thrive there. In Sumatra and Java, both just
places under pressure from human under 28 miles (45 km) away.

Krakatau’s deadly eruption sent
up an ash cloud 50 miles (80 km)
high that altered global weather
patterns and caused a temperature
drop of 2.2°F (1.2°C) for five years.

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150

IOTTHFIASNTUTMMHABETECTROESNRSSTANCY

ECOLOGICAL RESILIENCE

IN CONTEXT T he capacity for ecosystems population changes are not as
to recover following a important as whether the whole
KEY FIGURE disturbance—such as a system is being fundamentally
Crawford Stanley large fire, flood, hurricane, severe altered. The resilience of a system
Holling (1930–) pollution, deforestation, or the can be described either by the time
introduction of an “exotic” new it takes to return to equilibrium
BEFORE species—is known as ecological after a big shock or by its capacity
1859 Charles Darwin resilience. Any of these impacts to absorb disturbance.
describes the interdependence can upset food webs, often
between species as an dramatically, and human activity One example that Holling studied
“entangled bank.” is responsible for an increasing was the fisheries of the Great Lakes
number of them. in North America. A large tonnage
1955 In the US, Robert of sturgeon, herring, and other fish
MacArthur proposes Staying resilient was harvested in the early decades
a measure of ecosystem Canadian ecologist Crawford of the 20th century, but overfishing
stability that increases as Stanley Holling first proposed the dramatically reduced the catches.
the number of interactions idea of ecological resilience to Despite subsequent controls on
between species multiplies. describe the persistence of natural fishing, populations in the Great
systems in the face of disruptive Lakes did not recover. Holling
1972 In contrast with changes. Holling argued that
MacArthur, Australian natural systems require stability Ecosystems are dynamic—
ecologist Robert May and resilience, but—contrary constantly changing and
argues that more diverse to what previous ecologists had inherently uncertain, with
communities with more assumed—these are not always
complex relationships may be the same qualities. potential multiple futures …
less able to maintain a stable Crawford Stanley Holling
balance between species. A stable system resists change
in order to maintain the status quo,
AFTER but resilience involves innovation
2003 Australian ecologist and adaptation. Holling wrote
Brian Walker works with that natural, undisturbed systems
Crawford Holling to refine are likely to be continually in a
the definition of resilience. transient state, with populations
of some species increasing and
others decreasing. However, these

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ECOSYSTEMS 151

See also: The food chain 132–133 ■ The ecosystem 134–137 ■ Energy flow The role of budworm
through ecosystems 138–139 ■ Trophic cascades 140–143
Spruce budworm caterpillars
suggested that the intense fishing A thick green scum of algae covers have devastated balsam fir
had progressively reduced the parts of Lonar Lake, in Maharashtra, forests in eastern North
resilience of the ecosystem. India. Algae thrive in high-nutrient America six times since
conditions, but decomposing algae the 18th century. Holling
Holling argued that ecological consume oxygen, and depleted levels of described this process as
resilience is not always positive. oxygen lead to fewer fish surviving. having two very different
If a freshwater lake experiences states: one with young,
a large input of nutrients from components of the ecosystem fast-growing trees and few
agricultural fertilizers, for example, can change. One example is the budworms; and one with
it will become eutrophic: algae will disappearance of most American mature trees and very large
thrive, depleting the lake’s oxygen chestnuts from forests in eastern numbers of budworms.
and making it unsuitable for fish. North America, which was largely
Such a lake may be resilient, but it compensated for by the expansion Between outbreaks of
will become less biodiverse. Holling of oaks and hickories. For Holling, budworms, young balsam fir
claimed that three critical factors this counted as resilience, because grow alongside spruce and
determine resilience: the most a although the exact mix of tree white birch trees. Eventually,
system can be changed before species had changed, broad-leaved the fir becomes dominant.
crossing a threshold that makes forest still remained. A combination of this
total recovery impossible; the ease dominance and a sequence
or difficulty in making a big change Ecologists now understand that of very dry years stimulates
to the system; and how close to the ecosystems can have more than a huge increase in the
threshold a system is currently. one stable state. In Australia, for budworm population. The
example, woodlands dominated by mature fir is destroyed, giving
Changing states mulga trees can exist in a grass- the spruce and birch an
According to Holling’s view, rich environment that supports opportunity to regenerate.
resilience at the ecosystem level is sheep-farming, or in a shrub- By keeping the balsam fir
enhanced by its populations not dominated environment that is in check, the budworm also
being too rigid—meaning that the totally unsuitable for sheep. ■ maintains the spruce and
birch. Without it, the fir trees
would crowd out the others.
So the system is unstable but
at the same time resilient.

Spruce budworm larvae in
Quebec, Canada, feed voraciously
on fir and spruce before they
pupate. Moths emerge about a
month later, ready to mate.

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152

SUPOUNPBPURJLEECADTITCIEOTDNATSBOLAERFEORCES

THE NEUTRAL THEORY OF BIODIVERSITY

IN CONTEXT B iodiversity is shaped Caswell made a bold attempt
globally by new species to create a neutral theory of
KEY FIGURES appearing and others community organization.
Hal Caswell (1949–), becoming extinct. Community
Stephen P. Hubbell (1942–) ecology has traditionally held that Stephen P. Hubbell
interactions between species play
BEFORE a vital role in determining this Neutral theories of biodiversity have
1920 Frederic Clements process. If two species compete for dominated community ecology in
describes how plant species similar resources, for example, either recent years. However, an Australian
are associated with each other the stronger pushes the weaker study of coral reefs, published in
in communities. to extinction, or each is driven into 2014, focusing on once-dominant
a narrower niche of specialism. species that have been almost lost
1926 Henry Gleason proposes to overfishing, did not support the
that ecological communities In 1976, however, American theory. According to Hubbell,
are organized more randomly. ecologist Hal Caswell proposed species are interchangeable, so
a “neutral” theory of biodiversity. It others should have increased to take
1967 Richard Root introduces maintained that ecologically similar their place. The fact that this did not
the concept of the ecological species are competitively equal, and happen in this case suggests that
guild—a group of species whether species become common the neutral theory is flawed. The
exploiting resources in or rare is down to chance processes. question of what maintains diversity
similar ways. remains an open one. ■
The “null” model
AFTER In the early 2000s, American
2018 A review headed ecologist Stephen P. Hubbell
by Dutch ecologist Marten developed a mathematical model
Scheffer suggests that, known as the “null” hypothesis,
although species that use published in The Unified Theory
the same resources may of Biodiversity and Geography (2001),
be competitively equivalent, that supported Caswell’s theory.
they may also differ according He tested his model by studying
to their response to stress- real communities.
inducing factors, such as
drought or disease. See also: Human activity and biodiversity 92–95 ■ Island biogeography 144–149
■ Climax community 172–173 ■ Open community theory 174–175

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ECOSYSTEMS 153

OOTAHFNCELRHYCEAASONEMCCAEOPRMLOCEFMHXUREWRNEVSIHTEOHYALALESING

BIG ECOLOGY

IN CONTEXT A n in-depth understanding affect hydrology, biodiversity, and
of ecosystems requires carbon dynamics—the way carbon
KEY ORGANIZATION long-term study. In 1980, and nutrients move through the
National Science the US National Science Foundation ecosystem. There are many other
Foundation (created 1950) set up six Long Term Ecological long-term research sites worldwide
Research (LTER) sites to study with researchers logging data on
BEFORE long-term, large-scale ecological ecosystems. With free access to
1926 Russian geochemist phenomena. There are currently the information, the research can
and mineralogist Vladimir 28 sites, five of which have been be easily disseminated globally. ■
Vernadsky formulates the running since 1980. Ecologists are
theory of the biosphere amassing datasets that will enable
in which everything on in-depth knowledge to be shared.
Earth lives.
A forest ecosystem Log decomposition is being studied
1935 Pioneering British One of the six original research over a 200-year period at six old-growth
ecologist Arthur Tansley sites is Andrews Forest in Oregon. forest sites in Andrews Forest, Oregon.
defines an ecosystem It provides a good example of a The experiment began in 1985.
as encompassing all the temperate rain forest, enjoying
interactions between mild, wet winters and cool, dry
a group of living creatures summers. With 40 percent being
and their environment. old-growth conifer forest, there is a
high degree of biodiversity across
AFTER its forest, stream, and meadow
1992 At the Earth Summit ecosystems. Ecologists have
in Rio de Janeiro, there is recorded thousands of species of
international consensus insects, 83 bird species, 19 conifer
on the importance of species, and 9 species of fish.
protecting the biosphere. Projects aim to observe how land-
use (such as forestry) and natural
1997 The Kyoto Protocol phenomena (fires, floods, climate)
to reduce greenhouse gas
emissions is signed by See also: The ecosystem 134–137 ■ The biosphere 204–205 ■ Sustainable
192 countries. Biosphere Initiative 322–323 ■ Ecosystem services 328–329

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154

DOTHETPHEEEBNREDSSSTAORSNETRDWAOHTINAETGGY

EVOLUTIONARILY STABLE STATE

IN CONTEXT Animals come into T he field of behavioral
conflict with each other ecology seeks to explain
KEY FIGURE over food, territory, and how the behavior of
John Maynard Smith animals—what they eat, how they
(1920–2004) mate selection. socialize, and so on—has evolved
They have evolved to to suit their particular environment.
BEFORE react to the behavior of The driving force is natural selection
1944 Mathematician John von other animals in certain because the environment favors
Neumann and economist preprogrammed ways. individuals with certain genes—
Oskar Morgenstern use a some genes are “better” for certain
theory of games of strategy to The best strategy situations and not for others—
devise a mathematical theory depends on what which are then passed on to
of economic and social others are doing. offspring. Because the behavior of
organization. animals is influenced by genes,
behavior must be influenced by
1964 British biologist W.D. natural selection as well.
Hamilton applies game theory
to the evolution of social Adaptive behavior
behavior in animals. In 1972, British evolutionary
biologist John Maynard Smith
1965 Hamilton uses game introduced a theory known as the
theory to describe the evolutionarily stable strategy
ecological consequences (ESS), that helped explain how
of natural selection. behavioral strategies appear by
natural selection. Just as factors
1976 Richard Dawkins such as food and temperature can
popularizes the idea of affect animals, so can the behavior
evolutionarily stable strategies. of other species. Maynard Smith
suggested that an ESS adapts to
AFTER the behavior of other animals, and
1982 John Maynard Smith cannot be beaten by competing
applies the theory to evolution, strategies, thus giving animals the
sexual biology, and life cycles. best chance to pass on their genes.
He argued that only natural

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ECOSYSTEMS 155

See also: Evolution by natural selection 24–31 ■ The selfish gene 38–39 ■ Predator–prey equations 44–49 ■ Ecological
niches 50–51 ■ Trophic cascades 140–143 ■ Biodiversity and ecosystem function 156–157

Behavior arising from conflicts behavior can be quantified, balance between two or more
over space and territory might emerge so biologists can work out which strategies within the system
as evolutionarily stable strategies. Fruit strategies are likely to be most as a whole. The overall balance
bats jostle for the best spots in the stable by using mathematical is therefore better called an
trees, with alpha males driving weaker models (see box). If the model evolutionarily stable state, and
bats down to lower branches. does not match the behavior not a strategy. Such a balance
of animals in the real world, then emerges when all individuals have
selection could upset this balance— it suggests that stability has equal fitness: they pass on their
hence why an ESS is “stable”—and not evolved. genes to the same extent. The
that these behaviour patterns are state remains stable, even when
genetically preprogrammed. In real rather than hypothetical there are minor changes in the
ecosystems, it is not a single animal’s environment. ■
ESS has its roots in game theory: strategy that is stable, but the
a mathematical way of working out in posturing. Which strategy
the best strategy in a game. Many The hawk-dove “game” would be better for passing
examples of how animals behave on genes? Maynard Smith and
emerge as being evolutionarily The simplest demonstration his collaborators devised a
stable strategies, such as territorial of John Maynard Smith’s mathematical model to provide
behavior and hierarchies. For evolutionarily stable strategy the answer, and—in this
example, the genetically pre- (ESS) concerns a hypothetical instance—being more hawkish
programmed “rules” of “if resident, response to aggression known than dovish emerged as the
fight and defend” or “if visiting, give as the hawk-dove “game.” In ESS. It predicts a ratio of seven
in and retreat,” which would help this, individuals can either be hawks for every five doves,
animals retain territory, combine hawkish and fight until badly which is equivalent to any one
to make territorial behavior an ESS. injured, or dovish and posture, individual being hawkish
but then retreat. Hawks will seven-twelfths of the time, and
Balancing strategies outmatch doves, but could be dovish five-twelfths of the time.
The payoff that an individual seriously harmed in a fight with
animal gains—or the price it risks another hawk. Doves routinely
paying—by displaying a particular escape injury, but waste time

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156

SSTHPTAEEBCFIIULEINSTCMYTAOIOIFNNETINCAIGONSAYNSDTEMS

BIODIVERSITY AND ECOSYSTEM FUNCTION

IN CONTEXT I n an age when human A phytotron built in 1968 in North
activities are rapidly eroding Carolina, US, now includes 60 growth
KEY FIGURE the complex mix of species in chambers, four greenhouses, and a
Michel Loreau (1954–) different habitats, ecologists have controlled-environment facility for
increasingly focused on how studying plant diseases and insects.
BEFORE biodiversity loss affects the way
1949 At the California Institute ecosystems work. If species are Michel Loreau, director of the
of Technology in the US, the replaced or lost altogether, can an Centre for Biodiversity Theory
first phytotron (research ecosystem remain intact—or does and Modeling in Moulis, France,
greenhouse) is built to study this damage ecosystem function? outlined diverse research; some
how an artificial ecosystem looked more closely at species,
can be manipulated. Such questions were the focus others at what makes an ecosystem
of the Biodiversity and Ecosystem work. Loreau maintains that
1991 In the UK, an Ecotron, Function (BEF) conference held in a new unified ecological theory
a set of experimental Paris in 2000. More than 60 leading is necessary to combat extreme
ecosystems in computer- international ecologists, including
controlled units, is created at
Imperial College, London.

AFTER
2014 Leading ecologists in
the US say that the effect of
diversity loss on ecosystems
is at least as great as—or even
greater than—that of fire,
drought, or other drivers of
environmental change.

2015 A paper published in
Nature provides evidence that
biodiversity increases an
ecosystem’s resilience in a
broad range of climate events.

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See also: Mutualisms 56–59 ■ Keystone species 60–65 ■ The ecosystem
134–137 ■ Organisms and their environment 166 ■ Invasive species 270–273

Biodiversity loss… is likely When researching such issues, Habitat fragmentation
to decrease the ability of ecologists have tended to use both
ecosystems to resist the traditional observational fieldwork Barro Colorado Island in the
effects of climate change. and also sophisticated mathematical Panama Canal of Central
models. More recently, research America was formed in 1914,
Michel Loreau has begun to incorporate the when tropical rain forest was
manipulation of ecosystems flooded by damming, creating
environmental challenges. That, in a more controlled way, on plots an isolated fragment of forest
he says, requires the integration of land, for example, or within surrounded by water. Since
of community ecology (the study of closed systems housed in giant 1946, the area has been
how species interact in ecosystems) greenhouselike facilities called studied in detail by biologists
with ecosystem ecology (research phytotrons. The experiments help of the Smithsonian Institution
into the physical, chemical, and to establish what factors—such as and elsewhere to determine
biological processes that connect numbers of species, or species type the effects of this habitat
organisms and their environment). and dominance—affect ecosystems fragmentation: species
in the long term. Their findings diversity on the island has
Complex cycles show that the effects of biodiversity declined, and top predators are
Scientists of both disciplines firmly on ecosystem functions are among the most vulnerable
believe that biodiversity, especially complex. While the most diverse species. In the US, studies of
species and genetic diversity, is ecosystems tend to be the most habitat fragmentation and its
an important driver of ecosystem productive, their success also effects on diversity in the
functioning. Ecosystems are depends on climate and soil fertility. Florida Keys led to Robert
powered by an input of energy and MacArthur and E.O. Wilson’s
recycling of nutrients: plants and There is more to be learned seminal Theory of Island
animals grow, die, and decompose, about how plant diversity affects Biogeography (1967).
returning nutrients to the soil soil processes, the role of microbe
and restarting the cycle. These biodiversity in the soil, and the From such environments,
processes depend on the species effects of mutualistic species, such planners have learned
within the ecosystems, which in as flowering plants and pollinating important lessons about how
turn depend upon one another as insects. Much has been achieved, to conserve species in isolated
they interact—as predators and but questions remain, and the patches of habitat—sometimes
prey, for example. Many ecologists unifying theory that Loreau is in the midst of cities—that are
argue that a large variety of seeking has still to bedevised. ■ set aside as reserves. Barro
complementary species are needed Colorado, and places like it,
to keep an ecosystem working and One of the distinctive and have also provided vital
make it resilient to change. Others fascinating features of opportunties for study, where
say that a few key species may be ecologists can explore how
more important to stop ecosystems ecological systems is their changing species diversity
from collapsing. extraordinary complexity. affects the functioning of an
ecosystem at every level.
Michel Loreau

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IEONNRAVGCIARHNOAISNN

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MMGISENNGT

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160 INTRODUCTION

Alexander von Humboldt The earliest forms Andreas Schimper shows Frederic Clements coins
sets out for Latin America, of ecological survey how the link between a the term “climax
plant’s physiology and
on an expedition that lays are conducted in external conditions community” for the
the groundwork for modern studies of wild fish is key to plant ecology. process of stabilization
by Stephen A. Forbes. over time in ecological
plant geography.
communities.

1799 1880S 1898 1916

1845 1895 1899

Pierre-François In showing how plants The changing vegetation
Verhulst formulates an are related to their of sand dunes inspires
environments, Johannes Henry Chandler
equation to predict Warming unites the fields of Cowles’ idea of
population growth. botany and ecology. primary succession.

The distribution of organisms represented the true birth of the While studying the vegetation
through space and time is field of ecology. Pioneers included growing on sand dunes along the
a fundamental interest of American naturalist Stephen A. shore of Lake Michigan in the
ecology. Early in the 19th century, Forbes, who studied wild fish 1890s, American botanist Henry
Prussian explorer Alexander von populations in the 1880s, and Chandler Cowles realized that there
Humboldt, a founding father of Danish botanist Johannes was a succession of plant species,
ecology, made detailed studies of Warming, who examined the with “pioneer” plants being
plant geography in Latin America. interaction between plants and replaced by others, which were in
Philip Sclater described the global their environment and introduced turn themselves supplanted. Fellow
distribution of bird species, and the idea of plant communities. American Frederic Clements used
Alfred Russel Wallace did the same the term “climax community”
for other vertebrates, proposing six The link between climate and to describe the endpoint of this
zoogeographic regions that are a region’s dominant vegetation succession. In 1916, he proposed
largely still in use today. type was set out by German that global vegetation patterns
botanist Andreas Schimper, who could be thought of as “formations,”
Communities produced a worldwide classification or large communities of plants—
Early fieldwork concentrated on of vegetation zones in 1898. In the and the organisms that depended
the distribution and abundance early years of the 20th century, on them—which reflected the
of organisms, but later in the 19th ecologists devoted more attention regional climate. In relatively wet,
century scientists increasingly to the interrelatedness of all temperate regions, for example,
recognized that survey data could organisms within an ecosystem, deciduous forest may dominate,
also throw light on interactions exemplified by Russian scientist but grassland tends to dominate
between species. In a sense, this Vladimir Vernadsky’s concept in drier, more temperate areas.
of the biosphere.

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ORGANISMS IN A CHANGING ENVIRONMENT 161

The concept of the Robert May applies James H. Brown and Mathew Leibold’s
“ecological guild” is chaos theory to Robert Maurer devise the “metacommunities”
introduced in Richard predicting rates of concept of macroecology, concept looks at how
B. Root’s thesis on the growth and decline in populations of a single
blue-grey gnatcatcher. animal population in which ecological
patterns are analysed species disperse
dynamics. and interact.
across large areas.

1967 1976 1989 2004
1957 1975 1988 1991

The first satellite goes Citizen science John Odling-Smee Ilkka Hanski outlines
into space, heralding enables Fred and Norah suggests that “niche his metapopulation
new technologies in constructors” actively theory for species in
wildlife tracking. Urquhart to discover change their environment. fragmented habitats.
where monarch

butterflies go in winter.

Clements argued that these climax that “exploit the same class examples, from ancient oxygen-
communities were bound together of environmental resources,” producing cyanobacteria that altered
and could be thought of as single, regardless of how they do it. the composition of the atmosphere
complex organisms. in prehistoric times, to beavers
New ideas creating wetlands.
Clements was soon challenged Many new ideas enriched the
by American botanist Henry study of ecology in the late 20th Modern methods
Gleason, who agreed that plant and early 21st centuries. The Traditionally, the task of monitoring
communities could be mapped, but metapopulation concept was environmental change has been
argued that since individual plant advanced by the Finn Ilkka Hanski, the responsibility of academics
species have no common purpose, who argued that a population of and professional ecologists, but
the idea of integrated communities a species is made up of differing, millions of interested amateurs now
was invalid. His view found support dynamic components. One part of provide enormous amounts of raw
in the 1950s, in the field studies of a population may become extinct, data on everything from flowering
Robert Whittaker and the numerical while another thrives. The thriving dates to butterfly numbers, and
research of John Curtis. element may subsequently help from the state of coral reefs to the
reestablish the population that has breeding populations of birds. With
In 1967, American ecologist died out. computer power to quickly process
Richard Root proposed the idea of vast amounts of data, and with
the “guild,” a group of organisms— In the process, British ecologist Earth’s ecology changing faster
closely related or otherwise—that John Odling-Smee argued, so-called than ever, this “citizen science”
exploit the same resources. Later, “niche-constructor” species create looks set to become an invaluable
ecologists James MacMahon and a more favorable environment for resource for ecology. ■
Charles Hawkins refined the themselves—as seen in countless
definition of a guild to species

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162

POTRHFEENSPAEHTNUITLROWESCIOTOPHNHTNICHEAECLTPSSATSTUTHDEY

THE DISTRIBUTION OF SPECIES
OVER SPACE AND TIME

IN CONTEXT Species are Plants and animals move
distributed over time as Earth and its
KEY FIGURE throughout the world.
Alexander von Humboldt habitats change.
(1769–1859)
The philosophical Scientists study
BEFORE study of nature where and how species
1750 Carl Linnaeus explains connects the live now but also where
that the distribution of plants
is determined by climate. present to the past. they were before, and
what has changed.
AFTER
1831–36 Charles Darwin The distribution, or range, of species’ distributions, but the first
makes various observations biological communities and to make detailed studies of this
on the voyage of HMS Beagle, species varies according to aspect of zoology was the Prussian
confirming that many animals many factors—including latitude, polymath Alexander von Humboldt,
living in one area are not found climate, elevation, habitat, isolation, who traveled to Latin America with
in similar habitats elsewhere. and the species’ characteristics. French botanist Aime Bonpland in
The study of species distribution is 1799. Their five-year expedition
1874 British zoologist Philip called biogeography. Biogeography laid the basis of plant geography.
Sclater produces a description is also concerned with how and Humboldt believed observation in
of the zoogeography (the why the patterns of distribution situ to be paramount, and used
geographical distribution of change over time. sophisticated instruments to make
animals) of the world’s birds. meticulous records of both plant
Early zoologists and botanists and animal species, noting all the
1876 Alfred Russel Wallace such as Carl Linnaeus were well factors that could influence the
publishes his two-volume book aware of geographical variations in
The Geographical Distribution
of Animals, which becomes
the definitive biogeography
text for the next 80 years.

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ORGANISMS IN A CHANGING ENVIRONMENT 163

See also: Modern view of diversity 90–91 ■ Animal ecology 106–113 ■ Island
biogeography 144–149 ■ Big ecology 153 ■ Climate and vegetation 168–169

and New Zealand). The dividing line
between these last two regions,
which runs through Indonesia, is
still known as “Wallace’s Line.”

The unity of nature Plate tectonics Alexander von
means the interrelationship Wallace also made some remarkable Humboldt
discoveries from the fossil record.
of all physical sciences. For example, he worked out that Known as the “founder of plant
Alexander von early rodents had evolved in the geography,” Humboldt also
Humboldt Northern Hemisphere, moving via made valuable contributions
Eurasia into South America. Later, to geology, meteorology, and
data. This holistic approach is best in 1915, German geologist Alfred zoology. Born in Berlin in 1769,
illustrated in his highly detailed map Wegener proposed the radical idea he started collecting plants,
and cross section of Chimborazo that the continents of South shells, and insects at an early
mountain in Ecuador. America and Africa were once age. His expedition to Latin
connected, which allowed the America in 1799–1804
Wallace’s contribution spread of tapirs and other species. encompassed Mexico, Cuba,
Many 19th-century naturalists Venezuela, Colombia, and
contributed to biogeographical Wegener understood that the Ecuador, and his team broke
knowledge, but one of the most distribution of species was in part a the world altitude record when
significant was British naturalist record of geological history. Species they climbed to 19,285ft
Alfred Russel Wallace. After reading colonize new areas as conditions (5,878m) on Chimborazo.
Philip Sclater’s account of the global change, and over time have become
distribution of bird species, Wallace separated by barriers such as Humboldt also speculated
set out to do the same for other new oceans or mountain ranges. that volcanoes result from
animals. He examined all the factors Today, as human-made changes to deep subterranean fissures,
known at the time to be relevant, climate and the environment gather investigated the decrease in
including changes in land bridges pace—creating new barriers—this temperature with altitude, and
and the effects of glaciations. He understanding has taken on a new discovered that the strength
produced maps to demonstrate and vital importance. ■ of Earth’s magnetic field
how vegetation influenced animal decreases away from the
ranges, and he summarized the Tapirs evolved in North America at poles. The 23-volume work
distribution of all known families least 50 million years ago. They spread detailing his expedition set a
of vertebrates. to and now live in Central and South new standard for scientific
America, as well as southeast Asia, but writing, cementing his fame.
Wallace then proposed six died out in North America.
zoogeographic regions, which are Key works
still largely in use today: the Nearctic
(North America), Neotropics (South 1807 Essay on the Geography
America), Palearctic (Europe, north of Plants
Africa, and most of Asia), Afrotropics 1805–1829 Personal Narrative
(south of the Sahara), Indomalaya of Travels to the Equinoctial
(South and Southeast Asia), and Regions of the New Continent
Australasia (Australia, New Guinea, During Years 1799–1804

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164

LOOTIHFFMETTITHHVEIEERDPCTBOOUYPUAULNTLHTIANRETCYFIROEENRATISSILEITY

THE VERHULST EQUATION

IN CONTEXT P ierre-François Verhulst was did not take into account a larger
a Belgian mathematician population’s difficulty in finding
KEY FIGURES who, after reading Thomas food. He argued instead that “the
Thomas Malthus Malthus’s An Essay on the Principle population gets closer and closer
(1766–1834), Pierre-François of Population, became fascinated by to a steady state,” in which the rate
Verhulst (1804–49) human population growth. In 1845, of reproduction is proportionate to
he published his own model for both the existing population and
BEFORE population dynamics, which was the amount of available food. In
1798 Thomas Malthus argues later named the Verhulst equation. Verhulst’s model, after the point of
that populations increase maximum population growth—the
exponentially, based on a Although influenced by the “point of inflection”—the growth
common ratio, whereas food ideas of Malthus, Verhulst realized rate becomes progressively slower,
supplies grow more slowly at that there was a major flaw in his gradually leveling off to reach the
a constant rate, leading to predictions. Malthus had claimed “carrying capacity” of an area—the
potential food shortages. that human population tends to number of individuals it can sustain.
increase geometrically, doubling When visualized, Verhulst’s model
1835 Belgian statistician at regular time intervals. Verhulst produces an S-shaped curve, which
Adolphe Quetelet suggests thought this to be too simplistic, was later called a logistic curve.
that population growth tends reasoning that the Malthus model
to slow down as population
density increases. The hypothesis of Practical demonstrations
geometric progression Verhulst’s model was ignored for
AFTER can hold only in very several decades, partly because he
1911 Anderson McKendrick, special circumstances. himself was not entirely convinced.
working as an army physician, Pierre-François Verhulst However, in 1911, Scottish army
applies the Verhulst equation physician and epidemiologist
to bacteria populations. Anderson McKendrick used the
logistic equation to forecast
1920 American biologist growth in populations of bacteria.
Raymond Pearl proposes the Then, in 1920, Verhulst’s equation
Verhulst equation as a “law” was adopted and promoted in
of population growth. America by Raymond Pearl.

Pearl conducted experiments
with fruit flies and hens. He gave
a constant quantity of food to fruit

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ORGANISMS IN A CHANGING ENVIRONMENT 165

See also: Distribution of species over space and time 162–163 ■ Metapopulations
186–187 ■ Metacommunities 190–193 ■ Overpopulation 250–251

laid fewer eggs and, as their
fertility rate declined, the rate of
population growth slowly stabilized.

Biologists are at the Variable strategies Thomas Malthus
present time in no The two key variables in Verhulst’s
way likely to suffer equation are the maximum capacity Malthus was born in Surrey,
ostracism if they of a species to reproduce (r), and the UK, in 1766, the seventh child
venture to study carrying capacity of the area (K). of a prosperous family. After
human problems. Organisms are either r-strategists studying languages and
Raymond Pearl or K-strategists. R-strategists, such mathematics at the University
as bacteria, mice, and small birds, of Cambridge, he took a post
flies kept in a bottle. Initially, their reproduce rapidly, mature early, as curate of a rural church. In
fertility rate increased. However, and have a relatively short life. 1798, he published an essay
as the population density grew, K-strategists, such as humans, arguing that the rate of
competition for resources increased, elephants, and giant redwood increase in human populations
and eventually reached a bottleneck. trees, have a slower reproduction outstrips much steadier rises
After this, the flies’ fertility rate rate, take longer to mature, and in food production, leading to
dropped; their numbers continued tend to live longer. Ecologists inevitable starvation. Malthus
to increase but slowly, and generally study r-strategists, which are often went on to publish six further
the population level stabilized. found in unstable environments, editions of the essay, and he
to assess risks to their necessary made a number of visits to
Similarly, Pearl found that high reproduction levels, and study Europe to gather population
when the number of hens in a pen K-strategists in more predictable data. In 1805, he was appointed
increased, the birds struggled to environments to ensure long-term Professor of History and
find enough food. As the space species survival. ■ Political Economy at the East
between them reduced, the hens India Company College in
Fruit flies are small, common flies that Hertfordshire. He became
are attracted to ripe fruit and vegetables. increasingly involved in
They are popular for laboratory studies debate about economic policy,
because they reproduce so quickly and and criticized the Poor Laws
are easy to cultivate. for causing inflation and
failing to improve life for the
poor. Malthus died in 1834.

Key works

1798 An Essay on the Principle
of Population
1820 Principles of Political
Economy
1827 Definitions in Political
Economy

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166

IKTTSHHNAEEOWTFNHIALROTESURDTROGRAUEELGOQHOFURISDIETRE

ORGANISMS AND THEIR ENVIRONMENT

IN CONTEXT T he notion of a naturalist— analysis and experiments. These
someone who studies rounded ecological surveys created
KEY FIGURE organisms in the natural a picture of the natural order within
Stephen A. Forbes world—dates back to ancient an environment. By shedding light
(1844–1930) Greece. Aristotle made copious on the interrelated effects of its
observations of wildlife, and his plant and animal life, they could
BEFORE work laid the foundations for later also help explain the distribution of
1799–1804 Alexander von naturalists. It was not until the species and variations over time. ■
Humboldt pioneers the field 19th century, however, that the
of biogeography in his travels potential of such surveys was Satellite images enable ecologists to
in Latin America. really understood. observe large-scale changes easily. The
green areas in this image of the Caspian
1866 German naturalist The new study of ecology Sea are evidence of algal growth—the
Ernst Haeckel coins the term As naturalists undertook longer product of nutrient enrichment.
“ecology” to describe the study field trips, the global distribution
of organisms in relation to of species became more apparent,
their environments. and the concept of ecology as a
science gained traction.
1876 After traveling
extensively, British naturalist One of the first scientists to
Alfred Russel Wallace employ ecological methods was
publishes The Geographical American biologist Stephen A.
Distribution of Animals. Forbes. In the 1880s, while
studying fish in a Wisconsin lake,
AFTER he realized that survey data could
1890s Frederic Clements be interpreted to give a picture of
proposes the notion of interactions between different
ecological communities. species—not just their abundance.
Forbes extended the scope of the
1895 In Ecology of Plants conventional survey, combining
Johannes Warming describes practical fieldwork with theoretical
the impact of the environment
on the distribution of plants. See also: Classification of living things 82–83 ■ Animal ecology 106–113
■ Biodiversity and ecosystem function 156–157

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ORGANISMS IN A CHANGING ENVIRONMENT 167

POTLINMAAENSTDCSIFALFLIEEVREENT

THE FOUNDATIONS OF PLANT ECOLOGY

IN CONTEXT P lant ecology examines how That land is a community
plants interact with one is the basic concept
KEY FIGURE another and with their of ecology.
Johannes Eugenius environments. Danish botanist Aldo Leopold
Warming (1841–1924) Johannes Eugenius Warming first
brought the sciences of botany and American ecologist
BEFORE ecology together in his book The
1859 Charles Darwin’s Ecology of Plants in 1895. He biosphere, the parts of its surface
detailed descriptions of plants described how plants react to their and atmosphere where all living
and animals in their natural surroundings, and how their life organisms exist and interact.
environment mark the start of cycles and structures relate to where
an appreciation of what is later they grow. The book introduced the Plants are sensitive barometers
termed “ecology.” concept of plant communities, and of change within an environment.
outlined how a group of species The study of their anatomy,
AFTER interact and develop in reponse to physiology, distribution, and
1935 British botanist Arthur the same local conditions. abundance, as well as their
Tansley publishes an article in interactions with other organisms
Ecology in which he defines Plants and ecosystems and their response to environmental
the term “ecosystem.” For many years, plant ecology factors, such as soil conditions,
and animal ecology were studied hydrology, and pollution, can
1938 American botanists separately, but in the early 20th provide invaluable information
John Weaver and Frederic century a more connected about the entire ecosystem. ■
Clements further develop the perspective emerged. Important
concepts of plant communities theories on plant communities and
and succession. succession—the process by which
an ecological community changes
1995 David Attenborough’s over time—were established during
television documentary “The this time period. In 1926, Russian
Private Life of Plants” depicts geochemist Vladimir Vernadsky
plants as dynamic influencers introduced the idea of Earth’s
of their environment.

See also: Climate and vegetation 168–169 ■ Ecological succession 170–171
■ The biosphere 204–205 ■ Endangered habitats 236–239 ■ Deforestation 254–259

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168

DTAHIMFEOFENCRGAEUPNSLCEAESNSOTSF

CLIMATE AND VEGETATION

IN CONTEXT T hat different plants grow “Flowering stones” (Lithops) are
in different climates was native to southern Africa, their thick,
KEY FIGURE likely common knowledge fleshy leaves well suited to dry, rocky
Andreas Schimper for as long as agriculture has conditions. Related species also occur
(1856–1901) existed; many cultures have in similar arid habitats in the US.
traded plants for thousands of years.
BEFORE However, the clear link between a plant physiology (the functioning of
1737 Carl Linnaeus’s Flora region’s dominant vegetation type plants), it became the foundation of
Lapponica includes details of and climate was not categorically the study of plant ecology. Schimper
the geographical distribution spelled out until German botanist explained that the connection
of Lapland plants. Andreas Schimper published his between the structures of plants
ideas on plant geography in 1898. and the external conditions they
1807 Alexander von Humboldt faced in different places was the
publishes his seminal Essay Botanists such as Carl Linnaeus key to what he described as
on the Geography of Plants. and Alexander von Humboldt had “ecological plant-geography.”
written about plant distributions in Vegetation was divided into broad
AFTER the 18th and early 19th centuries. tropical, temperate, arctic,
1916 In Plant Succession: The widely traveled Humboldt mountain, and aquatic zones, then
an Analysis of the understood that climate was one subdivided further, according to
Development of Vegetation, of the key factors governing where
Frederic Clements describes plants did and did not grow.
how communities of species Schimper went one step further
are indicators of the climate than Humboldt by explaining
in which they have matured. that similar vegetation types arise
under similar climatic conditions
1968 “The Role of Climate in different parts of the world.
in the Distribution of He then produced a global
Vegetation,” by American classification of vegetation zones
geographers John Mather that reflected this observation.
and Gary Yoshioka, explains
how temperature and rainfall Schimper’s 1898 book Plant-
alone are not enough to define geography upon a Physiological
plant distributions. Basis ran to 870 pages and is one
of the largest ecology monographs
written by a single author. A
synthesis of plant geography and

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ORGANISMS IN A CHANGING ENVIRONMENT 169

See also: Evolution by natural selection 24–31 ■ Ecophysiology 72–73 ■ The ecosystem 134–137 ■ The foundations of plant
ecology 167 ■ Biogeography 200–201 ■ Biomes 206–209

… the time is not far contrivances for regulating the were linked by warm temperatures
distant when all species passage of water.” To illustrate this, and year-round moisture—traits of
he chose a type of vegetation with what he called a tropical rain forest.
of plants and their tough leaves, short internodes (the
geographical distribution distances between the leaves along Although the broad geographic
a stem), and leaf orientation parallel divisions devised by Schimper still
will be well known. or oblique to direct sunlight. This hold true, there is now a better
Andreas Schimper type grew in various parts of the understanding of how vegetation
world, where arid conditions meant develops in response to many
the prevailing climate. For example, that water was scarce. The name different stimuli beyond simple
tropical vegetation was divided into Schimper gave to these plants— climatic differences. For example,
savanna, thorn-forest, woodland, sclerophyll, from the Greek words measures of potential water
tropical rain forest, or woodland skleros (“hard”) and phullon (“leaf”)— evaporation into the atmosphere,
with a pronounced dry season, is still used today. water surplus, and water deficit,
according to whether the climate which can be combined in a
was wet all year round, seasonally Epiphytes, plants that grow on moisture index, are more useful
wet, or mostly dry. the surface of other plants and determinants of plant distribution
derive their moisture and nutrients than simple temperature and
from the air or rain, also fascinated rainfall figures. ■
Schimper. He observed epiphytes
such as Spanish moss growing in Like other epiphytes, Spanish moss
the southern US and the Caribbean lives on other species but draws water
islands and similar species in and nutrients from the air rather than
South America, South Asia, and from its host. It thrives in tropical and
southeast Asia. He found that they subtropical environments.

Adaptations for extremes
Schimper made a close study of
plant physiology—the structures of
plants and how they had adapted to
varying temperature and moisture
conditions. He was particularly
interested in plants growing in
extreme climatic conditions. Salty
environments, for example, require
plants to survive high levels of
soil and water salinity. Schimper
found that vegetation growing on
the coastal mangroves of Brazil, on
Caribbean and Sri Lankan beaches,
and in sulfur-emitting volcanic
craters in Java, were similarly
tolerant to salt.

Schimper also studied how
plants coped in the challenging
conditions of arid environments.
He found that plants growing in
hot, dry places had evolved “varied

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170

IFAHIATVHEIGNRAESATEED

ECOLOGICAL SUCCESSION

IN CONTEXT T he Indiana Dunes comprise 15,000 years ago, there would only
a windswept section of have been bare sand around Lake
KEY FIGURE shifting sand along the Michigan’s shore. Vegetation developed
Henry Chandler Cowles southern shore of Lake Michigan, in a physical gradient, with sand nearest
(1869–1939) US. In 1896, American botanist the water and forests farthest back.
Henry Chandler Cowles saw these
BEFORE dunes for the first time, and so decomposing matter created
1825 Adolphe Dureau de began his career in the emerging favorable conditions for other plants.
la Malle coins the term field of ecology. Dunes are among As these new plants died, even more
“succession” when describing some of the planet’s least stable plants could grow.
new growth in forest cuttings. landforms, and therefore changes
to their ecology happen relatively Based on his observations,
1863 Austrian botanist quickly. As Cowles walked among Cowles developed the idea of
Anton Kerner publishes a the dunes, he noticed that when ecological succession, although
study of plant succession in certain plants died off, their groundwork for the concept had
the Danube river basin. been laid by earlier naturalists. In

AFTER
1916 Frederic Clements
suggests that communities
settle into a climax, or stable
equilibrium, at the end of a
succession period.

1977 Ecologists Joe Connell
and Ralph Slatyer argue that
succession occurs in diverse
ways, highlighting facilitation
(preparing the way for later
species), tolerance (of lower
resources), and inhibition
(resisting competitors).

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ORGANISMS IN A CHANGING ENVIRONMENT 171

See also: Field experiments 54–55 ■ The ecosystem 134–137 ■ Climax community 172–173 ■ Open community theory
174–175 ■ Biomes 206–209 ■ Romanticism, conservation, and ecology 298

Primary succession

The process of primary succession begins in barren
environments such as bare rock. Hardy species, usually lichens,
appear first and then give way to a stable climax community of
more complex and diverse life forms over hundreds of years.

Soil

Bare rock Lichens Small annual Grasses and Grasses, Shade-
plants and perennials shrubs, tolerant trees
lichens and shade-
intolerant trees

Hundreds of years

Pioneer species Intermediate Climax
species community

an 1860 address to members of the include pioneer plants (often lichens resulting from the pioneer species,
Middlesex Agricultural Society, and mosses), followed by grassy shrubs and oak, pine, and hickory
Massachusetts, Henry David plants, small shrubs, and trees. trees will begin to grow. As the
Thoreau had stated: “Though I do trees grow higher, shading out more
not believe that a plant will spring Life after disturbance of the underbrush, the grasses are
up where no seed has been, I have Secondary succession occurs after a replaced by plants able to survive
great faith in a seed.” disturbance that destroys plant life, with low sunlight, and, after around
such as a flood or a fire. The plant 150 years, the forest once more
Growth of an ecoystem life reestablishes itself and develops resembles the prefire community. ■
French geographer Adolphe Dureau into an ecosystem similar to the one
de la Malle is regarded as the first that existed before the disturbance. I … found indisputable
person to use the term “succession” The stages of secondary succession evidence (a) that forests
with reference to ecology when he are similar to those of primary succeeded prairie, and
witnessed the progression of plant succession, although the ecosystem
communities after all the trees may start at different points in the (b) that prairie had
were removed from a forest. Cowles process, depending on the level of succeeded forest.
provided a more formal articulation damage caused by the trigger. Henry Allan Gleason
of his ecological succession theory,
in The Ecological Relations of the A common example of secondary American ecologist
Vegetation on the Sand Dunes of succession occurs after a wildfire in
Lake Michigan, published in 1899. oak and hickory forests. Nutrients
In this seminal paper, he proposed from burned plants and animals
the idea of primary succession— provide the right conditions for
the gradual growth of an ecosystem growth of annual plants. Pioneer
originally largely devoid of plant life. grasses soon follow. After several
The stages of primary succession years, due at least in part to the
environmental and soil changes

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172

MTAHRAEITSUCEROSEM,SGM,RAUONNWDITSDY,IES

CLIMAX COMMUNITY

IN CONTEXT In every region, plants The term “climax community”
grow and develop was first proposed in 1916
KEY FIGURE through a series by American botanist
Frederic Clements of successions. Frederic Clements. He used it to
(1874–1945) At each stage, they describe an enduring ecological
become bigger, community that has reached a
BEFORE more complex, and steady state, such as a naturally
1872 German botanist interconnected. stable forest of old-growth trees
August Grisebach classifies that has not undergone or been
the world’s vegetation patterns Eventually the vegetation subjected to any unnatural
in relation to climate. takes on the most changes, such as logging.

1874 British philosopher complicated interconnected Regional communities
Herbert Spencer suggests that form the climate will allow. In the 19th century, German
the human population can be botanists August Grisebach and
thought of as a giant organism. Once a community Oscar Drude were among those
reaches this who recognized that patterns of
1899 In the US, Henry Cowles vegetation around the world reflect
proposes that vegetation “climax,” vegetation factors such as climate variations.
develops in stages, a process stops changing. It was clear, for example, that the
called succession. typical vegetation in a wet, tropical
climate was very different to that in
AFTER a dry, temperate climate. Then in a
1926 US ecologist Henry landmark paper in 1899, American
Gleason argues that a climax botanist Henry Cowles described
community is a coincidental how plants colonized sand dunes
collection of individuals. around Lake Michigan in stages—
or “successions”—of increasing
1939 British botanist Arthur size and complexity.
Tansley suggests there is not
a single climax community but In an influential book, Plant
“polyclimaxes” responding to Succession (1916), Frederic
various factors. Clements developed Cowles’s
idea, which he combined with the
biogeographic thinking of the two

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ORGANISMS IN A CHANGING ENVIRONMENT 173

See also: The ecosystem 134–137 ■ The distribution of species over space and time 162–163 ■ Ecological succession
170–171 ■ Open community theory 174–175 ■ The ecological guild 176–177 ■ Biomes 206–209

The Sonora Desert is often seen as
an example of a climax community. It
has both winter and summer rains, so
its unique plants, which include the
tall saguaro cactus, are unusually lush.

German botanists to produce stages of growth, he argued that for identifying such a community,
a theory of the development of it can be considered as a single offered by American botanist Frank
natural communities. complex organism. A community Egler in the 1950s, was never
grows toward a climax in the claimed. Despite the difficulties,
Clements suggested that the same way that an individual ecologists continued to use the
way to understand patterns of develops through life stages. theory of a climax community to
vegetation across the world is Clements expanded the idea to decide how to respond to invasive
to think in terms of “formations.” embrace all organisms in a “biome” species that threatened to disturb
A formation is a large, natural that comprised “all the species of an established native community,
community of plants dominated plants and animals at home in a and in recent decades Clements’s
by a range of life forms that reflects particular habitat.” From this, ideas have regained support.
the regional climate. In each region, the idea of the ecosystem as a
plants go through stages or “superorganism” later developed. Succession remains a core
successions until they reach the principle of ecology. In general,
most complex, highly developed A fluctuating process early succession phases consist of
form of vegetation possible. Once Clements’s ideas were challenged fast-growing and well-dispersed
it finally reaches this climax, the from the start, although the idea of species that are replaced by more
community stabilizes, in what a “steady state” proved influential competitive species. Initially,
was later termed a “steady state,” and dominated thinking about ecologists thought that ecological
and stops changing. ecosystems up until the 1960s. succession ended in what they
However, scientists realized that described as the climax phase,
Clements then proposed that communities change constantly in when the ecosystem reached a
climax communities are bound response to conditions, and it is stable equilibrium. However, it
together. Although an ecological almost impossible to observe a true is now accepted that ecological
community is made up of a climax community. A $10,000 prize succession is a dynamic process
multitude of plants at different that is constantly in flux. ■

For Clements, climates are
like genomes, and vegetation

is like an organism whose
characteristics its

genome determines.
Christopher Elliott

Philosopher of science

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174

IBASUNNTAOASTSCAOONCINIOACRTIIGDOEANNNCISEM

OPEN COMMUNITY THEORY

IN CONTEXT Plants grow according to There is no evidence of
their individual needs integrated development
KEY FIGURE
Henry Allan Gleason between plants
(1882–1975)
An ecological They grow randomly,
BEFORE community is not influenced only by the
1793 Alexander von Humboldt environmental conditions
uses the word “association” to an organism
sum up the range of plant
types in a particular habitat. W hen American plant could see none of the integration
ecologist Frederic proposed by Clements. Instead,
1899 In the US, Henry Cowles Clements proposed the Gleason believed that groups of
states that vegetation develops idea of climax communities in 1916, plants were random growths
in stages, in a process he calls he envisioned the community as a of individuals and species,
plant succession. superorganism in which all plants responding to local conditions.
and animals interact to develop the
1916 Frederic Clements posits community. A year later, American Individual needs
the idea of a climax community plant ecologist Henry Gleason Gleason maintained that the
as a single organism. dismissed the idea; he argued that changes that occur during plant
plant species have no common succession, as the composition
AFTER purpose but merely pursue their of a community evolves, are
1935 Arthur Tansley coins own individual needs. Gleason’s not integrated stages, as in the
the term “ecosystem.” hypothesis became known as the development of a single organism.
“open community” theory. The Rather, they are a combination of
1947 Robert H. Whittaker dispute initiated a debate that still responses from individual species
begins field studies that will rages in ecological circles today. as they seek to meet their own
refute Clements’s holistic idea needs within a locality. “Every
of plant communities. Gleason did not deny that plant species of plant,” Gleason argued,
communities could be mapped and “is a law unto itself.” Gleason also
1959 John Curtis boosts their interactions identified, but he
Henry Gleason’s reputation
with numerical studies of
prairie plant communities.

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ORGANISMS IN A CHANGING ENVIRONMENT 175

See also: The ecosystem 134–137 ■ The distribution of species over space and time 162–163 ■ Ecological succession
170–171 ■ Climax community theory 172–173 ■ The ecological guild 176–177 ■ Biomes 206–209

Diseases such as American chestnut
blight challenge the idea of a fully
integrated climax community, as the
loss of the dominant tree species should
cause the entire ecosystem to collapse.

denied that there is any endpoint or need not worry too much about during the 1930s as holism became
climax community; he believed that disturbing the balance of the progressively supported by the idea
communities are always changing. natural environment—because of the interactive “ecosystem.”
there is no balance. Gleason’s ideas
Changing opinions were therefore forgotten in the Nonetheless, as ecologists
Gleason’s argument with Clements enthusiasm for developing ecology continued to study the world, they
caused quite a stir at the time. as a science. He became so found more and more flaws in
Clements seemed to be creating an frustrated that he gave up ecology Clements’s theory. In the 1950s, the
overview in which natural patterns work of American plant ecologists
of vegetation were determined by Henry Allan Gleason Robert H. Whittaker and John Curtis
clear rules, just as in Newtonian showed how impossible it was to
science the movement of the planets Born in 1882, Henry Gleason identify communities as neat units
is dictated by incontrovertible laws. studied biology at the University of holistic theory, and that the real
Clements and his supporters were of Illinois. He held faculty posts world was more nuanced and
able to look at the bigger picture, and conducted acclaimed early complex. When it comes to studying
while Gleason was viewed as a ecological research in Sand ecosystems in the field, Gleason’s
reductionist, myopically intent on Ridge State Forest, Illinois. In ideas seem to provide a better fit.
the details and challenging the the 1920s, Gleason’s theory of
entire idea of ecology as a science individualistic—rather than In the ensuing decades, while
controlled by laws. holistic—plant communities was environmentalists continue to
not accepted by ecologists. This champion holistic ideas, ecologists
Gleason appeared to be saying rejection led Gleason to abandon have also increasingly incorporated
that there are no patterns in nature: ecology in the 1930s. He had Gleason’s concepts into their work.
it is all random. Worse still, he was long held posts at the New York He is now considered to be one
accused by some of justifying Botanical Garden and became of the most significant figures in
exploitative farming, since his famed for his work on plant 20th-century ecology. ■
ideas seemed to imply that man
classification. With botanist
Arthur Cronquist, he co-wrote a
definitive guide to the plants of
the northeastern US. He retired
in 1950 but continued to write
and study. He died in 1975.

Key works

1922 “On the Relation between
Species and Area”
1926 “The Individualistic
Concept of the Plant
Association”

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176

ITTANHHGAEARITSROEIUMEXPNIPLVOLAIFORRISOTWPNEMACYEINEST

THE ECOLOGICAL GUILD

IN CONTEXT E cologists have long sought into its dry, scrubby chaparral
to understand how species environment. The thrasher’s
KEY FIGURE in a community interact to “niche” describes the aspects
Richard B. Root (1936–2013) exploit resources. A key concept of its habitat for which it is
in the explanation of this interplay suitably adapted.
BEFORE is the idea of guilds, first developed
1793 Alexander von Humboldt by American biologist and ecologist Root observed that the Blue-
uses the word “association” to Richard B. Root in 1967. gray Gnatcatcher feeds on insects
describe the mix of plant types that live on oak leaves. By
within a particular habitat. Root had researched the way analyzing stomach contents, he
the Blue-gray Gnatcatcher exploits showed that several other birds
1917 In the US, Joseph its ecological niche for his doctoral
Grinnell coins the term “niche” thesis. The concept of ecological The Blue-gray Gnatcatcher is a
to describe how a species fits niches dates back to 1917, when member of a guild of small birds that
into its environment. American biologist Joseph Grinnell eat insects living on oak trees. Other
used the term to describe how members of the guild include Hutton’s
1935 British botanist the California Thrasher fitted Vireo and Oak Titmouse.
Arthur Tansley identifies
ecoystems—integrated biotic
communities—as fundamental
units of ecology.

AFTER
1989 In the US, James
MacMahon suggests that it
does not matter how ecological
guild members use resources.

2001 Argentinian ecologists
Sandra Diaz and Marcelo
Cabido propose grouping
species that have a similar
effect on their environment.

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ORGANISMS IN A CHANGING ENVIRONMENT 177

See also: Evolution by natural selection 24–31 ■ Predator–prey equations 44–49 ■ Optimal foraging theory 66–67 ■ Animal
ecology 106–113 ■ Open community theory 174–175 ■ Niche construction 188–189 ■ Metacommunities 190–193

also consume oak-leaf insects Different These species Species
and proposed that these oak-leaf species may are linked that
feeding birds could be grouped into by their
a “guild”—the “oak-foliage gleaners exploit shared share a
guild”—because they exploited the the same resource. resource
same resource. resource. can be
grouped
Shared resources in a guild.
Root defined a guild as a group of
species that “exploit the same class The guild concept was a major Richard B. Root
of environmental resources in a breakthrough in thinking about
similar way.” It does not matter connections between organisms American biologist and
whether species in a guild are in ecosystems. The theory implied ecologist Richard Root was
related or not—all that matters is that the entire functioning of an born in Dearborn, Michigan,
how they use their environment. ecosystem could be understood by in 1936. He grew up on a farm,
They do not even have to occupy identifying all the guilds within it. exploring nature and longing
the same niche; they just have to Although that was potentially a to know “how the woods
use the same resource. huge undertaking, ecologists have worked.” By the time he
now managed to identify many completed his doctorate at the
Guilds are typically identified more guilds that confirm links University of Michigan, Root
by the food resource they have in between species. For example, was already a knowledgeable
common, although it could be any the birds of North America can ecologist. His 1967 thesis on
other resource that they share. be grouped into guilds of gleaners, the Blue-gray Gnatcatcher, in
Sharing the same resource means excavators, hawkers, aerial chasers, which he introduced the key
that guild members often compete and scavengers. concept of the guild, cemented
with one another, but they are not his reputation. Root was
necessarily in constant competition. Broad associations invited to join the staff of
For example, although they may In the rush to identify guilds, there Cornell University, where he
compete for the same food, on other was some confusion over just what taught biology and ecology.
occasions they might cooperate to the term meant. By the 1980s, the While there, he researched
deal with predators. American ecologists Charles the relationship between
Hawkins and James MacMahon arthropods (a large group of
…does it matter that a felt the need to redefine the term. invertebrates including insects
particular insect species They argued that the words “in a and arachnids) and goldenrod
is captured by a silken similar way” should be dropped flowers. Root received many
spider web as opposed from Root’s original definition. It awards during his career,
does not matter, they maintained, including the Ecological
to a bird’s beak? whether an organism removes a Society of America’s Eminent
Charles Hawkins and tree leaf to build a nest or for food. Ecologist award in 2003
It is the resource of the tree leaf and its Odum award in 2004.
James MacMahon that matters rather than the way
it is utilized. Either way, the leaf- Key works
users belong to a common guild
because they are exploiting the 1967 “The niche exploitation
same resource. ■ pattern of the Blue-gray
Gnatcatcher”

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THE CITIZEN

NVEOTWLOURKNDTEPEENEDRS OSN

CITIZEN SCIENCE

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180 CITIZEN SCIENCE

IN CONTEXT North American migration pathways

KEY FIGURES KEY Migratory birds
Fred Urquhart (1911–2002), Pacific flyway in North America
Norah Urquhart (1918–2009) Central flyway use paths that can
BEFORE Mississippi flyway be divided into four
1883 The Bird Migration Atlantic flyway north–south zones,
and Distribution recording called flyways—Pacific,
program starts in the US. Central, Mississippi,
1966 The North American and Atlantic. Citizen
Breeding Birds Survey, scientists can play a
conducted by volunteers, key role in recording
begins in Maryland. the birds as they stop
AFTER to feed or rest along
2007 The Global Biodiversity the way, during their
Information Facility (GBIF) flights north in spring
launches a global online portal and south in fall.
for collecting data on plants
and animals from citizen C itizen science is research migration of birds, the Scottish
scientists and professionals. and observation carried enthusiasts using lighthouses
2010 The eBird online project, out by nonprofessional around the coast as observation
created in the US in 2002 by individuals, teams, or networks posts. Then, in the early 1880s, the
the Cornell Laboratory of of volunteers, often in partnership idea of collective observation was
Ornithology for volunteers to with professional scientists. It is extended onto a national scale by
report real-time bird sightings, based on an appreciation that the American ornithologist Wells
becomes a global survey. scientific community should be Cooke, who began a project to show
responsive to the environmental arrival dates for migratory North
Butterflies—millions concerns of society as a whole, and American birds and provide
upon millions … carpeted an understanding that citizens can evidence for migration pathways.
produce reliable scientific evidence Cooke’s project ran until World War
the ground in their that leads to greater scientific II, gathering 6 million data cards
flaming myriads on this knowledge. The involvement of on more than 800 bird species and
Mexican mountainside. ordinary people allows research utilizing 3,000 volunteers at its
bodies to accomplish projects that peak. In 2009, the North American
Fred Urqhuart would be far too expensive or time- Bird Phenology Program began
consuming to run otherwise. to digitize the data from the cards,
which has provided valuable
Early enthusiasts evidence of changed bird migration
While the term “citizen science” dates and routes resulting from
is relatively new, dating from the global climate change.
1980s, the concept and practice
of using the public to observe the The world’s longest-running
natural world and record data has citizen science survey is the
a long pedigree. In the 1870s, Christmas Bird Count (CBC), held
small groups of ornithologists each year in the US. Christmas
in Germany and Scotland began “side hunts” of birds were a popular
to collect reports on the fall pastime in many rural districts
of the US in the 19th century,

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ORGANISMS IN A CHANGING ENVIRONMENT 181

See also: A system for identifying all nature’s organisms 86–87
■ Big ecology 153 ■ The distribution of species over space and time 162–163

regardless of whether the birds a tagging scheme in an attempt Fred and
were suitable for eating. In 1900, to find where the insect ended its Norah Urquhart
Frank Chapman, an officer of the journey after setting out from
Audubon Society—named after southern Canada and the northern Born in 1911, Fred Urquhart
American ornithologist and painter states of the US in fall. They grew up near a railroad line on
John James Audubon—proposed enlisted the help of a small group the edge of Toronto, Canada,
counting birds, rather than of “citizen scientists” to help tag and became intrigued by the
shooting them. He encouraged 27 the wings of the butterflies and monarch butterflies that laid
birdwatchers to participate in the report sightings. From a dozen or their eggs close to the track.
first event, and the counts then so helpers, their Insect Migration After graduating in 1937 from
grew every year. In 2016–17, 73,153 Association, as it became known, the University of Toronto with
observers submitted counts from grew to hundreds of volunteers bachelor’s and master’s
2,536 different locations in North who persisted for years, tagging degrees in biology, Urquhart
and Latin America, the Pacific, and hundreds of thousands of monarchs began to research the
the Caribbean. The data on the with the message “Send to Zoology, butterfly. Having taught
distribution and number of birds University of Toronto.” meteorology to pilots during
has provided a huge data set for World War II, he returned to
ecologists, allowing comparison Despite the Urquharts’ best the university to lecture
over time and between habitats. efforts, the trail went cold in Texas. zoology and married Norah
Finally, on January 2, 1975, two Roden Patterson, another
In search of the monarch amateur naturalists, Ken Brugger Toronto graduate, who joined
Perhaps the most celebrated act of and Catalina Aguado, discovered his quest to find the monarch’s
citizen science was one that set out the butterflies’ wintering site in winter home. Fred Urquhart
to solve the mystery of where the montane forest north of Mexico ❯❯ also worked as Curator of
migrating monarch butterfly went Insects and Director of
in winter. In 1952, a Canadian Observations of birds made and Zoology and Paleontology at
couple, zoologists Fred and Norah recorded by “citizen scientists” in parks the Royal Ontario Museum.
Urquhart, who had long been and gardens can provide ecologists In 1998, Fred and Norah
fascinated by the butterfly, set up with vital data on many species, such Urquhart were awarded their
as the European Goldfinch. nation’s highest civilian
award, the Order of Canada.

Key works

1960 The Monarch Butterfly
1987 The Monarch Butterfly:
International Traveler

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182 CITIZEN SCIENCE

Science should be
dominated by amateurship

instead of money-biased
technical bureaucrats.

Erwin Chargaff

Austro-Hungarian biochemist

Monarch butterflies form a cluster fall. Thousands of people their own homes, but simply
to stay warm during migration. Tagging in Mexico, the US, and Canada to record what they saw in their
by volunteers revealed the monarch’s are helping build an ever clearer gardens, backyards, or streets.
migratory routes, and continues with picture of what routes the monarch By 2018, more than 500,000 people
the annual “Monarch Watch.” follows and how it deals with were participating, recording
changing weather patterns. 7 million birds. The vast amount
City. No tagged monarchs were of data gathered can now be
found, however, and it was not Citizens march on compared for every year back
until the following January that the More volunteer-based projects to 1979. Without public help, this
Urquharts found one—tagged by were launched during the 1960s would simply not be possible.
two schoolboys in Minnesota the and 1970s, including the North
previous August. Citizen science American Breeding Bird Survey, In 1989, the term “citizen
had provided the hard evidence the British Nest Records Card science” first appeared in print,
that the butterflies migrated from project, and a survey of sea turtle in the journal American Birds. It
North America to Mexico. Now egg laying in Japan. In 1979, the was used to describe a volunteer
it is known where millions of Royal Society for the Protection of project sponsored by the Audubon
monarchs spend the winter, the Birds (RSPB) launched the Big Society that sampled rain for
emphasis has changed to tracking Garden Birdwatch in the UK, which acidity. The aim of the project
their movements each spring and did not even require people to leave was to raise awareness of the
acidification of rivers and lakes that
was killing fish and invertebrates,
and, indirectly, the birds that
preyed on them. It was also
designed to put pressure on the
US government, which soon after
introduced the 1990 Clean Air Act.

Citizen science has also proved
its worth for marine conservation.
In the Bahamas, a report in 2012
on declining numbers of the queen
conch, a large sea snail, led to the
formation of “Conchservation,” a
campaign that encourages locals
to tag conches. Another project,
set up in the US in 2010, at the

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ORGANISMS IN A CHANGING ENVIRONMENT 183

University of Georgia, uses an Young volunteers at Siyeh Pass, Painting the
app, the Marine Debris Tracker, in the state of Montana, record their complete picture
to record sightings of debris in sightings of mountain goats for the
the ocean. Understanding patterns high country citizen science project Citizen scientists are now
of trash buildup in the world’s seas in the Glacier National Park. the biggest global providers
helps scientists to track how of data on the occurrence of
it is transported by currents and introduce bias into recordings, living organisms. Data is
where to concentrate removal efforts such as by the omission of a easier than ever to submit
for maximum effect. species that cannot be identified. and artificial intelligence (AI)
algorithms can process data
The advent of new technology Most simple citizen science in minutes where once it
has led to a proliferation of citizen tasks, though, require no training, would have taken weeks. For
science projects. Online recording and some other, more complex, example, if a person records
systems allow people to log procedures can be tackled after sightings of birds coming to
sightings of anything from stag basic tuition. People are often a garden feeder and sends a
beetles to wildflowers or migrating attracted to citizen science precisely report from a phone to Cornell
birds. In the UK, for example, the because they gain new skills in the University’s eBird website, the
Greenspace Information for Greater process. Increasing pressure on information is compared with
London (GiGL) website, created by Earth’s natural environments and previous data on factors such
the National Biodiversity Network, resources creates an ever greater as population numbers and
allows people to submit records need for data that records presence, migration routes. More than
online or by phone, adding to a absence, and change in species, 390,000 people have submitted
database used by scientists working their habitats, and the wider millions of bird sightings to
to conserve species and habitats. ecosystems. Projects such as eBird from nearly 5 million
Zooniverse, the world’s largest locations around the world.
Limitations and potential citizen science platform, help This data is fed into the Global
Some ecology research projects fill this need, accumulating data Biodiversity Information
are beyond the reach of untrained from around 1.7 million volunteers Facility (GBIF, coordinated in
amateurs because they require worldwide. Such projects will be an Denmark), which collects
too high a degree of skill, or invaluable resource for conservation information on plants, animals,
technology that is too complex organizations, research institutions, fungi, and bacteria. GBIF now
or expensive. People unfamiliar nongovernment agencies, and contains more than 1 billion
with scientific methods may also governments for years to come. ■ observations, and the number
is growing daily.
Scientific study often relies on the collection
of large quantities of data.

The more data, the more Volunteer networks are
representative the able to collect vast
results are of reality.
quantities of data, often
from widespread areas.

The citizen’s network depends
on volunteers.

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184

WPRBOEEHPPCEURONLOMATDETHUICECOHTNRAIAODOTNYTENISCOAOFMAIRCSS

CHAOTIC POPULATION CHANGE

IN CONTEXT C haos theory—the idea that Chaos: when the present
predictions are limited by determines the future, but
KEY FIGURE time and the nonlinear the approximate present
Robert May (1936–) nature of behavior—took hold in the
1960s. American meteorologist does not approximately
BEFORE Edward Lorenz observed the effect determine the future.
1798 Thomas Malthus argues in weather patterns, and described
that human populations will it in 1961. Since then, the theory Edward Lorenz
increase at an ever-faster rate, has been applied to many sciences,
inevitably causing suffering. including population dynamics. patterns at the lowest rates of
growth, May found that the logistic
1845 Belgian demographist Chaotic populations equation produced erratic results
Pierre-François Verhulst argues In the 1970s, Australian scientist when the growth rate was equal to
that checks to population Robert May became interested in or above 3.9. Instead of producing
growth will increase in line animal population dynamics, and repeating patterns, the map
with population growth itself. worked on a model to forecast plotted trajectories that appeared
growth or decline over time. This completely random. May’s work
AFTER led him to the logistic equation. showed how a simple, constant
1987 Per Bak, Chao Tang, and Devised by Belgian mathematician equation could produce chaotic
Kurt Wiesenfeld, a research Pierre-François Verhulst, this behavior. His logistic map is now
team in New York, describe equation produces an S-shaped used by demographers to track and
“self-organized criticality”— curve on a graph—showing predict population growth. ■
elements within a system population growing slowly at first,
interacting spontaneously then rapidly, before tapering off
to produce change. into a state of equilibrium.

2014 Japanese ecologist May experimented with
George Sugihari uses a chaos Verhulst’s formula to create the
theory approach called empirical “logistic map,” which showed
dynamic modeling to produce the population trends on a graph.
a more accurate estimate of Although it created predictable
salmon numbers in Canada’s
Fraser River. See also: Predator–prey equations 44–49 ■ Non-consumptive effects of predators
on their prey 76–77 ■ The Verhulst equation 164–165 ■ Metapopulations 186–187

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ORGANISMS IN A CHANGING ENVIRONMENT 185

TTTAHOKEVEBISAIGUDAPILSIICTZTAEUNRTEV,IEW

MACROECOLOGY

IN CONTEXT S cientists seeking faster mammal species, Brown was able
ways to analyze and counter to work out the extinction risk on
KEY FIGURE the many threats to plant each ridge as temperatures rose,
James H. Brown (1942–) and animal populations increasingly and suggest conservation priorities.
turn to macroecology. The term, Enhancing fieldwork
BEFORE coined by American ecologists Macroecology often supplements
1920 Swedish ecologist James Brown and Brian Maurer fieldwork and can lead to surprising
Olof Arrhenius produces in 1989, describes studies that discoveries. In Madagascar,
a mathematical formula for examine relationships between satellite data was used to develop
the relationship between organisms and their environment models for chameleon species and
area and species diversity. across large areas to explain predict them in areas beyond
patterns of abundance, diversity, their known ranges. As a result,
1964 British entomologist distribution, and change. scientists investigating these areas
C.B. Williams documents found several new sister species. ■
patterns of species abundance, Brown had tried and tested this
distribution, and diversity in methodology in the 1970s while By comparing community studies
his book Patterns in the studying the potential effects of made in deserts around the world,
Balance of Nature. global warming on species in cool, macroecologists can determine the
moist forest and meadow habitats greatest threats to a desert species
AFTER on 19 isolated ridges of the Great such as this banner-tailed kangaroo rat.
2002 British ecologists Tim Basin, in California and Utah. He
Blackburn and Kevin Gaston realized it would take years of fresh
argue—contrary to some— fieldwork to collect enough data.
that macroecology should be Instead, he used existing findings
treated as a discipline distinct to draw new conclusions. First, he
from biogeography. predicted how much shrinkage
would occur in the area of ridge-top
2018 A team of scientists uses habitat with an assumed increase
practical macroecological in temperature. Using known data
methods to show that bird on the minimum area required to
species living on islands have support a population of each small
relatively larger brains than
their mainland relatives. See also: Field experiments 54–55 ■ Animal ecology 106–113 ■ Island
biogeography 144–149 ■ Big ecology 153 ■ Endangered habitats 236–239

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186

OAFPPOOPPUULLATAITOIONNS

METAPOPULATIONS

IN CONTEXT A species becomes A species colonizes
extinct in one an empty habitat patch.
KEY FIGURE habitat patch.
Ilkka Hanski (1953–2016)
Extinction and colonization are dynamic processes.
BEFORE
1931 In the US, geneticist A local extinction does not signal
Sewall Wright explores the the extinction of the species.
influence of genetic factors
on species populations. A metapopulation is a other places. The species is like a
combination of separate, family whose members have moved
1933 In Australia, ecologist local populations of the to different cities yet are still
Alexander Nicholson and same species. The term was coined related. The combined effect of
physicist Victor Bailey develop by American ecologist Richard many populations may boost the
their model of population Levins in 1969 to describe how long-term survival of the species.
dynamics to describe the insect pest populations rise and fall
host–parasite relationship. on farm fields. Since then, its use Apart but together
has expanded to cover any species A crucial aspect of metapopulation
1954 In The Distribution and broken up into local populations in theory is the level of interaction
Abundance of Animals, fragmented habitats, both on land between the separate local
Australian ecologists Herbert and in the oceans. populations. If the level is high,
Andrewartha and Charles it is not considered to be a
Birch challenge the idea that A particular species of bird, for metapopulation—all the local
species populations are instance, may be found in separate groups are part of one big
controlled by density alone. populations in a lowland forest, in population. In a metapopulation
mountain woodlands, and various
AFTER
2007 American ecologist
James Petranka links
metapopulation theory to
the metamorphosis stages
of amphibians.

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ORGANISMS IN A CHANGING ENVIRONMENT 187

See also: Animal ecology 106–113 ■ Clutch control 114–115
■ Island biogeography 144–149 ■ Metacommunities 190–193

contact between the various local leaving vacant patches for another Ilkka Hanski
groups is limited, and they remain population to recolonize. Hansk
partly cut off in their own local argued that there is persistent Widely seen as the father of
habitat or “patch.” Yet there has to balance between “deaths” (local metapopulation theory, Ilkka
be at least some interaction. It may extinctions) and “births” (the Hanski was born in Lempäälä,
be just a single brave or outcast establishment of new populations Finland, in 1953. As a child, he
member of one group that enters at unoccupied sites). He likened collected butterflies, and after
another patch and mates with the this balance to the spread of finding a rare species, he
local population there. Isolation for disease, with the susceptible and devoted his life to ecology,
too long pushes local populations the infected representing in turn studying at the universities
apart to the point where they can empty and occupied “patches” of Helsinki and Oxford.
no longer mate with one another, for disease-carrying parasites.
and in time they become separate Ecologists at the time
species or subspecies. Ecologists see the concept of paid little attention to the
metapopulations as increasingly distribution of local species
In the 1990s, Finnish ecologist important in understanding how populations, but Hanski
Ilkka Hanski showed that at the species will survive, particularly realized this was crucial,
core of metapopulation theory is the in the face of human influence on and spent much of his career
notion that local populations are habitats. The theory helps them testing his metapopulation
unstable. The metapopulation as analyze the way populations rise theory by mapping out and
a whole may well be stable, but the and fall, using mathematical models recording more than 4,000
local populations are likely to rise to play out interactions, and enables habitat patches for the
and fall in their individual patches them to predict how much habitat Glanville fritillary butterfly
in response to inside and outside fragmentation a species can endure on the Åland Islands. This
influences. Some patch members before it is driven to extinction. ■ work earned Hanski global
may emigrate and join a much fame, and enabled him to
reduced population in danger The Glanville fritillary butterfly establish the Metapopulation
of extinction, giving it renewed metapopulation, in its fragmented Research Centre in Helsinki,
strength—a metapopulation feature habitats on Finland’s Åland Islands, which became one the world’s
known as the “rescue effect.” Other provided the ideal subject for Ilkka leading focuses of ecological
groups may completely vanish, Hanski’s studies into species patches. research. Hanski died of
cancer in May 2016.

Key works

1991 Metapopulation
Dynamics
1999 Metapopulation Ecology
2016 Messages from Islands

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188

IOCNROWGNASHNTICIRSHUMCTSTHCETHYHAELNIWVGEOERALNDD

NICHE CONSTRUCTION

IN CONTEXT All organisms alter the He argued that they actively
environment to cater to construct and modify their
KEY FIGURE their own needs. Animals environment, and affect their own
F. John Odling-Smee dig burrows, build nests, create evolution in the process: the lynx
(1935–) shade from the sun, and create and the hare, for example, shape
shelter from the wind to provide a each other's evolution and shared
BEFORE more secure environment, while environment by striving to outrun
1969 British biologist Conrad plants alter soil chemistry and cycle each other. Odling-Smee similarly
Waddington writes about nutrients. When organisms modify argued that niche construction and
ways in which animals change their own and each other’s place “ecological inheritance”—when
their environments, calling in the environment, this is “niche inherited resources and conditions
this “the exploitive system.” construction”—a term coined such as altered soil chemistry are
by British evolutionary biologist passed on to descendants—should
1983 Richard Lewontin, an F. John Odling-Smee in 1988. be seen as evolutionary processes.
American biologist, argues
that organisms are active American evolutionary biologist Levels of construction
constructors of their own Richard Lewontin had previously Some common examples of niche
environments, in Gene, suggested that animals are not construction are obvious, while
Organism, and Environment. passive victims of natural selection. others operate at a microscopic
scale. Beavers build impressive
AFTER Hares do not sit around dams across rivers, creating lakes
2014 Canadian ecologist Blake constructing lynxes! But and altering river courses. This
Matthews outlines criteria for alters the composition of the water
deciding whether an organism in the most important and materials carried downstream,
is a niche constructor. sense, they do. creates new habitats for other
organisms to take advantage of,
Richard Lewontin and also changes the composition
of the river’s plant and animal
communities. British biologist
Kevin Laland has suggested that,
while a beaver’s dam is clearly of
great evolutionary and ecological
importance, the impact of its dung
may also be significant.

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ORGANISMS IN A CHANGING ENVIRONMENT 189

See also: Ecological niches 50–51 ■ The ecosystem 134–137 ■ Organisms and Ecosystem engineers
their environment 166 ■ The ecological guild 176–177
Niche constructors have been
Earthworms leave castings that British biologists Nancy Harrison described as “ecosystem
make them valuable natural fertilizers. and Michael Whitehouse have also engineers,” a term coined in
They not only transform the soil for suggested that when birds form 1994 by scientists Clive Jones,
themselves but also help plants to grow. mixed-species flocks—as many do John Lawton, and Moshe
outside of the breeding season— Shachak. They outlined two
Earthworms are highly effective they are altering their relationship kinds of ecosystem engineers.
niche constructors, constantly with competitors to find more food The first, allogenic ecosystem
transforming the soil in which they resources and gain more protection engineers, change physical
live. They break down vegetable from predators. The complex social materials. Take, for example,
and mineral matter into particles environment they create modifies beavers building dams,
small enough for plants to ingest. their own ecology and behavior. woodpeckers excavating
The worm casts they secrete are nest holes, and people mining
five times richer in usable nitrogen, In his explanation of niche for gravel; these activities
have seven times the concentration construction, Odling-Smee pointed modify the availability of
of phosphates, and are about 11 to ancient cyanobacteria, which resources for other species.
times richer in potassium than the produced oxygen as a by-product of When woodpeckers abandon
surrounding soil. photosynthesis more than 2 billion their holes, smaller birds and
years ago. This was a key factor other animals move in. If water
Similarly, microscopic diatoms in the Great Oxygenation Event, floods a gravel pit, ducks and
living in seafloor sediments secrete which changed the composition dragonflies can colonize it.
chemicals that bind and stabilize of Earth’s atmosphere and oceans,
the sand. In Canada’s Bay of Fundy, massively modifying our planet's Other ecosystem engineers
for example, the changes diatoms environment. The oxygen boost are autogenic, which means
make to the physical state of the helped create the conditions for the that simply by growing, they
seabed allow other organisms, such evolution of much more complex life provide new habitats for other
as mud shrimp, to colonize it. forms—including humans. ■ plants and animals. A mature
oak tree, for example, is a
suitable environment for a
broader range of insects, birds,
and small mammals than an
oak sapling. Likewise, a coral
reef provides homes for more
fish and crustaceans as it
grows larger.

A European Starling in Arizona,
US, takes advantage of a hole
abandoned by a Gila Woodpecker
to make its own nest.

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190

TLCHOOACLTOALENXICSCOTHMSAMNGUENITIES IN CONTEXT

METACOMMUNITIES KEY FIGURE
Mathew Leibold (1956–)

BEFORE
1917 Arthur Tansley observes
that two species of Galium
plants grow differently in
different soil patches.

1934 Georgy Gause develops
the competitive exclusion
principle stating that two
species competing for the
same key resource cannot
coexist for long.

2001 Stephen Hubbell’s
“neutral theory” argues that
biodiversity arises at random.

AFTER
2006 Mathew Leibold and
fellow American ecologist
Marcel Holyoak refine and
develop the theory of
metacommunities.

O ne of the limitations
of traditional community
ecology was that it tended
to look at communities purely
locally and take little account of
what happens at different scales
or across different places. Therefore,
over the last few decades, ecologists
have been developing theories of
“meta” communities; the concept
was summed up in 2004 in a key
paper led by American ecologist
Mathew Leibold.

The idea of metacommunities
is linked to that of metapopulations.
While studies of metapopulations
examine the different patches
where populations of the same
species coexist, in metacommunity

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ORGANISMS IN A CHANGING ENVIRONMENT 191

See also: Competitive exclusion principle 52–53 ■ The ecosystem 134–137 ■ The neutral theory of biodiversity 152
■ Metapopulations 186–187

Mountain goats in Colorado live
in a metacommunity of species in
a mountain range—the Rocky
Mountains—but within a population
of goats on one single peak.

theory the different patches consist
of entire communities that include
a number of interacting species.

What is a metacommunity? feed, shelter, or breed. Differing of seemingly contradictory
Metacommunities are essentially types of habitat will influence this observations. One ecologist’s study,
groups or sets of communities. balance between interlinked and for instance, might look at the way
The communities making up a independent development. The species live and interact together
metacommunity are separated in theory of metacommunities provides in a small local community. This
space, but they are not completely a framework for studying how and narrowly focused study finds that
isolated and independent. They why variations develop and their competition between species for
interact as various species move impact on biodiversity and resources is a crucial factor in the
between them. For example, a population fluctuations. workings of the community.
metacommunity might consist of a Another study might look at the
set of separate forest communities, Local versus regional picture across a larger community.
spread across a region. The various A major advantage of looking at This macro-study discovers that
species within each patch of forest communities in this spatial way competition plays virtually no
habitat interact as an independent is that it may help resolve a number part. So which result is correct? ❯❯
community. However, certain
species, including deer or rabbits,
may migrate or disperse to another
community in the metacommunity,
moving to a different patch of forest
in search of better opportunities to

Wildlife crossings Many different species cross from one habitat to another. The
naturally between separate idea of providing wildlife with
habitat patches. This movement ways through is not new. For
can be seasonal, as in annual example, fishways for fish to
migrations, or prompted by bypass dams go back centuries.
natural disasters, such as fire or Wildlife crossings—from bridges
flood, or may take place over long for bears in Canada to tunnels
timespans. It creates connections for California’s desert tortoises—
that are often essential for the are becoming an increasingly
health and survival of species and common feature of construction
communities, providing renewal work. Thousands of crossings,
or new resources at pivotal among them bridges, viaducts,
moments. Increasingly, however, and underpasses—often planted
manmade barriers, such as with vegetation—have been
clearances for agriculture, road, built to conserve habitats and
railroads, and urban sprawl, are to avoid fatal collisions between
breaking up this natural interflow animals and vehicles.

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192 METACOMMUNITIES

The answer may be that both are conflicting theories. It may make stochastic processes, such as the
right, and the difference simply it easier, for example, to resolve spread of a species by freak storms
depends on scale. The benefit of the century-old debate between the or a die-off due to an epidemic.
metacommunity theory is that it “deterministic,” niche-based theory It also acknowledges that regional
allows ecologists to reconcile these of community ecology, in which changes can be caused by the
differences. It enables them to look species diversity is determined combined effect of local ones.
for explanations on both a local and by each species’ ecological
regional scale. niche, and “stochastic” (random) Finding metacommunities
theory, which emphasizes the One of the problems with Leibold’s
A metacommunity might be a importance of chance colonization concept is that in practice it is
set of half a dozen deciduous trees and ecological drift (random not so straightforward to identify
within a park, with each tree an fluctuations in population sizes). the separate components of a
individual community. However, metacommunity. For the fish and
it could equally be all the deciduous Metacommunity theory provides other water creatures in different
forests in temperate zones all around an umbrella framework for seeing lakes within a lake district, for
the world. What metacommunity how deterministic and stochastic instance, each lake may clearly be
theory does is allow ecologists to processes can interact to form a distinct community. However, for
work at any scale, at least in theory. natural communities. It allows those birds able to fly between the
ecologists to state that patterns lakes in minutes, the different lakes
Umbrella framework of biodiversity are determined both are all part of the same single
According to Mathew Leibold, the by local biological features, such community. This may explain why
study of metacommunities brings as the balance of sun and shade in much of the continuing work and
together many seemingly disparate rock pools or variations in water research on metacommunities
branches of ecology and apparently quality in streams, and by regional

Metacommunity

perch dragonfly pond weed
dragonfly
lake 1
lake 2
rushes heron heron frog
frog
lake 3 cormorant

rushes perch mosquito

algae carp cormorant

lake 4 lake 5

duck mosquito algae

mayfly

In this example of a metacommunity, arrows show
how species move between lakes to feed or breed. Seeds
and the spores of algae are dispersed by the wind.

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ORGANISMS IN A CHANGING ENVIRONMENT 193

Rockpools in a wave-cut platform
form a metacommunity on Eysturoy
in the Faroe Islands. The rockpools are
separate between tides, but become
joined as one when the tide comes in.

for a period of time following a
storm, patches of fungal fruiting
bodies that live just a few days
or weeks, and even pitcher plants
that, after dew or rain, provide a
short-lived aquatic home for both
bacteria and insects.

has been theoretical and abstract study and there is a vast literature Blurred communities
rather than rooted in fieldwork. on island biogeography, reaching Leibold’s 2004 paper acknowledged
Some metacommunities are easy back to Charles Darwin’s famous that the metacommunities with
to identify, such as islands in an study of variations between finches blurred boundaries are perhaps the
island group, or rockpools that are in the Galapagos Islands in the hardest to define. Coral reefs, for
separate between tides but joined Pacific Ocean. Neatly separate example, may look neatly separate,
when the tide comes in. In their patches make good subjects for but many of the species that live
2004 paper, Leibold and his study, which is why they have been among them swim freely and
colleagues acknowledged that local popular with community ecologists. respond to a host of changing
communities, or patches, do not But, of course, birds and many outside influences, such as
always have clear boundaries that other organisms blown across by shifts in ocean currents.
make them recognizably separate, the wind or washed in by the sea
and that different species may ensure that even island communities Since most of the world’s life
respond to things happening at a are never completely isolated. This exists within such vaguely defined
different scale. They identified three is why some metacommunity patches, theorists have attempted
kinds of metacommunity: markedly studies focus on the space between further clarification. Leibold and
separate patches; short-lived but the communities even where the his colleagues have suggested
distinct patches that appear in a patches are distinct, as they are two different ways of identifying
habitat from time to time at varying with ponds and lakes, and analyse metacommunities for study:
size; and permanent patches with how species move between them. distinct communities embedded
vague or “blurred” boundaries. within a “matrix” habitat, such
Short-lived but distinct patches as clearings in a forest rich in
Distinct patches may be much harder to identify, resources; and arbitrary sampling
The most obvious markedly separate simply because of their ephemeral patches in a continuous habitat,
patches are islands in the ocean. nature. Nonetheless, ecologists such as a random circle of trees
These are a convenient subject to have made metacommunity studies within a forest.
of holes in trees that fill with water
The work is still at an early
stage. The world is entering a
biodiversity crisis, and countless
species and communities appear
to be under threat from the effects
of human activity. Metacommunity
theory may, in time, help to provide
a better understanding of how
natural communities will respond,
and how local changes to habitats
may ripple through a region, either
adversely or positively. ■

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ETAHRETLHIVI

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NG

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196 INTRODUCTION

Louis Agassiz shows that Svante Arrhenius is the Vladimir Vernadsky’s
an ice sheet once covered first to argue that carbon book The Biosphere explains
Switzerland, and suggests dioxide emissions can lead how atmospheric gases are
that an ice age occurred
in recent geological history. to global warming. created by biological
processes.

1840 1896 1926
1869 1912 1935

The father of biogeography Alfred Wegener presents his Arthur Tansley coins the term
Alfred Russel Wallace theory that Earth was once “ecosystem” to describe
a single landmass from an interdependent
reports a clear evolutionary
division in fauna species which continents community of biological and
drifted apart. nonbiological components.
on neighboring islands.

For centuries, scientists must indicate a truly ancient origin continents were once joined and
in the Western world tried for the planet—an idea which Lyell had broken away. It was not until
to reconcile the findings developed further in the 1830s. the 1960s that a viable mechanism
of geologists and fossil hunters Soon after, Swiss-American was found for such movement.
with literal interpretations of geologist Louis Agassiz proposed Geophysicists discovered patterns
biblical stories about Creation that the topography of some regions of magnetic anomalies running in
and the Great Flood. In 1654, for had been shaped by glaciations. parallel stripes on either side of
example, Archbishop Ussher dated Hutton and Lyell also noted that ocean ridges and identified the
Earth’s creation to October 22, fossils of animals and plants process of seafloor spreading—hot
4004 BCE. A series of discoveries vanished from the geological magma bubbling up through cracks
challenged this narrative and led record. Lyell believed this to be in the oceanic crust and forming
to new ideas about the dynamic evidence of extinction, challenging new crust as it cools and moves
history of life on Earth. the prevailing belief that species away. This gradual process shifts
were immutable. and shapes continents.
Evidence in the rocks
Two Scottish geologists—James Fossils also offered clues to The birth of biogeography
Hutton and Charles Lyell— movements of Earth’s continents. In the Age of Exploration from the
advanced our understanding of German meteorologist Alfred 16th century on, scientists began to
Earth’s age. In Theory of the Earth Wegener noted that similar fossils study the geographical distribution
(1795), Hutton argued that the could be found on both sides of the of plants and animals. By the 1860s,
repeated cycles of sedimentation South Atlantic, even though they Alfred Russel Wallace viewed these
and erosion necessary to create were thousands of miles apart. In patterns, clearly defined by physical
thousands of feet of rock strata his 1912 theory of continental drift, barriers such as mountains and
Wegener cited this as evidence that

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THE LIVING EARTH 197

In their book Bioecology, Eugene and Howard Odum James Lovelock’s Gaia
Frederic Clements and describe the living planet hypothesis presents
Victor Shelford popularize
the idea of the biome. as a global collection of Earth as a single,
interlocking systems. self-regulating system.

1939 1953 1974
1947 1970 1980

Lesley Holdridge’s The first Earth Day is Luis and Walter
biogeographic classification celebrated, and the idea Alvarez suggest that the
maps 38 life zones where that humans should view mass extinction of the
dinosaurs was caused
vegetation is determined Earth holistically
by rain and heat. grows in popularity. by a meteor strike.

seas as a key supporting argument areas at or near the surface of the Almost two centuries earlier Hutton
for evolution. Wallace noted, for Earth where organic life can exist. had articulated a similar idea—that
example, the ocean straits that In 1926, the Russian geochemist biological and geological processes
produced a sharp division between Vladimir Vernadsky explained are interlinked and that Earth could
the flora and fauna of Australasia the biosphere’s close interaction be viewed as a superorganism. In
and Southeast Asia. with the planet’s rock (lithosphere), Hutton’s words, “The globe of this
water (hydrosphere) and air earth is not just a machine but also
With a better understanding of (atmosphere). This in turn led an organized body as it has a
Earth’s biogeography, 20th-century American biologist Eugene Odum regenerative power.”
ecologists divided the planet into to advocate a holistic approach to
biomes—broad communities of flora ecology. Odum argued that it was Heading for extinction?
and fauna that interact in different not possible to understand a single Life has survived on Earth for
habitats, such as tropical rain forests organism, or a group of organisms, billions of years, despite the ravages
or tundra. Botanist Leslie Holdridge without studying the ecosystem in of five mass extinctions. However,
refined the concept in 1947 with his which they live. He described this environmentalists now question
life zone classification, in which he view as “the new ecology.” whether it will survive another.
mapped zones based on the two Indeed, some contend that a sixth
crucial influences on vegetation: In 1974, British scientist James mass extinction has already started,
temperature and rainfall. Lovelock advanced the Gaia as a result of human activity. Yet,
hypothesis that the interaction if Lovelock’s Gaia theory is correct,
A “whole Earth” approach of living and nonliving elements it seems likely that the planet will
The word “biosphere” was coined in the biosphere reveal Earth to be a endure—even if humans and many
by Austrian geologist Edward complex, self-regulating system that other current life forms do not. ■
Suess in 1875 to signify all the perpetuates the conditions for life.

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198

GWTHRAEESAGTGLOPADLC’OISEWR

ANCIENT ICE AGES

IN CONTEXT I n the early 19th century, there Earth’s history has been a process
were contradictory explanations of slow change, punctuated by
KEY FIGURE for the development of Earth’s catastrophic events. The study
Louis Agassiz (1807–73) landforms, plants, and animals. of glaciers, and the landforms they
Supporters of catastrophism argued create, informed these ideas. After
BEFORE that a series of destructive shocks, observing parallel striations in rocks
1795 Scottish geologist James such as the Great Flood described in of the Swiss Alps, German–Swiss
Hutton argues that erratic the Bible, had re-formed the surface geologist Jean de Charpentier (or
boulders (rock fragments that of the planet many times, reshaping Johann von Charpentier) postulated
are different from the existing mountains, lakes, and rivers that glaciers in the Alps had once
underlying rock) in the and wiping out many plant and been more extensive and had
Alps were transported by animal species. In contrast, followers caused the scratches as they moved
moving glaciers. of uniformitarianism contended that and their sediment cut into the rock.
Earth’s features were the result of Geologist Jens Esmark drew similar
1818 In Sweden, naturalist continuous and uniform natural conclusions in Norway.
Göran Wahlenburg publishes processes of erosion, sedimentation
his theory that ice once (the depositing of particles carried Glacier movements
covered Scandinavia. by fluid flows), and volcanism. Swiss zoologist Louis Agassiz
developed Charpentier’s and
1824 Danish–Norwegian Detailed geological studies Esmark’s ideas further. In 1837,
mineralogist Jens Esmark demonstrated that neither camp he proposed that vast sheets of
theorizes that glaciers were was right. They established that ice had once covered much of the
once larger and thicker and northern hemisphere, from the
had covered much of Norway North Pole to the Mediterranean and
and the adjacent seafloor. Caspian coastlines. Agassiz also
undertook some detailed studies
AFTER of glacier movement in Switzerland
1938 Serbian mathematician and published his Études sur les
Milutin Milankovic´ publishes
a theory to explain the Animals enter Noah’s ark in a
recurrence of ice ages based depiction of the Great Flood described
on changes in Earth’s orbit in the Bible. Catastrophists believed that
around the Sun. the Great Flood was one of the formative
shocks that shaped the geology of Earth.