B.5 Bioin ForM atics ( ah l)
the human genome sequence while allowing the company
to house the sequence on their own database. In 2 002 , Science
published a version o the rice genome while allowing the
company Syngenta to keep the data on their own private
database. These two papers broke the industry standard o the
previous 20 years that had seen data being published on the public
database GenBank. It also did not comply with a second tradition
o publication that was much more longstanding. Traditionally
data supporting published reports has always been assumed
to be published and thereore reely available to the scientifc
community so that, at a minimum, verifcation was possible.
Bioinformatics
BLAST searches can identiy similar sequences in
diferent organisms.
Once a researcher frst identifes a sequence o interest by sequencing
a protein, identiying an open reading rame or fnding high levels o a
certain type o mRNA within a cell, their next step would be to conduct
a BLAST search.
The acronym reers to Basic Local Alignment Search Tool. The tool
fnds regions o similarity between sequences. The computer program
compares protein or nucleotide sequences housed in databases
and carries out statistical calculations to determine matches with
other sequences.
There are three main nucleotide databases: GenBank, EMBL and
D D JB . Two o the most important protein sequence databases are PIR
International and SwissProt.
BLASTn and BLASTp searches Figure 1
BLASTn allows nucleotide sequence
alignment while BLASTp allows protein
alignment.
A researcher can identiy open reading rames
in nucleotide sequences. Once an open reading
rame is identiied, a BLASTn search can be
conducted which involves searching through
nucleotide databases to determine i a similar
open reading rame exists in another species.
A BLASTp search uses a protein sequence to search a
protein database.
A BLASTx searches a protein database based on the
translated sequence o an open reading rame.
Alternatively, i a researcher has ound a protein
and wants to determine the location o a gene, they
can conduct a tBLASTn search using a computer
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B BIOTECH NOLOGY AN D BIOIN FORM ATICS
search o multiple genomes using the translated sequence to search
or potential genes that could have been transcribed to produce
the protein.
Figure 1 shows a BLASTn search that is about to be conducted. A
sequence rom human mitochondrial DNA has been entered to search
or similar sequences in mouse DNA.
Matching new sequences with those found in
databases
Databases can be searched to compare newly identifed
sequences with sequences o known unction in other
organisms.
I a researcher has a sequence o unknown unction, they can search a
database to determine i a similar sequence has been identifed in another
organism.
I the sequence were a protein sequence, they could conduct a BLASTp
search. The outcome would allow the researcher to determine i a
protein o similar sequence exists in another organism and what its
unction might be.
I the researched sequence were a nucleotide sequence, they might
conduct a BLASTn search to determine i a similar sequence o
known unction exists in another organism or a BLASTx search to
see i a gene product o a similar sequence has been identifed in
another organism.
Knockout mice
Use o knockout technology in mice to determine gene unction.
One method o determining gene unction is mutation. Figure 2 shows a wild type mouse on
to genetically modiy mice by knocking out the right and an obese (ob/ob) knockout mouse
a gene. This involves replacing the unctional on the let. This is part o the evidence that leptin
sequence with a non-unctional sequence within plays a role in regulating at deposition and
stem cells and then using the stem cells with energy metabolism.
an embryo. The resulting mouse is a chimera.
The chimeras are mated with normal mice.
Heterozygotes are interbred until a purebred
knockout mouse is generated.
The loss o the activity o the gene will oten lead
to a detectable change in the phenotype o the
mouse. This allows researchers to determine the
likely unction o the gene.
The gene or the production o the hormone Figure 2
leptin was knocked out by introducing a point
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Model organisms
Gene unction can be studied using model organisms with
similar sequences.
A model organism is a species that has been extensively studied
based on the assumption that discoveries made in the model
organism will have relevance to other organisms. Some of the most
extensively studied model organisms are Caenorhabditis elegans ( a soil
roundworm) , Mus musculus ( the common house mouse) , Drosophila
melanogaster ( the fruit fly) , Arabidopsis thaliana ( a plant with the
common name Thale cress) , E. coli and Saccharomyces cerevisiae ( yeast) .
The genomes of these organisms have been sequenced as has
the genome of humans. Across the diversity of life, there are
some conserved metabolic pathways and some conserved genetic
sequences. Model organisms can be used as living, or in vivo, models
of diseases related to these conserved pathways or diseases related to
mutations in sequences.
Such studies might not be feasible or might be unethical in humans.
Computer-based sequence alignment
Sequence alignment sotware allows comparison
o sequences rom diferent organisms.
Sequences that are similar between organisms suggest evolutionary
re lationships. The greater the similarity, the closer the re lationship.
Visual comparison is possible when comparing two relatively short
sequences, but comparing longer sequences or multiple sequence
comparison relies on the use of computer algorithms.
There are a number of software programmes used to carry out
sequence alignment including ClustalW and MUSCLE. Increasingly
alignments can be carried out using web-based interfaces. For
example the BLAST search web page of the National Centre of
Biotechnology Information (NCBI) carries out the alignment of two
sequences and the ClustalOmega web page will carry out multiple
sequence alignment.
Figure 3 shows a DNA sequence alignment of nine different
organisms generated using the programme ClustalX.
Figure 3
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B BIOTECH NOLOGY AN D BIOIN FORM ATICS
Sequence alignment tools oten start with the deault o
searching or global relationships over the entire length o the
sequence. However, in terms o unctions, two proteins might
share a ew common areas that are closely linked to a common
unction with other regions having little or no homologous areas.
For this reason, alignment tools oer a choice between local or
global alignment.
Using BLAST to align two proteins
Use of software to align two proteins.
There are a number o applications or aligning two protein
sequences. The ollowing instructions are or using the BLAST
sequence alignment tool at the NC B I website ( http: //www. ncbi.
nlm.nih.gov/protein/) . In this example, we will conduct a sequence
alignment using the cytochrome oxidase (cox1 ) protein or two
species o primates called tarsiers. Horsfeld' s tarsier, variously
classifed as Cephalopachus bancanus and Tarsius bancanus, is a
threatened species that lives in Borneo and Sumatra. The cox1
sequence or this tarsier will be compared to the sequence o the
same gene or the Philippine tarsier ( Tarsius syrichta) . There is some
uncertainty over the classifcation o Horsfeld's tarsier and it is this
type o sequence comparison which is oten used to resolve this kind
o controversy.
Figure 4 Horsfelds tarsier Figure 5 Philippine tarsier
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Choose the protein
database rom the
NCBI site and enter
cox1 tarsius
From the next screen,
choose FASTA and the
sequence or the
protein will be shown.
Alternatively, copy the
two accession numbers:
NP_148740.1 and
YP_002929466.1
Go to the BLAST home page,
( h tt p : //bl a st. n cbi. n l m .
nih.gov/Blast.cgi) ,
choose protein, blast.
Figure 6 Using BLAST to align two proteins On the Enter Query
Sequence page, check
the box or sequence
alignment, paste in the
accession numbers and
click on the BLAST
button.
Scroll down to review
the diferences between
the sequence or this
protein in the two
species.
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B BIOTECH NOLOGY AN D BIOIN FORM ATICS
Multiple sequence alignment
Multiple sequence alignment is used in the study
of phylogenetics.
Phylogeny is the evolutionary history o a species or a group o species.
A phylogenetic tree is a diagram that describes phylogeny.
When multiple sequences are compared, a consensus sequence is oten
identifed based on the amino acid or nucleotide that appears at a certain
position in the aligned sequences. As an example, i you aligned six
sequences and the nucleotides at position 1 0 are G, A, G, G, C and G,
then the consensus sequence will have a G at position 1 0.
Similarities in sequences can be caused by actual evolutionary
relationships in which case the sequence similarities are said to
homologous. Alternatively sequences which are the same by chance are
reerred to as analogous.
Most homologous sequences have many positions where mutations
have occurred several times. However, not all mutations have the
same eect. A mutation in a coding region which results in a change
in amino acid sequence is less likely to persist in a population. The
probability o a match by chance is higher or DNA sequences than
it is or protein sequences. Nonetheless, computer based algorithms
have been developed that can use sequence alignments to suggest
evolutionary relationships.
Constructing phylograms and cladograms using computer applications
Use of software to construct simple cladograms and phylograms of related
organisms using DNA sequences.
A phylogenetic tree that is created using the 3 Choose the species that you want to be
cladistics methods discussed in sub-topic 5.4 included in the tree.
is a cladogram. This type o tree only shows a
branching pattern and the length o its branch 4 Under the Genomic regions, transcripts and
spans do not represent time or the relative products, choose FAS TA.
amount o change that occurs along a branch.
A phylogram is a phylogenetic tree that has Highlight all o the DNA sequence including the
branch lengths that are proportional to the title (or example >gi|1 961 23578:5667-7670
amount o character change (see fgure 8) . Homo sapiens neanderthalensis.)
The ollowing activity requires the use o two 5 O pen either Notepad rom your PC or TextEdit
types o sotware: ClustalX and PhyloWin. This on a Mac.
activity is based on an activity developed by
the American Museum o Natural History. In 6 Paste your sequence into the text editing
this activity, we will conduct multiple sequence document.
alignment or the gene or cytochrome oxidase or
a number o primate species. 7 Repeat with several other sequences rom
dierent organisms.
1 Visit the NC B I website and choose gene.
8 Edit the titles but remember to include the >
2 Search cox1 primate. symbol and to separate words in the title with
an underscore. For example: >Homo_sapiens_
neanderthalensis.
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Figure 7 A screen capture of an image generated using PhyloWin
9 When your document is complete, there is an cytosine to a thymine back to a cytosine back
extra step or Mac users. Under the Format to a thymine is a possible series o events, but
menu choose make plain text. maximum parsimony presumes that the change
was simply cytosine to thymine. This means that
10 Save your fle as sequences.asta you are choosing the tree that involves the least
evolutionary change. Figure 8 is one possible
11 Open the ClustalX sotware. phylogenetic tree showing the evolutionary
relationship o the nine primates.
12 Under the File menu, chose load sequences.
Figure 8 A phylogram
13 Browse your fles and open the sequences.
asta fle.
14 Once the sequences are loaded, choose do
complete alignment under the Alignment
menu. Make a note o where the output fle
sequences.asta.aln is saved.
15 Open PhyloWin.
16 Browse or the sequences.asta.aln sequence.
17 In the tree building window, choose max.
parsimony. There are a number o possible ways
the sequences could have ended up the way
they have. For example, a change between a
Expressed sequence tags
EST is an expressed sequence tag which can be used to
identify potential genes.
I a gene is being expressed, then mRNA transcribed rom that gene will
be ound within the cell. The mRNA can then be used to search or the
gene that produced it using expressed sequence tags ( E STs) .
Scientists use the mRNA along with the enzyme reverse transcriptase to
produce cDNA. This cDNA will not have any introns in it. Scientists use
this DNA to synthesize ESTs. These are short sequences o DNA about 200
to 500 nucleotides long that are generated rom both the 5 end and the
3 end. The 5 end tends to have a sequence that is conserved across species
and within gene amilies. The 3 end is more likely to be unique to the gene.
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B BIOTECH NOLOGY AN D BIOIN FORM ATICS
Using ESTs to The location o the gene within the genome then can be located through
locate genes physical mapping techniques or by searching through database libraries
o known ES Ts.
Discovery o genes by
EST data mining. Exploring chromosome 21
Because o their useulness and Explore the chromosome 21 in databases (or example
the ease with which they are in Ensembl).
generated, a very large number
o ESTs have been generated. The Ensembl project collates genome inormation or 75 organisms.
The sequences have been It allows or detailed exploration o the coding and non-coding
deposited within their own sequences o each o the chromosomes rom these species.
database called dbEST. This
database contains ESTs rom Chromosome 21 is the shortest human chromosome and perhaps best
over 300 organisms. Scientists known or Downs syndrome, or trisomy 21 .
can conduct a BLAST search
once they have an EST to activity
determine i it matches a DNA
sequence rom a known gene To explore the inormation available about chromosome 21, visit the website o
with an identifed unction. the web-based database Ensembl (www.ensembl.org) .
The frst column shows the position o the centromere as being acrocentric
which means to one side o the middle.
1 Click on a red bar to go to a detailed view o that coding region.
2 Click on three protein coding regions to determine the gene that they code or.
The search can be refned by looking at protein coding regions to determine
what genes have a locus on the chromosome.
Visually, it can be seen that there the q arm (the longer arm) has ar more
coding sequences per unit length that have been discovered.
600
Questions
Questions
1 Release o sewage in marine waters is a c) For an accidental sewage spill, suggest,
common practice but it can cause water giving a reason, which o the two
contamination with pathogens. A series o microbes may be most useul as a ecal
experiments were conducted to compare indicator two days ater the spill. [1 ]
inactivation rates o two dierent groups o
microbes with dierent sunlight exposures.
One group were ecal coliorm bacteria and the 2 Wastewater rom actories producing polyester
fbres contains high concentrations o the
other were coliphage viruses. Experiments were
chemical terephthalate. Removal o this
conducted outdoors using 300-litre mixtures o
compound can be achieved by certain bacteria.
sewage-seawater in open-top tanks.
The graph below shows the relationship
A two-day experiment was carried out with between breakdown o terephthalate and
untreated sewage added to seawater. B oth conversion into methane by these bacteria in an
days were sunny with no clouds. The fgure experimental reactor.
below shows the inactivation o the microbes
in seawater as a unction o the cumulative 4 100
amount o sunlight and time. The survival terephthalate concentration 80
curves o the two microbes are plotted against methane production
sunlight exposure (lower x axis) during daylight
periods and against time during the overnight 3
counts of bacteria virises/100 ml-1
concentration/mg dm-3
m e t h a n e /m l
period (upper x axis) . The y axis gives counts o 60
bacteria and viruses per 1 00 ml. 2
hours after untreated sewage added 40
20
0 5 10 15 20 25 30 1
105
Day 1 Day 2
104 00
4 8 12 16 20
103 t i m e /d a y s
102 Source: Jer-Horng Wu, Wen-Tso Liu, I-Cheng Tseng, and Sheng-Shung
Cheng, Characterization of microbial consortia in a terephthalate-
10 degrading anaerobic granular sludge system, Microbiology,
Volume 147 (2001) , pp. 373382, Society for General
Microbiology. Reprinted with permission.
dark period a) The reactor has a volume o 1 2
litres. Calculate the initial amount o
<1 20 25 30 35 terephthalate in the reactor.
5 10 15
cumulative amount of sunlight/MJ m-2 [1 ]
coliphage viruses b) Describe the relationship between [2]
fecal coliform bacteria terephthalate concentration and
methane production.
Source: adapted from L W Sinton, et al., (1999) , Applied and
Environmental Microbiology, 65 (8) , pages 3605 3613 c) Suggest which bacteria can be used or
the degradation o terephthalate. [1 ]
a) Identiy the time at which ecal [1 ] d) Evaluate the efciency o the
coliorm bacteria counts ell below terephthalate breakdown into methane. [2]
1 unit per 1 00 ml.
b) Deduce, using the data in the graph, the
eect o sunlight on
(i) ecal coliorm bacteria. [2]
(ii) coliphage viruses. [2]
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B BIOTECH NOLOGY AN D BIOIN FORM ATICS
3 The evolution o hemoglobin molecules has a) State how many years ago the hemoglobin
been studied extensively by comparing the
amino acid sequences in both myoglobin and split into chains and chains. [1 ]
hemoglobin. Myoglobin is used or oxygen
storage while hemoglobin is used or oxygen b) Estimate the number o gene duplication
transport. Ancient prehistoric animals had a
single chain o simple globin or oxygen storage events that have occurred rom the
and transport. About 500 million years ago, a
gene duplication event occurred and one copy simple globin. [1 ]
became the present day myoglobin and the
other evolved into an oxygen transport protein c) Using fgure B, compare the phylogenetic
that gave rise to the present day hemoglobin.
relationship o myoglobin with vertebrate
The ollowing fgures are phylogenetic trees o
hemoglobin in dierent organisms. and invertebrate hemoglobin. [1 ]
d) Suggest a reason or the dierence in
unction o hemoglobin between plants
and animals. [1 ]
e) Explain why changes observed in the
sequence o amino acids may lead to an
underestimate o the actual number o
mutations. [2]
Figure A Note: each shaded area o the chromosomes below represents a gene.
chromosome 22 chromosome 16 chromosome 11
Mo 1 2 1 A z
millions of years ago 0 primates higher chains chains
mammals hemoglobin
myoglobin
200 mammals
400 bony sh
lampeeys
600
800 simple globin
1000
Source: Adapted from C K Mathews, K E van Holde and K G Ahern (2000) , Biochemistry, 3rd edition,
Benjamin Cummings, page 241
Figure B
taxa protein function induced by
O2 transport low O2
vertebrate hemoglobin O2 storage
vertebrate myoglobin
invertebrate hemoglobin O2 transport low O2?
plant hemoglobin O2 storage low O2?
protist hemoglobin electron light (alga)
bacteria hemoglobin transfer low O2
cyanobacteria phycocyanin electron light
transfer
harvest light
Source: R Hardison (1999) , American Scientist, 87, pages 126137
602
C ECOLOGY AND CONSERVATION
CInEtroLduLctioBn I O L O G Y
Ecology is research into relationships between ecosystem. Changes in community structure
organisms and their natural environment. affect and are affected by organisms. Human
It underpins conservation measures that are activities impact on ecosystem function. For
1 .1 U l tra stru ctu re o f cel lsaimed at ensuring the survival of as much of
the Earths biodiversity as possible. Community
this reason, entire communities need to be
the target of conservation in order to preserve
structure is an emergent property of an b io d i v e r s i ty.
C.1 Species and communities
Understanding Applications
The distribution o species is aected by Distribution o one animal and one plant
limiting actors. species to illustrate limits o tolerance and
zones o stress.
Community structure can be strongly aected
by keystone species. Local examples to illustrate the range o ways in
which species can interact within a community.
Each species plays a unique role within a
community because o the unique combination The symbiotic relationship between zooxanthellae
o its spatial habitat and interactions with other and ree-building coral reespecies.
species.
Interactions between species in a community
can be classifed according to their eect.
Two species cannot survive indefnitely in the
same habitat i their niches are identical.
Nature of science Skills
Use models as representations o the real Analysis o a data set that illustrates the
world: zones o stress and limits o tolerance distinction between undamental and realized
graphs are models o the real world that have niche.
predictive power and explain community
s tru ctu re . Use o a transect to correlate the distribution o
plant or animal species with an abiotic variable.
603
C ECOLOGY AND CONSERVATION
TOK Limiting factors
How do human values underlie the The distribution o species is aected by limiting actors
pursuit o truth in science? How, i at
all, do they infuence methodology? A limiting actor is the actor that is most scarce in relation to an
organisms needs.
In scientic investigations, scientists
have to choose between hypotheses. Plant distributions are aected by abiotic variables: temperature,
Inevitably, human values like simplicity, water availability, light intensity, soil pH, soil salinity and availability
accuracy o data and explanatory power o mineral nutrients. Every plant species has a range o tolerance or
are oten used in choosing between each o these actors, and is excluded rom areas that are outside the
hypotheses. Ecological systems range or one or more o the actors. For example, plant species rom
are oten difcult to reduce to single the tropics are not adapted to survive rosts so would not survive in
independent and dependent variable northern regions. Plants rom these northern regions have chemicals
cause and eect relationships. The in their cells that act like anti-reeze and prevent rost damage rom
mistaken presumption is that across the ice crystal ormation. However, these northern plant species are not
sciences there is a uniormity o values. adapted to grow in the tropics. They would transpire excessively
and their method o photosynthesis would be very inefcient at
In statistical testing, we test null high temperatures.
and alternate hypotheses. There
are two types o error that can occur Animal distributions are aected by temperature, water, breeding sites,
in hypothesis testing. The null ood supply and territory. E xtremes o temperature require special
hypothesis is a hypothesis that a given adaptations. For example, the large ears o elephants are adaptations or
actor has no observable eect. An dissipating heat. This allows them to live in hot environments. Some
experimenter can mistakenly reject the animals have adaptations or living in arid conditions. For example, the
null hypothesis when it is true. This is kidneys o desert rats have longer loops o Henl.
a type I error. Second, an experimenter
can accept the null hypothesis when Many species o animals need a special type o breeding site and can only
it is alse. This is a type II error. It is not live in areas where these sites are available. The natterj ack toad ( Epidalea
possible to minimize the likelihood o calamita) is native to sandy and heathland areas o northern E urope. The
one type o error without increasing pools in which they lay their eggs need to have a very slight slope with
the likelihood o the other type o sparse vegetation on the banks and in the water.
error. This choice involves a value
judgement. For example, i our null Some species o animals establish and deend territories either or
hypothesis says that an introduced breeding or or eeding. Some animal species have very specifc ood
species does not have an eect on the requirements, or example the leaves o only one plant species, which
host community, then minimizing a limits their distribution.
type I error will make it more difcult to
reject the null hypothesis even when it Food supply can aect animal distribution. Birds o temperate regions
is alse. Similarly, minimizing a type II migrate because o the diminished ood supply brought on by winter
error will make it much easier to reject and also to escape cold weather. Tropical birds migrate because o the
the null hypothesis even though it is diminished ood supply brought on by the dry season.
true. Which error we avour involves a
value judgment. Using transects
Use o a transect to correlate the distribution o plant or
animal species with an abiotic variable.
A sample is random i every member o a population has an equal
chance o being selected in the sample. A transect is a method used
to ensure that there is not bias in a students selection o a sample
and it can be used to correlate the distribution o a plant or animal
species with an abiotic variable. For example, a transect rom an area
o grassland into woodland would reveal changes in distribution
associated with light intensity and other variables.
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C.1 SpeCieS anD COmmUniTieS
There are a number o types o transects including: Figure 1 Students carrying out a survey o
the plants in a grassy area by combining two
Line transects where a tape is laid along the ground between two diferent methods. The quadrat (square grid)
poles. In a line transect, sampling can be confned to describing all is being used at intervals along a line transect
o the organisms that touch the line or distance o samples rom (straight line) . This is sometimes reerred to
the line can be recorded. as an interrupted belt transect
Belt transects are where sampling is carried out between
two lines separated by a fxed distance such as 0.5 metres or
1 .0 metres.
Point transects are used in studies o bird populations.
Randomly selected points are selected and the researcher
stands at that point and makes observations within a certain
radius o the point.
Dt-bsd qustos: Intertidal zonation
The kite diagram (fgure 2) illustrates the distribution o common
intertidal species 300 m south o Bembridge Lieboat Station on
the Isle o Wight, UK. The thickness o the shaded region indicates
whether the organism is abundant, common, requent, occasional or
rare according to the key (abundance scale) .
height above shingle large shallow rock pool
edge of ledge
chart datum(m) sand
abundance scale shore distance
4 = 5m
nteromorpha sp. 1
Fucus spiralis
Arenicola marina
Fucus serratus
Sargassum muticum
Littorina mariae
Anemonia viridis
Littorina littorea
Chondrus crispus
Patella vulgata
S. balan oides
Laminaria digitata
Gibbula cineraria
Laurencia pinnatida
Nucella lapillus
A C FO R
Figure 2 Species abundance as a unction o distance rom the shore
1 Examine the kite diagram and explain the methods used to [3]
collect the data.
2 State the species that is most abundant in the survey area. [1 ]
3 Using the scale bar, determine the length o the large shallow
rock pool. [2]
4 Deduce one species adapted to: a) shingle b) sand c) [3]
rock pools.
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C ECOLOGY AND CONSERVATION
5 Several species are only ound near the lower edge o the
intertidal zone. Suggest reasons or them being absent rom the
upper parts o the intertidal zone. [4]
6 Using the data in the kite diagram, predict two species that are
adapted to the same abiotic environment. [2]
Ecological models
Use models as representations of the real world: zones of stress and limits
of tolerance graphs are models of the real world that have predictive power
and explain community structure.
Figure 4 is a model o how environmental appears to preer a water depth o approximately
gradients aect population levels o a species. 20 to 60 cm. Further increases o depth cause a
The range o values o a biotic or abiotic actor precipitous decline in the dry biomass o the plant
that is tolerated is a characteristic o a species, (see fgure 3).
but within a population there is variability. S ome
members o the population are more tolerant o 80 transplants without competition
extreme conditions than others and the limits o 70 (g. ash-free dry wt./tub)
tolerance and where the zones o stress start is 60
sometimes difcult to quantiy. Another limitation 50 20 60 70
o the model is that it is oten presented as a 40 water depth (cm)
symmetrical graph, when a shortage may have 30
a more acute aect than an abundance or vice 20
versa. For example, there is oten an upper limit 10
o a toxin that can be tolerated but oten no lower 0
limit. Consider the eect o water depth on the
broadlea cat-tail ( Typha latifolia) rom Michigan -20
state in the US . It can grow out o water, but
Figure 3
lower limit of tolerance optimum range upper limit of tolerance
populations zone of zone of area of greatest abundance zone of zone of
high intolerance stress stress intolerance
species low low species
absent population population absent
low low
Figure 4 gradient high
606
C.1 SpeCieS anD COmmUniTieS
Application of an ecological model
Distribution of one animal and one plant species to illustrate limits of tolerance
and zones of stress.
Dt-bsd qustos 180 relative shoot dry mass (grams)
160
In the graph in fgure 5, the relative shoot 140
mass is shown or two plants in increasing 120
concentrations o NaC l: sea blite (Suaeda 100
maritima) is represented by the green line and 80
the salt water cress ( Eutrema halophilum) is 60
represented by the red line. 40
20
Use the graph to suggest the value o the
ollowing: 0
0
1 The optimum range o NaCl concentration
Figure 5
or both plants [1 ]
2 The starting value o the lower zone o 200 400 600 800
NaCl (mM)
stress. [1 ]
3 Explain why it is difcult to determine the
limits o tolerance or the two plant species
rom the data given. [3]
Dt-bsd qustos: Maintaining conditions or aquarium fsh
Ornamental fsh or decorative aquariums are Maintaining the water quality within the
sometimes captured rom wild populations in range tolerated by the fsh is important or
the Amazon and exported. One study ound minimizing mortality.
that between 30 and 70% o the fsh captured
die beore being delivered to the fnal consumer. Table 1 shows the lower and upper lethal
The cardinal tetra ( Paracheirodon axelrodi) is the limit o temperature at which 50% o fsh do
most popular ornamental fsh in terms o export not survive ( LT50) , the lower and upper lethal
demand. According to one case study, our out pH (LC50) , and the upper LC50 o ammonia
o fve fsh imported rom Brazil into the US and nitrite.
were lost due to mortality.
Tolerance
LT Acid pH LC N i tri te
50 50
Low temp. High temp. Alkaline pH Ammonia
19.6 C 33.7 C 2.9 8.8 23.7 mg/L 1.1 mg/L
Table 1 Lethal lower and higher temperatures (LT ) , and lethal concentrations (LC ) of acid
50 50
and alkaline pH, total ammonia and nitrite to cardinal tetra (Paracheirodon axelrodi)
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C ECOLOGY AND CONSERVATION
1 Sketch a possible zone o tolerance graph or Figure 6 Cardinal tetras (Paracheirodon axelrodi)
temperature and another one or pH or the in an aquarium
cardinal tetra.
2 Sketch an upper zone o tolerance graph or
ammonia and nitrite.
3 Use your models to suggest the optimum
values o these water qualities to
recommend to shipping agents who handle
the cardinal tetra.
The niche concept vol u m e
Each species plays a unique role within a communitynumber of individuals
because o the unique combination o its spatial habitat
and interactions with other species.
Within an ecosystem, each species ullls a unique role, called its ecological
niche. This includes the spatial habitat (where the species lives in the
ecosystem) , how the species obtains its ood and the interactions with other
species. For a species to be able to inhabit an area, there must be a suitable
habitat where the abiotic variables which infuence its survival are within
the zone o tolerance. It must be able to obtain or synthesize ood, and the
other species with which it needs to interact must also be present.
Competitive exclusion principle
Two species cannot survive indefnitely in the same
habitat i their niches are identical.
In the 1 930s the Russian scientist Carl Friedrich Gauss investigated
competition between two species o Paramecium: P. caudatum and
P. aurelia. Gauss quantied biomass by estimating the volume o the
paramecia. When cultured separately, under ideal laboratory conditions,
both thrived. When cultured together, the numbers o both were
reduced, but P. caudatum was reduced disproportionately.
200
150 P. aurelia
P. caudatum
100
50
500 P. aurelia
400
P. caudatum
300
2 200
1 100
0 2 4 6 8 10 12 14 16 18 20 22 24
days
608 Figure 7 P. caudatum has a higher volume than P. aurelia
C.1 SpeCieS anD COmmUniTieS
The bay-breasted warbler and the yellow-rumped warbler are migratory
birds that appear to occupy the same niche, as they eed on similar prey
items and can be ound oraging together on the same tree. Figure 8
illustrates observed parts o the tree where each warbler most commonly
orages. Note that the birds eed in such a way as to avoid competition
with one another.
It appears rom these observations that two species cannot coexist in
the same habitat i their niches completely overlap. This is known as
the competitive exclusion principle. Either one species will lead to the
decline and extirpation o the other, or one or both o the competitors
will narrow their niches to avoid competition.
Fundamental and realized niches Yellow-rumped Bay-breasted
warbler warbler
Analysis of a data set that illustrates the distinction
between fundamental and realized niche. Figure 8 The yellow-rumped warbler and bay-
breasted warbler have similar prey yet they
The undamental niche o a species is the potential mode o existence, tend to orage in diferent parts o the same
given the adaptations o the species. It reers to the broadest range o tree to avoid competition
habitats it can occupy and roles it can ulfll. The realized niche is the
actual mode o existence, which results rom the combination o its
adaptations and competition with other species.
Dt-bsd qustos: Competitive exclusion in cat-tails
Figure 9 shows the distribution o two species o wetland plant over
a range o depths o water. The plants are called cat- tails Typha
latifolia and Typha angustifolia. Negative depth means out o the water.
The upper graph shows the situations where both species occur in
a natural habitat together. The lower graph shows distributions in
situations where the two species are grown separately.
1 C ompare the distribution o T. angustifolia in the presence and
absence o T. latifolia. [3]
2 With respect to this data, explain the concept o undamental and
realized niche. [4]
1600 T. latifolia
T. angustifolia
800
g ash-free dry wt 0
80
40
0 20 60 100 Figure 9 Yellow-rumped ( top) and
-20 water depth (cm) bay-breasted warblers
Figure 10 609
C ECOLOGY AND CONSERVATION
Data-based questions: Character displacement in ants
It has been suggested that competition between 1 Name the ant species with the smallest
species may not only restrict a species to a narrower mean mandible size. (1)
niche, but cause a change in some physical 2 Compare the requency distribution o
characteristics too. This is character displacement Veromessor pergandei mandible size between
the character changes when competition occurs. An the our areas. (3)
example o character displacement is seen in seed-
eating ants rom the southwestern United Sates. 3 Suggest what might be the undamental
The size o the mandibles (chewing mouth parts) niche o Veromessor pergandei in terms o size
o Veromessor pergandei determines the size o seeds o seed eaten. (2)
they eat. The histograms in gure 1 1 show the 4 Evaluate the hypothesis that the presence
number o V. pergandei in each requency class o
mandible size rom dierent locations. The names o multiple competitors decreases the
o other seed-eating ants ound in each habitat are
included showing their mean mandible size. variability o mandible size o Veromessor
pergandei. (3)
frequency of size classes 60 P. californicus 60 P. californicus
Tacna, Arizona Mojave, California
40 40
S. xyloni 20
20
0 N. cockerelli 0 P. magnacanthus
60 60
Ajo, Arizona Baker, California
40 40
P. pima 20
20
0 0
0.45 0.65 0.85 1.05 0.45 0.65 0.85 1.05
mandible size classes (mm)
Figure 11
Interspecifc interactions
Interactions between species in a community can be
classifed according to their eect.
Within ecosystems, the interactions between species are complex.
Five common types o interaction are described here. Competition occurs
when two species require the same resource and the amount obtained by
one species reduces the amount available to the other. Bracken and bluebells
compete or light, but bluebells minimize the competition by starting into
growth earlier than the taller-growing bracken. Red and grey squirrels
compete or ood in Britain where they occur together, with the grey squirrels
usually obtaining so much more ood that the red squirrels disappear.
Herbivory is primary consumers eeding on producers. Bison eed on
grasses and limpets eed on algae growing on rocks in the intertidal
zones o rocky shores.
Predation involves a consumer eeding on another consumer or example the
bay-breasted warbler, which winters in Guatemala, eeds on insects including
dragonfies and the dingo in New South Wales eeds on the red kangaroo.
610
C.1 SpeCieS anD COmmUniTieS
Parasitism is when one organism eeds o another but does not normally
kill it. The predatory organism in this case is termed a parasite and
the prey a host. The host is harmed and the parasite benets. North
American bighorn sheep are requently parasitized by the lungworm
Prolostrongylus stilesi. Protists o the genus Schistosoma use people as hosts.
In mutualism, two species live in a close association where both
organisms benet rom the association. Many mammals that consume
grass have bacteria living in their guts, which digest cellulose in the
grass. Many fowering plants and their insect or mammal pollinators
have mutualistic relationships.
In commensalism, one organism benets and the other is neither
harmed nor helped. A broad category o plants called epiphytes live on
other plants and rely on them or support but do not normally get their
nutrition rom their host. Examples include many dierent kinds o moss.
The role o zooxanthellae in ecosystems
The symbiotic relationship between zooxanthellae and reef-building
coral reef species.
Most corals that build rees contain mutualistic such as glucose and amino acids. The association
photosynthetic algae called zooxanthellae. ensures the recycling o nutrients which are in
The coral provides the alga with a protected short supply in tropical waters.
environment and a substrate that can hold
it in place or photosynthesis to occur. The Zooxanthellae are responsible or the unique
zooxanthellae provide the coral with molecules coloration o many corals and make coral rees
one o the most biologically productive ecosystems.
Local examples o interspecifc interactions
Local examples to illustrate the range of ways in which species can interact
within a community.
Below are examples o the dierent types o Fire coral is a stinging coelerentate. The Hawksh
interaction between organisms ound in and is immune to the eects o the coral and so gains
around the Bahamian island o New Providence. protection rom the coral without helping or
harming it. This is an example o commensalism
Figure 1 2 shows dodder. This is a non- (see gure 1 3) .
photosynthetic vine that invades plant tissues and
obtains both nutrients and support rom the plant.
This is a orm o parasitism.
Figure 12 Figure 13
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C ECOLOGY AND CONSERVATION
A major herbivore that consumes tissues o the Visits to fowers by pollinating hummingbirds
buttonwood tree is the bagworm moth ( Biopsyche such as the Bahama woodstar is a orm o
thoracia) shown in gure 1 4. mutualism. The bird gains nectar as a ood source
and the plant gets assistance with pollination.
Figure 14 Figure 15 Bahama woodstar (Calliphlox evelynae)
species 16 15 Keystone species
12
88 Community structure can be strongly afected
4 by keystone species.
0
A keystone species is one which has a disproportionate eect on the
before removal after removal structure o an ecological community. Robert Paine was the rst scientist
to use the term related to his studies o the sea star Pisaster. He articially
Figure 16 removed the sea star rom one part o the community and let the
population intact in another area.
Figure 17 Ochre sea star Pisaster ochraceus
The ollowing changes occurred as a consequence o the removal:
The remaining members o the ood web in the study area
immediately began to compete with each other to occupy the newly
available space and resources. Further, the sea star is an important
predator o the species that eventually over-ran the study site.
Within three months o the removal, the barnacle Balanus glandula
had become dominant within the study area.
Nine months later, Balanus glandula had been replaced by a
population o another barnacle Mitella and the mussel Mytilus.
S uccession continued until Mytilus became the dominant species. The
sea star is an important predator o Mytilus.
Eventually the succession o species wiped out populations o benthic
algae.
Some species, such as the limpet, emigrated rom the study area
because o lack o ood and/or space.
Within a year o the starshs removal, species diversity had
decreased in the study area rom teen to eight species (gure 1 6) .
O ther examples o keystone species include the sea otter, elephants, the
mountain lion and the prairie dog.
612
C.2 COm m Uni TieS an D eCOSySTemS
C.2 Couts d cossts
Understanding Applications
Most species occupy dierent trophic levels in Conversion ratio in sustainable ood production
multiple ood chains. practices.
A ood web shows all the possible ood chains Consideration o one example o how humans
in a community. interere with nutrient cycling.
The percentage o ingested energy converted to Skills
biomass is dependent on the respiration rate.
Comparison o pyramids o energy rom
The type o stable ecosystem that will emerge dierent ecosystems.
in an area is predictable based on climate.
Analysis o a climograph showing the
In closed ecosystems energy but not matter is relationship between temperature, rainall and
exchanged with the surroundings. ecosystem type.
Disturbance infuences the structure and rate Construction o Gersmehl diagrams to show
o change within ecosystems. the inter-relationships between nutrient stores
and fows between taiga, desert and tropical
Nature of science rainorest.
Models are representations o the real world: Analysis o data showing primary succession.
pyramids o energy model the energy fow Investigation into the eect o an
through ecosystems.
environmental disturbance on an ecosystem.
Trophic levels
Most species occupy dierent trophic levels in multiple
ood chains.
An organisms trophic level is its eeding position in a ood chain.
Because eeding relationships within an ecosystem are oten web-
like, an organism can occupy more than one trophic level. For
example, the diet o an owl involves animals which occupy dierent
trophic levels.
An owl pellet is a mass o undigested parts o the owls diet which it
regurgitates. The contents o the pellet can be used to gather inormation
about the owl and its community without disturbing the bird. The
contents might include such things as exoskeletons o insects, bones
(including skulls) , ur and claws.
I the species ound within the pellet can be identifed, their trophic level
can be ound. Alternatively, it may be possible to deduce the trophic
613
C ECOLOGY AND CONSERVATION
levels rom the adaptations. The contents o a pellet oten show that an
owl has been eeding at more than one trophic level.
The three skulls in fgure 1 are dierent species o rodent that might be
ound in an owl pellet. The dentition indicates whether the animal was a
primary consumer, eeding on plant material, or a secondary or tertiary
consumer, eeding on primary or secondary consumers.
When stating an organisms trophic level, reerence needs to be made to
a particular ood chain.
Figure 1 Rodent skulls
Data-based questions: Fishing down marine food webs
Trophic levels can be represented by a number mean trophic level 3.5
indicating the position o a species within an 3.4
ecosystem. By defnition, producers occupy the 3.3
frst trophic level (TL) and so have a TL o 1 . 3.2
For primary consumers TL = 2, and so on. The 3 .1
larger the number, the more energy- transer steps 3.0
between the organism and the initial fxing o the 2.9
suns energy. Trophic levels are not always stated 2.8
as whole numbers. Fish and other animals that 2.7 fresh water
eed at more than one level oten have estimated 2.6 marine
mean trophic levels. 2.5
1970 1975 1980 1985 1990 1995 2000
year
O ne eect o commercial over-fshing is the Figure 2 How the mean trophic level o landed fsh has
reduction in the number o fsh that eed at changed over a 30-year period
higher trophic levels, such as long-lived fsh. The b) Suggest why there is a dierence in the
phrase fshing down marine ood webs reers two trends. [2]
to the increased tendency or marine landings to
consist o animals that eed at lower trophic levels 3 Explain why the mean trophic level might
(see fgure 2). increase with the age o an individual fsh. [2]
1 Suggest a method that might be used to deduce 4 D educe the change in age o captured fsh
the trophic level o a fsh once it is captured. [2 ] over the period shown. [2]
2 a) Compare the changes in mean trophic 5 Explain two advantages o humans
level o landed fsh rom marine and catching and consuming fsh at a lower
reshwater fsheries since 1 970. [3] mean trophic level. [4]
614
C.2 COm m Uni TieS an D eCOSySTemS
Food webs actvt
A ood web shows all the possible ood chains in a Use the data in table 1 to
community. construct a ood web.
Trophic relationships within ecological communities tend to be complex Spcs Fds
and web-like. This is because many consumers eed on more than one o
species and are ed upon by more than one species. A ood web is a
model that summarizes all o the possible ood chains in a community. 1 caribou 4
Figure 3 shows a simplied ood web or a pond. 2 ground 4
squirrels 1,4,8
When a ood web is constructed, organisms at the same trophic level are
oten shown at the same level in the web. This isnt always possible, as 3 jaegers
some organisms eed at more than one trophic level.
4 grasses
Moorhen and sedges 4, 2
8
5 grizzly
bears
6 gulls
Roach (sh) 7 owls and 2,8
hawks 4
Dragony Great diving Water boatman Pond skater 2,8
larvae beetle (beetle) 8 voles and
lemmings
9 weasels
Haliplid Pond snails Trumpet Water eas Mayy Moth larvae 10 wolves 1,2,8
beetles (Lymnaea) snails (small larvae ( Nym ph ula)
crustacea) Table 1
Filamentous Planktonic (free Water lilies
algae oating) algae
Figure 3 A pond food web
Pyramids of energy as models
Models are representations o the real world: pyramids
o energy model the energy fow through ecosystems.
A pyramid o energy is a type o bar chart that is used to show the
relative amounts o energy fowing through each trophic level. The
bars are horizontal and are arranged symmetrically. The lowest bar
represents the production o the producers, either gross or net. The
bar above represents the primary consumers, with the secondary
consumers above that, and so on upwards. When constructing a
pyramid o energy, every bar should be labelled and the units should
be indicated usually kJ m2 year1. The same scale should used or
each bar, i possible, though many pyramids in text books are not
drawn to scale. The limitation o the model is that energy transer
rates can vary over seasons. Further, diet analysis is necessary or
organisms occupying dierent trophic levels in dierent ood chains.
The percentage composition o their diets may vary according to
season or opportunity.
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C ECOLOGY AND CONSERVATION
Data-based questions: Energy pyramids
The diagram shows energy fow in a stream in a) State the amount o energy fowing to the
Concord, Massachusetts. The debris consisted primary consumers. [1 ]
almost entirely o leaves and other parts o plants b) Calculate the percentage o the energy
that dropped into the stream. fowing to the herbivores that fows on to
1 Explain how the heat shown in the diagram is the primary consumers. [2]
produced. [2] 4 Construct an energy pyramid or our trophic
2 Calculate the net production o the herbivores levels in the stream. The gross production o
(primary consumers) . [1 ] producers is estimated to be 30,600 kJ m2
3 The amount o energy fowing to the ye a r1 . [4]
herbivores is 2 , 3 00 kJ m2 year1
Food conversion ratios
Conversion ratio in sustainable food production practices.
The production o meat or consumption requires The implication o these ratios or sustainability
the animals to be ed. Feed conversion ratios reer is that there are some dietary choices which
to the quantity o dietary input in grams required are more sustainable. Lower eed inputs mean
to produce a certain quantity o body mass in lower energy inputs or ood production.
livestock or sh. Avoiding the consumption o meat means that
there would be lower energy losses due to
For example, a eed conversion ratio o 1 .2 means eed conversion.
that 1 20 grams o eed are required to produce
1 00 grams o body mass. The nature o the eed inputs are a
consideration or sustainability. C onsider the
Table 2 shows the eed conversion ratios o several example o aquaculture operations to raise
animals armed or human consumption as reported salmon. While armed salmon is ed protein
in one document. Such numbers vary signicantly meal ormed rom other sh, livestock oten
in the reported literature due to variation in the consume plant matter. Fish armers can use eed
content o ood used, eeding methods, the age o that is easier to digest so there is less ecal waste
the animals and other variables. rom sh. Feeding can be closely monitored to
ensure that eed levels are adjusted to eliminate
meat production Feed conversion ratio estiate uneaten ood. Uneaten ood and ecal waste
Salmon 1.2 lower the carrying capacity o ponds used to
Beef 8.8 raise sh and so more energy is required to
Pork 5.9 produce the same quantity o sh.
Chicken 1.9
Table 2
616
C.2 COm m Uni TieS an D eCOSySTemS
The impact of climate on ecosystem type
The type of stable ecosystem that will emerge in an area
is predictable based on climate.
Climate is a property that emerges rom the interaction o a number o
variables including temperature and precipitation.
Temperature infuences the distribution o organisms. Temperature
infuences rates o cell respiration, photosynthesis, decomposition and
transpiration and ultimately has an impact on productivity.
Precipitation also impacts productivity by infuencing rates o
photosynthesis and rates o decomposition. Inormation about the
relative combinations o these two actors in an area can allow or
predictions about what kind o stable ecosystem will exist in that
area. High rainall results in the ormation o a orest, moderate or
seasonal rains will result in grassland. Very little or no rainall results
in a desert.
Very high rainall and high temperatures result in a tropical rainorest
whereas very high rainall and cooler temperatures result in a
temperate rainorest.
Interpreting a Whittaker climograph
Analysis of a climograph showing the relationship between temperature,
rainfall and ecosystem type.
A climograph is a diagram which shows - 15
the relative combination o temperature arctic-alpine
and precipitation in an area. Figure 4 is
a modied climograph rst developed by - 10
tundra
the ecologist Robert Whittaker. It shows mean actual temperature (C) -5 boreal cold
the most likely stable ecosystem that will -0 forest temperate
emerge in an area under certain climactic
conditions. The dashed line in the graph
represents regions where the type o 5 hard-leawveododelvaenrdgreen
biome is strongly infuenced by other
actors such as re, soil type, animal 10 shrubland temperate
grazing and the seasonality o drought. deciduous
15 temperate forest temperate warm
a) Determine the types o ecosystems grassland rain forest temperate
which can exist where a mean
annual precipitation level o 1 75 cm 20 thorn scrub thorn tropical tropical tropical
exists. 25 desert woodland deciduous rain forest
forest
b) Determine the range o conditions
under which a tropical rainorest will 30
orm. 0 50 100 150 200 250 300 350 400 450
c) List other variables that likely mean actual precipitation (cm)
infuence the type o stable Figure 4
ecosystem that orms.
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C ECOLOGY AND CONSERVATION
Comparison o pyramids o energy rom diferent ecosystems
The length o ood chains is determined by the open ocean
level o net primary productivity. The higher continental shelf
the productivity, the longer the ood chains and extreme desert, rock, sand, ice
the broader the trophic level at each stage o the desert and semidesert scrub
pyramid. Figure 5 shows the dierences in net tropical rainforest
productivity o dierent ecosystems.
savanna
Energy conversion efciencies are aected by the cultivated land
organisms involved. For this reason, pyramids o boreal forest (taiga)
energy dier between ecosystems. temperate grassland
woodland and shrubland
tundra
tropical seasonal forest
temperate deciduous forest
temperate evergreen forest
swamp and marsh
lake and stream
estuary
algal beds and reefs
upwelling zones
0 500 1000 1500 2000 2500
average net primary productivity (g/m2/yr)
Figure 5
activity
Counities dier in their energy conversion efciency.
1 For each o the ollowing communities, construct energy pyramid models,
drawn to scale, based on the energy conversion efciency shown.
) an upwelling area with a 20% energy conversion efciency.
The ood chain consists o phytoplanktonanchovy
b) a coastal region with a 15% energy conversion efciency
phytoplanktonherbivorous zooplanktoncarnivorous
zo o p l a n kto n h e rri n g
c) the open ocean with 10% energy conversion efciency
phytoplanktonherbivorous zooplankton
carnivorous zooplanktoncarnivorous shtuna
2 Table 3 shows the annual energy xed in biomass in joules per square
centimetre in each trophic level o two separate ecosystems.
) Use the data to construct two separate pyramids o energy. They
should both be drawn to the same scale.
b) Compare the two pyramids.
c) Explain the low biomass and low numbers o organisms in higher
trophic levels.
Trophic level Cedr Bog Lke Lke mendot
Tertiary consumers 0.2
0.8 1.4
Secondary consumers 3.6 35.1
Primary consumers
Producers 27.1 104.4
Table 3
618
C.2 COm m Uni TieS an D eCOSySTemS
Gersmehl nutrient cycle diagrams
Construction o Gersmehl diagrams to show the inter-relationships between
nutrient stores and fows between taiga, desert and tropical rainorest.
A Gershmehl diagram is a model o nutrient compartments: biomass, litter and the soil. Storage
storage and fow or terrestrial ecosystems. compartments, or pools, are represented by circles
Figure 6 shows three Gersmehl diagrams or or ovals. Arrows represent nutrient fows, or
three dierent ecosystems. Figure 7 provides a fuxes. The thickness o the arrows represent rates
detailed explanation o the diagram or a tropical o fow o nutrients. One arrow can represent
rainorest. The model presumes three storage more than one process.
taiga desert tropical rainforest
B B B
L L L
S
S S
Figure 6
high precipitation all continual tall, dense & rapid
year can bring in supply of growth of vegetation;
signicant store of
sediments in ood waters litter nutrients in biomass
biomass
small store of nutrients
in litter because of high
rate of decomposition
litter
high rate of nutrient rapid decomposition rapid uptake of
runo because of high as heat & moisture nutrients by
ideal for decomposers many plants
rainfall
small store of
soil nutrients in soil
due to leaching
rapid leaching
due to high
precipitation
rapid chemical
weathering due to
heat and rainfall
Figure 7
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C ECOLOGY AND CONSERVATION
activity Primary succession
Look at fgure 6. Analysis o data showing primary succession.
1 Identiy the ecosystem Ecological successions are the changes that transorm ecosystems over
type with the largest time. The changes involve both the species making up the community
nutrient store being and their abiotic environment. They are the result o complex
the soil. interactions between the community and the environment.
2 Identiy an ecosystem In an ecosystem, abiotic actors set limits to the distribution o living
type where the rate o organisms, and the organisms have an eect on abiotic actors. Consider a
litter decomposition orest next to an area o grassland. Relative to the grassland, the orest will
is low. have lower light intensity and be cooler and more humid, largely because
o the presence o the trees. Lea litter rom the trees will increase the rate
3 Identiy arrows which o water infltration in the soil, increase the nutrient concentration o the
could represent the soil and will directly and indirectly aect the aeration o the soil.
ollowing processes:
Communities o living organisms may change the abiotic actors to
) run-o such an extent that the environment becomes limiting to some o
them and other species join the community as they are better adapted.
b) mineral absorption by This happens during succession.
plants
Two categories o succession are recognized: primary and secondary.
c) regurgitation o an Primary succession begins with an environment, such as a retreating
owl pellet glacier where living organisms have not previously existed. At the start o
a primary succession, there are only organisms that can survive on rock
4 Compare the nutrient suraces, such as bacteria, lichens and mosses. Small amounts o soil are
cycles o taiga, desert ormed allowing small herbs to colonize and, as a deeper soil develops,
and tropical rainorests. successively larger plants colonize tall herbs, shrubs and fnally in
most areas trees. Consumer populations will change with the plant
populations, as will populations o decomposers and detritivores. Figure 8
shows a photo o the same area separated by 1 7 years. The top photo was
taken in 1 985, the bottom photo in 2002. The sign in the picture indicates
that the area was covered in the ice o a retreating glacier in 1 920.
activity Figure 8
Compare the site as shown
in fgure 8 in 1985 and
2002 and iner some o
the changes that would
have occurred to biotic and
abiotic variables in the area.
620
C.2 COm m Uni TieS an D eCOSySTemS
Dt-bsd qustos 1 a) Outline the changes in mean stem [2]
diameter with time.
C aptain George Vancouver visited the area
now known as Glacier B ay, Alaska in 1 794. b) Explain the change in mean stem [2]
He made detailed notes regarding the position d ia m e te r.
o the glaciers. This has allowed researchers to
determine the time since the start o primary Figure 1 0 shows the number o species ound
succession as the glacier retreated. in Glacier B ay, Alaska as a unction o time
since the glacier covered the area.
The rst species to colonize the bare rock are
bacteria, lichens and moss. Mountain avens number of species 40 trees
( Dryas drummondii) is a fowering shrub that
dominates ater the moss stage. Deciduous alder tall shrubs
trees ( Alnus sinuata) invade next ollowed by 30 low shrubs and herbs
the most stable ecosystem which is a spruce and
hemlock orest. mosses, liverworts and lichens
20
Figure 9 shows the mean stem diameter and 10
range o diameter o plants as a unction o time
since the tongue o the glacier covered the area at 0
eight sites (E1 -E8) . 10 23 33 44 108 200
terrain age/years
stem diameter (cm) Figure 10
0.6 E6
E5 E8 2 a) Outline the changes in the number o
0.4 E7 species (species richness) . [2]
E3
b) Outline the changes in the relative numbers
0.2 E1 E4 o species types (species evenness) [2]
E2 Figure 1 1 shows changes in the properties o
0 soil as the dominant plant species change.
0 40 80 120 160 200 >230
terrain age (years) 3 a) Outline the changes in soil properties
Figure 9 that are seen. [1 2]
b) Deduce the stage where the greatest
changes in soil properties are observed. [2 ]
organic content (mg/g) 100 moisture (mg/g) 700 nitrogen (mg/g) 1.8
75 525 1.2
50 350 0.6
25 175 0
pioneer dryas alder spruce
0 0
pioneer dryas alder spruce pioneer dryas alder spruce
bulk density ( g/cm3)1.8 pH 8
1.2 6
0.6 4
0 2
pioneer dryas alder spruce
0
Figure 11 pioneer dryas alder spruce
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C ECOLOGY AND CONSERVATION
gross production Respiration rates and biomass accumulation
total biomass The percentage of ingested energy converted to biomass
is dependent on the respiration rate.
total community respiration
Production in plants happens when organic matter is synthesized
0 time (years) 100 by photosynthesis. In animals it occurs when ood is absorbed ater
digestion. Energy units are usually used or measuring production e.g.
Figure 12 kilojoules. The amounts o energy are given per unit area, usually per m2
and per year. Gross and net production values can be calculated using
this equation:
net production = gross production - respiration
Gross production is the total amount o organic matter produced per unit
area per unit time by a trophic level in an ecosystem.
Net production is the amount o gross production remaining ater
subtraction o the amount used or respiration by the trophic level.
In the early stages o primary production, the high availability o sunlight
means that gross production is high and there is little total biomass in the
community. As a result, the total amount o respiration to support the small
biomass is low. As succession proceeds, the standing biomass increases and
the total amount o respiration increases. Further, the amount o gross
production begins to decline once all available spaces or stems become
lled. An equilibrium is reached where the total community production
to total community respiration (P/R) ratio equals 1 . When this occurs, the
ecosystem has reached a relatively stable stage.
Data-based questions: Calculating productivity values
The energy fow diagram in gure 1 3 is or a 2 Compare the percentage o heat lost
temperate ecosystem. It has been divided into through respiration by the autotrophs
two parts. One part shows autotrophic use o with that lost by the heterotrophs. [1 ]
[1 ]
energy and the other shows heterotrophic use o 3 Most o the heterotrophs are animals.
energy. All values are kJ m2 yr1. Suggest one reason or the dierence in
1 Calculate the net production o the heat losses between the autotrophs and
autotrophs. [1 ] animal heterotrophs.
autotrophs heterotrophs
heat heat
23 , 9 3 0 14,140
autotrophic heterotrophic
respiration
respiration
gross net feed i n g storage
14,690 540
photosynthesis production production
43 , 510 X
storage
4,900
Figure 13 An energy fow diagram or a temperate ecosystem
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C.2 COm m Uni TieS an D eCOSySTemS
Secondary succession open young
pioneer closed herb scrub broad- climax,
Disturbance infuences the structure and rate o change community community (shrubs, leaved old
within ecosystems. (annuals) (perennials) small woodland woodland
S econdary succession takes place in areas where there is already, or trees)
recently has been, an ecosystem. The succession is initiated by a change
in conditions. Construction sites or roads might become disused and 12 35 1630 3150 <150
eventually plants grow up in the remains. Old-feld succession occurs Time after ploughing/years
when an arable feld or meadow (feld o grassland) is abandoned. The
lack o tillage or grazing initiates the succession. Figure 1 4 shows the Figure 14 Secondary succession is the
sequence o communities ollowing the abandonment o an arable progression of communities where a pre-
feld, with approximate timings. Examining the time scale in fgure 1 4 existing climax community has been disturbed
indicates that the pace o change slows as succession proceeds. Close to but the soil is already developed
the time o the disturbance, rates o system respiration and productivity
increase rapidly and there is an accumulation o biomass. Species
diversity increases close to the time o the disturbance. At the climax
stage shown in the diagram, changes are still occurring, but they are
slower and the ecosystem is viewed as being more stable and resistant to
change at the climax stage.
Dt-bsd qustos: Secondary succession
The three boxes in fgure 1 5 show a feld 1 Explain what happened to species [2]
undergoing secondary succession. It is shown 2 number 3 during the succession.
5 years, 25 years and 30 years ater the original [1 ]
disruption. Each numbered shape represents a Deduce the changes that might [1 ]
distinct plant species. have been occuring in [1 ]
[1 ]
4 4 2 42 a) gross plant production
23 23 2 [2]
2 b) species diversity
1 1 6
5 5 c) soil depth
1
5 d) amounts o minerals being recycled.
2 Predict, with reasons, the species
composition o this area ater 50 years.
5 years 25 years 30 years 3
Figure 15 Community changes 5 years, 25 years and 30
years after an initial disturbance
Studying secondary succession
Investigation into the eect o an environmental disturbance on an ecosystem.
In your local area there may be opportunities Lea area index
to investigate secondary succession. Abandoned
felds, wooded areas with disused roads and felds Volume o lea litter
recovering rom a fre are all examples o sites
where succession can be studied. A number o Water cycle variables including infltration
possible variables that can be studied include: rates and run-o rates
Species diversity Soil variables including soil structure,
soil moisture, soil nutrient levels and
Stem density compaction levels
Above ground biomass Light levels
B ulk soil density.
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C ECOLOGY AND CONSERVATION
Figure 17 Biosphere 2 rainforest building near Closed ecosystems
Tucson, Arizona. Biosphere 2 was created to
explore the possible use of closed biospheres In closed ecosystems energy but not matter is exchanged
in space exploration with the surroundings.
There are three categories o systems that can be modelled (gure 1 6) .
Open systems exchange matter and energy with their surroundings.
Closed systems, such as the mesocosm that you constructed as part o
your study o the core and Biosphere 2 (gure 1 7) , exchange energy but
not matter with the surroundings. Isolated systems, which are largely
theoretical, exchange neither matter nor energy with their surroundings.
Ecological systems exist along the continuum. Natural systems exchange
both matter and energy with their surroundings and so are categorized
as open systems. In undisturbed systems, the rate o exchange o matter
with the surroundings occurs most notably due to the water cycle and
nutrient cycles that have a gaseous phase. Human intererence increases
the exchange o matter either through harvesting o crops or addition or
depletion o nutrients.
matter
energy energy
energy
energy open closed isolated
system system system
matter (a) (b) (c)
Figure 16
Disruptions to nutrient cycling
Consideration of one example of how humans interfere with nutrient cycling.
While natural systems usually exchange matter regular inputs o nutrients must be added to the
with their surroundings, especially with respect to soil so that agriculture can continue in the area.
the water cycle and all nutrient cycles that have Phosphate and nitrogen are key components
a gaseous phase, human activity can accelerate o ertilizer.
nutrient fows into and out o ecosystems.
Phosphate is mined, converted to ertilizer and
Agriculture is an example o a human activity shipped around the world or use in agriculture.
which intereres with nutrient cycling. The
harvesting o crops and transport o the products Nitrogen produced rom gaseous N2 in the Haber
out o the area where they were grown depletes process has signicantly increased inputs into the
the area o the nutrients that are locked in to nitrogen cycle that would not occur naturally.
the biomass o the crop. As a consequence, Runo rom agricultural elds results in build-up
in waterways and leads to eutrophication.
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C.3 impaCTS OF H Uman S On eCOSySTem S
C.3 icts of hus o cossts
Understanding Applications
Introduced alien species can escape into local Study o the introduction ocane toads in Australia
ecosystems and become invasive. and one other local example o the introduction o
an alien species.
Competitive exclusion and the absence o
predators can lead to reduction in the numbers Discussion othe trade-o between control othe
o endemic species when alien species become malarial parasite and DDT pollution.
invasive.
Case study o the impact o marine plastic debris
Pollutants become concentrated in the tissues on Laysan albatrosses and one other named
o organisms at higher trophic levels by species.
biomagnifcation.
Macroplastic and microplastic debris has
accumulated in marine environments.
Nature of science Skills
Assessing risks and benefts associated with Analysis o data illustrating the causes and
scientifc research: the use o biological control consequences o biomagnifcation.
has associated risk and requires verifcation
by tightly controlled experiments beore it is Evaluation o eradication programmes and
approved. biological control as measures to reduce the
impact o alien species.
Alien and invasive species
Introduced alien species can escape into local
ecosystems and become invasive.
Human activity oten results in an organism being introduced to an area
where it did not previously occur. Species that are native to an area
are reerred to as endemic whereas species that are not native but are
introduced by humans are reerred to as alien species.
The impacts o an alien species are usually only signifcant i it increases
in number and spreads rapidly. S pecies that do this are described as
invasive. Many alien species are invasive, because the normal limiting
actors in their original habitat are missing. The predators, diseases and
vigorous competitors that controlled numbers in its native habitat are
usually absent.
Many o these invasive species have signifcant eects on the ecosystems
where they are released. Rats introduced to New Zealand contributed to
the extinction o ground nesting bird species by predating their eggs. The
signal crayfsh, introduced rom North America to Britain, competes with
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C ECOLOGY AND CONSERVATION
the native white-clawed craysh and has also brought a disease (craysh
plague) to which the native craysh are not resistant, so large numbers
have been killed. The foating ern, Salvinia molesta, has spread over the
suraces o many lakes in the tropics, eliminating the native aquatic
plants by competition. Most o the impacts o alien species are harmul,
particularly the excessive predation o native species, and interspecic
competition due to niche overlap with native species.
Figure 1 Red squirrel ( Sciurus vulgaris) Alien species compete with endemic species
Figure 2 Eastern grey squirrel (Sciurus Competitive exclusion and the absence o predators can
carolinensis) lead to reduction in the numbers o endemic species
when alien species become invasive.
An alien species can become so reproductively successul and aggressive
that it dominates the new ecosystem and poses a serious threat to
biodiversity. O rganisms that are endemic to an area may occupy similar
niches as the alien species. The competitive exclusion principle predicts
that two species with overlapping niches cannot continue occupying
overlapping niches indenitely.
One consequence o the competition might be that either or both species
may occupy smaller realized niches. I the alien species lacks predators
it may be able to out-compete native species and become invasive. In
the UK, the invasive Eastern grey squirrel ( Sciurus carolinensis) occupies a
similar niche to the native red squirrel ( Sciurus vulgaris) and is a superior
competitor. Whenever grey squirrels are introduced to an area, the
native red squirrel population is reduced and oten extirpated.
Alternatively, the ability o a new ecosystem to resist an alien species can
prevent it rom becoming invasive. The western thrips ( F. occidentalis) is
an invasive insect pest that has spread rom the Western United States
to many parts o the globe but has been less successul at colonizing the
Eastern United States. One hypothesis is that it is being competitively
excluded by a thrips species that is native to the Eastern US ( F. tritici) .
Figure 3 F. occidentalis The risk of biological control
Assessing risks and benefts associated with scientifc
research: the use o biological control has associated
risk and requires verifcation by tightly controlled
experiments beore it is approved.
In some cases, biological control can be used to limit an invasive
species. This involves introducing natural predators o the invasive
species to limit its spread.
Figure 4 shows the aquatic plant taxiolia ( Caulerpa taxiolis) being
consumed by the violet sea slug ( Flabellina afnis) . Taxiolia is used
as an ornamental plant in aquariums but it has become highly
invasive in a number o areas. This is due in part to the toxin that the
626
C.3 impaCTS OF H Uman S On eCOSySTem S
plant contains that allows it to resist predation. The violet sea slug
is immune to these toxins and it has been suggested that it can be
used as a form of biological pest control, but there are concerns that
it could become invasive itself.
A risk-averse approach to introducing a natural enemy to control an
invasive species involves holding the natural enemy in an approved
facility that ensures it is quarantined. This prevents escape until
research can establish that the natural enemy will have minimal
negative impact in the new area where it is released.
Figure 4
Case studies of introduced alien species
Study of the introduction of cane toads in Australia and one other local example
of the introduction of an alien species.
Biological control can go wrong. One of the 19351974 19 8 6 2 0 01
most troublesome invasive alien species, 1975 19 8 0
ironically, was originally introduced with the 19 81 19 85 20022004
aim of it acting as a biological control. The predicted distribution
cane toad ( Bufo m arinus) was introduce d to
Australia to control the cane beetle ( Dermoleida
albohirtum) . The toad is a native of C entral and
S o uth America. Unfortunate ly, the toad has
become a generalist predator and a competitor
for food resources. Research suggests that it
has its biggest ecological impact on predators
that consume the toad. The toad has a gland
behind its head that can release a toxin when
it is disturbed. The toad is lethal to consume
for many predators because of the release of
the toxin.
Figure 5 shows a map of Australia that indicates Figure 5
changes in the distribution of the cane toad
since its introduction in 1 935.
The zebra mussel ( Dreissena polymorpha) is an
invasive species of the North American Great
Lakes system that is native to the Black Sea
and the Caspian Sea.
Empty cargo ships often fill their hulls with Figure 6 A section through a water pipe which has been
water as ballast to help them remain stable opened to reveal an interior clogged with zebra mussels,
when they are not carrying cargo. When this Dreissena polymorpha
ballast water is transported to other locations
on the planet, it can lead to invasions of alien
species if precautions are not taken when the
ballast water is released. The zebra mussel is
believed to have been transported to North
America in ballast water.
627
C ECOLOGY AND CONSERVATION
Since their introduction to the Great Lakes, zebra and interere with hydroelectric power generation.
mussels have spread to many North American One proposed biological control mechanism o the
river systems. They have covered the undersides zebra mussel is the use o Pseudomonas fuorescens,
o docks and boats. Populations can grow so dense a bacterium that produces a toxin that appears to
that they block pipes, clog municipal water systems selectively aect the zebra mussel.
Evaluation of methods to control alien species
Evaluation o eradication programmes and biological control as measures
to reduce the impact o alien species.
Data-based questions: The mango mealy bug
The mango mealy bug (Rastrococcus invadens) 5 S uggest one risk o releasing G. tebygi
became a serious pest o crops in Ghana ater it in Ghana.
was frst ound there in 1 982. Insecticides did [1 ]
not control it successully, so a species o wasp,
Gyranusoidea tebygi, was introduced. This wasp Time between egg hatching R. G.
eeds on adult mango mealy bugs and also lays and adult emerging/days invadens tebygi
its eggs inside the larvae. When the wasps eggs
hatch, the larvae that emerge eed on the mealy 61 25
bug larvae, eventually destroying them. Table 1
gives a comparison o data or the two species. Time between adult emale
emerging and starting to
1 S tate two interactions between G. tebygi and reproduce/days 16 2
2.4 4.4
R. invadens. [2] Mean number ofspring
produced per emale per day
2 State the name o this type o pest control. [1 ]
3 Calculate the total lengths o the lie cycles Percentage o ofspring that
are emale
o G. tebygi and R. invadens. [2] 15 75
4 Using the data in the table, explain reasons
or expecting G. tebygi to be an eective Table 1
means o controlling R. invadens. [4]
Purple loosestrie is a European plant that has
become invasive in North America. It is oten
discussed in the context o successul biological
control programmes. Two members o the
beetle genus Galerucella have been introduced
to eat the plant and this has been used to limit
its spread as it specializes in eeding on the
loosestrie.
Figure 7 Purple loosestrife plant showing feeding damage
by Galerucella
628
C.3 impaCTS OF H Uman S On eCOSySTem S
Dt-bsd qustos: Control of purple loosestrife
Galerucella beetles were frst introduced to The eects were determined as a unction o
several sites in Connecticut in 1 996 and were distance rom the release site.
released annually to the same areas in 1 997
and 1 998. The eects on purple loosestrie a) Outline the relationship between eeding
plants were assessed by looking or eeding
damage (fgure 8) and height o plants damage and time since frst release. [1 ]
(fgure 9).
b) Outline the relationship between plant
height and introduction o Gallerucella. [1 ]
c) Discuss the eect o biological control o
Galerucella feeding damage loosestrie by Galerucella. [4]
5
4 2
1.8
3 plant height (m) 1.6
1.4
2 1.2
1 1997 19 9 8 1 19 9 6
0.8 19 97
distance from release quadrat (m) 10 15 0.6 10 5 release 5 10 19 9 8
15 10 5 release quadrat 5 0.4
quadrat 15
15 distance from release quadrat (m)
feeding damage
Figure 9
1 = 0% 2 = 1 to 5% 3 = 6 to 25% 4 = 26 to 50%
5 = 51 to 75% 6 = 76 to 100%
Figure 8
Biological control is not the only mechanism to completion, the support o local communities
by which invasive species can be controlled. and preventing re-invasion. Knowledge o the
Eradication programmes involve application o ecology o the invasive species is important.
herbicides and selective harvesting o invasive Removal o the invader may cause an explosion
plants as well as trapping and culling o in the prey species or example.
invasive animals. Some o the most successul
examples have been the removal o invasive 100,000
mammal species rom islands. Eradication 10,000
techniques have improved and increasingly 1000
large islands can be cleansed o the invader. 100
For example in New Zealand eradication o 10
invasive Norway rats ( Rattus norvegicus) has 1
been achieved or all islands up to 1 0,000 ha
(see igure 1 0) . Figure 10
area hectares (log scale)
The requirements or a successul eradication 1111999975660550
programme include removing the invader 2211111999900999807085505050
aster than it can reproduce, an ongoing
commitment to see the eradication through
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C ECOLOGY AND CONSERVATION
TOK Biomagnifcation
To what extent does amphiboly Pollutants become concentrated in the tissues o
obscure the communication o organisms at higher trophic levels by biomagnifcation.
scientifc inormation?
Some toxins build up in the body o organisms, particularly i
Amphiboly is an error in reasoning that the toxin is at-soluble and not easily excreted. This is known as
applies to situations where words are bioaccumulation. For example, organic compounds containing mercury,
treated as being synonymous when such as methyl mercury, are more likely to be stored in at tissue than
they are not. For example the term metallic mercury.
mercury pollution is oten used to
indicate both elemental mercury and Biomagnication is the process by which chemical substances become
compounds containing mercury such more concentrated at each trophic level. At each stage in a ood chain,
as methyl mercury. The latter orm is the predator will accumulate higher concentrations o the toxin than
ar more harmul to ecological systems. its prey. This is because the predator consumes large quantities o prey
during its lietime and bioaccumulates the toxins that they contain.
The consensus defnition o Some organisms have greater concentrations o body lipids and so the
biomagnifcation is that it is the accumulation is not even across trophic levels. Sometimes, the toxin can
transer through ood chains o oreign be taken up directly rom the abiotic environment rather than entering
chemicals that can accumulate through the ood chain.
in tissues. The result is higher
concentrations in organisms higher up The concentration o toxins in the highest trophic levels may be lethal,
the ood chain. One study analysed the even when the concentrations in organisms at the start o the ood chain
contents o 148 papers with the term were very low. B ioaccumulation and biomagnication o toxins such as
biomagnifcation in the title and ound DDT caused catastrophic alls in the populations o some birds o prey
that less than hal were using the term such as peregrine alcons and ospreys in the 1 950s and 1 960s.
according to the consensus defnition.
Many o the papers were equating Figure 1 1 shows the concentrations o PCBs in an aquatic ood chain in
biomagnifcation with bioconcentration the Great Lakes. These chemicals were used as insulators in electrical
which is the process o uptake o devices and as fame-retardants. It was demonstrated in the 1 950s that
chemicals rom the surrounding moderate doses killed experimental rats and manuacture o them
water. The consequence was a lack o stopped in the 1 970s. However, PC B s have persisted in the environment
recognition o distinct mechanisms that and biomagnication can result in organisms in higher trophic
occur in aquatic invertebrates and fsh. levels having concentrations up to 1 0 million times greater than the
concentrations in the water.
phytoplankton
0.025 ppm
zooplankton herring gull eggs
0.123 ppm 124 ppm
smelt
1.04 ppm
lake trout
4.83 ppm
Figure 11 The concentration of pollutants called PCBs in each level of the North America
Great Lakes aquatic food chain (in parts per million, ppm)
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C.3 impaCTS OF H Uman S On eCOSySTem S
The causes and consequences o biomagnifcation
Analysis o data illustrating the causes and consequences o biomagnifcation.
Dt-bsd qustos: Biomagnifcation o caesium
In addition to nutrients, other atmospheric b) Explain the annual variation in
elements may also enter the ecosystem.
Radioactive caesium-1 37 was released into caesium-1 37 concentrations in caribou
the atmosphere by atomic bomb tests in 1 961 .
The caesium-1 37 was deposited in the soil and and Inuit. [2]
on to plants. Figure 1 2 shows the amount o
radioactivity ound in the tissues o lichens (an 4 Predict, with reasons, whether the
alga and a ungus growing together) , caribou (a
member o the deer amily) and Inuit people in concentrations o caesium-1 37 would have
the Anaktuvuk Pass o Alaska.
dropped to zero in caribou and Inuit by the
1 The three organisms orm a ood chain.
Deduce the trophic level o end o 1 966. [2]
increasing radioactivity(nCi g-1) Inuit
a) lichens [1 ]
b) Inuit. [1 ]
2 Describe the level o caesium-1 37 in
the Inuit rom June 1 962 through to caribou
December 1 964.
[2]
3 a) Identiy the time o year when
caesium-1 37 concentrations were lichens
highest in
June Dec June Dec June Dec June Dec June Dec June
(i) caribou 1961 1962 1963 1964 1965 1966
(ii) Inuit.
Figure 12 Radioactivity levels in various trophic levels
[1 ] in an Alaskan community after an atmospheric atomic
[1 ] bomb test
Dt-bsd qustos 3 Outline the relationship between PCB [2]
concentration and trophic level in the
Biomagnifcation is the increase in concentration terrestrial ood web.
between trophic levels. The process o
biomagnifcation or the same chemical may 4 Deduce the ood web where -HCH does
dier between aquatic and terrestrial ood webs
or between marine mammals and marine gill not biomagniy. [2]
breathing animals (fgure 1 3) . Certain chemicals
that are moderately lipid soluble but can still 5 Compare the concentration o -HCH at the
dissolve in water can be eliminated into water by third trophic level in the terrestrial ood web
gill breathing organisms but are not eliminated and in the marine mammalian ood web. [2]
into the air by lung breathing organisms.
6. Explain the dierences in biomagnifcation
1 Determine the trophic level o sculpin. [1 ] o -HCH in the terrestrial ood web and the
marine mammalian ood web. [3]
2 Explain how it is possible to have a non-
whole number trophic level. [2]
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C ECOLOGY AND CONSERVATION
a) PCB-153 marine sh food web
100
10 -HCH
10 capelin salmon algae cod salmon
sculpin
1 algae cod sculpin 1
bi va l ve s
0.1 bivalves
0 0.1
zooplankton
12345 0.01 6
6 012345
b) terrestrial food web
concentration ( ng.g-1 lipid equivalent) 1000 PCB-153 wolf 1000 -HCH wolf
100 100
10 10
1 caribou 1
0.1 lichen caribou
0.01 0.1 lichen
0123456
0.01
0123456
c) marine mammalian food web
10000 PCB-153 polar bear 1000 -HCH human milk
1000 100 polar bear
100 walrus beluga walrus
10 eider duck
1 human milk 10 eider duck
0.1
0.01 a l ga e capelin ringed seals algae cod beluga ringed seals
0 cod salmon 1 salmon
sculpin
bivalves
0.1 bivalves sculpin
zooplankton
123456 0.01
0123456
trophic level (TL)
Figure 13
(source o data: http://www.sciencemag.org/content/317/5835/236.fgures-only)
The benefts and risks o DDT use
Discussion o the trade-of between control o the malarial parasite
and DDT pollution.
DDT (dichlorodiphenyltrichloroethane) is an ticks and mosquitos during and immediately
insecticide that was used widely in the mid-20th ater the S econd World War and later on as an
century, frst to control disease vectors such as agricultural insecticide.
632
C.3 impaCTS OF H Uman S On eCOSySTem S
having thin-shelled eggs and consequently leading
to their ailure to reproduce successully. As a
consequence, DDT was banned or agricultural
use under the terms o the Stockholm Convention
on persistent organic chemicals, though residual
indoor spraying to control mosquitos was
permitted. This use remains controversial. The
World Health O rganization endorses the use o
DDT or this purpose.
Where the use o DDT was discontinued or
malaria vector control in an area, rates o malaria
climbed. Substitute strategies to spraying DDT
were attempted but were not as successul.
Many countries that had banned the use o DDT
completely reapproved its use or residual indoor
spraying.
Figure 14 A soldier demonstrating the DDT spraying equipment Concerned scientists argue that DDT may have
used to control the lice which carried the bacterium that a variety o human health eects, including
causes typhus reduced ertility, genital birth deects, cancer
and damage to developing brains. Its metabolite,
DDT was made amous by the writing o Rachel DDE, can block male hormones. The pesticide
C arson. In her book Silent Spring she expressed accumulates in body at, and in breast milk, and
concern about how the indiscriminate use o evidence that it persists in the environment or
DDT was leading to ecological eects. As DDT decades is strong.
biomagnifed up ood chains, it led to birds o prey
With its strong record in reducing malaria cases
and the WHO endorsement, the use o DDT
is increasing globally. Pressure is mounting
or governments and intergovernmental
organizations to rely on DDT only as a last resort
and the call is growing or the development o an
alternative orm o malaria vector control.
Plastics in the ocean Figure 15 Grey reef shark ( Carcharhinus
amblyrhynchos) with macroplastic sheeting
Macroplastic and microplastic debris has accumulated in its mouth. It may have attempted to eat the
in marine environments. plastic, mistaking it for prey
Plastic is a broad term that describes a number o dierent polymers
that are used in a growing number o disposable consumer items. Some
plastic enters the ocean through direct disposal rom ships and platorms,
but the majority comes rom litter being blown into water systems.
Macroplastic is large visible debris including nets, buoys, buckets and
trash that has not degraded (see fgure 1 5) .
Physical and chemical degradation o macroplastic results in
microplastic ragments that are harder to see but are more
omnipresent.
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C ECOLOGY AND CONSERVATION
Ocean currents transport garbage to fve concentration areas
across the globe called gyres. These are very large patches
within the ocean where circular currents concentrate the plastic
waste (fgure 1 6) .
Some o the consequences o marine plastic pollution are:
The degradation o the plastic at sea releases persistent
organic chemicals into the ocean that can bioaccumulate
and biomagniy.
Plastics absorb other persistent organic chemicals and thus
concentrate these toxins.
Animals eat or become tangled in plastic pollution.
NORTH NORTH
PACIFIC GYRE ATLANTIC GYRE
SOUTH SOUTH I N DI AN
PACIFIC GYRE ATLANTIC GYRE OCEAN GYRE
Figure 16
Marine plastics and the Laysan albatross
Case study of the impact of marine
plastic debris on Laysan albatrosses
and one other named species.
Macroplastic is a concern or marine animals as it
may be mistaken as a ood source and ingested.
The Laysan albatross is a large marine bird that
nests on the island o Midway Atoll in the Pacifc
Ocean. The North Pacifc Gyre contacts the shore
o the island transporting large volumes o plastic
onto its beaches. Parent Laysan albatrosses eed
plastic pieces to chicks resulting in signifcantly
higher mortality.
Figure 17 Carcass of Laysan albatross chick that has been fed
plastic debris
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C.4 COn ServaTiOn OF BiODi verSiTy
Dt-bsd qustos: Plastic ingestion by the leatherback turtle
The leatherback, Dermochelys coriacea, is a large 3 S uggest a reason why such a large
sea turtle that preys on jellyfsh. Figure 1 8 percentage o leatherback turtles ingest
shows the results o a literature review o all plastic. [2]
reported cases o autopsies o dead leatherback
turtles. The reported autopsies are grouped 50 5-year bins 37
into fve year bins. The numbers labelling 40 116
each point represent the number o autopsies % with plastic 30
reported in the literature or that fve-year 20 15
period. The percentage o turtles with plastic in
their stomach is noted. 8
31
1 Identiy the frst year that an autopsy 91
9
55
reported plastic being ound in the stomach 13
o a leatherback. [1 ] 10
2 Estimate the total percentage o leatherback 211 333 428
0 1925 6
turtles with plastic in their digestive tract 1900 1950 1975 2000
over the past 50 years. [2]
Figure 18
C.4 Costo of bodst
Understanding Applications
An indicator species is an organism used to Case study othe captive breeding and
assess a specifc environmental condition. reintroduction o an endangered animal species.
Relative numbers o indicator species can be Analysis othe impact obiogeographic actors on
used to calculate the value o a biotic index. diversity limited to island size and edge eects.
In situ conservation may require active
management o nature reserves or national parks.
Ex situ conservation is the preservation o
species outside their natural habitats.
Biogeographic actors aect species diversity.
Richness and evenness are components o
b i o d i ve rs i ty .
Nature of science Skills
Scientists collaborate with other agencies: the Analysis o the biodiversity o two local
preservation o species involves international communities using Simpsons reciprocal index
cooperation through intergovernmental and o diversity.
non-governmental organizations.
635
C ECOLOGY AND CONSERVATION
Indicator species
An indicator species is an organism used to assess
a specifc environmental condition.
An indicator species is an organism that occurs only when specic
environmental conditions are present. The presence or absence o these
species on a site is a good indicator o environmental conditions. For
example, the distribution o understorey plants in a orest is a good
indicator o such things as soil ertility or water drainage. Fruticose
lichens are pollution-intolerant, so their presence is an indicator o clean
air. The presence o black greasewood ( Sarcobatus vermiculatus) would
indicate alkaline saline soils.
Figure 1Fruticose lichens indicate Calculation of a biotic index
the absence of air pollution
Relative numbers o indicator species can be used to
1 Stoney nymph 2 Mayy larva calculate the value o a biotic index.
(up to 30 mm) (up to 15 mm)
A biotic index compares the relative requency o indicator species. For
3 Asellus 4 Chironomid example, the macroinvertebrate biotic index is a measure o stream
(freshwater louse) (bloodworm; a midge health. The number o individuals o each indicator species in a sample
(up to about 12 mm) larva) (up to 20mm) is determined. Each number is multiplied by a pollution tolerance
actor and a weighted average is determined. One possible biotic index
5 Rat-tailed maggot 6 Tubifex multiplies the number o a certain kind or organism by its pollution
larva (up to 55 mm (sludge worm) tolerance rating. Each o these products is then added to the others and
including tube) (up to 40 mm) divided by the total number o organisms in the habitat.
Figure 2 Benthic macroinvertebrates Figure 2 shows six dierent benthic (bottom-dwelling)
macroinvertebrates that are ound in rivers. Benthic macroinvertebrates
are useul indicators o stream health or a number o reasons: they live
in the water or the duration o the aquatic stage o their lie cycle and so
they refect conditions in the water over a period o time; they are easy
to capture; and most importantly, they vary in their response to chemical
and physical changes in their habitat.
In situ conservation
In situ conservation may require active management
o nature reserves or national parks.
In situ conservation measures involve endangered species remaining in
the habitat to which they are adapted. This allows the species to interact
with other wild species, conserving more aspects o the organisms
niche. Nature reserves are areas that are specially designated or the
conservation o wildlie. Terrestrial, aquatic and marine nature reserves
have all been established.
Establishment o a nature reserve is oten not enough active
management is required.
This may involve:
controlled grazing
removal o shrubs and trees
636
C.4 COn ServaTiOn OF BiODi verSiTy
removal o alien plant species and culling invasive animals
reintroduction o species that have become locally extinct
re-wetting o wetlands
limiting predators
controlling poaching
eeding the animals
controlling access.
Ex situ conservation Figure 3 White rhinoceros (Ceratotherium
simum) horn removal, Umhlametsi Private
Ex situ conservation is the preservation of species outside Nature Reserve, South Africa. Horns are
their natural habitats. removed as an anti-poaching measure. The
horn, which is made entirely from keratin
Ex situ conservation measures involve removal o organisms rom their protein, is removed with a chainsaw at ten
natural habitat. centimetres above the base. Rhinoceros
horns are used as ornaments and for some
Plant species can be grown in botanic gardens. The seeds o plants can be traditional medicines
stored in seed banks at low temperatures, which maintain their viability
or long periods.
Captive breeding o animals is sometimes used, ollowed by release o
the captive-bred individuals into their natural habitats.
Ex situ conservation is used to back up in situ conservation measures,
or where endangered species cannot saely remain in their natural
habitats. Populations o endangered bird species in New Zealand have
been moved to oshore islands to protect them rom attacks by alien
predators or example.
Captive breeding to restore populations of endangered species
Case study ofthe captive breeding and reintroduction ofan endangered animal species.
The peregrine alcon ( Falco peregrinus) became
endangered in parts o the United States, Canada
and Europe because o the widespread use o DDT
in the 1 960s and 1 970s. Biomagnifcation caused
high levels o toxic metabolites in the at tissue
o the birds. This reduced the calcium content
o eggshells. The thinner eggshells meant ewer
successul hatching events occurred (see fgure 4) .
The captive breeding programme or peregrine Figure 4 Two peregrine falcon eggs. The egg on the left is
alcons involved conservation workers collecting normal. The one on the right has been weakened due to the
thin-shelled eggs rom nests and replacing them mothers exposure to DDT
with porcelain replicas. They incubated the thin-
shelled eggs in a hatching acility under careully
controlled conditions ensuring greater requency
o successul hatching.
637
C ECOLOGY AND CONSERVATION
Fledglings were then replaced in the nest number of occupied territories70
to be reared by wild peregrine alcons as well 65
as by oster prairie alcons. Captive breeding 60
pairs also generated eggs that were incubated 55 northern Alberta population
articially. S ome fedglings were raised to 50 southern Alberta population
the age o independence by providing them 45 total Alberta population
with ood in hack boxes that were open to 40
the wild or them to increasingly nd ood on 35
their own. 30
25
In 1 973, there were no breeding pairs o peregrine 20
alcons detected in Southern Alberta, Canada 15
and ew detected in Northern Alberta. A captive 10
breeding programme was initiated and the success 5
o the programme is evident in gure 5. 0
1970 1975 1980 1985 1990 1995 2000 2010
year
Figure 5
Diferent groups work together to conserve biodiversity
Scientists collaborate with other agencies: the preservation of species involves
international cooperation through intergovernmental and non-governmental
organizations.
Scientic research can inorm best practice but independently rom any orm o government.
needs the support o agencies that can eect NGOs are typically non-prot groups that pursue
proposals or conservation. National governments wider social aims and lack political aliation. The
can take enlightened steps when they set aside WWF is an example o an NGO. It raises unds or
land as nature reserves. educational programmes and lobbying eorts.
Because threats to biodiversity extend beyond Figure 6 Teacher and school children holding tree saplings
borders, conservation involves international whilst listening to a World Wide Fund for Nature (WWF)
cooperation. I one national government places conservation worker (left) . These saplings will be planted
restrictions on harvesting products based on as part of a tree planting in Sagarmatha National Park,
endangered species, nationals rom other Himalayas, Nepal. The scheme is aimed at replacing forest
countries might ree ride on their restraint. lost due to deforestation caused by tourism
Intergovernmental organizations such as the
International Union or the Conservation o Nature
(IUCN) can acilitate agreement between nations.
The IUCN publishes the Red List o threatened
species which publishes the status o the
conservation o species. This organization acilitated
the creation o the Convention on International
Trade in Endangered Species (C ITES) which is a
treaty which regulates the international trade in
specimens and products o wild plants and animals.
This is done in an eort to ensure that trade does
not threaten survival o the organism in the wild.
Non-governmental organizations (NGOs) such as
the World Wide Fund or Nature ( WWF) operate
638
C.4 COn ServaTiOn OF BiODi verSiTy
Components o biodiversity sample A
sample B
Richness and evenness are components o biodiversity.
Biological diversity, or biodiversity, has two components. Richness reers to
the number o dierent species present. In fgure 7, sample A has greater
richness as three species are present. Evenness reers to how close in numbers
each species is. I two individuals were to be chosen rom the sample,
evenness would be an indicator o the likelihood that the two individuals
would be rom dierent species. By this standard, sample B is more even.
Simpsons diversity index Figure 7
Analysis o the biodiversity o two local communities actt
using Simpsons reciprocal index o diversity.
Groups o students studied the
The Simpsons reciprocal index quantifes biodiversity by taking into species diversity o the beetle auna
account richness and evenness. The greater the biodiversity in an area, ound on two upland sites in Europe.
the higher the value o D. The lowest possible defned value o D is 1 The same number o students
and would occur i the community contained only one species. The searched or a similar length o time
maximum value would occur i there was perect evenness and would be in each o the two sites. The two sites
equal to the number o species. were o equal area.
The ormula or Simpsons reciprocal index o diversity is: The number o individuals o the our
species ound at each site is given in
D = _N( N - 1 ) the table below.
n(n - 1)
Spcs St a St B
D = diversity index, N = total number o organisms o all species
ound and n = number o individuals o a particular species. Trichius fasciatus 10 20
Biogeography can infuence diversity Aphodius lapponum 5 10
Biogeographic actors afect species diversity. Cicindela campestris 15 8
The eectiveness o nature reserves at conserving biodiversity depends Stenus geniculatus 10 2
on their biogeographical eatures.
) Calculate the reciprocal Simpson
Large nature reserves are more eective than small ones at
maintaining biodiversity. This is consistent with the island diversity index (D) or the beetle
biogeography model i nature reserves are like islands. The larger an
island is, the greater the biodiversity ound there. The larger the area, auna othe two sites. [3]
the higher the population o a certain species that can be supported
and the less likely that small populations will be extirpated by b) Suggest a possible conclusion that
random events.
can be ormed. [2]
Connected nature reserves are more eective than isolated ones. I there
are several small reserves near to one another, then corridors between Source: International Baccalaureate November
them can increase eectiveness at preserving biodiversity. E ven narrow 07 exam.
wildlie corridors allow organisms to move between ragmented habitats,
or example through tunnels under busy roads.
Because the ecology o the edges o ecosystems is dierent rom the
central areas, the shape o nature reserves is important. I the central area
can be maximized and the total length o the perimeter can be minimized,
then the reserve can preserve biodiversity better. A circular reserve would
thereore be superior to an extended strip o land with the same total area.
639
C ECOLOGY AND CONSERVATION
Impact o island size and edge efects on diversity
Analysis o the impact o biogeographic actors on diversity limited to island size
and edge efects.
Island biogeography studies have found that two Proximity to the mainland will lead to new
important determinants of biodiversity on an colonization.
island are:
If the island is small, rates of extinction will be
proximity to the mainland, and higher. The total size of a population on an island
with low area is more likely to be small and
the area of the island. low in genetic diversity. Random accidents can
have a large negative impact on a small island
These variables lead to a balance between population.
colonization and extinction.
Data-based questions: Island size and diversity
Figure 8 shows the relationship between a) Estimate the number of bird species on an
species richness and island area for reptiles and
amphibians in the West Indies. Figure 9 shows island of 1 0,000 square miles. [1 ]
the relationship between species richness and
island area for birds in the Sunda Islands. Both b) Outline the relationship between [2]
sets of data are from: R. H. MacArthur and the number of amphibian and reptile
E. O. Wilson, The Theory ofIsland Biogeography, species and island area.
Princeton University Press Princeton, N.J. (1 967) .
Birds (Sunda Islands, Malaysia)
Amphibians and reptiles (West Indies)
1,000
number of species
number of species
100 100
10 10
1 10 102 103 104 105 1 10 102 103 104 105
1 area (mi2) 1 area (mi2)
Figure 8 Figure 9
Data-based questions: Forest size and songbird density
Figure 1 0 shows the probability of sighting three b) In a 32 ha forest, which is the [1 ]
bird species whose preferred habitat is the forest (i) most likely species to be observed [1 ]
interior away from forest edges. The dotted lines (ii) least likely species to be observed.
represent the range of probability.
a) (i) In a 1 0 ha forest, determine the range c) Based on this data, suggest with a reason,
of probability of observing a wood the minimum size a conservation area
thrush. [1 ] should be to preserve populations of
woodland interior species. [2]
(ii) In a total of 20 point transects undertaken
in a 3.2 ha forest, how many times is a
red-eyed vireo likely to be observed. [2]
640
C.4 COn ServaTiOn OF BiODi verSiTy
probability of occurrence red-eyed vireo probability of occurrence wood thrush
1.0 1.0
0.9 0.9
0.8 0.8
0.7 0.7
0.6 0.6
0.5 0.5
0.4 0.4
0.3 0.3
0.2 0.2
0.1 0.1
0.3 1.0 3.2 10 32 100 320 1000 3000 0.3 1.0 3.2 10 32 100 320 1000 3000
area of forest (ha) area of forest (ha)
probability of occurrence scarlet tanager
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.3 1.0 3.2 10 32 100 320 1000 3000
area of forest (ha)
Figure 10
641
C ECOLOGY AND CONSERVATION
C.5 poultion ecology (aHL)
Understanding Applications
Sampling techniques are used to estimate Evaluating the methods used to estimate the
population size. size o commercial stock o marine resources.
The exponential growth pattern occurs in an Use o the capture-mark-release-recapture
ideal, unlimited environment. method to estimate the population size o an
animal species.
Population growth slows as a population
reaches the carrying capacity o the Discussion o the eect o natality, mortality,
environment. immigration and emigration on population size.
The phases shown in the sigmoid curve can Analysis o the eect o population size, age
be explained by relative rates o natality, and reproductive status on sustainable fshing
mortality, immigration and emigration. practices.
Limiting actors can be top-down or bottom-up. Bottom-up control o algal blooms by shortage
o nutrients and top-down control by herbivory.
Nature of science
Skills
Avoiding bias: a random number generator
helps to ensure population sampling is ree Modelling the growth curve using a simple
rom bias. organism such as yeast or species o Lemna.
Estimating population size
Sampling techniques are used to estimate population size.
The simplest method of estimating population size or population density
is to count the number of individuals in a given area. This is only
feasible if the individuals are large and the area is small. For most other
cases, ecologists use population sampling techniques. This requires the
researcher to determine the population size in a small area and use
this to estimate the entire population. This is referred to as population
sampling. The sample is assumed to be representative of the entire
population. Normally, several samples are taken to limit the effect of
choosing a sample which is not representative.
Using a random number generator
Avoiding bias: a random number generator helps to ensure population sampling is
ree rom bias.
In order for the sample to be representative of There are several methods of generating a
the entire population, the selection of the sample random sample. A computer or graphic calculator
should be random. A random sample is one can be used to generate a random sample. The
where every member of the population has an activity box describes a method that uses a
equal likelihood of being selected. graphic calculator to generate a random sample.
642 Alternatively, a random number table can be used.
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