CHAPTER 2: ECOLOGY

CHAPTER 2: ECOLOGY SES SEMESTER II: DB024

CHAPTER 2: ECOLOGY

2.1 INTRODUCTION TO ECOLOGY

(A) DEFINITION ECOLOGY

ECOLOGY
The study of interactions between organisms and their natural environment.

(B) BASIC TERMINOLOGIES IN ECOLOGY

Terminologies Description

a. Niche ▪ The specific ecological or functional role of an organism in its environment

* A niche is like an ▪ Two different species CANNOT occupy same niche

occupation in an ▪ E.g. Aphids on the tree leaves, feed on tree sap.
ecosystem Monkey at the tree top, eat tree fruits.

Bugs at the tree root, eat decayed material

b. Habitat ▪ A place or natural environment where organisms live or grow

* Habitat is like an ▪ Protect habitants from extreme weather, predators and conducive site (for nesting,

address in an birthing, feeding & hibernation)
ecosystem ✔ Macrohabitat - large scale environment. E.g. A tree in a tropical forest.

✔ Microhabitat - particular locations within the same overall habitat, e.g. Aphids

live on the tree leaves.

c. Organism ▪ Any living things, either consist of many cells, multicellular or one cell, unicellular
▪ E.g. one human, one monkey

d. Population ▪ A group of organisms of the SAME species that live in the same area
▪ Can freely interbreed, producing fertile offspring.
▪ E.g. a group of proboscis monkey.

e. Community ▪ A group of populations of DIFFERENT species that interact and live in the SAME
area

▪ E.g. a forest community contains group of monkey, birds, trees, fungi and insects.

f. Ecosystem ▪ A community of organisms (biotic components) interacting with each other and

with their abiotic environment
▪ E.g. Lake ecosystem – consists of many types of aquatic life, plants, rocks, etc.

g. Biome ▪ Large and distinct region (terrestrial or aquatic) that has SIMILAR climate (weather,
temperature), soil, plants and animals.
✔ Terrestrial biome: e.g. Tropical Rain forest, savanna, desert
✔ Aquatic biome: Lake, Wetland, Estuaries ,Stream and rivers , Coral reef

h. Biosphere ▪ The entire portion of Earth inhabited by living organisms.
▪ Hydrosphere (aquatic), lithosphere (soil & rock), atmosphere (gaseous surround the

earth) and troposphere (mountain)

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CHAPTER 2: ECOLOGY SES SEMESTER II: DB024

2.2 LIFE HIERARCHICAL ORDER

LIFE HIERARCHICAL ORDER

Organism Population Community Ecosystem
A goat A group of goat
Groups of goats, lions, giraffes, All the living organism

zebra and others in a forest and non-living things

Biome Biosphere

Ecosystems with similar climates and communities A region of earth inhabited by living organisms

2.3 ECOSYSTEM CONCEPT

(A) ECOSYSTEM CONCEPT

ECOSYSTEM
1. Ecosystem is made up of:

▪ Biotic (living) component consists of producers, consumers and decomposers / detritivores
▪ Abiotic (non-living) components or the physical environment

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CHAPTER 2: ECOLOGY SES SEMESTER II: DB024

(B) EXAMPLES OF ECOSYSTEM

i. TERRESTRIAL ECOSYSTEM OF TROPICAL RAIN FOREST
▪ Located at the tropical region and received large amount of rain throughout the year (rainfall production)
▪ High humidity
▪ Layer/stratification of tropical rainforest:

Emergent layer Emergent
- The tallest trees (30 - 40m tall) Canopy
- Receives lot of sunlight. Usually supported by buttress Understory
Shrub
roots. Forest floor
- Exposed to strong wind & high temperature (lowest
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humidity)
- Plant: Kapok, Tualang, Jati, Cengal,
- Animal: Eagle, hawk, hornbill, bat, lebah tualang
Canopy layer
- Trees at 30m-35m tall
- Greatest biodiversity is found- containing over 50% of the

rainforest wildlife

- Leaves & branches interlock to form a roof for the forest,
thus little sunlight

- Animal: Birds, monkeys
- Plant: Consists of epiphytes such as orchids, mosses and

lichen attached to tree trunk & branch.
Understory
- Tree is about 20m tall
- Not as dense, as it receives less sunlight under the

canopy; Consists of smaller trees
- Plant: Many plants adapted to climb already-established

host trees e.g: Lianas sp. (woody tropical vines)
- Animal: snakes, tree frog, lizard
Shrub layer
- Consist of smaller plant such as fern
- Less than 2-5% sunlight.
- Has the densest plant growth
- Plant: shrubs, ferns
- Animals: honey bee, spiders, insects
Forest floor/ Ground layer
- Usually dark and damp with very high humidity,
- Receive 0-1% of sunlight.
- Contain layer of rotting leaves and dead animals that form

thin humus, rich in nutrient.
- Plant: bryophytes/ mosses, grass
- Animals: millipede, ants, worm, snail and microorganism

CHAPTER 2: ECOLOGY SES SEMESTER II: DB024
ii. LAKE ECOSYSTEM
P : Littoral zone
Q : Limnetic zone
R : Profundal/ aphotic zone
S : Photic zone
T : Benthic zone

Lake environment is generally classified on the basis of three physical criteria
1. light penetration (photic and aphotic zones)
2. distance from shore and water depth (littoral and limnetic zones)
3. whether the environment is open water (pelagic zone) or on the bottom (bentic
zone)

Lake ecosystem based on LIGHT PENETRATION (stratified vertically)

Photic zone Aphotic/ Profundal zone Benthic zone

• Shallow water • Deep water zone located just below the • The bottom layer / “floor” of
• Sufficient light for
photic zone. Little light penetrates. any aquatic biome containing
photosynthesis
• Plankton (e.g. • Insufficient light for photosynthesis sand and organic and

phytoplankton, (Plant & algae DO NOT live here) inorganic sediments.

zooplankton) and • Little life, except for bacteria. • Zone of decomposition.
• This zone does NOT exist in shallow • Occupied by communities of

many fish species lake - Because sunlight reaches ALL organism called benthos/

occur the way to the bottom of the lake animals live on the bottom
• Comprise of littoral • The energy source for organism in this
(e.g.: snails, clams)
and limnetic zone. zone is dead organic matter / detritus • Major source of food for

that drift down from photic zone benthic is detritus (dead

(littoral and limnetic zones) organic matter).
The photic and aphotic zones together make up the pelagic zone • Biotic components: bacteria,

detritivores, fungi, benthos

Compensation point:
• The point when the rate of photosynthesis is EQUAL to the rate of respiration
• Determined by intensity of light at a given temperature

Lake ecosystem based on DISTANCE FROM SHORE AND WATER DEPTH (stratified horizontally)

Littoral zone Limnetic zone
• Close to shore, shallow and well lit • Further from the shore to open surface water and
• Biotic components: Aquatic plants (rooted,
well lit
submerged and floating plant), small fishes • Biotic components: Phytoplankton, zooplankton

and invertebrates (microscopic animals) and fishes.
• Surface organisms - water strider
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CHAPTER 2: ECOLOGY SES SEMESTER II: DB024
(C) COMPONENTS OF THE ECOSYSTEM

COMPONENTS OF THE ECOSYSTEM

i. BIOTIC COMPONENTS

Producer (Autotroph) Decomposer (saprophyte)

▪ All photosynthesizing organisms that ▪ A heterotroph that secrete digestive enzymes to

synthesizes complex organic substances breakdown dead organic materials and absorb the

(sugar) from simple inorganic substances resulting products

▪ The process using sunlight, CO2, H2O ▪ e.g Bacteria, fungi.
▪ e.g green plants, algae, cyanobacteria

Consumer (Heterotroph)

▪ An organism that CANNOT synthesize its own food from inorganic raw materials and therefore must

obtain from other organisms

▪ Organisms that feed on other organisms or substances as their food. Can be divided into:

Herbivores Carnivores Omnivores Detritivores

Animal that Animal that consumes Organisms that Animal that consumes/ ingests

consume plant animal only. consumes BOTH small fragments of dead

only plants and animals organisms (detritus)

Primary consumer Secondary, tertiary, and e.g human e.g dung beetle, crab,

e.g grasshopper, quaternary consumer. earthworm, maggots, snail,

rabbit, cow e.g Tiger, snake, eagle millipede, centipede, shrimp

ii. ABIOTIC COMPONENTS
▪ Abiotic component is any of the non-living chemical and physical factors

Hydrosphere Atmosphere Lithosphere
All the WATER on the Earth’s A layer of GASES Soil and rock / the "solid, outer" part of
surface surrounding the earth and Earth.
Include the aquatic biomes retained by the earth's Two parts:
e.g. lakes, rivers, estuaries, gravity ▪ The crust.
intertidal zones, coral reef, ▪ The upper mantle including terrestrial
oceanic pelagic, abyssal zones
biomes)

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CHAPTER 2: ECOLOGY SES SEMESTER II: DB024

2.4 ENERGY FLOW

(A) TERMS

i.Food chain
▪ Food chain is the pathway for the transfer of energy from one trophic level to another / A path of food

consumption beginning with producers.
▪ Shows a linear feeding relationship
▪ The arrow indicates direction of energy flow// consumption of organism// eaten by

1. Grazing Food chains:
- Begin with plants (producer) at the first trophic level then goes to primary, until tertiary
consumer.
- Energy for this food chain comes from the sun (solar radiation / light energy)
(i) Predatory food chain

(ii) Parasitic food chain
✔ Either the producers or the consumers are infected by parasites
✔ Food energy passes from larger to smaller organisms (the energy transfer through
this food chain is not significant)

2. Detritus Food chains:
- Begin with litters (detritus/ dead organic matter) at the first trophic level, then eaten by
detrivore, then their predators.
- Detritus: Fallen leaves, plant parts or dead animal bodies
- Energy for this food chain (Primary energy source) comes from detritus (less dependent on
direct solar energy)

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CHAPTER 2: ECOLOGY SES SEMESTER II: DB024

ii. Food web

• A complex interconnection of
food chains in an ecosystem/ A
complex network of food chains

• Food web exist because usually
most animal feed on more than one
species of organism

iii. Trophic levels
▪ Trophic level is the different feeding levels/ position of an organism in a food chain/ food web.
▪ It is composed of all the organism that feed at particular link in food chain
▪ Involved producers & consumers:

✔ Producers/ autotroph = First trophic level

✔ Consumers = Second, third, fourth, fifth trophic level & so on
▪ Usually each food chain has 4 or 5 trophic levels
▪ Decomposers (or detritivores) are sometimes considered to occupy their OWN trophic level / NO

designated trophic level

Why food chain does not consist of more than 5 trophic levels?
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CHAPTER 2: ECOLOGY SES SEMESTER II: DB024

Trophic level is usually LESS than FIVE because: -
1. When energy is transferred from one trophic level to another, large amount of energy is lost (as heat to
surrounding)

In animals, energy lost / heat lost through respiration, decomposition, excretion
(urine, sweat) / egestion (defecation)
In plants, energy lost / heat lost through respiration, decomposition

2. Each trophic level receives less energy than the level below it
→ Because the size of organism is bigger in higher level & required more energy

3. At the fourth or fifth trophic level, only a small amount of energy is left
4. This may be insufficient to support further trophic level
5. Therefore, limiting the number of organisms / trophic levels in a food chain

(C) ENERGY TRANSFER IN THE PADDY FIELD ECOSYSTEM

Energy flow in each trophic level
Sun is the original source of energy in an ecosystem. It releases
amounts of solar energy into space.
▪ Paddy (producer) take about 1% of the available light energy

for biomass production (photosynthesis).
▪ About 99% amount of light (unit: kJ m-2 year-1) is immediately

lost from the plant are reflected away / not absorbed by plants/
do not fall on plants.

▪ Mice (primary consumer) feed on paddy. Energy is
transferred from the FIRST trophic level to the SECOND
trophic level

▪ ONLY 10% of the energy is transferred to the next trophic
level.

▪ 90% of energy is lost to environment through respiration as
heat.

▪ Energy also loss through excretion (urine) and egestion (feces).

▪ Snake (secondary consumer) feed on mice. Energy is
transferred from the SECOND trophic level to the THIRD
trophic level.

▪ Eagle (tertiary consumer) feed on snake. Energy is transferred
from the THIRD trophic level to the FORTH trophic level.

▪ Carnivores (secondary & tertiary consumer) capture and
consume about 10% of the energy stored by the herbivore. 90%
of energy is lost to environment.

▪ When all the organisms die, they were decomposed by
decomposer.

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CHAPTER 2: ECOLOGY SES SEMESTER II: DB024

2.5 BIOGEOCHEMICAL CYCLES

(A) DEFINITION

Biogeochemical cycle
The cyclic movement of elements between living organisms (biotic) and their nonliving (abiotic)
surroundings. E.g. Carbon cycle, nitrogen cycle and phosphorus cycle.

(B) EXAMPLES OF BIOGEOCHEMICAL CYCLES
(i) CARBON CYCLE

1. Photosynthesis : Plants (autotroph) fix carbon during photosynthesis.
2. Dissolve in water : CO2 dissolved in water in form of carbonate ion (CO32-) and bicarbonate ion, HCO3-
3. Respiration : Carbon returns as CO2 to environment. Occur in plants and animals.
4. Decomposition : CO2 is released during decomposition of death plants and animals by decomposer

(bacteria and fungi)
5. Combustion/ burning : Combustion of fossil fuel (coal, peat and oil) returns CO2 to atmosphere.
6. Decaying / fossilization : Dead organism (plant) decay and fossilized to become fossil fuel (peat, coal,

petroleum)
7. Weathering : Limestone hill / rocks undergoes weathering and erosion thus releasing CO2 to the

atmosphere and water. (When mollusks die, their shells that contain CaCO3 sink to the bottom and deposited
as limestone. The process of chemical and physical weathering slowly erodes it away to return CO2 to
atmosphere and water)

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CHAPTER 2: ECOLOGY SES SEMESTER II: DB024
Name the following process for the CARBON CYCLE:

A: Combustion

B: Respiration
C: Photosynthesis

D: Feeding/ eating/
consumption

5 ii. NITROGEN CYCLE
1 3

3 1
2

4
2

1

Process Process involved in carbon cycle:
1. Nitrogen fixation Explanation
2. Nitrification
3. Assimilation the conversion of nitrogen gas to ammonia // nitrate
4. Ammonification
5. Denitrification the conversion of ammonia// ammonium ion to nitrate

the conversion of nitrate// ammonia// ammonium ion to proteins

the conversion of organic nitrogen to ammonia// ammonium ion

the conversion of nitrate to nitrogen gas

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CHAPTER 2: ECOLOGY SES SEMESTER II: DB024
iii. PHOSPHORUS CYCLE

Illustration of Phosphorus Cycle

Inorganic
Phosphate in rocks

Weathering/ erosion

Inorganic Rainwater Inorganic Phosphate
Phosphate in soil Leaching in rivers, sea

Decomposition

Death, excretion

Death

Organic Phosphate Organic Phosphate
in plant in animals

2.6 HUMAN IMPACT ON THE ECOSYSTEM AND THE BIOSPHERE

i. Agricultural effects on nutrient cycling
▪ Clearing vegetation from land for agriculture often increases runoff and can reduce infiltration that

recharges underground water supplies.
▪ Use of groundwater for irrigation increases evaporation over land and depletes groundwater supplies
▪ Excess nitrogen compounds released into environment via improper disposal of livestock waste/manure
▪ Nitrate and phosphate-rich fertilizers used heavily in agriculture ==> can lead to eutrophication of

freshwater ecosystems due to fertilizer-contaminated runoff from farmland.

ii. Combustion of fossil fuel
▪ Fossil Fuels are formed from the buried remains if of plants and animals over a period of millions of years.

Examples: coal, petroleum and natural gas.

▪ They release heat when they are burned and this is used directly in many applications, such as heating
homes, and to generate electricity in power stations.

▪ The combustion of fossil fuels emits different pollutants such as fly ash and various gases into the
atmosphere. Both may have an adverse impact on the environment.

▪ When fuels are incompletely burnt, they release carbon monoxide gas into the atmosphere. This gas is very
dangerous as it is poisonous in nature.

▪ The combustion of fossil fuels also releases a large amount of carbon dioxide into the atmosphere. Carbon
dioxide is a greenhouse gas which is responsible for global warming.

▪ Emissions of sulfur dioxide and nitrogen oxides, both of which are acidic, mix with moisture in the
atmosphere to create so-called acid rain, which damages buildings and trees.

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CHAPTER 2: ECOLOGY SES SEMESTER II: DB024

iii. Global warming
▪ Burning of fossil fuels and deforestation have led to increase of atmospheric CO2
▪ These activities increase the atmosphere’s ability to hold in heat (greenhouse effect) and is resulting in

climate change (global warming)
▪ Greenhouse effect: process by which carbon dioxide and other gases in the atmosphere absorb infrared

radiation from the sun, forming a “heat blanket” around the Earth
▪ Some sunlight is reflected and other is trapped as heat to warm the Earth
▪ Enhanced greenhouse effect: caused from an increase of carbon dioxide, methane, and nitrous oxides from

human activities into the air which traps more heat and raises the temperatures of the Earth’s surface
▪ Global Warming: an average increase in the Earth's temperature, which in turn causes changes in climate.
▪ A warmer Earth may lead to changes in

✔ rainfall patterns

✔ A rise in sea level

✔ A wide range of impacts on plants, wildlife, and humans

2.7 POPULATION ECOLOGY

(A) POPULATION ECOLOGY

Population Ecology
▪ Population: A group of individual of the same species which live in a particular area at the same time.
▪ Ecology: The studies of interaction among living things and their environment
▪ Population ecology: The branch of ecology that studies the structure and dynamics of populations// A

study of how members of a population interact with their environment

(B) POPULATION GROWTH

Population Growth

▪ The changes in the number of individuals in a population over time. It can be

✔ Positive population growth (increase in population size)

✔ Negative population growth (decrease in population size)

✔ Zero population growth (no net increase or decrease in population size)

▪ Population growth is mainly determined by birth, death, immigration and emigration
✔ Increase population size = birth (natality) + immigration
✔ Decrease population size = death (mortality) + emigration

▪ Population growth is also affected by biotic potential (r), environmental resistance and carrying
capacity (K)

▪ Biotic potential (r) - The maximum reproduction capacity of an organism under optimum environmental
condition

▪ Environmental resistance - Environmental factors (combination of biotic and abiotic) that limit growth of
the population

▪ Carrying capacity (K) - The maximum population size that a particular environment can support

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CHAPTER 2: ECOLOGY SES SEMESTER II: DB024

(C) NATALITY AND MORTALITY AND THEIR EFFECTS ON THE RATE OF POPULATION
GROWTH

Natality Mortality

Birth rate. Death rate.

The number of offspring produced in a given time The number of individuals died in a given time

period period

▪ If natality > mortality, population size increases; If mortality > natality, population size decreases

▪ If natality = mortality, population is stable (net growth / growth rate is zero)

(D) POPULATION GROWTH CURVES

i. Exponential growth curve ii. Logistic growth curve
▪ Characterized by J-shape curve ▪ Characterized by S-shaped/ sigmoid curve shape

shape

▪ Eg; human population growth ▪ Eg; Growth of Paramecium sp. in the lab

* both graph cannot start with 0

END OF THE TOPIC

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