chapter 02 - relationships in an ecosystem

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Chapter 2 – Relationships inan Ecosystem



CHAPTER 2 Relationships in an Ecosystem

UNIT I LIVING ORGANISMS IN THE ENVIRONMENT

Feeding Relationships between Organisms

You should be able to:

■ identify the relative positions of producers and

consumers in a food chain, and relate the positionsto their modes of feeding;

■ understand the terms herbivore, carnivore and

omnivore;

■ identify predator or prey relationships in the

selected habitats;





2.1 Feeding Relationships between Organisms


■ explain the role of decomposers;

■ construct a food web to include different trophic

levels;

■ discuss the interdependence of organisms within a

food web; and

■ discuss the advantages and disadvantages of specialrelationships between organisms.





The Ecosystem

• Ecology is the study of relationships between organisms and

their environment.

•

The living (biotic) environment includes all the living thingsthat an organism interacts with;

• The physical (abiotic) environment includes the non-living

aspects such as light, temperature and water.

• All these interacting factors in a specific area make up an

ecosystem.







Fig 2.2: Different ecosystems





The Ecosystem

• There are many habitats within an ecosystem. A habitat is the

place where an organism lives.

• Organisms of the same species living in a particular habitat

make up a population.

• All the different populations of the various species living

together in a particular habitat make up a community.







Fig 2.4: The different habitats






Fig 2.3: The different populations found in a

freshwater pond community





The Ecosystem

• All the environmental conditions and resources required for an

organism to survive, reproduce and function in a community is

termed as the ecological niche.

• The habitat and ecological niche are not the same. Manydifferent organisms can share the same habitat, but they

cannot occupy the same niche, as the niche is unique to a

particular species in a community.

• No two species can occupy exactly the same niche.






The Ecosystem

• When shared resources such as light, food, space, oxygen are

shared by organisms, then competition results.

• Competition can arise between members of the same species

(e.g. competing for a mate) or between different species (e.g.competing for territory and shelter).

• Competition affects population size and distribution of species.

• Members of the same species may occupy different ecological

niches and trophic levels at different points in their life cycle avoid competition for resources among the same species e.g.

butterflies and caterpillars.






The Ecosystem

The living organisms in any ecosystem are made up ofproducers, consumers and decomposers.

•

Producers manufacture organic substances using water, carbondioxide and energy from light or from chemical reactions.

• Photoautotrophs use light energy to drive the process calledphotosynthesis.E.g. green plants, algae and certain bacteria

• Chemoautotrophs use energy from chemical reactions E.g. incertain bacteria such as nitrifying bacteria that are important inthe nitrogen cycle.






The Ecosystem

• Consumers are animals that eat other organisms to obtain

energy and nutrients.

• Herbivores are animals that only eat plants and are known as

primary consumers.

• Carnivores are animals that eat other animals.

• Omnivores eat both plants and animals.

• Carnivores that feed on herbivores are called secondary

consumers and tertiary consumers feed on secondaryconsumers.


C 2 l i hi i





The Ecosystem

• Decomposers or detritivores are organisms that feed on deadorganisms to obtain energy. The complex compounds arebroken down into simpler compounds, thus releasing valuableminerals and nutrients into the soil for the plants.E.g. Bacteria and fungi are decomposers; earthworms, beetles

and termites are detritivores.

• Mould is a species of fungi that play a major role in the

decomposition of organic materials. Mould cannotphotosynthesise like plants but obtain nutrients by breakingdown the organic material where they are found in.


CHAPTER 2 R l ti hi i E t






Fig 2.11: Decomposers and Detritivores






Food Chains and Food Webs

• Food chains represent the feeding relationships between

organisms.

• A food chain always begins with a producer which is eaten by a

primary consumer. The latter which is then eaten by asecondary consumer.

• Each stage in the food chain is called a trophic level. Producers

make up the first trophic level.








• Food chains usually do not have more than four trophic levels.

This is because energy is lost at each trophic level, thus there is

less and less energy available for organisms at the higher

trophic levels.

• Hence, most food chains consist of only four to five trophic

levels as there will be insufficient energy to support an

organism at higher trophic levels.


CHAPTER 2 Rel tio hi i E o te





• The arrows on the food chain represent the direction in which

the organism is being eaten.


Fig 2.12: A simple food chain







Fig 2.14 Food chains found in different habitats







• In a particular habitat, organisms are usually involved in morethan one food chain. A food web is formed when many food

chains link together.


Fig 2.15: A simple food web







Fig 2.16 A complex food web






Inter-Dependence of Organisms and their

Environment

Nutritional Interdependence

• Green plants are the main producers of a food web.

They can synthesize organic food substances throughphotosynthesis.

• Herbivores feed on plants for nutrition.

• Carnivores are indirectly dependent on them for their food and

energy because they eat the herbivores.• If there were no plants in an ecosystem, there would not be any

herbivores left to feed the carnivores.







Inter-Dependence of Organisms and their Environment

Oxygen and Carbon Dioxide Interdependence

• Living organisms give out carbon dioxide and take in oxygen

during respiration. Carbon dioxide is also produced during the

decomposition of dead organisms.• Plants take in carbon dioxide from the air and give out oxygen

during photosynthesis.

• In this way, the carbon dioxide and oxygen balance in the

environment remains relatively constant.








Interdependence in Pollination

• Many insects such as the butterfly and the bee obtain nectar as

food from flowering plants.

• As they move from flower to flower, the insects transfer pollengrains from one flower to another, thus helping to pollinate the

flowering plants so that the plants can reproduce.








Interdependence in Dispersal of Seeds and Fruits

• Animals aid in the dispersal of seeds and fruits of flowering

plants.

• Seeds may get attached to the bodies of animals and carriedaway to other places.

• Animals which eat the fruits cannot digest the seeds and pass

them out through the faeces. The seeds which are still able to

germinate are thus dispersed to other places.








• Living things and the environment are also interdependent. The

environment provides living things with energy, materials for food

and respiration, space, shelter, and warmth.

• Activities of organisms affect the environment as well.• Decomposers and detritivores feed on the wastes and dead

remains of organisms

• Trees help to keep the land stable, provide shelter for many

insects and animals, and keep the environment cool.








• Living organisms, as they grow, help to break up rock surfaces

which cause further erosion.

• Processes - respiration, photosynthesis and decomposition

which take place in organisms, and human activities such ascombustion of fossil fuels - keeps the amount of oxygen and

carbon dioxide in the environment at a relatively constant level.

• Human activities have the greatest effect on the environment.







Special Relationships between Organisms

Predation

• An animal that feeds on another animal is called a predator and

the animal eaten by the predator is called the prey. Predation

occurs when a predator kills and eats its prey.


Fig 2.17: The bear is a

predator. Fish are the prey ofbears.







Predation

• In a habitat, the relationship between predators and their prey

has an effect on their population size. The population size of

the predators and their prey fluctuates in a cyclical nature. Theaverage size of the prey population is larger than the predator

population.

• However, there are many other factors involved in an

ecosystem (e.g. the presence of other prey for the predator)that can cause the change in their population size.







• The effect of predator-prey relationship on their population size

is shown in the graph below.







It can be seen from the graph that:

• An increase in the prey population means more food for the

predators and an increase in the predator population.

•

When predators increase in numbers, the prey population issubsequently reduced because of an increase in predation.

• With less prey available, the predator population decreases.

• With fewer predators, the prey population increases again.





p y



What are some adaptations that some predator and prey have

evolved?


Fig 2.19: This lizard camouflages by blending with the lichen on rocks,

while the tortoise has a hard shell to deter would-be predators.




p y



• Interactions between predator and prey are often brief. When

two different organisms interact with each other for long

periods of time, a special relationship develops and is referred

to as symbiosis.

• Parasitism, commensalism and mutualism are examples of

symbiotic relationships.





p y



Parasitism

• A parasitic relationship is one in which one organism, the

parasite, lives off of another organism, the host, harming it and

possibly causing death.• The parasite lives on or in the body of the host.

• Common parasites are viruses, bacteria, fungi, protozoans,

flatworms (tapeworms and flukes), nematodes, insects (fleas,

lice), and arachnids (mites).


tapeworm

Fungus -

ringworm




p y


Fig 2.23: Aphids are insects that eat the sap from the plants on

which they live. They are parasites to the plant. However,

ladybugs which live on these plants will eat the aphids and

benefit by getting food, while the plant benefits by being rid of

the aphids.




p y



Commensalism

• A symbiotic relationship where one organism benefits and the

other neither benefits nor gets harmed.


Fig 2.25: The sea anemone protects

the clown fish from the predators as

most fish avoid the poisonous

tentacles of the sea anemone. The

clown fish have special mucus on

their bodies which prevents themfrom getting stung. They have no

effect on the sea anemone.





Fig 2.26: An epiphyte is a plant that

grows on another plant for support. It

is not parasitic, but uses the host

plant for support only. Epiphytic

plants have aerial roots that absorb

moisture from the air, thus allowing itto develop on the tree.






Mutualism

• A symbiotic relationship where two organisms of different

species work together and benefit from the relationship.


Fig 2.27: The birds obtainfood from the ticks and

insects found on the body of

the ox thus helping the ox to

get rid of these parasites.





Fig 2.29: Nitrogen-fixing bacteria found

in the root nodules of leguminous

plants such as the pea plant help theplant to obtain nitrogen in a process

called nitrogen fixation. The plants in

turn provide nutrients and shelter for

the bacteria.





2.2 Energy Flow Within a Food Chain or

Food Web


■ explain energy flow within a food chain or food

web and discuss limitations of food chains in

supporting more than four trophic level;

■ construct pyramids of energy, biomass and

numbers; and■ explain the continual re-use of materials in nature.





Energy Flow

• The two processes that are important to an ecosystem

are:

1) the energy flow through the system, and

2) the cycling of nutrients within the system.

2.2 Energy Flow Within a Food Chain or Food Web





Energy Flow

• The 1st source of energy in an ecosystem is the Sun.

• Producers, mainly made up of plants, capture about 1% of light

energy from the sun and convert it into chemical energy during

photosynthesis.• Energy is used by organisms for respiration, growth, movement

and reproduction. Energy not used by the cells is stored and

provides food for other consumers.

•

However, not all the energy is used or stored efficiently. Onlyabout 10% of energy from one trophic level is passed on to the

next trophic level.






Energy Flow





Energy Flow

At each trophic level, energy is lost to the environment in the

following ways:

• as heat from respiration,

• in excretory products such as urine,

• in indigestible material such as faeces,

• in dead organisms or uneaten body parts.






Energy Flow

• Since energy is lost at each trophic level, less and less

energy is available for organisms at the higher

trophic levels.

• Hence, most food chains consist of only four to five

trophic levels as there will be insufficient energy to

support an organism at higher trophic levels.






Energy Flow

• Energy lost to the environment cannot be recycled

energy flow in an ecosystem does not flow in a

cycle and is described as non-cyclic.






The flow of energy in an ecosystem can be summarised in the

figure below:



l h d h d b




Ecological Pyramids

Ecological pyramids can be constructed to represent the

numbers, biomass and energy of the organisms at each

trophic level of a food chain.

• Pyramid of numbers – shows the no. of organisms at eachtrophic level at a particular time

• Pyramid of biomass – shows the dry mass (mass of an

organism when completely dried - without water)

of organisms at each trophic level at a particular time.• Pyramid of energy – shows total energy content of organisms

at each trophic level over a certain period of time







2 2 E Fl Wi hi F d Ch i F d W b




Ecological Pyramids

• There are some disadvantages in representing a food chain

with a pyramid of numbers, as the size and the age of the

organism are not considered when we are counting the

number of organisms present at each trophic level.



2 2 E Fl Withi F d Ch i F d W b




• This can be seen in the food chain below, where one tree is

equated to one caterpillar regardless of its size, thus giving an

inaccurate representation of the food chain.







Ecological Pyramids

• Measuring biomass of the organisms at each level is a more

reliable and accurate representation of a food chain than

counting the organisms at each trophic level.

• Thus the food chain above can be better represented with a

pyramid of biomass.







Ecological Pyramids

• Pyramids of energy are the most accurate representation of a

food chain.

•

However, collecting such data is difficult and needs to becollected over a period of time, usually a year.

• As more and more energy is lost at higher trophic levels, a

pyramid of energy is always broad at the bottom and narrowtowards the top.






Fig 2.36 (C): A pyramid of energy






2 2 Energy Flow Within a Food Chain or Food Web




Cycling of Nutrients

• Carbon, oxygen, nitrogen and water are essential nutrients for

life. They are returned to the soil when decomposers break

down dead organisms.

• Nutrients are not lost to the environment but are recycled

and used again by plants. The flow of nutrients in an

ecosystem is thus cyclical, unlike the flow of energy.

• In a balanced ecosystem, nutrients are continually recycled by

physical, chemical and biological processes.







The Carbon Cycle

• Carbon is present in the environment in the form of

carbon dioxide (CO2).

The carbon cycle is important to

• ensure there is a continuous supply of carbon

dioxide for plants to carry out photosynthesis;

• keep the amount of carbon dioxide in theenvironment at a relatively constant level.







The Carbon Cycle

These processes release CO2 into the environment:

• respiration of living organisms,

• combustion of fossils fuels,

• decay of dead organisms.

Fossil fuels are natural resources formed by the remains ofdead organisms buried millions of years ago. They consist of

carbon and hydrogen atoms bonded together. When burned,the bonds break to release large amounts of heat energy andcarbon dioxide gas.







The Carbon Cycle

These processes remove CO2 from the environment:

• photosynthesis of plants

• storage of carbon compounds in animals

• storage of carbon compounds in fossil fuels






Fig 2.38: The carbon cycle






The Nitrogen Cycle

• Nitrogen is an important component of proteins, nucleic acids

and other nitrogen-containing compounds.

• Nitrogen gas makes up about 80% of the atmosphere.

• Plants take in nitrogen in the form of nitrate ions in the soil

through active transport into the root hair cells.

• Animals obtain nitrogen-containing compounds from the food

in their diet.







The nitrogen cycle consists of five main processes:

• Nitrogen fixation – nitrogen gas is converted into

nitrogen-containing compounds by lightning, industrial

processes and microorganisms.

• Assimilation – nitrogen is assimilated in root nodules

of some plants or absorbed from soil through root hair

cells; animals assimilate nitrogen in the form of

protein obtained from the food in their diet.







The nitrogen cycle consists of five main processes:

• Ammonification – ammonia compounds produced from the

breakdown of dead and decaying material by decomposers.

• Nitrification – ammonium compounds are converted first tonitrites, then to nitrates by nitrifying bacteria. Oxygen and

energy are required.

• Denitrification – nitrate ions in the soil are converted into

gaseous nitrogen by anaerobic denitrifying bacteria. This

reduces the amount of nitrogen available in the soil for plants.






Fig 2.39: The nitrogen cycle





Key Concepts

• Ecology is the study of relationships between organisms and

their environment.

• The biotic and abiotic factors in an environment make up an

ecosystem.

• Producers are organisms that manufacture organic substances

using light energy, water and carbon dioxide in the process

called photosynthesis.

• Consumers are animals that eat other organisms to obtain

energy and nutrients. Herbivores, carnivores and omnivoresare consumers.





Key Concepts

• Decomposers are organisms that break down dead organisms

into simpler compounds to obtain energy, thus releasing

valuable minerals and nutrients back into the soil for the plants

to use.

• Food chains represent the feeding relationships betweenorganisms.

• A food web is formed when many food chains link together.

• In a habitat, the relationship between predators and their prey

has an effect on their population size.• When two different organisms interact with each other for long

periods of time, a special relationship develops and is referred

to as symbiosis.





Key Concepts

• A parasitic relationship is one in which one organism, the

parasite, lives off of another organism, the host, harming it

and possibly causing death.

• Commensalism is a relationship where one organism benefits

and the other neither benefits nor is harmed.

• Mutualism is a relationship where two organisms of different

species work together and benefit from the relationship.

• The first source of energy in an ecosystem is the Sun.

Producers capture light energy from the Sun duringphotosynthesis.





Key Concepts

• In a food chain, only about 10% of energy from one trophic

level is passed on to the next trophic level.

• Energy is lost to the environment as heat, in excretory

products, indigestible material and in dead organisms or

uneaten body parts.

• Most food chains consist of only four to five trophic levels as

there will be insufficient energy to support an organism at

higher trophic levels.

• Energy lost to the environment cannot be recycled and isdescribed as non-cyclic.




Key Concepts

• Ecological pyramids can be constructed to represent the

numbers, biomass and energy of the organisms at each

trophic level of a food chain.

• Carbon, oxygen, nitrogen and water are essential nutrients for

life. The flow of nutrients in an ecosystem is cyclical.

chapter 02 - relationships in an ecosystem

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