Communities, Adaptations & Interdependence

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CognitoEcosystems, communities and adaptations

Key facts & methods

Ecosystems and communities

Population: all individuals of one species in an area.
Community: all the different populations in an ecosystem.
Ecosystem: community + abiotic (non-living) environment.
Habitat: the place where an organism lives.
Organisms are interdependent — they rely on each other for food, shelter, pollination etc.
A stable community has populations in equilibrium — birth rates, death rates and interactions are balanced.

Abiotic and biotic factors

Abiotic factors (non-living): light intensity, temperature, moisture level, soil pH and mineral content, wind speed, CO₂ concentration, O₂ concentration.
Biotic factors (living): availability of food, new predators, new pathogens/diseases, competition for resources.
Changes in abiotic or biotic factors can affect population sizes.
E.g. increased predator → reduced prey population → predator population then falls too (predator-prey cycle).

Competition

Intraspecific: competition between individuals of the same species. For: food, mates, territory, water.
Interspecific: competition between different species. For: food, water, space, light.
The species best adapted to compete for resources will survive and reproduce more.
Invasive species with no natural predators can outcompete native species.

Adaptations

Structural: body features (e.g. thick fur, large ears, streamlined shape).
Behavioural: actions (e.g. migration, hibernation, nocturnal behaviour).
Physiological: internal processes (e.g. antifreeze proteins in fish, efficient water retention in camels).
Extremophiles: organisms adapted to extreme conditions (high temperature, high salt, high pressure). E.g. bacteria in hot springs with heat-stable enzymes.
Adaptations evolve by natural selection over many generations.

Exam questions — 5 questions · 11 marks · AQA 8461 style

1 markBiotic vs abioticAQA 8461 style

Which of the following is a BIOTIC factor affecting a population?

A Temperature

B Soil pH

C The arrival of a new predator species

D Light intensity

3 marksAdaptation exampleAQA 8461 P2 style

A polar bear has a thick layer of subcutaneous fat, a white coat, and small ears. Explain how each of these features is an adaptation to its Arctic environment. (3 marks)

Hint: One mark per adaptation. State the feature + explain how it helps survival in the cold/snowy environment.

+30 XP

1 markInterdependenceAQA 8461 style

In a stable community, what happens to the predator population when prey numbers decrease significantly?

A Predator numbers increase because they compete less with each other

B Predator numbers decrease because there is less food available

C Predator numbers stay constant because they switch to alternative food

D Predator numbers increase immediately because there is less competition

4 marksIntraspecific vs interspecific competitionAQA 8461 style

Red squirrels and grey squirrels both live in the same woodland and eat similar foods. Grey squirrels were introduced from North America and are outcompeting red squirrels. (a) Name this type of competition. (b) Explain why grey squirrels might be more successful competitors. (4 marks)

Hint: (a) Two different species competing = interspecific. (b) Think about: food range, disease resistance, aggression, reproduction rate.

+40 XP

1 markExtremophilesAQA 8461 style

Bacteria living in deep ocean hydrothermal vents at very high temperatures are examples of:

A Parasites

B Decomposers

C Extremophiles

D Vectors

Communities, Adaptations & Interdependence

Ecosystems and communities

Abiotic and biotic factors

Competition

Adaptations

Module complete! 🎉