Communities (AQA A Level Biology): Revision Note

Key terms in ecology

Ecosystems

• An ecosystem can be defined as:

The interaction between a community the living (biotic) factors, and the non-living (abiotic) factors of the environment

• There is a flow of energy within an ecosystem and the nutrients within it are recycled (e.g. the carbon, nitrogen and phosphorus cycles)

• Ecosystems vary greatly in size and scale

  • Both a small pond in a back garden and the open ocean could be described as ecosystems

• Ecosystems vary in complexity:

  • A desert is a relatively simple ecosystem

  • A tropical rainforest is a very complex ecosystem

Population

• A population is defined as:

A group of organisms of the same species living in the same area at the same time

Community

• A community can be defined as:

Multiple populations (of different species) living and interacting in the same area

• Within a community, each species depends on other species for food, shelter, pollination, seed dispersal etc

• If one species is removed it can affect the whole community

• This is called interdependence

Habitat

• A habitat is:

The local environment in which a species normally lives

• E.g. badgers, deer, oak trees and ants are all species that would live in a woodland habitat

• Organisms adapt to their habitat through natural selection in order to survive and reproduce successfully

Niche

• A niche is the role an organism plays in its ecosystem, including:

  • Its use of resources

  • Its responses to abiotic factors (e.g. temperature, pH, light)

  • Its interactions with biotic factors (e.g. predators, prey, competition)

• Each species has a unique niche – only one species can occupy a particular niche

• If two species overlap in niche:

  • Competition occurs

  • One species will outcompete the other

  • The less successful species must adapt to a new niche or may become locally extinct

• A species’ niche is determined by its adaptations:

  • Structural, physiological or behavioural traits that allow survival under specific conditions

  • Only one species can occupy each exact niche in a habitat

Example: Warbler species

• Three North American warbler species live in the same conifer habitat

• They reduce competition by feeding at different heights in the trees

• This niche differentiation allows them to co-exist in the same habitat