Ecosystems (AQA A Level Biology): Revision Note

Key terms in ecology

Biotic and abiotic factors

• Biotic factors are defined as:

the living components of an ecosystem that affect the survival and reproduction of organisms

• Examples include:

  • predation

  • competition

  • disease

  • food availability

• Abiotic factors are defined as:

the non-living components of an ecosystem that affect living organisms,

• Examples include:

  • temperature

  • light intensity

  • pH

  • water availability

  • mineral ions

Ecosystems

• An ecosystem can be defined as:

a community and its interactions with the non-living factors in the environment

• There is a flow of energy within an ecosystem and the nutrients within it are recycled

  • E.g. in the carbon, nitrogen and phosphorus cycles

• Ecosystems vary greatly in size and scale

  • E.g. both a small pond in a back garden and the open ocean could be described as ecosystems

Populations

• A population is defined as:

a group of organisms of the same species living in a particular space at a particular time that can potentially interbreed

Communities

• A community can be defined as:

multiple populations living and interacting in the same area

• Within a community, each species depends on other species, e.g. for food, shelter and pollination

• If one species is removed it can affect the whole community; this is called interdependence

Habitats

• 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

  • responses to abiotic factors

  • interactions with biotic factors

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

• If the niches of two species overlap then the species compete with each other; this can result in either:

  1. one species outcompeting the other; the less successful species may adapt to a new niche or may become locally extinct

  2. both populations continue to exist, but with smaller population sizes than they would have in the absence of competition

• A species’ niche is determined by its adaptations:

  • Adaptations are structural, physiological or behavioural traits that allow survival under specific conditions

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