Factors Affecting Ecosystems and Interdependence — AQA GCSE Biology

Species within an ecosystem depend on one another, so changes to one population can affect many others.

Interdependence

Within a community, every species depends on other species for things such as food, shelter, pollination and seed dispersal. This mutual dependence is interdependence. Because the species are linked (through food webs and other relationships), the removal or change of one species can have knock-on effects on many others.

Stable communities

In a stable community, the species and the abiotic factors are in balance, so population sizes stay roughly constant. Examples include tropical rainforests and ancient oak woodlands.

Factors that change ecosystems

Both environmental (abiotic) changes and biotic changes can affect a community:

• A change in a physical factor (temperature, water, light) can change population sizes.
• The arrival of a new predator, competitor or pathogen can reduce a population.
• Removing a species can disrupt the whole food web.

Worked reasoning

For example, if a disease wipes out a plant species, the herbivores that eat it decline, and so do the carnivores that eat those herbivores — showing the interdependence of the community.

Exam tips

• Define interdependence and give examples (food, shelter, pollination, seed dispersal).
• Explain how removing one species affects others through the food web.
• A stable community has balanced, roughly constant populations.
• Be able to predict knock-on effects of a change to one population.