GCSE BIOLOGY REVISION: ECOLOGY
Please note: Text in bold is what the AQA GCSE biology specification requires an understanding of.
Students should be able to describe:
• different levels of organisation in an ecosystem from individual organisms to the whole ecosystem
• the importance of interdependence and competition in a community.
A stable community is one where all the species and environmental factors are in balance so that population sizes remain fairly constant.
Plants in a community or habitat often compete with each other for light and space, and for water and mineral ions from the soil.
Animals often compete with each other for food, mates and territory.
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.
Let’s firstly begin with a few key terms you most definitely need to know!
Ecosystem- a biological community of interacting organisms and their physical environment
Population- all the organisms in the same or closely related species that occupy the same habitat
Habitat- the place in which organisms live
Community- two or more populations of organisms
Ecosystems typically contain various different populations.
From your lessons, you may be familiar with hierarchies, food chains and food pyramids, these are very important for your understanding and you may be asked to draw one in your exam! Organisms within an ecosystem are organised into levels:
Producers- these are plants and algae. These organisms can photosynthesise
Primary consumer- these are herbivores, organisms which eat producers
Secondary consumers- these are carnivores, they eat primary consumers
Tertiary consumers- these are also carnivores, and you may have guessed it… Tertiary consumers eat secondary consumers!
Producers are the most abundant and go at the bottom of a food chain pyramid. Tertiary consumers go at the top of the food pyramid.
So, a question for you to think about…
If we have a snake, grass, frog, grasshopper and hawk, which order in the food chain do these organisms go?
Every organism depends on other organisms. When population size changes, this has an effect on the population itself, and other populations too. Whether they rise or fall, this changes the rest of the ecosystem. For example, starfish eat mussels. If the mussel population massively decreases, this reduces food availability for starfish, causing a struggle for survival. This in turn, reduces the starfish population. Adversely, if the mussel population significantly rises, this increases food availability for starfish allowing the starfish to thrive and grow. However, a higher population of starfish can cause a decrease in mussels as more starfish will require food. This means that populations can be regulated by predator-prey relationships.
All organisms compete. Producers compete for the resources needed to photosynthesise, for example light, water, minerals and space. Consumers compete for space, food, shelter, and water. Not only is there competition within a population, but with other populations too. Additionally, within a population, there will be competition for mates. Intraspecific competition is the term used to describe competition within a species. Interspecific competition is competition between different species.
Stable communities are those which the size of the populations remain relatively constant over time. This is the ideal situation for an ecosystem.