Ecology
Ecosystems You must be able to: Describe different levels of organisation in an ecosystem Explain why different organisms in an ecosystem show interdependence Describe the factors that determine where organisms can live Describe some of the techniques used by scientists to study ecosystems.
• • • •
Relationships Between Organisms • •
• • • • •
• • •
An ecosystem is all the organisms living in a habitat and the non-living parts of the habitat. There are different levels of organisation in an ecosystem: – individual organisms – populations – groups of individuals of the same species – communities – made up of many populations living together. To survive and reproduce, organisms require certain resources from their habitat and the other living organisms there. Trying to get enough of these resources results in competition. Plants in a community or habitat often compete with each other for light, water, space and mineral ions from the soil. Animals often compete with each other for food, mates and territory. As well as competing with each other, species also rely on each other for food, shelter, pollination, seed dispersal, etc. This is called interdependence. Because of interdependence, removing one species from a habitat can affect the whole community. In a stable community, all the species and environmental factors are in balance so that population sizes stay fairly constant. Tropical rainforests and ancient oak woodlands are examples of stable communities.
Key Point All ecosystems should be self-supporting, but they do need energy. Energy is usually transferred into the ecosystem as light energy for photosynthesis in green plants, which are the start of the food chain.
Adaptations • •
•
74
Factors that can affect communities can be abiotic (non-living) or biotic (living). Abiotic factors include: – light intensity – temperature – moisture levels – soil pH and mineral content – wind intensity and direction – carbon dioxide levels for plants – oxygen levels for aquatic animals. Biotic factors include: – availability of food – new predators arriving – new pathogens / diseases – one species outcompeting another.
GCSE Combined Science Revision Guide
227841 AQA Higher Tier Combined Science All-in-One_P072_087.indd 74
6/29/16 11:03 AM