7.1.1: Communities
Not started yet — this one needs some love.
Individual organism: one living thing.
Population: all the organisms of one species in a habitat.
Community: all the populations of different species living in a habitat.
Ecosystem: the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment.
To survive and reproduce, organisms need materials from their surroundings and from other living organisms.
Plants often compete for light, space, water and mineral ions from the soil.
Animals often compete for food, mates and territory.
Interdependence: 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.
Stable community: one where all the species and environmental factors are in balance so that population sizes remain fairly constant.
Common exam mistakes
Do not use habitat, population, community and ecosystem interchangeably; they describe different scales of organisation.
For competition questions, name the exact limited resource instead of writing vague phrases like "they compete to survive".
For interdependence questions, name the species relationship and the effect of removing one species.
On population graphs, predator numbers usually change after prey numbers because there is a time lag.