Populations and Communities

Ecology uses a few precise terms to describe groups of organisms. You need to use them exactly.A habitat is the place where an organism lives, for example a rocky shore, a pond or the leaf litter of a woodland floor.A population is all the organisms of one species living in a habitat at the same time. Members of a population can interbreed, and they compete with each other for the same resources. For example, all the grey squirrels in a particular wood form one population.A community is all the populations of different species living in the same place at the same time. The community of a wood includes the populations of oak trees, bluebells, squirrels, woodlice, fungi, bacteria and every other species there.So a community is made of many populations, and a population is made of many individuals of one species.Populations in a community interact with each other. One population may be food for another, two populations may compete for the same resource, or one may depend on another for shelter or pollination. These interactions mean that a change in the size of one population, such as a fall in the number of rabbits, can affect many other populations in the community.Population sizes are not fixed. They change as individuals are born, die, arrive (immigration) and leave (emigration). Much of this topic is about explaining and measuring these changes.