A population is a group of organisms of the same species living in the same area at the same time, which can interbreed. A community is all the populations of different species living and interacting in the same area at the same time.For example, in a pond the frogs form one population, the water lilies another and the water fleas another. Together with all the other populations of plants, animals, fungi and microorganisms in the pond, they make up the pond community. The community plus the abiotic environment is the ecosystem.Populations in a community interact in many ways:
• Feeding relationships: producers, herbivores, carnivores and decomposers linked in food webs.
• Competition for resources such as light, space, food and mates, both within a species (intraspecific) and between species (interspecific).
• Predation and parasitism, which affect the numbers of both species.
• Mutualism, where both species benefit, such as flowering plants and their pollinators.Because of these interactions, a change in one population affects others. If most of the rabbits in a grassland community are killed by disease, the foxes that eat them decline, grazing falls and the grass grows taller, which may shade out small flowering plants.Communities change over time. The sequence of communities that develops on a newly exposed area is called succession, and it ends in a stable climax community. Both are covered in later lessons.
• Feeding relationships: producers, herbivores, carnivores and decomposers linked in food webs.
• Competition for resources such as light, space, food and mates, both within a species (intraspecific) and between species (interspecific).
• Predation and parasitism, which affect the numbers of both species.
• Mutualism, where both species benefit, such as flowering plants and their pollinators.Because of these interactions, a change in one population affects others. If most of the rabbits in a grassland community are killed by disease, the foxes that eat them decline, grazing falls and the grass grows taller, which may shade out small flowering plants.Communities change over time. The sequence of communities that develops on a newly exposed area is called succession, and it ends in a stable climax community. Both are covered in later lessons.