Scientists also study ecology at the population level . A population is usually defined as all of the individuals of the same species that live in a given area. For instance, we can speak of the population of humans in New York City, or the population of moose on Isle Royale, Michigan. Population dynamics , the study of how populations interact with other populations and the environment, reveals the role, or niche , occupied by a population within an ecosystem. Population size and growth reflect key processes that are happening in an ecosystem, and this information is useful in predicting change.
Community ecology looks at all of the populations within a given area and how they interact.
For instance, a lake community would involve studying the phytoplankton, zooplankton, filter-feeding fish, carnivorous fish, amphibians, birds, parasites, all of the invertebrates, decomposers, aquatic plants, as well as animals such as beavers, and muskrats. Understanding community interaction often leads to a clearer picture of how populations evolve.