Ecology

Ecology can be defined as the study of the relationships of organisms with their living and nonliving environment. Most ecologists are interested in questions involving the natural environment. Increasingly, however, ecologists are concerned about degradation associated with the ecological effects of humans and their activities. Ultimately, ecological knowledge will prove to be fundamental to the design of systems of resource use and management that will be capable of sustaining humans over the longer term, while also sustaining other species and natural ecosystems.

The individual

In the ecological and evolutionary contexts, an individual is a particular, distinct organism, with a unique complement of genetic information encoded in DNA. (Note that although some species reproduce by nonsexual means, they are not exceptions to the genetic uniqueness of evolutionary individuals.) The physical and physiological attributes of individuals are a function of (1) their genetically defined capabilities, known as the genotype, and (2) environmental influences, which affect the actual expression of the genetic capabilities, known as the phenotype. Individuals are the units that are "select ed" for (or against) during evolution.

The population

A population is an aggregation of individuals of the same species that are actively interbreeding, or exchanging genetic information. Evolution refers to changes over time in the aggregate genetic information of a population. Evolution can occur as a result of random "drift," as directional selection in favor of advantageous phenotypes, or as selection against less well-adapted genotypes.

The community

An ecological community is an aggregation of populations thar are interacting physically, chemically, and behaviorally in the same place. Strictly speaking, a community consists of all plant, animal, and microbial populations occurring together on a site. Often, however, ecologists study functional "communities" of similar organisms, for example, bird or plant communities.

The ecological landscape

This level of ecological organization refers to an aggregation of communities on a larger area of terrain. Sometimes, ecological units are classified on the basis of their structural similarity, even though their actual species may differ among widely displaced locations. A biome is such a unit, examples of which include alpine and arctic tundra, boreal forest, deciduous forest, prairie, desert, and tropical rainforest.

The biosphere

The biosphere is the integration of all life on Earth, and is spatially defined by the occurrence of living organisms. The biosphere is the only place in the universe known to naturally support life.