abiotic. Having to do with the chemical, geological, and physical aspects of an entity; i.e., the nonliving components.
absolute decomposition. The amount of detritus consumed by microbial decomposers (e.g., bacteria, fungi) and detritivores (e.g., earthworms).
acid–base reactions. A class of chemical reactions involving the transfer of protons without electrons.
acquisition. Any of various processes of acquiring resources from the environment, such as photosynthesis in leaves and nutrient uptake by roots.
adaptation. The evolution of a population by a process of natural selection in which hereditary variants most favorable to organismal survival and reproduction are accumulated, and less advantageous forms are discarded.
adaptive management. Dynamic resource management that incorporates new information gathered from scientific monitoring to systematically improve management practices.
adaptive radiation. The rapid diversification of an ancestral species into several ecologically different species, associated with adaptive morphological, physiological, and/or behavioral divergence.
adaptive syndrome. The suite of morphological, physiological, and behavioral characters that determine an organism’s ability to survive and reproduce.
aerobe. An organism that requires the presence of atmospheric oxygen to live. Distinguished from ANAEROBE.
aerobic. Relating to or occurring in the presence of oxygen. Distinguished from ANAEROBIC.
age structure. The distribution of various chronological ages in a given population.
agroecosystem. An ecosystem designed and managed by humans to produce agricultural goods.
agroforestry. An agricultural system in which woody perennials are deliberately integrated with crops and/or animals on the same unit of land.
airshed. A region sharing a common flow of air.
albedo. Energy reflected from the land or water surface. Generally, white or light-colored surfaces have high albedo, and dark-colored or rough surfaces have low albedo.
alien. Describing a species that occurs outside its natural range and dispersal potential, especially one that becomes established in an ecosystem and threatens native biological diversity or has other negative ecological and economic impacts.
Allee effect. An inverse relationship between population density and per capita population growth rate. Allee effects can accelerate the decline of a shrinking population. (First described by Warder Clyde Allee.)
allele. One of two or more alternative forms of a gene occupying the same chromosomal locus.
allocation. The partitioning of resources among alternative structures or functions within a plant. The principle of allocation states that resources used for one purpose will be unavailable for other purposes, creating trade-offs that strongly influence plant growth and life cycles.
alternative stable state. A relatively stable ecosystem structure or composition that is different from the stable state which was present before a disturbance.
altruism. Behavior that is detrimental to the individual actor performing it but beneficial to one or more other individuals; costs and benefits are measured in terms of effects on fitness, which can be quantified by lifetime reproductive success. Thus, altruistic.
anaerobe. An organism that can live in an environment in which atmospheric oxygen is absent. Distinguished from AEROBE.
anaerobic. Describing or occurring in the absence of oxygen. Distinguished from AEROBIC.
anoxia. The absence of oxygen. Thus, anoxic.
anthropocentrism. 1. Human-centeredness; the perspective that humans are the central entity of the universe. 2. Specifically, the fact of viewing the natural environment primarily in terms of its direct benefit to humans. Thus, anthropocentric.
anthropogenic. Human-caused; describing a phenomenon or condition of the natural world that results from, or is significantly influenced by, human activity.
anthroponosis. A disease transmitted directly from person to person. Compare ZOONOSIS.
apparent competition. An indirect interaction between prey species in which a given prey species experiences more intense predation because of the presence of the alternative prey, as a result of changes in either predator abundance or predator behavior.
assisted migration. A directed dispersal or translocation of organisms across the landscape.
attenuation. A decline in the number of species represented on islands with distance from a source of colonists.
autotroph. A self-feeder; i.e., an organism that can convert inorganic carbon to organic materials and thus does not need to ingest or absorb other living things. Green plants use light energy to make this conversion. Thus, autotrophic.
balance of nature. A popular term for the concept that different species in an ecosystem will tend to interact with each other in a manner that produces a stable state, with populations remaining relatively constant over an extended time.