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Evolution - Definition of Evolution
The term evolution is defined as simply change over time. But when applied to lifeforms, the term evolution--or more precisely biological evolution--takes on an added dimension of meaning. Biological evolution is defined as descent with modification.
Echinodermata
The phylum of animals whose members are pentaradially (five-axis) symmetrical as adults, have a water-vascular system, and an endoskeleton. Members of this phylum include sea stars, sea urchins, sea cucumbers, and sea lilies.
Ecocline
A gradient of vegetation structure that correlates to variation in one or more environmental characteristics in a geographical area.
Ecolocation
A method of sensing surrounding objects that employs pulses of high-frequency sound.
Ecological Efficiency
A measure of the amount of energy in the biomass that is produced by one trophic level and is incorporated into the biomass produced by the next (higher) trophic level.
Ecological Isolation
The isolation of competing species of organisms made possible by differences in each species food resources, habitat use, activity period, or geographical range.
Ecological Release
The expansion of habitat and resource usage by populations into areas of lower species diversity. Ecological release results from lower levels of interspecific competition.
Ecology
The study of the ecosystems, communities, habitats, and other elements of the natural environment that examines the relationships among organisms as well as relationships between organisms and their environment.
Ecomorphology
The study of the relationship between the ecological role of an individual and its morphological adaptations.
Ecosystem Approach
An approach to resource management that recognizes that all components of an ecosystem (function, structure, and species composition) are interrelated and must be considered when protecting and restoring natural balances.
Ecosystem
All the parts and interactions of the physical environment and the biological world.
Ecotone
A habitat created by the juxtaposition of distinctly different habitats; an edge habitat; a zone of transition between habitat types.
Ecotype
A genetically differentiated subpopulation that is restricted to a specific habitat.
Ectasian
Ectasian
Ectoparasite
A parasite, for example, a tick, that lives on, or attached to the host's surface.
Ectothermy
Capcity to maintain body temperature by gaining heat from the environment, either by conduction or by absorming radiation.
Ediacaran Period
Ediacaran Period
Effective Population Size
The average size of a population expressed in terms of individuals assumed to contribute genes equally to the next generation; generally smaller than the actual size of the population, depending on the variation in the reproductive success among individuals.
Egestion
Elimination of undigested food material.
Egg Dumping
"The practice of placing eggs in a nest built by another bird."
El Niño
A warm current from the tropics that intrudes each winter along the west coast of northern South America.
Elliptical
"Egg shape equally rounded at both ends and broadest in the middle."
Embryo
A plant or animl in an early stage of development; generally still contained within the seed, egg, or uterus.
Emigration
Movement of individuals out of a population.
Endangered Species Act (ESA)
Federal legislation that is intended to provide a means to conserve the ecosystems upon which endangered and threatened species depend and provide programs for the conservation of those species, thus preventing extinction of plants and animals.
Endangered Species
An animal or plant species in danger of extinction throughout all or a significant portion of its range.
Endemic
Confined to a certain region.
Endoparasite
A parasite that lives within the tissues or bloodstream of its host.
Endothermic
Able to maintain a constant, warm body temperature, regardless of external conditions.
Endothermy
Capacity to maintain body temperature by the metobolic generation of heat.
Enhancement of Survival Permit
A type of permit issued by the US Fish and Wildlife Service under the authority of the Endangered Species Act.
ENSO
El Niño/Southern Oscillation; an occasional shift in winds and ocean currents, centered in the South Pacific region, with worldwide consequences for climate and biological systems.
Environment
Surroundings of an organism, including the plants, animals, and microbes with which it interacts.
Estivation
A temporary state of inactivity during a time that the animal is usually active (for example, snails go into estivation in summer months if it is too hot or too dry)
Eucaryotic Cell
A cell containing a distinct membrane-bounded nucleus, characteristic of all organisms except bacteria.
Eukaryote
Eukaryotes are organisms made up of cells that possess a membrane-bound nucleus (that holds genetic material) as well as membrane-bound organelles.
Eyeshine
The shine that is present in the eyes of various birds (goatsuckers, owls, kiwis, and other nightbirds). Caused by reflection off of the tapetum, the vascular membrane of the retina within the eye.
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