Ecology Terms Starting With E

Ecological footprint is a measure of how much biologically productive land and water area a person, city, or nation requires to produce the resources it consumes and absorb the waste it generates.

Researchers calculate an ecological footprint by summing six land-use categories: cropland, grazing land, fishing grounds, forest for timber and fiber, built land, and carbon-absorption forest. Mathis Wackernagel and William Rees developed the concept at the University of British Columbia in the early 1990s as a way to compare human demand against Earth’s total biocapacity. Global biocapacity currently stands at roughly 1.6 global hectares per person, yet the average human footprint exceeds 2.7 global hectares, meaning humanity collectively overshoots Earth’s regenerative capacity each year.

High-income nations typically carry footprints three to five times larger than low-income nations, reflecting differences in diet, transportation, and energy sources. Tracking footprint trends over time helps policymakers identify which consumption sectors offer the greatest opportunity for reduction.

Ecological succession is the gradual, directional process by which biological communities change in species composition and structure over time following a disturbance or the formation of new habitat.

Succession begins either on bare substrate with no prior soil, called primary succession, or on disturbed land that retains soil and seed banks, called secondary succession. Pioneer species such as lichens and mosses colonize bare rock first, physically and chemically weathering the surface to generate thin soil that later-arriving plants can exploit. As soil depth and organic matter increase over decades, shrubs and fast-growing trees replace early colonizers, and shade-tolerant species eventually dominate the canopy.

At Glacier Bay, Alaska, researchers have documented a full successional sequence from bare glacial till to Sitka spruce forest over roughly 200 years as glaciers retreated. Succession does not always reach a single stable endpoint; recurring disturbances such as fire, windthrow, or herbivory can reset or redirect community trajectories.

Ecotone is a transition zone between two adjacent ecological communities where environmental gradients, species composition, and physical conditions shift gradually from one community type to the other.

An ecotone contains species drawn from both neighboring communities as well as specialist species that thrive specifically in the intermediate conditions the boundary provides. Marsh ecotones between open water and upland forest experience fluctuating water levels that exclude both fully aquatic and fully terrestrial specialists, creating habitat for hydrophytic plants such as cattails and for amphibians that require both water and land. Light intensity, soil moisture, and temperature shift gradually across ecotones rather than changing abruptly, producing a gradient of microhabitats within a relatively short distance.

Ecotones typically support higher species richness and density than either adjacent community, a pattern called the edge diversity effect or edge effect. The width of an ecotone varies enormously, from a few meters at a pond margin to tens of kilometers where boreal forest grades into Arctic tundra.

Edge effect is the change in environmental conditions, species composition, and ecological interactions that occurs near the boundary between two different habitat types.

Forest edges experience greater solar radiation, wind exposure, and temperature fluctuation than interior forest, producing a microclimate that can extend 30 to 200 meters inward depending on forest type and surrounding land use. These altered conditions favor light-demanding pioneer plants and generalist species while excluding shade-dependent interior specialists such as certain ferns and old-growth songbirds. Ground-nesting songbirds at forest edges suffer 50 to 90 percent higher nest predation rates because predators and brood parasites such as brown-headed cowbirds (Molothrus ater) concentrate along open boundaries.

Edge effects shrink the effective area of interior habitat, a particularly severe problem for large predators that require hundreds of square kilometers of unbroken territory. Roads, power lines, and suburban development multiply edge habitat at the expense of interior forest, fragmenting habitats into patches too small to sustain viable populations of area-sensitive species.

Endangered species are wild organisms facing a very high risk of extinction because their populations have declined severely or their remaining numbers fall below thresholds that make long-term survival unlikely without intervention.

The International Union for Conservation of Nature classifies a species as endangered when its population has declined by at least 50 to 70 percent over three generations, or when fewer than 2,500 mature individuals remain and the population continues to decline. Habitat loss drives approximately 85 percent of modern species endangerment, while overexploitation, invasive species, pollution, and climate change compound the pressure. The Arabian oryx (Oryx leucoryx) was declared extinct in the wild in 1972, when the last wild individual was shot; coordinated captive breeding programs subsequently restored more than 1,000 individuals to protected reserves in Oman and Saudi Arabia by the 2010s.

Endangered status triggers legal protections in many countries, including habitat preservation orders, trade bans under the Convention on International Trade in Endangered Species, and government-funded recovery plans. Small, isolated populations face genetic bottlenecks that reduce immune function and adaptability, accelerating decline even when direct threats are reduced.

Energy flow is the one-way movement of energy through an ecosystem, entering as sunlight or chemical energy captured by producers and progressively dissipating as heat at each successive trophic level.

Producers such as grasses and phytoplankton capture roughly 1 to 5 percent of incoming solar radiation through photosynthesis and store it as chemical energy in organic molecules. Primary consumers, including herbivorous insects and grazing mammals, obtain only about 10 percent of the energy stored in the plants they eat; the remaining 90 percent is lost as metabolic heat, movement, and undigested material. Each subsequent trophic transfer follows the same approximate 10-percent efficiency, so secondary and tertiary consumers receive progressively smaller energy subsidies, which limits most food chains to four or five levels.

This steep energy attenuation explains why a grassland can support vastly more wildebeest than lions: the Serengeti ecosystem sustains roughly 1.3 million wildebeest but fewer than 3,000 lions across the same area. Decomposers such as fungi and bacteria recover energy from dead organic matter at every trophic level, channeling a substantial fraction of total ecosystem energy through the detrital pathway rather than through living consumers.

Eutrophication is the process by which a body of water becomes overloaded with nutrients, stimulating excessive growth of algae and aquatic plants and ultimately depleting dissolved oxygen as that organic matter decomposes.

Excess nitrogen and phosphorus from agricultural fertilizer runoff, septic systems, and sewage discharge stimulate algal growth far beyond rates controlled by natural nutrient limitation. Dense algal blooms shade the water column, blocking light from submerged aquatic plants, which then die and sink to the bottom. Aerobic bacteria decomposing the accumulated organic matter consume dissolved oxygen at rates that can exceed 10 milligrams per liter per day, producing hypoxic or anoxic dead zones where fish and most invertebrates cannot survive.

In Lake Erie during the 1960s, phosphorus loading from detergents and agricultural runoff reduced dissolved oxygen to near zero in deeper waters, collapsing commercial fisheries and prompting the United States and Canada to sign the Great Lakes Water Quality Agreement in 1972. Reducing phosphorus inputs through upgraded wastewater treatment and agricultural buffer strips has partially reversed eutrophication in Lake Erie, though harmful algal blooms driven by warming temperatures continue to recur.