early successional plant species Plant species found in the early stages of succession that (1) grow close to the ground, (2) can establish large populations quickly under harsh conditions, and (3) have short lives. Compare late successional plant species, midsuccessional plant species. 

ecological diversity Variety of forests, deserts, grasslands, oceans, streams, lakes, and other biological communities interacting with one another and with their nonliving environment. See biodiversity. Compare functional diversity, genetic diversity, species diversity. 

ecological efficiency Percentage of energy transferred from one trophic level to another in a food chain or web. 

ecological footprint Measure of the ecological impact of the (1) consumption of food, wood products, and other resources, (2) use of buildings, roads, garbage dumps, and other things that consume land space, and (3) destruction of the forests needed to absorb the CO2 produced by burning fossil fuels. 

ecological land-use planning Method for deciding how land should be used; development of an integrated model that considers geological, ecological, health, and social variables. 

ecological niche Total way of life or role of a species in an ecosystem. It includes all physical, chemical, and biological conditions a species needs to live and reproduce in an ecosystem. Also niche. See fundamental niche, realized niche. 

ecological population density Number of individuals of a population per unit area of habitat. Compare population density. 

ecological restoration Deliberate alteration of a degraded habitat or ecosystem to restore as much of its ecological structure and function as possible. 

ecological succession Process in which communities of plant and animal species in a particular area are replaced over time by a series of different and often more complex communities. Also community development is used. See primary succession, secondary succession.

Ecologist Biological scientist who studies relationships between living organisms and their environment. Compare conservation biologist, conservationist, environmentalist, environmental scientist, preservationist, restorationist. 

Ecology Study of the interactions of living organisms with one another and with their nonliving environment of matter and energy; study of the structure and functions of nature.

economic decision Deciding (1) what goods and services to produce, (2) how to produce them, (3) how much to produce, and (4) how to distribute them to people.

economic depletion Exhaustion of 80% of the estimated supply of a nonrenewable resource. Finding, extracting, and processing the remaining 20% usually costs more than it is worth; may also apply to the depletion of a renewable resource, such as a fish or tree species.

economic development Improvement of living standards by economic growth. Compare economic growth, environmentally sustainable economic development. 

economic growth Increase in the capacity to provide people with goods and services produced by an economy; an increase in real GNP. Compare economic development, environmentally sustainable economic development, sustainable economic development.

economic resources Natural resources, capital goods, and labor used in an economy to produce material goods and services. See natural resources. 

economic system Method that a group of people uses to choose (1) what goods and services to produce, (2) how to produce them, (3) how much to produce, and (4) how to distribute them to people. See capitalist market economic system, pure command economic system, pure free-market economic system. 

economic threshold Point at which the economic loss caused by pest damage outweighs the cost of applying a pesticide. 

economy System of production, distribution, and consumption of economic goods. 

ecosystem Community of different species interacting with one another and with the chemical and physical factors making up its nonliving environment. 

ecosystem services Natural services or natural capital that support life on the earth and are essential to the quality of human life and the functioning of the world's economies. See natural resources. 

ecotone Transitional zone in which one type of ecosystem tends to merge with another ecosystem. See edge effect. 

edge effect Existence of a greater number of species and a higher population density in a transition zone (ecotone) between two ecosystems than in either adjacent ecosystem. See ecotone. 

electromagnetic radiation Forms of kinetic energy traveling as electromagnetic waves. Examples are radio waves, TV waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma rays. Compare ionizing radiation, nonionizing radiation.

endangered species Wild species with so few individual survivors that the species could soon become extinct in all or most of its natural range. Compare threatened species. 

endemic species Species that is found in only one area. Such species are especially vulnerable to extinction.

energy Capacity to do work by performing mechanical, physical, chemical, or electrical tasks or to cause a heat transfer between two objects at different temperatures.

energy efficiency Percentage of the total energy input that does useful work and is not converted into low-quality, usually useless heat in an energy conversion system or process. Also use energy productivity. See energy quality, net energy. Compare material efficiency. 

energy quality Ability of a form of energy to do useful work. High-temperature heat and the chemical energy in fossil fuels and nuclear fuels are concentrated high-quality energy. Low-quality energy such as low-temperature heat is dispersed or diluted and cannot do much useful work. See high-quality energy, low-quality energy. 

environment All external conditions and factors, living and nonliving (chemicals and energy), that affect an organism or other specified system during its lifetime. 

environmental degradation Depletion or destruction of a potentially renewable resource such as soil, grassland, forest, or wildlife that is used faster than it is naturally replenished. If such use continues, the resource becomes nonrenewable (on a human time scale) or nonexistent (extinct). See also sustainable yield. 

environmental ethics Our beliefs about what is right or wrong environmental behavior. 

environmental justice Fair treatment and meaningful involvement of all people regardless of race, color, sex, national origin, or income with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies. 

environmental movement Efforts by citizens (mostly at the grassroots level) to demand that political leaders enact laws and develop policies to (1) curtail pollution, (2) clean up polluted environments, and (3) protect pristine areas and species from environmental degradation. 

environmental resistance All the limiting factors that act together to limit the growth of a population. See biotic potential, limiting factor. 

environmental revolution Cultural change involving halting population growth and altering lifestyles, political and economic systems, and the way we treat the environment so we can help sustain the earth for ourselves and other species. This involves working with the rest of nature by learning more about how nature sustains itself. See environmental wisdom worldview. Compare agricultural revolution, huntergatherers, industrial revolution, information and globalization revolution. 

environmental science Study of how we and other species interact with one another and with the nonliving environment (matter and energy). It is a physical and social science that integrates knowledge from a wide range of disciplines, including physics, chemistry, biology (especially ecology), geology, geography, resource technology and engineering, resource conservation and management, demography (the study of population dynamics), economics, politics, sociology, psychology, and ethics. 

environmental wisdom worldview Beliefs that (1) nature exists for all the earth's species, not just for us, and we are not in charge of the rest of nature; (2) there is not always more, and it is not all for us; (3) some forms of economic growth are beneficial and some are harmful, and our goals should be to design economic and political systems that encourage earthsustaining forms of growth and discourage or prohibit earth-degrading forms; and (4) our success depends on learning to cooperate with one another and with the rest of nature instead of trying to dominate and manage earth's life-support systems primarily for our own use. Compare frontier environmental worldview, planetary management worldview, spaceship-earth worldview. 

environmental worldview How people think the world works, what they think their role in the world should be, and what they believe is right and wrong environmental behavior (environmental ethics). 

Environmentalist Person concerned about the impact of people on environmental quality who believes that some human actions are degrading parts of the earth's life-support systems for humans and many other forms of life. Compare conservation biologist, conservationist, ecologist, environmental scientist, preservationist, restorationist. 

Environmentally sustainable economic development Development that (1) encourages environmentally sustainable forms of economic growth that meet the basic needs of the current generations of humans and other species without preventing future generations of humans and other species from meeting their basic needs and (2) discourages environmentally harmful and unsustainable forms of economic growth. It is the economic component of an environmentally sustainable society. Compare economic development, economic growth.

Environmentally sustainable society Society that satisfies the basic needs of its people without depleting or degrading its natural resources and thereby preventing current and future generations of humans and other species from meeting their basic needs. 

EPA U.S. Environmental Protection Agency; responsible for managing federal efforts to control air and water pollution, radiation and pesticide hazards, environmental research, hazardous waste, and solid waste disposal. 

Epidemiology Study of the patterns of disease or other harmful effects from exposure to toxic chemicals or disease organisms within defined groups of people to find out why some people get sick and some do not. 

epiphyte Plant that uses its roots to attach itself to branches high in trees, especially in tropical forests. 

Erosion Process or group of processes by which loose or consolidated earth materials are dissolved, loosened, or worn away and removed from one place and deposited in another. See weathering. 

estuary Partially enclosed coastal area at the mouth of a river where its fresh water, carrying fertile silt and runoff from the land, mixes with salty seawater. 

eukaryotic cell Cell containing a nucleus, a region of genetic material surrounded by a membrane. Membranes also enclose several of the other internal parts found in a eukaryotic cell. Compare prokaryotic cell. 

euphotic zone Upper layer of a body of water through which sunlight can penetrate and support photosynthesis.

eutrophic lake Lake with a large or excessive supply of plant nutrients, mostly nitrates and phosphates. Compare mesotrophic lake, oligotrophic lake. 

Eutrophication Physical, chemical, and biological changes that take place after a lake, estuary, or slow-flowing stream receives inputs of plant nutrients--mostly nitrates and phosphates--from natural erosion and runoff from the surrounding land basin. See cultural eutrophication. 

evaporation Conversion of a liquid into a gas. 

even-aged management Method of forest management in which trees, sometimes of a single species in a given stand, are maintained at about the same age and size and are harvested all at once. Compare uneven-aged management. 

evergreen plants Plants that keep some of their leaves or needles throughout the year. Examples are ferns and cone-bearing trees (conifers) such as firs, spruces, pines, redwoods, and sequoias. Compare deciduous plants, succulent plants. 

Experiment Procedure a scientist uses to study some phenomenon under known conditions. Scientists conduct some experiments in the laboratory and others in nature. The resulting scientific data or facts must be verified or confirmed by repeated observations and measurements, ideally by several different investigators. 

exploitation competition Situation in which two competing species have equal access to a specific resource but differ in how quickly or efficiently they exploit it. See interference competition, interspecific competition. 

exponential growth Growth in which some quantity, such as population size or economic output, increases by a fixed percentage of the whole in a given time period; when the increase in quantity over time is plotted, this type of growth yields a curve shaped like the letter J. Compare linear growth. 

external benefit Beneficial social effect of producing and using an economic good that is not included in the market price of the good. Compare external cost, full cost.

external cost Harmful environmental or social effect of producing and using an economic good that is not included in the market price of the good. Compare external benefit, full cost, internal cost. 

Externalities Social benefits ("goods") and social costs ("bads") not included in the market price of an economic good. See external benefit, external cost. Compare full cost, internal cost. 

Extinction Complete disappearance of a species from the earth. This happens when a species cannot adapt and successfully reproduce under new environmental conditions or when it evolves into one or more new species. See also endangered species, mass depletion, mass extinction, threatened species. Compare speciation.