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Glossary of terms used in the Conservation Ecology (BIO 134) by Douglas G. Alexander. The terms in bold are also in the glossary.


Abiotic factors Nonliving factors used when describing ecosystem components to emphasize the interaction between living (biotic) and nonliving (abiotic) components.

Abyssal communities Interacting groups of deep sea animals found on the dark floor (benthos) of the ocean and generally dependent on organic energy that falls through the water from euphotic communities.

Accelerated extinction An increased rate of extermination or complete loss of species populations induced by a major global change or by the current level of human activity.

Acid deposition The increase in acid conditions in atmospheric fallout caused by human activity. This involves rain, snow, mist, fog and solid deposition. Sulfuric and nitric acid released by human activity can reduce the pH of rain considerably below the normal pH of 5.7.

Acute biological impacts Chemical influences of toxic pollutants on biological systems detected immediately or in a short time. Contrast with chronic biological impacts.

Age class pyramid A graphic representation of the relative numbers of males and females of different ages. The width of "pyramid" components illustrate the proportion of males and females in different age groups with the oldest group the highest point above the base line. Although a pyramid shape implies large numbers of young and few older individuals, the age class "pyramid" can assume other shapes.

Age specific birth rate The number of births over one year produced by a given number of individuals (e.g., 10,000; or 1,000; or 100 for percentage reproduction) of a specific age group. This statistical term uses a group of average individuals to represent the population rather than the average for a single individual.

Age specific death rate The number of deaths over one year occurring in a given number of individuals (e.g., 10,000; or 1,000; or 100 for percentage mortality) of a specific age group. This statistical term uses a group of average individuals to represent the population rather than the average for a single individual. Infant mortality is the age specific death rate that results after one year of life considering 1000 live births.

Agricultural shelter belts Trees placed to prevent wind erosion on soil and reduce wind loss on crops.

Agroecosystems Any field agricultural activity. It is important to realize that these are interconnected with the adjacent ecosystems.

Alien (exotic) species Introduced populations that are native to different areas (generally continents).

Alternative hypothesis A hypothesis increased in likelihood because of the rejection of the null hypothesis that means the difference between test and control is real. With the rejection of the null, scientists must consider a variety of alternative hypotheses.

Anaerobic Without oxygen.

Anthropocentric An attitude that considers human values and experiences as most important. Contrast with biocentric.

Applied science Practical science used directly for human or perceived human use. Contrast with basic (pure) science.

Aquatic ecosystems Ecosystems found in water.

Aquifer A water carrying underground layer of rock, sand or gravel that can supply water to springs and function as a water source.

Arboretum Specific locations that cultivate trees and shrubs from around the world. This diverse assemblage of plants is attractive and educational.

Area source (of pollution) Pollutants discharged over a region such as those that result from automobile exhaust or general agricultural run off. Contrast with point source (of pollution).

Assimilation biocide A pesticide or herbicide that has a biological impact when incorporated into the body from the digestive tract and is not destroyed by digestion. Contrast with contact (skin) biocide.

Autecology The ecological study of the environmental responses of individual organisms also called physiological ecology.

Autotroph Organism capable of producing organic compounds using inorganic materials. Chemoautotrophic organisms use chemical energy to support this synthesis and photoautotrophic organisms use solar energy. See also primary producer.

Autotrophic succession Predictable replacement of terrestrial communities dominated by plants and controlled by an interaction with the soil formation, climate, and the frequency of disturbance events. Primary succession and secondary succession are types of autotrophic succession.

Auxin Organic substances (e.g., indoleacetic acid) that have an impact on plant functions such as rate of cell growth. Plant responses to differential concentrations include stem or root directional changes, root formation, bud inhibition, or leaf abscission.

Baseline studies The baseline is a known quantity used as an experimental control. In considering changes in the environment we refer to the original condition, and its natural variability, as the baseline that provides for a reference to determine if significant change has occurred.

Basic (pure) science Science that considers the advancement of knowledge as of primary importance without considering if this information is of practical use to humans. Contrast with applied science.

Beneficial herbivores Animals that feed on weeds used as a form of biological control. Effective herbivores are those that feed on the reproductive parts of the weeds.

Beneficial parasites Organisms that live on or in pest species and derive their energy from the pest called the host. These parasites are contributing to the biological control of the pest.

Beneficial parasitoids Larval insects that start out much as parasites with eggs deposited directly into the host; however, the host is killed. These are excellent biological control organisms because the adults typically lay their eggs only in specific species.

Beneficial pathogens Disease causing organisms often bacteria and viruses that impact pest species. This effectively contributes to biological control because the impacts are often species specific.

Beneficial predators Organisms that eat pest species. The most effective predators are those that exclusively feed on pest species.

Binomial name The scientific name of a species that consists of two latinized words used together. The first word designates the genus. The second word, the species, agrees grammatically with the genus and is typically not capitalized.

Biocentric An attitude that considers all forms of life as equal to human values and experiences. Contrast with anthropocentric.

Biochemical oxygen demand (BOD) This is a measure of the oxygen needed to decompose the dissolved organic matter in water samples. The BOD test uses standard temperature conditions in the dark. A sewage effluent with a low BOD indicates effective removal of dissolved organic material during sewage treatment. See also secondary sewage treatment.

Biocide A general term to include pesticides (insecticides) and herbicides. because the same chemicals can influence plants and animals in a variety of ways.

Biocide toxicity Toxicity is the quality of the compound that makes it poisonous or harmful to to target and non target organisms as well as humans Biocide is a general term including pesticides and herbicides.

Biodegradable The quality of of organic compounds that results in rapid decomposeition. Compare with persistent.

Bioengineers Organisms that cause changes in biotic and abiotic materials that directly or indirectly control resources of other organisms.

Biogeochemical (nutrient, elemental) cycle The pathway of any one element picked up in inorganic form, used in the metabolism of living systems, and released in inorganic form to eventually follow these or other pathways again. Although there are over 30 elements important to living systems, hydrogen, oxygen, carbon, and nitrogen are the most abundant. Many of these elements have no gas form in standard earth conditions and display sedimentary nutrient cycles. Carbon, oxygen, nitrogen and sulfur have a gaseous phase and have gaseous nutrient cycles.

Biological control The control of weeds and pests that use beneficial herbivores, beneficial predators, beneficial pathogens, beneficial parasitoids, and beneficial parasites.

Biomagnification See food chain concentration.

Biomass The total weight of an individual, population or community. Biomass is the total dry weight of organic material (or the energy equivalent) per unit area.

Biome Major terrestrial divisions of continents that have similar communities found in distinctive climates and containing similar dominant plants and animals. Examples of biomes include: tropical rain forest, desert, grassland, chaparral, deciduous forest, coniferous forest, tundra. There are additional minor biomes and the major biomes have important subdivisions.

Biotic potential (BP) The population's potential for growth. The intrinsic rate of natural increase, a population characteristic, is the maximum biotic potential without mortality. Controlling or mortality factors called environmental resistance counter the biotic potential pressure for growth.

Birth rate (crude) Total births produced by an average 1,000 individuals over one year. This statistical term uses a group of average individuals to represent the population rather than the average for a single individual. This "crude" calculation uses all individuals in the population (young and old, male and female).

Carbon cycle The carbon cycle is a biogeochemical cycle that illustrates energetics as well. A first level description of the carbon cycle must include the uptake of carbon in carbon dioxide by photosynthesis to produce organic compounds and use of these compounds by respiration to obtain useful energy and release carbon dioxide. The relatively small amount of atmospheric carbon has a high exchange rate compared to the low exchange rate of carbon in lithosphere and hydrosphere nutrient reservoirs. Carbon dioxide in the atmosphere is a greenhouse gas that has been increasing in level due to human activity.

Carcinogenic pollutant Pollutants that contribute to the production of cancer.

Carnivore An organism that feeds on animals and is part of the third trophic level or higher.

Carrying capacity A relatively constant population size maintained in a specific habitat often considered to result from a balance between biotic potential and environmental resistance. A variety of fields, such as range management or parks management, use carrying capacity for specific management activities. Human activities in sanitation and expanding agricultural production have elevated the human carrying capacity; in contrast, exploitation of natural resources and pollution will lower the human carrying capacity.

Channelization of stream beds The conversion of a natural stream into a diked channel that has greatly reduced biological quality. This activity is often counterintuitive in that the objective of flood control becomes more difficult during severe floods.

Chemoautotrophs Organisms that use chemical energy to support the synthesis of organic compounds using inorganic materials. See vent communities.

Chronic biological impacts Chemical influences on biological systems caused by low-level, long term exposure. These impacts are potentially not detected for some time. Clinical detection of cancer triggered by exposure to one or more chemicals (e.g., mutagenic pollutants) is potentially delayed for years if not decades. It is easier to detect high level short term exposures, acute biological impacts.

Clear cutting of forests The harvest of all trees from a block of forest. This often results in a regeneration system that favors a single species stand of uniform age trees. Large clear cuts reduce the ability of forests to support wildlife and result in increased erosional loss of forest soil. Compare with selective cutting of forests.

Climax community The steady state, end stage of autotrophic succession.

Community (ecological community) An assemblage of interacting populations found in a specific location or habitat. The distinctive ways that plants and animals interact with each other and the physical environment result in different communities across the surface of the earth. Biomes represent groups of similar communities found in distinctive climates and containing similar dominant plants and animals. We can also refer to vent communities on the floor of the ocean dependent upon chemoautotrophic microorganisms or communities dominated by decomposers such as soil communities.

Compensation level The specific depth in the upper layers of water where photosynthesis is equal to respiration. Measurements to determine the compensation level must combine night and day. The compensation level is the floor of the euphotic zone.

Contact (skin) biocide A pesticide or herbicide that is effective on direct contact with the skin. Human contact biocides are fat soluble. Contrast with assimilation biocide.

Critical population See Minimum viable population

Crop rotation The planting of different crops in succession on the same land. This reduces the demand on the soil by a single crop and legumes will improve the soil nitrogen.

Cultural control of pests The use of techniques such as plowing, crop placement, crop rotation, crop isolation, trap crops, sanitation (e.g., disposal of crop wastes) to control weeds and pests.

Darwinism Darwinism refers to Charles Darwin's observations that natural selection describes descent with modification.

Death rate (crude) Total deaths that occur on the average to 1,000 individuals over one year. This statistical term uses a group of average individuals to represent the population rather than the average for a single individual. This "crude" calculation uses all individuals in the population (young and old, male and female).

Decomposition The use of detritus as a energy source by decomposers. In some forest ecosystems, the release of nutrients by decomposition controls the rate of primary production.

Decreasers (range plant classification) Range plants that are nutritious, palatable and decrease under most grazing pressures. Compare with increasers and invaders.

Deforestation The removal of forests.

Delayed toxicity Toxicological impacts that occur some time after uptake. For example, pesticides picked up in the summer that result in winter mortality.

Demographic transition The theory that a human population decrease in birth rate will follow a decline in death rate The initial drop in the death rate results in an increase in population growth and this growth rate will decrease as the birth rate lowers. This theory often assumes the complete transition results as nations become industrialized.

Demography The study of the structure and function of populations. Nonprofessionals restrict this to the study of human populations.

Denitrification A bacterial process that results in the conversion of more readily available nitrogen into nitrogen gas that goes to the atmosphere. This aspect of the nitrogen cycle, typically associated with anaerobic environments, effectively moves nitrogen the opposite direction of nitrogen fixation.

Density The average number of individuals in a population per unit area.

Desertification The formation of deserts as a result of poor land use (e.g., overgrazing, deforestation, overcultivation) or climate change. Desertification often occurs in areas next to existing deserts.

Detoxification The act of removing a poison. A healthy liver acts to detoxify substances

Detritus food web A consumer food web that derives energy from organic material not part of living organisms. Soil organisms form a detritus food web. The detritus food web and grazing food web are connected by top carnivores.

Detritus Organic material not part of a living organism, examples include discarded leaves and hair or bodies of dead animals and plants.

Diapause Diapause is a period of dormancy or no developmental activity in an embryo, larva or pupa. Diapause occurs under unfavorable environmental conditions but these conditions do not necessarily control the initiation or termination of diapause.

Dispersal The active or passive movement of adult or developmental stages of organisms from one place to another.

Domestication The process of imposing new selection pressures and sheltering a population (the domesticated population) by another population (the domesticator population). The domesticated population becomes genetically modified by this process and becomes part of the environment of the domesticator. In close associations, the domesticator potentially becomes dependent upon the domesticated population.

Doubling time The number of years it would take for a human population to double in size if the current rate of growth remains constant.

Dust dome An urban dust cloud that potentially recycles because of the urban heat island. The hot city air goes up over the city and moves laterally and descends in areas next to the city and reenters the city at ground level producing a vortex.

Ecological community See community

Ecologist (applied and basic) An individual that studies organisms in the environment. The basic or pure ecologist develops an understanding without concern for human welfare. Concern with human use and well-being drives the applied ecologist.

Ecology The scientific study of organisms in the environment. This involves topics such as considering the environmental responses of individual organisms called autecology (or physiological ecology) and synecology the study of populations or the study of interactions between plants and animals in ecological communities or ecosystems.

Economic threshold A theoretical pest level that allows profitable agricultural activity at this (and lower) pest levels. In contrast, higher pest levels result in a business loss. Modern pest control strategies work to keep pests below the economic threshold but do not attempt to completely remove the pests.

Ecosystem A unit of nature that includes both the nonliving environment and the associated plants and animals. Energy flow and nutrient cycling are functional characteristics that separate adjacent ecosystems.

Emphysema A respiratory disease associated with air pollution such as cigarette smoke that results in loss of elasticity or rupture of the alveoli of the lung reducing the ability to pick up oxygen and release carbon dioxide.

Endangered Species Act An act, initially written in 1973, that mandates the U.S. Fish and Wildlife Service and the National Marine Fisheries (most marine species) to establish lists of species in immediate danger of becoming extinct (endangered species) or likely to become extinct (threatened species) due to human activity. Listed species cannot be killed directly or indirectly, and the importing, exporting or selling of these species alive or dead (even dead parts) is prohibited. The act requires the government agencies to start programs to help the endangered species with the goal of removing the species from listing.

Endangered species (legal use in the United States) Species listed by the U.S. Fish and Wildlife Service and the National Marine Fisheries as being in immediate danger of becoming extinct due to human activity.

Endemic species Species found only in a restricted area are endemic.

Entropy A measure of disorder or random movement of molecules. Random molecular movement does not provide available energy and develops unless more energy is used.

Environmental resistance (ER) The sum of the environmental factors that limit the rate of growth of a population. If the the environmental resistance counters the biotic potential a relatively constant population size called the carrying capacity results.

Environmentalist Individuals that have a high respect for the natural world and favor environmental concerns when there is a conflict with human activities and land use. Although many ecologists are also environmentalist, some very effective environmentalists are individuals well known in fields such as entertainment and politics. The environmentalist generally has a biocentric orientation.

Erosion (natural and cultural) The loss of rock and soil by factors such as weathering and transport. The development of soil slows erosion.Cultural erosion is erosion accelerated by human activities. On-site impacts of erosion include soil loss in agriculture and off-site impacts include eutrophication.

Estuary A coastal system where a large river flows into an arm of the ocean. Heavy boat traffic, pollution, overfishing and modifications of the shore line reduce the productivity of these zones.

Euphotic zone Surface layers of water that have sufficient light penetration to permit photosynthesis to be as large as or greater than total community respiration. See compensation level.

Eutrophication (natural and cultural ) Excessive growth by primary producers due to an increase in nutrients especially phosphates and nitrates in aquatic environments that are nutrient limiting. Eutrophic aquatic systems potentially develop oxygen deficiency below a thick algal mat. This is a natural process in small ponds. Cultural eutrophication results from human accelerated nutrient deposition.

Evapotranspiration Transpiration is the loss of water from green plants. Evapotranspiration combines evaporative loss from the surface of the earth with transpiration.

Evolution Existing species populations have developed from preexisting populations through modification in the genetic information. This descent with modification is not always in the direction of progress. Natural selection best explains evolution of living organisms.

Exclusive economic zones (EEZ) The 200 mile (330 kilometer) wide zone extending from the coastline that gives maritime countries the sole right to control the removal of fish and mineral resources. Although the EEZ generally includes the neritic zone, it is a political zone determined by surface distance and not by subsurface topography. The UN established this zone under the Law of the Sea Convention. Establishing the EEZ shifted an area that had resources "controlled" by the freedom of the seas to control by individual nations. This does not necessarily insure that good management will occur.

Exploitation The destruction of a natural resource by excessive harvest. Compare with sustained yield.

Exponential population growth A rate of population size increase that increases with larger populations resulting in a J-shape population growth curve. All populations have this potential for rapid growth.

Extinction The extermination or complete loss of species populations. The extinction of existing species and the formation of new species (speciation) is an ongoing evolutionary process. A rapid change in the earth climate (e.g., caused by an asteroid hitting the earth) will accelerate extinction. Currently human activity is resulting in accelerated extinction.

Feedback loops (positive & negative) Feedback occurs when a system output has an influence on the further output levels. Positive feedback continues or supports the current output pattern, either causing further increase in production or further decrease in production. Exponential popultaion growth illustrates increase resulting in further increase. Populations reduced to a very small size (below minimum viable population) may display positive feedback loops and they continue to decrease to extinction without external influence such as the activity by the U.S. Fish and Wildlife Service on endangered species. Negative feedback reduces high production or increases low production. Many biosystems display negative feedback control such as population growth after a decline (potentially caused by an increase in per capita resource availability). Negative feedback control also occurs at the high end when increasing populations stop this growth (potentially caused by lowering per capita resource availability).

Feral population Previously domesticated populations that have gone wild, e.g., feral (wild) horses or burros of the West.

Field experiments Use of the scientific method testing hypotheses in natural ecosystems. Properly established field experiments are more realistic than laboratory experiments

Fitness Fitness as used in biology refers to the ability to produce viable young. Fitness is not the number of progeny but the number of young produced that eventually reproduce.

Food chain concentration (biomagnification) The retention of materials by organisms that results in increasingly higher concentrations at higher trophic levels of a food chain. Fat soluble materials (e.g., DDT) have potentially toxic accumulations in the top carnivores.

Freedom of the seas An established international right that allows ships of any nation to travel on open sea waters. Before the establishment of the exclusive economic zone that replaced freedom of the seas with control by Maritime nations, individual nations established control of different size territorial zones.

Game species Species removed by hunting and fishing controlled by government agencies.

Gaseous nutrient cycles A biogeochemical cycle that involves elements that have a gas form in the inorganic form. Examples include: oxygen, carbon, nitrogen and sulfur.

Genetic pest resistance Resistance to toxic chemicals displayed by pests and weeds. Resistance has a genetic basis and the use of these toxic pollutants results in an increase in the proportion of resistant individuals making control more difficult and eventually impossible. Mosquitoes of the California Central Valley have resistance to most commonly used pesticides.

Grazing food web A consumer food web that derives energy from living plants. The detritus food web and grazing food web are connected by top carnivores.

Green revolution crops Crop varieties developed to improve agricultural productivity. The high production of some green revolution crops depends upon intensive agriculture (pesticides and fertilizers). The idea that increased agricultural production will solve world hunger must also include regulation of population growth.

Greenhouse effect A general warming of the lower atmosphere due to the accumulation of greenhouse gases.

Greenhouse gas Atmospheric gases that absorb long wave heat reradiation of the earth but have little effect on the incoming short wave solar radiation. Examples of greenhouse gases include: water, carbon dioxide, nitrous oxide and methane. The direct and indirect changes in greenhouse gas levels by humans will potentially shift global climate that would cause major disruptions in natural ecosystems and human activities.

Habitat The place of growth of an individual population (deer habitat) or the location of a biological community (mountain meadow or stream riffle).

Herbicide A chemical (often synthetic) used to modify plant function (e.g., cause defoliation "out of season") and to kill plants. See biocide.

Herbivore A plant eating organism. A primary consumer on the second trophic level. Some herbivores are generalists and others have become extreme specialists (e.g., the Giant Panda of China).

Heterotrophic succession A predictable time sequence replacement of communities dominated by heterotrophic organisms that assemble due to an available organic energy source such as a downed tree or dead animal. With the organic energy consumption, the communities either disappear or become part of the surrounding community.

Home range The area occupied by an animal during its life. (Compare with territory)

Human overpopulation Malthusian overpopulation results in a density of individuals above the number supported by available food (resulting in extensive starvation). Technological (industrial) overpopulation involves the negative impacts of industrialization (e.g., pollution, poor land use, loss of regulatory ecosystems, exploitation of natural resources) that reduce survival and the quality of life.

Hypotheses (sing hypothesis) Testable postulates (assumptions) made by scientists in an attempt to explain the function of the natural world. Hypotheses can never be proven correct. See the scientific method.

Increasers (range plant classification) Range plants that are nutritious and increase under low to moderate grazing pressures but will eventually decrease under very heavy grazing pressure. Compare with decreasers and invaders.

Indoor air pollution Air pollution within houses and buildings. Insulation in the name of energy savings has increased indoor pollution.

Industrial melanism Industrial activity darkens surfaces with soot and kills light colored lichens, forcing the development of melanism (darkening) in insects reducing bird predation by protective coloration.

Industrial overpopulation See human overpopulation

Industrial smog Air pollution by sulfur oxide pollutants and transformation materials including sulfuric acid. Industrial smog is more intense in cold moist climates (winter pollution of "rust-belt" cities). Ultraviolet light and very little particles in the atmosphere increase the reaction rate. Sulfur oxides were a major contributor to winter air pollution in cities that burned high sulfur content coal (e.g., London). Most large cities have a combination of photochemical and industrial smog.

Infant mortality rate The number of deaths during the first year out of 1000 live births. This statistical term uses a group of average individuals to represent the population.

Insecticide A substance used to kill or control insects. Terms like insecticide, herbicide and pesticide have impact on a variety of organisms other than the intended target organisms.

Integrated pest management (IPM) The agricultural management of pests that employs a variety of biological, cultural, limiting factor and chemical techniques attempting to keep the biocide use to low levels.

Intercropping Agricultural activities that use a variety of crop types in a single field.

Intertidal zone The zone at the edge of the sea extending from high tide level down to low tide level often frequented by large numbers of organisms.

Invaders (range plant classification) Range plants that are undesirable (some are not palatable and others are poisonous) these increase rapidly on range land degraded by overgrazing. Although some invaders are native, some are alien species. Compare with increasers and decreasers.

Inverse greenhouse effect The global cooling due to the atmospheric accumulation of fine particles that reflect short wave solar radiation and have little effect on long wave terrestrial radiation. The large amount of debris injected into the atmosphere by nuclear wars (nuclear winter) or the impacts of asteroids would cause cooling and accelerated extinction.

Invitro research Research using the cultivation of tissue in an artificial environment (e.g., in glass).

Invivo research Research using living intact plants or animals.

Ionizing radiation High energy particles such as those released from fission reactions that can be extremely damaging to living tissue because they change electron arrangements in organic molecules.

Keystone species A single species that controls the species composition of a community. The keystone species can provide important resources, control diversity as a top predator, or influence others as a bioengineer.

Laboratory experiments Use of the scientific method testing hypotheses in the greenhouse, laboratory or walk-in cold room.

Land ethic An idea advanced by Aldo Leopold that calls for humans to respect all forms of life that use the land.

Land steward An individual who acts to manage land. The objectives of this management could include preservation or management of range animals (range manager).

Land use planning The consideration of a variety of land uses before development.

Lethal dose 50 (LD50) The dose level of a toxin that kills 50% of the experimental population. The response of experimental populations to toxic chemicals such as air pollutants generally follow an s-shape curve with a few individuals killed above the threshold response followed by an area of rapid mortality and then a few individuals resist dose levels before the dose level that kills 100% of the experimental population. If these responses show a wide dose range, the LD50 is not a useful descriptor.

Life expectancy The average number of years of remaining life as projected for any age group, determined from existing survival patterns. If no age is designatied, life expectancy is from birth.

Limiting factor modification Agricultural pest management that uses field modification to make agroecosystems exceed the range of tolerance of pest populations. For example, the use of high or low soil moisture to control sugar beet wire worm larvae.

Macroconsumers Organisms on the second or higher trophic level, that are multicellular and generally have a digestive system with a mouth.

Malthusian overpopulation See human overpopulation

Mariculture (marine aquaculture) The raising of marine organisms in pools or enclosures along the edge of the ocean. Although considered a revolution in food availability, mariculture agroecosystems replace naturally productive environments and many have a short life because of pollution and reductions in available food.

Maximum (range of tolerance) This is the highest level or concentration of an environmental factor that allows survival when considering the range of tolerance of a species.

Mercury A metallic element (symbol Hg) that forms potentially toxic compounds. Insoluble mercury in aquatic sediments converted to a soluble form by microorganisms will become magnified in the food chain.

Microconsumers Unicellular consumers, organisms on the second or higher trophic level typically represented by bacteria and protozoa.

Microcosms Experimental units that include some degree of natural complexity. This could include a terrarium or aquarium in the laboratory, a constructed unit such as a small pool, or a large plastic container suspended in a lake.

Minimum (range of tolerance) This is the lowest level or concentration of an environmental factor that allows survival when considering the range of tolerance of a species.

Minimum tillage Agricultural activities that reduce the need for plowing.

Minimum viable population (MVP) [text uses critical population] The lowest population density necessary for a species to maintain population numbers. Population densities lower than the MVP display positive feedback loops and continue to decrease to extinction without external influence such as the activity by the U.S. Fish and Wildlife Service on endangered species.

Monoculture The modern agricultural activity that cultivates a single crop variety over a large area. Early agriculture had multiple crops (polyculture) sone modern agricultural activity reverses this trend in a variety of ways such as intercropping and the use of cover crops.

Mutagenic pollutant A chemical discharged by human activity that causes changes in the genetic message. This change is potentially lethal when diploid.

Natural experiments The scientific method using natural conditions to test hypotheses. For example, if we state that the size of the island controls the number of species, we can go out and count the species on islands of different sizes.

Natural resource An ecosystem product harvested by humans. Natural resources are renewable in that they have the capability of replacing the harvest removed.

Natural selection An explanation of evolution that states different reproductive success results in the survival of species best adjusted to the immediate conditions under which they live. The theory of natural selection recognizes that individuals inherit diverse traits, produce large numbers of progeny, and that the interaction of the organism with the environment controls differential reproductive success. This is an ongoing process. Different genetic combinations of traits (caused by mutation and recombination) and environmental change due to other organisms changing and changes in physical conditions result in differential survival.This is not a statement about improvement or progress but simply retention of some genetic qualities and elimination of others.

Negative feedback System output that reverses the current output pattern resulting in a decrease becoming an increase or an increase becoming a decrease. Natural systems display negative feedback control. See feedback loops (positive & negative).

Neritic zone The marine zone extending from low tide to the outer edge of the continental shelf. This involves much shallower water than the oceanic zone. This zone is an area of extremely high productivity representing up to 95% of marine harvest and is generally within the exclusive economic zone. This zone has marine pollution problems.

Niche The sum of the functional roles of a single species within an ecosystem. This describes how this species interacts with other species and contributes to the community organization.

Nitrogen cycle The nitrogen cycle is a complex biogeochemical cycle that involves many important organic compounds in living systems as well as urea, uric acid, ammonia, nitrate, nitrite in the soil and water and nitrogen gas and nitrogen oxides in the atmosphere. See also denitrification, nitrogen fixation. Human activities, including industry and modern agribusiness, are changing the global nitrogen cycle.

Nitrogen fixation The conversion of nitrogen gas in the atmosphere to nitrogen used by plants. The fixation can be by lightning, unique nitrogen fixing organisms (both free-living and found exclusively in association with plants) and agribusiness (using energy to obtain nitrogen fertilizer). Currently humans are doubling the global amount of nitrogen removed from the atmosphere in nitrogen fixation.

Non degradable pollutants Pollutants that retain their toxicity and do not decompose.

Non threshold response (to pollution) Chemicals that cause a biological response (e.g. toxicity) at all levels down to single molecules. In contrast, some chemicals have a threshold level below which there is no impact (often because of detoxification abilities).

Nonrenewable resource A resource destroyed when used. Energy is a nonrenewable resource. Recycling of materials makes nonrenewable resources renewable.

Null hypothesis The assumption that chance alone causes the difference between the test and control samples. Rejection of the null hypothesis supports a variety of alternative hypotheses.

Nutrient cycle See biogeochemical cycle.

Nutrient reservoir Areas of high nutrient concentration when considering biogeochemical cycles. For example, nitrogen in the atmosphere is a reservoir for the nitrogen cycle. The rate of uptake and release from the distinctive reservoirs of each element is unique.

Oceanic (pelagic) zone The open sea as distinguished from areas such as the neritic zone.

Oceanography The science that considers the ocean. Oceanography is a unified field with interconnecting subdivisions such as physical or biological oceanography.

Omnivore An organism that feeds on both animals and plants. This individual functions on several trophic levels.

Optimal condition The specific environmental factor (e.g., temperature, light) that results in the highest response measured (e.g., high respiration, high fitness, high reproduction). Because environmental factors interact, there is a low probability of finding a "real world" location optimal to for all controlling environmental factors. See also range of tolerance.

Ozone layer Ozone is a human generated air pollutant close to earth (trophosphere). The naturally occurring stratospheric ozone layer diminishes the penetration of potentially lethal ultraviolet radiation. There is no connection between the trophosphere ozone pollution and the stratospheric ozone layer.

PAN Peroxiacetyl nitrate and peroxiacetyl nitrite a toxic secondary pollutant formed as part of photochemical smog.

Pasture Land where high quality grass or other plants are intensively grown for grazing animals.

Persistent The quality of organic compounds that reduces their rate of decomposition. These compounds (e.g., chlorinated hydrocarbons such as DDT or PCB) exist for longer than usual times in the environment and increase in concentration along trophic levels. Compare with biodegradable and see food chain concentration.

Pest resurgence Increase in pest population size due to a combination of factors including pest resistance, the destruction of beneficial insects and changes in agroecosystems that favor the pest.

Pesticide A chemical (often synthetic) used to kill pest animals. See biocide.

Pests Animals that consume agricultural products or destroy their marketability or cause human disease or discomfort.

Pheromone Chemicals used as communication (e.g., sex attractants or trail markers) between individuals of the same species.

Phosphorus cycle The phosphorus biogeochemical cycle is an example of a sedimentary nutrient cycle. Plants pick up phosphate to synthesize organic compounds. Consumers use the plant organic material containing phosphorus. Decomposition releases the organic phosphate. Local availability of phosphorus depends upon rate of cycling and the availability of various inorganic forms.

Photoautotroph Organisms that use solar energy to produce biological energy and support the synthesis of organic compounds using inorganic materials.

Photochemical smog Air pollution influenced by ultraviolet light interacting with nitrogen oxide pollutants (nitrogen dioxide, nitric oxide) also including ozone, nitric acid, hydrocarbons and PAN (summer pollution of "sun-belt" cities with many motor vehicles discharging nitrogen oxides). Most large cities have a combination of photochemical and industrial smog.

Photoperiod The relative length of day and night in one 24 hour period. Seasonal changes in day length are cues controlling activities such as flowering of plants or migration of birds.

Photosynthesis The synthesis of organic materials from solar energy, carbon dioxide and water by photoautotrophs that also releases oxygen (from the water). The development of photosynthesis over three billion years ago supported the evolution of complex living systems because of the accumulation of oxygen as well as the production of organic compounds.

Phytoplankton Aquatic plants, generally single cell algae, that passively float and are moved by water currents. The phytoplankton form the base of the food chain in open water environments where they are the only primary producers.Plants such as diatoms that are part of plankton.

Pioneer community The first or colonizing community in primary succession. Examples include lichens on rocks or emergent vascular plants invading a small pond.

Plankton Aquatic animals and plants that passively float or have weak powers of locomotion. These are generally very small organisms (see phytoplankton and zooplankton).

Point source (of pollution) Pollutants discharged at a specific location such as a specific factory smokestack. Contrast with point source (of pollution).

Pollution The release of substances that reduce the natural survival of biosystems of the earth. This includes compounds that are toxic, carcinogenic, mutagenic, & teratogenetic because of specific molecular targets; compounds that disrupt biogeochemical (nutrient) cycles (e.g., acid deposition, eutrophication); and compounds that potentially modify global climate. Although many pollutants are anthropogenic, some pollutants are of natural origin. The division of pollution into air pollution, water pollution and solid waste is a political division and not effective ecologically.

Polyculture The cultivation of a variety of crops in one area. Much of modern agricultural activity involves a single variety over some area (monoculture).

Population All the individuals of a species in a specific locality that contribute to a common gene pool (these individuals typically produce young that ecologically replace the adults).

Population density The number of individuals found in a standard unit of space.

Population growth The change in the size of a population through time. Populations change starting with few individuals and increasing smoothly into the carrying capacity is called sigmoid or S-shape population growth. Other populations grow rapidly and overshoot the carrying capacity (J-shape population growth curve). A population crash (producing cyclic or irregular patterns) will follow the population overshoot. These different growth patterns are the result of interaction between biotic potential and environmental resistance.

Population momentum The continual increase in size of a population after the birth rate equals death rate (TFR at replacement level) This happens because populations contain a high number of reproductive and prereproductive individuals produced previously during high growth.

Population overshoot When the population density exceeds the carrying capacity density.

Positive feedback System output continues or supports the current output pattern resulting in a potentially runaway system continually increasing or continually decreasing. See feedback loops (positive & negative).

Primary pollutant Pollutants in the form emitted such as sulfur oxides released from burning sulfur containing fossil fuel. Compare with secondary pollutant.

Primary producer Organisms on the first trophic level (also known as an autotrophs) able to produce organic material from inorganic substances and solar or biochemical energy.

Primary productivity Gross primary production is the total chemical energy produced by autotrophs. Net primary production is this total chemical energy produced by autotrophs less the energy they use in respiration. The primary productivity of terrestrial ecosystems dominated by autotrophs is the total photosynthesis expressed in grams of organic material or calories produced per unit area per unit time.

Primary sewage treatment Sewage treatment that removes the solid material by filtering and settling. Although this includes a considerable amount of organic material, it does not remove the dissolved organic material. Compare with secondary sewage treatment and tertiary sewage treatment.

Primary succession The predictable replacement sequence of communities in environments that did not initially have terrestrial ecosystems. This includes the succession that produces a terrestrial community from exposed rock formations or aquatic environments (e.g., a small pond). The succession starts with a pioneer community and ends with a climax community.

Productivity The ability of a natural ecosystem to produce organic material. See primary productivity.

Qualitative pollutant Pollutant that is a problems because of distinctive structure (e.g., chlorinated hydrocarbons such as DDT or PCB). These are potentially persistent because of their chemical structure.

Quantitative pollutant Pollutant that is a problem because of the amount discharged by human activity. Some of these substances occur naturally at lower levels. For example, the nutrient ions (especially phosphate and nitrate) that cause eutrophication.

Quarantine to control pests The restraint of travel and the movement of commerce as a method to control the spreading of plant or animal pests.

Range Land used by grazing herbivores such as cattle, sheep, horses and goats. If properly managed, the natural climate conditions will typically maintain effective grazing conditions. With water availability, rangeland can be converted to cultivated agriculture. The division of rangeland into smaller "rural farms" for individuals that do not depend upon ranching for a living has destroyed quality rangeland. See range plant classification.

Range of tolerance The environmental living range of a species considering specific environmental factors such as temperature or pH. The optimal condition can be anywhere between the minimum and maximum levels tolerated.

Range plant classification A classification of range plants considering nutrition and palatability to grazing animals and their ability to grow under different levels of grazing pressure. The resulting control on community composition will vary with the type of grazing animal. See also decreasers, increasers and invaders.

Rare species A species that has low population size. If specific habitats are not destroyed, some rare species remain viable, other rare species are at risk of extinction.

Rate of natural increase (RNI) The percentage annual growth rate of a population calculated by subtracting death rate from birth rate.

Renewable resource A natural ecosystem product (natural resource) that has the capability of replacing the harvest. Sustained yield controls harvest to maintain renewability. Renewable resources become nonrenewable when exploited or polluted.

Resilience of biosystems The ability of biosystems to return to the original state when disturbed (this aids biosystem stability).

Resistance of biosystems The ability of biosystems to resist disturbance. The physical barrier of the skin that controls the internal environment as well as physiological regulation (e.g., the ability to maintain a constant temperature under hot and cold external temperatures) are examples of biosystem resistance.

Respiration Respiration in cells is the oxidation of organic molecules to release energy and carbon dioxide. The highest energy released by cellular respiration requires oxygen. Respiration by organisms refers to breathing (the uptake of oxygen and the release of carbon dioxide). Ecologists refer to the total respiration of an ecosystem.

Restoration ecology The conversion of an environment modified if not destroyed by human activity back to a form similar to the original natural ecosystem.

Salinization The accumulation of salts as a result of the evaporation of irrigation water. Although fresh water used in agricultural activity has only a few salts, salts will accumulate over several years of evaporation in arid environments.

Salt water intrusion The extension of marine water (water with a high salt content) into freshwater aquifers. The removal of freshwater from aquifers connected to the ocean will increase salt water intrusion.

Scientific method A method of study that requires the formation of testable hypotheses developed from a systematic use of careful observation and accessible knowledge accepting only ideas not rejected by experimentation and statistical testing.

Scientific theories The accepted principles that form the knowledge base for science. Only hypotheses that withstand extensive testing become theories.

Secondary pest New pest populations that develop after pesticides kill native predators that controlled these populations.

Secondary pollutant Pollutants resulting from environmental transformation of primary pollutants. These transformations may involve many reaction sequences. Nitric acid and PAN of photochemical smog and sulfuric acid of industrial smog are examples of secondary pollutants.

Secondary sewage treatment Sewage treatment that removes the dissolved organic material. Compare with primary sewage treatment and tertiary sewage treatment.

Secondary succession The predictable replacement sequence of communities following above ground destruction by human harvest or fire. This replacement is dependent on soil conditions.

Sedimentary nutrient cycles Elements that have biogeochemical cycles without a gas form under normal earth conditions. Examples include: sodium, calcium, potassium, magnesium, cobalt, zinc, iron, iodine and others. Organisms use these elements in small but critically important amounts and some become toxic in higher concentrations.

Selective harvest in forests A forest harvest strategy that removes specific trees determined by species and age. This type of harvest is generally labor intensive. This type of harvest retains diverse forest ecosystems and has a reduced impact on erosion and wildlife. Compare with clear cutting of forests.

Septic tank The use of bacterial action to decompose sewage in an underground tank that has a drainage field that removes the nutrients released by this decomposition.

Sewage treatment Sewage in the United States is a combination of human excrement, organic material, sediments, infectious organisms, detergents and a variety of chemicals (some toxic) disposed of in water. Urban areas develop plants to remove solids, the organic material and kill infectious organisms in sewage. See also primary, secondary and tertiary sewage treatment.

Snag A standing dead tree. Snags support important insect eating birds.

Soil The upper layer of the earth that supports plants. Soil is composed of a complex mixture of solids, liquids and gases and contains a large number of diverse organisms.

Species (spelled the same in singular and plural) A group of individuals having common characteristics that produce individuals that are part of a common gene pool. The species name is a binomial name.

Sterile male control of pests (reproductive control) The control of pest populations with the release of sterile male organisms that are capable of mating but produce nonviable eggs. If enough males mate, the next generation will be smaller and the release program will increase in effectiveness. Individuals (reared in the laboratory) are subjected to radiation levels that kill females and sterilize males before release in areas of pest activity.

Succession The replacement of one community by another in a predictable time sequence. See also heterotrophic succession and autotrophic succession.

Sulfur cycle A biogeochemical cycle in which plants pick up sulfate to synthesize organic compounds. Consumers use the plant organic material containing sulfur. Decomposition with oxygen available releases sulfate. Decomposition in anaerobic environments (e.g., wetland sediments) releases hydrogen sulfide that becomes oxidized in the atmosphere. The release of sulfur oxides as primary pollutants and the conversion of these into sulfuric acid (a secondary pollutant contributing to acid decomposition) are changing the sulfur cycle.

Survivorship curve A graphic representation of the average chance to live for individuals of different ages presented as the number of survivors of an established sample unit (cohort) remaining in years following birth.

Sustained yield The controlled harvest of a natural resource that permits the regrowth or replacement of this resource before the next harvest. The diverse and unpredictable regulation of many natural populations makes sustained yield hard to maintain.

Synecology The ecological study of groups of organisms in populations or ecological communities

Synergistic The interaction between multiple factors where the interaction impact is greater than individual impacts in isolation. Ecological studies that consider single factors are not effective because many natural system interactions are synergistic. Some pollutants are not very toxic alone and are more potent when found in combination.

Systemic pesticide Pesticide absorbed into a plant that kills insects that feed on the plant.

Teratogenetic pollutant A pollutant that causes birth defects.

Terrestrial ecosystem Ecosystems found on land.

Territory An area defended by an individual excluding other individuals of the same species. (Compare with home range)

Tertiary sewage treatment The final, most costly (and often not completed) stage in sewage treatment that removes the ions such as phosphates and nitrates from the water. Tertiary sewage treatment removes nutrients released during secondary sewage treatment. Compare with primary sewage treatment.

Thermal pollution A change in water temperature that adversely affects aquatic ecosystems. A small increase in water temperature can have a severe impact on aquatic systems that typically experience very little temperature change.

Threatened species (legal use in the United States) Species listed by the U.S. Fish and Wildlife Service and the National Marine Fisheries that have decreased population viability resulting in a high probability of become endangered. See Endangered Species Act.

Threshold response (to pollution) The dose level of a pollutant that causes a toxic response. Detoxification potentially counters toxic impacts at lower dose levels.

Total fertility rate (TFR) The total number of children an average woman would have determined by the age-specific fertility for women 15 to 49 for any specific time (e.g., year). This is roughly the same as average family size. According to the Population Reference Bureau, the 1997 world TFR is 3 with the more developed parts at 1.6, the less developed parts (excluding China) at 4 and the TFR for Africa at 5.6 (with Middle Africa at 6.4) Replacement total fertility rate of countries that have passed through the demographic transition is around 2.1 and that of countries growing rapidly is 2.5.

Toxic pollutant Pollutants that act as poisons.

Transformer Microorganism that changes nutrients as part of biogeochemical cycles. All organisms transform nutrients but some, such as nitrogen fixing bacteria, have important ecosystem roles.

Transpiration The evaporative loss of water from the surface of vascular plants in the air primarily through stomata.

Trophic level An ecological classification that places organisms in different feeding levels starting with primary producers or green plants as the first trophic level followed by herbivores and then carnivore levels. Some animals feed on several trophic levels (omnivores). The trophic level pyramids are graphic illustrations of the relative number, weight, or energy flow contribution of trophic levels in different ecosystem types.

Upwelling The movement of water from the ocean bottom to the surface. Because surface water is nutrient limited and the subsurface water is often nutrient rich, areas of upwelling are areas of increased productivity.

Urban growth The increase in the urban population influenced by the city population rate of natural increase (births -- deaths) and the movement of individuals in or out of the city.

Urban heat island The heat-absorbing nature of building materials, the discharge of large quantities of heat, the potential for retention and the recycling of this heat all combine to make cities much warmer than adjacent natural ecosystems or the ecosystems they replaced.

Urban population The percentage of the total population living in cities.

Vector An organism capable of transmitting a pathogen from one organism to another. Insects that feed on blood are often vectors and some have a specific biological role in the life cycle of the pathogen.

Vent communities Distinctive marine communities found in deep waters where there is an escape of subsurface materials that support chemoautotrophic bacteria that support a variety of heterotrophs (some quite large).

Visitor carrying capacity The number or density of visitors to a natural preserve that will not destroy the natural system.

Water (hydrological) cycle The movement of water throughout the earth between major reservoirs such as the ocean, glaciers, ground water, freshwater streams and lakes and the atmosphere. The relatively small part of the total water volume in evaporation (powered by solar energy) and precipitation is essential to life and contributes to major differences between terrestrial and aquatic environments.

Watershed The land area (catchment area or basin) that receives all the surface water that eventually drains into a stream or lake.

Weed Plant species considered pests.

Wetland Area with permanent or occasional water that have emergent plants. The standing water controls the type of soil and selects for vegetation that resists standing water. Importance of wetlands determined by area covered alone is incomplete because wetlands are essential to adjacent natural ecosystems and numerous wildlife populations.

Wilderness Act of 1964 The establishment of a federal land wilderness system with the objective to maintain land as wilderness and exclude development and motorized vehicles. The act restricted wilderness to natural areas 5,000 or more acres in size and allowed for legislative expansion, requiring a survey of federal land to locate potential wilderness. The Forest Service survey for wilderness areas was called a roadless inventory.

Wilderness Native or near native ecosystem. The perception of what is wilderness varies considerably.

Wildlife Wildlife is a general term for native animals (vertebrates and invertebrates). Originally wildlife was birds, mammals and fish hunted for sport or food, resulting in the term "non-game wildlife."

Yield The total harvest of a natural resource (e.g., board feet of trees removed from a forest or pounds of fish harvested from the ocean). See also exploitation and sustained yield

Zero population growth (ZPG) A movement to change the increasing rate of human population growth to replacement conditions where births equal deaths. Many populations continue to expand under this condition because of population momentum. Some individuals are advocating negative population growth (NPG) because of the need to reduce the current world human population.

Zooplankton Animals such as copepods and larval fish that are part of plankton. The zooplankton of the open ocean form an important trophic link between the single cell phytoplankton and fish.