GLOSSARY OF ECOLOGY TERMS
N to S

Our glossary contains most of the scientific terms you'll encounter while using this site:

A-D | E-H | I-M | N-S | T-Z

N | O | P | Q | R | S

N

Natural resources, n: Nutrients and minerals in the soil and deeper layers of the earth's crust; water; wild and domestic plants and animals; air; and other resources produced by the earth's natural processes.

Natural selection, n: One of several gradual mechanisms through which evolution occurs. Process by which a particular beneficial gene (or set of genes) is reproduced more than other genes in succeeding generations due to selective pressures in the environment that favor the beneficial gene. The result of natural selection is a population that contains a greater proportion of organisms better adapted to certain environmental conditions.

Negative feedback loop, n: Situation in which a change in a certain direction provides information that causes a system to change less in that direction. This is a common regulatory mechanism and is widely used in animals to control hormone levels in the blood. For example, the hormones that control ovulation in humans are on a negative feedback loop.

Nitrogen cycle, n: Cyclic movement of nitrogen in different chemical forms from the environment to organisms and then back to the environment.

Nitrogen fixation, n: The process of chemically converting nitrogen gas (N 2 ) from the air into compounds, such as nitrates (NO 3 ), nitrites (NO 2 ), or ammonia (NH 3 ), that can be used by plants in building amino acids and other nitrogen-containing organic molecules.

Nonbiodegradable, adj: Not able to be consumed and/or broken down by biological organisms. Nonbiodegradable substances include plastics, aluminum, and many chemicals used in industry and agriculture. Particularly dangerous are nonbiodegradable chemicals that are also toxic and tend to accumulate in organisms.

Nonrenewable resource, n: Resource that exists in a fixed amount (stock) in various places in the earth's crust and has the potential for renewal only by geological, physical, and chemical processes taking place over hundreds of millions to billions of years. Examples are copper, aluminum, coal, and oil. We classify these resources as exhaustible because we are extracting and using them at a much faster rate than they were formed.

Nutrient, n: Any food or element an organism must take in to live, grow, or reproduce. Plant: An essential element in a particular ion or molecule that can be absorbed and used by he plant. For example, carbon, hydrogen, nitrogen, and phosphorus are essential elements; carbon dioxide, water, nitrate (NO 3 ), and phosphate (PO 4 ) are respective nutrients. Animal: Materials such as protein, vitamins, and minerals that are required for growth, maintenance, and repair of the body and also materials such as carbohydrates that are required for energy.

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O

Obligate aerobe, n: See aerobe.

Obligate anaerobe, n: See anaerobe.

Old-growth forest, n: Virgin and old, second growth forests containing trees that are often hundreds, sometimes thousands, of years old. These are the richest forest biomes with the widest arrays of niche microhabitats and the broadest biodiversity, especially in the tropics.

Open system, n: A system, such as a living organism, in which both matter and energy are exchanged between the system and the environment.

Optimum sustainable population, n: the number of animals which will result in the maximum productivity of the population or the species, keeping in mind the carrying capacity of the habitat and the health of the ecosystem.

Organic, adj: All living things, and products that are uniquely produced by living things, such as wood, leather, and sugar. 2. All chemical compounds or molecules, natural or synthetic, that contain carbon atoms as an integral part of their structure.

Overburden, n: Layer of soil and rock overlying a mineral deposit, removed during surface mining.

Overconsumption, n: Situation in which some people consume much more than they need at the expense of those who can not meet their basic needs- and at the expense of earth's present and future life-support systems for humans and other forms of life.

Overfishing, n: Harvesting so many fish of a species (especially immature fish) that there is not enough breeding stock left to replenish the species, such that it is not profitable to harvest them, leading to commercial extinction .

Overgrazing, n: Destruction of vegetation when too many grazing animals feed too long and exceed the carrying capacity of a rangeland area.

Overnutrition, n: Diet so high in calories, saturated (animal) fats, salt, sugar, and processed foods, and so low in vegetables and fruits that the consumer runs high risks of diabetes, hypertension, heart disease, and other health hazards.

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P

Paleoecology, n: The study of ancient ecosystems. Paleoecologists use data from such sources as tree rings, geologic deposits, fossils (pollen is a particularly popular tool), and coral bores to reconstruct the climate and ecology or ancient ecosystems.

Phosphorus cycle, n: Cyclic movement of phosphorus, in varying chemical forms, from the environment to organisms and then back to the environment.

Pioneer species, n: First hardy, often xerophytic , species (often microbes, mosses, and lichens) that begin colonizing a site as the first stage of ecological succession.

Pollutant, n: A particular chemical or form of energy that can adversely affect the health, survival, or activities of humans or other living organisms.

Population, n: A group within a single species, the individuals of which can and do freely interbreed. Breeding between populations of the same species is less common because of differences in location, culture, nationality, and so on.

Population change, n: An increase or decrease in the size of a population. It is equal to (births + immigration) - (deaths + emigration).

Population density, n: Number of organisms in a particular population found in a specified area.

Population dispersion, n: General pattern in which the members of a population are arranged throughout its habitat.

Population distribution, n: Variation of population density over a particular geographical area. For example, a country has a high population density in its urban areas and a much lower population density in rural areas.

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Positive feedback loop, n: Situation in which a change in a certain direction provides information that causes a system to change further in the same direction. This can lead to a runaway or vicious cycle.

Potentially renewable resource, n: Resource that theoretically can last indefinitely without reducing the available supply, either because it is replaced more rapidly through natural processes than are nonrenewable resources or because it is potentially inexhaustible (solar energy). Examples are trees in forests, grasses in grasslands, wild animals, fresh surface water in lakes and streams, most groundwater, fresh air, and fertile soil. If such a resource is used faster than it is replenished, it can be depleted and converted into a nonrenewable resource.

Poverty, n: Inability to meet basic needs for food, clothing, and shelter.

Primary producer, n: An organism, such as a plant or microbe, that makes its own food and forms the bottom-most tier in a trophic system. Primary producers are the basis of the food web in most ecosystems (the exceptions are open system communities based entirely on scavenging nutrients flushed into the system from elsewhere, such as some deep sea communities -- though even in these cases, the food flushed into the system comes from another system where primary producers are the basis of the trophic pyramid ). Primary producers are able to convert abiotic raw materials into biotic tissue, either by capturing the sun's energy through photosynthesis (plants) or by harnessing the energy in chemical bonds through chemosynthesis (some microbes).

Pyramid of biomass, n: Diagram representing the biomass (total dry weight of living organisms) that can be supported at each trophic level in a food web. The bottom of the pyramid is comprised of primary producers , while the peak of the pyramid is topped by one (or at most a small handful) apex predator . Humans are abnormal in that we cross all ecosystems and biomass pyramids, and in almost every one (excepting the polar caps and deepest of oceanic environments) we are the dominant apex predator.

Pyramid of energy flow, n: Also called a trophic pyramid . Diagram representing the flow of energy through each trophic level in a food chain or food web. With each energy transfer, only a small part (typically 10%) of the usable energy entering one trophic level is transferred to the organisms at the next trophic level, with the remaining 90% lost as heat or expended in metabolic processes.

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R 

Resource economics, n: The study of natural ecosystem services and the economic values, in terms real-world currencies and capital valuations, of those services. One of the goals of resource economics is to assist policy makers in performing the cost-benefit analysis of various plans of action or inaction with regard to the natural world. The value of an ecosystem service is determined by calculating what it would cost to perform the same service artificially if the naturally-occuring service were disrupted or destroyed.

Resource partitioning, n: Process of dividing up resources in a ecosystem so that species with similar requirements (overlapping ecological niches) use the same scarce resources at different times, in different ways, or in different places.

Runoff, n: Surface water effluent (usually from precipitation but may be from human activities such as irrigation) that moves too quickly to be absorbed into the ground. It flows down contour gradients to enter stream and river systems, carrying with it anything light enough to be borne in the volume of water, which may be light after a small rain or tremendous in the wake of a storm, when even large boulders and trees get swept up in the runoff. When runoff travels over deforested or unplanted agricultural lands, it carries away large quantities of topsoil . Runoff from agricultural areas often carries heavy doses of biocides , fertilizers, and other nutrients, which can lead to eutrophication when introduced into aquatic systems.

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S

Salinization, n: Accumulation of salts in soil that can eventually make the soil unable to support plant growth.

Second law of thermodynamics, n: In any conversion of heat energy to useful work, some of the initial energy input is always degraded to lower quality, more dispersed, less useful energy -- usually low-temperature heat that flows into the environment; every energy system has "leaks" and looses energy or heat to attenuation.

Soil Erosion, n: The loss of topsoil through silt-laden runoff , strong winds, or other forces that transport soil away from its natural location.

Specialist species, n: Species with a narrow ecological niche. They may be able to live in only one type of habitat, tolerate only a narrow range of climatic or other environmental conditions, or they may use only one or a few types of food.

Speciation, n: Formation of two species from one species as a result of divergent natural selection in response to changes in environmental conditions; usually takes thousands or tens of thousands of years.

Species, n: The boundaries of this taxonomic level (the most precise in the hierarchical system of binomial nomenclature ) are hotly debated among scientists and there is little real consensus about where to draw the lines between species, subspecies, morphs, races, variants, etc. In general, a species is a group of organisms that resemble one another in appearance, general behavior, ecological niche, chemical makeup and processes, and genetic structure. Organisms that reproduce sexually are classified as members of the same species only if they can actually or potentially interbreed with one another and produce fertile offspring. It should be noted that some (though quite few) taxonomists believe the species level of classification is frequently invalid and these scientists only recognize classifications down to the level of genus (again, these taxonomists represent a very small minority view).

Sulfur cycle, n: Cyclic movement of sulfur in different chemical forms, from the environment to organisms and then back to the environment.

Sustainability, n: Ability of a system to survive for some specified (finite) time.

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Sustainable agriculture, n: Method of growing crops and raising livestock based on organic fertilizers, soil conservation, water conservation, biological control of pests, and minimal use of non-renewable fossil-fuel energy.

Sustainable development, n: Forms of economic development and activities that do not deplete or degrade the natural resources upon which present and future economic growth and life depend.

Sustainable living, n: Taking no more potentially renewable resources from the natural world than can be replenished naturally and not overloading the capacity of the environment to cleanse and renew itself by natural processes.

Sustainable society, n: A society that manages its economy and population size without doing irreparable environmental harm by overloading the planet's ability to absorb environmental insults, replenish its resources, and sustain human and other forms of life over a specified period-usually hundreds to thousands of years. During this period it satisfies the needs of its people without depleting earth capital and thereby jeopardizing the prospects of current and future generations of humans and other species.

Sustainable system, n: A system that survives and functions over some specified (finite) time; a system that attains its full expected lifetime.

Sustainable yield (sustained yield), n: Highest rate at which a potentially renewable resource can be used without reducing its available supply throughout the world or in a particular area.

Symbiont, n: See symbiosis .

Symbiosis, n: Literally means "living together" in Latin. Any intimate relationship or association between members of two or more species. The members of the relationship are symbionts. Obligate symbionts rely so heavily on the relationship that they cannot feed, reproduce, or perform some other crucial life function in the absence of their symbiotic partner(s). There are three main categories of symbiosis: commensalism , mutualism , and parasitism , with some degree of blending at the edges of these definitions in many cases.

Symbiotic, adj: Refers to a component or member of a system of symbiosis. "These organisms have a symbiotic relationship."

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