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An ongoing current event in which a large number of living species are threatened with extinction or are going extinct because of environmentally destructive human activities. The Earth is presently in the midst of a mass extinction event. In the…

The response of corals to environmental stress in which they eject the single-cell algae that live within the transparent coral tissue, making the white coral skeleton visible. Corals (Fig. 1) are animals that live in a partnership (symbiosis) with…

The interaction of the behavior and ecology of hosts with the biology of pathogens as relating to the impact of diseases on populations. Although human diseases have been studied from an ecological perspective for centuries, diseases in plant and…

The adaptation of an animal or plant through breeding in captivity to a life intimately associated with and advantageous to humans. Domesticated plants and animals differ genetically and morphologically from their wild counterparts, often in ways…

A species translocated from one region or continent to another outside its normal range, particularly when the translocation is the result of human activity (intentional or otherwise). Many thousands of species, including animals, plants, fungi,…

Any of the plant growth forms characteristic of the upper reaches of mountain slopes. Alpine vegetation refers to the plants that grow in mountainous areas above the limit of subalpine trees and other subalpine vegetation. In such environments,…

An intergrading region on a mountain slope characterized by specific plant life forms or species composition, and determined by complex environmental gradients. Along an altitudinal transect of a mountain, there are sequential changes in the…

The application of ecological principles to the solution of human problems and the maintenance of a high quality of life. Applied ecology is a branch of ecology that applies concepts of ecology to address contemporary problems involving natural…

The application of chemical techniques to the study of archeological materials in order to elucidate aspects of the human past. The materials used in archeological chemistry might be anthropogenic (for example, pottery or metal) or natural (from…

Any of several leguminous plants, or their seeds, long utilized as food by humans or livestock. There are more than 40,000 varieties of beans, with only a small number of these being mass-produced for human or animal consumption. In particular,…

The study of skeletal remains from archeological sites by biological (or physical) anthropologists. Bioarcheology differs in several ways from traditional skeletal research (see illustration). Previous work focused on individual case studies (for…

The number of different plant and animal species living in a defined ecosystem or study area; a contraction of biological diversity. Biodiversity includes genetic diversity (variability in the genetic makeup among individuals in a single species),…

A nutrient-poor, acid peatland. A bog is a type of peatland, which is a terrestrial wetland ecosystem. Bogs (Fig. 1) are nutrient-poor and acidic, and they contain vegetation in which peat mosses (Sphagnum species) and ericaceous dwarf shrubs play a…

Any terrestrial or aquatic animal that is capable of excavating holes in the ground for protection from adverse environmental conditions, as well as for storing food. Burrowing animals are uniquely adapted species, having the capacity to dig burrows…

A member of the mammalian family Camelidae in the order Artiodactyla. Camels are even-toed, hoofed mammals (ungulates). There are three extant camel species: the Bactrian camel (Camelus bactrianus; Fig. 1), the wild Bactrian camel (C. ferus), and…

Any living or fossil member of the plant division Pinophyta, consisting chiefly of woody trees or shrubs that produce cones and evergreen needles. Conifers are predominantly cone-bearing, evergreen trees and shrubs belonging to the order Pinales, as…

An unharvested crop grown to improve soil quality or enhance pest management. Increasing numbers of farmers plant cover crops as a means of conserving soil, enhancing subsequent production, and reducing off-farm inputs. The sustainable agriculture…

Marine animal life inhabiting the portion of the oceans below the upper limit of the continental slopes. The marine animals that make up the deep-sea fauna live below the photic zone of the oceans. In general, the deep sea may be regarded as that…

The deliberate conversion of forest to nonforest land that results in the long-term reduction of tree canopy below a minimum level. Deforestation, also known as land clearing, permanently eliminates forests to utilize the land for other purposes…

Any of various species of diving, air-breathing animals. Diving animals, which are found in every class of terrestrial vertebrates (amphibians, reptiles, birds, and mammals), are air-breathing species that have almost complete freedom in the aquatic…

Plants occupying sand dunes and the slacks, or swales, and flats between them. Dunes are mobile accumulations of sand that occur along shorelines and in deserts because of wind action. The formation and stability of dunes are affected significantly…

An assemblage of living organisms occurring together in an area. Ecological communities are aggregations of organisms characterized by a distinctive combination of two or more ecologically related species (Fig. 1). The nature of the forces that knit…

The study of the flow of energy within an ecological system from the time the energy enters the living system until it is ultimately degraded to heat and irretrievably lost from the system. It is also referred to as production ecology, because…

The methods required for the measurement of features of plant and animal populations or for quantifying energy flow or other aspects of ecological communities. Ecologists are concerned with such a wide range of variables that they may use many other…

The use of computer simulations or mathematical equations to address questions that cannot be answered solely by experiments or observations. Ecological models have two major aims: to provide general insight into how ecological systems or ecological…

A directional change in an ecological community. Populations of animals and plants are in a dynamic state. Through the continual turnover of individuals, a population may expand or decline depending on the success of its members in survival and…

The biological study of insects that have a direct influence on humanity. Economic entomology is a subdiscipline of entomology (the biological science that deals with the investigation of insects) and focuses on the effects of insects on human…

A species of animal, plant, or other living organism that is in serious danger of extinction throughout all or a significant portion of its range. When a species is categorized as endangered, its numbers are so small that the species is at risk of…

The process by which water bodies, such as estuaries, coastal waters, and lakes, become enriched in dissolved nutrients, such as phosphorus and nitrogen, resulting in increased growth of algae and aquatic plants as well as the deterioration of the…

The death and disappearance of a species. The extinction of a species usually represents an end point in a long series of population extinctions. During the extinction process, unique evolutionary history is lost at every stage, but the death of the…

An organism that tolerates and grows optimally under extreme environmental conditions. Extremophiles are organisms, predominantly microorganisms, that thrive in environmental conditions hostile to most life, including extremes of temperature (both…

The subdiscipline in mycology and ecology that examines community composition and structure; responses, activities, and interactions of single fungal species; and the functions of fungi in ecosystems. Fungi (that is, the true fungi, or Eumycota)…

Soil ingestion by animals. Grazing animals such as sheep and cattle ingest varying amounts of soil when they graze herbage contaminated with it.Pastures become contaminated with soil when livestock walk across the herbage, particularly in wet…

General terms applied to conditions of dormancy and torpor found in certain animals. Hibernation and estivation are physiological states of reduced metabolic activity exhibited by certain animals. In particular, many cold-blooded (poikilotherm or…

The study of the distribution and abundance of elements within landscapes, the origins of these elements, and their impacts on organisms and processes. A landscape is a distinct association of landforms that are visible within a single view or…

An ecological interaction between two species that benefits both of them. Within populations, individuals that interact with mutualists experience higher success than those that do not. Hence, behaving mutualistically is advantageous to the…

Accidental or intentional releases of crude oil or other petroleum products into the environment. Oil spills can occur almost anywhere in the world and cause a great deal of ecological, social, and economic harm, particularly when oil is released…

The oldest archeological cultures of the New World, the ancestors of modern Native Americans. The Paleoindian colonizing populations of the Americas were Homo sapiens sapiens who arrived during the late Pleistocene (Ice Age) from Asia, though…

The study of disease in the ancient past. Paleopathology is the investigation of ancient diseases and their origins. The term applies to any evidence of disease in any form of life, including both plants and animals. However, the research emphasis…

The scientific study of parasites and parasitism. Parasitology is the branch of biology dealing with parasitic organisms (see illustration), with particular focus being directed toward understanding the relationship between the parasite and the…

A relationship between two different species of organisms in which the larger, or host, organism transports a smaller organism, the guest. Phoresy is regarded as a type of commensalism in which the relationship is limited to transportation of the…

Mostly autotrophic microscopic algae which inhabit the illuminated surface waters of the sea, estuaries, lakes, and ponds. Many are motile. Some perform diel (diurnal) vertical migrations, others do not. Some nonmotile forms regulate their buoyancy.…

Movement of signals or cues, chemical in nature, among individual plants or plant parts. Plant communication is a phenomenon of chemical ecology (see illustration). In particular, chemical cues or signals are released by plants in response to damage…

The examination of the ecology of interacting plants and animals by using an evolutionary, holistic perspective. Plant–animal interactions can take many forms. For example, the chemistry of defensive compounds of a plant species may be altered by…

The process by which groups of living organisms expand the space or range within which they live. Dispersal operates when individual organisms leave the space that they have occupied previously, or in which they were born, and settle in new areas.…

The spatial distribution at any particular moment of the individuals of a species (typically plant or animal). Under natural conditions, organisms are distributed either by active movements, or migrations, or by passive transport by wind, water, or…

The ability of a population to persist and to avoid extinction. Population viability is an important facet of conservation biology. The viability of a population will increase or decrease in response to changes in the rates of birth, death, and…

A type of fossorial ground squirrel belonging to the genus Cynomys in the family Sciuridae in the order Rodentia. Prairie dogs are stout, short-tailed, short-legged ground squirrels that inhabit open plains, short-grass prairies, and plateaus in the…

The set of ideas that prescribe the manufacture and use of implements before written history. Technology is the principal means through which the human species has succeeded in occupying most of the world. The prehistoric record documents that for…

An order of small arachnids that have pincerlike pedipalps as in scorpions, but that lack a long tail and sting; also known as Pseudoscorpiones or Chelonethida. Members of the order Pseudoscorpionida (Pseudoscorpiones or Chelonethida) are commonly…

A eukaryotic, spore-producing, funguslike organism that feeds primarily upon bacteria and other microorganisms in terrestrial habitats. Although formerly classified as fungi, slime molds (Fig. 1) are not true fungi. Instead, they are considered…

Wet flatlands, where mesophytic vegetation is areally more important than open water. Swamps, marshes, and bogs are commonly developed in filled lakes, glacial pits and potholes, and poorly drained coastal plains or floodplains. Swamp (see…

The analysis of how ecosystem function is determined by the components of an ecosystem and how those components cycle, retain, or exchange energy and nutrients. Systems ecology is a quantitative branch of ecosystem ecology. In general, an ecosystem…

A community of organisms and their environment that occurs on the land masses of continents and islands. Terrestrial ecosystems are land-based communities of organisms interacting with biotic and abiotic elements in a given environment or area. When…

The use of verbal models, analytical models, or simulation models to explain patterns, suggest experiments, or make predictions in ecology. Because ecological systems are idiosyncratic, extremely complex, and variable, ecological theory faces…

The study of the structure of feeding relationships among organisms in an ecosystem. Trophic ecology investigates how various organisms at different feeding (trophic) levels interact within an ecosystem. In general, feeding or trophic relationships…

A biome or vegetation zone of treeless, usually lowland areas in cold regions. The term tundra is derived from Lapp or Russian origin, signifying treeless plains of predominantly cold northern regions (Fig. 1). In general, tundra supports some…

Phocoena sinus, a small and critically endangered cetacean found in the Gulf of California. The vaquita (Fig. 1) is one of the smallest cetaceans (marine mammals belonging to the order Cetacea) in the world, with mature individuals measuring…

A natural process in which harmful or beneficial effects are caused by secondary metabolites that spread from a donor organism to a recipient and are produced by plants, algae, bacteria, and fungi. Allelopathy is a key ecological process and has…

A discipline within the field of animal behavior that focuses on the reception and use of signals. Animal communication could well include all of animal behavior because a liberal definition of the term signal could encompass all stimuli perceived…

The scientific study of past material culture. The initial objective of archeology (often spelled archaeology) is to construct cultural chronologies that order past material culture into meaningful temporal segments. The intermediate objective is to…

The study of behavior change in response to drugs, chemicals, or other environmental conditions or agents. Behavioral toxicology investigates the effect of toxic exposure on organismal behavior. The toxic exposure can involve various chemicals,…

The destruction of organic compounds by microorganisms. Biodegradation is a process (carried out by microorganisms) that decomposes organic material into its constituent elements or new compounds. Microorganisms, particularly bacteria (and fungi to…

A microbial (often bacterial) community that is enveloped by an adhesive substance (the glycocalyx) at the interface of a liquid and a surface. Biofilms (see illustration) are defined as highly structured communities of microorganisms that are…

The study of the cycling of chemicals between organisms and the surface environment of the Earth. The chemicals either can be taken up by organisms and used for growth and synthesis of living matter or can be processed to obtain energy. The chemical…

The use of parasitoids, predators, and pathogens to reduce injurious pest insect populations and consequently the damage that they cause. Biological insect control (or insect biocontrol) is the regulation of insect populations by biological means.…

Management of the human use of natural resources to provide the maximum benefit to current generations while maintaining capacity to meet the needs of future generations. Conservation includes both the protection and rational use of natural…

Pathological conditions affecting the health of coral and causing its physiological dysfunction. Broadly defined, coral disease (Fig. 1) is any impairment to coral health resulting in physiological disturbance and breakdown. It usually involves…

A measure of the three-dimensional structure of live coral communities on reefs. Coral reef structural complexity is an intrinsic element of coral reef ecosystems and quantitates the surface area of coral in relation to its linear area. The…

A large, tawny brown wild cat, Puma concolor (family Felidae), once widespread over most of the Americas; also known as catamount, mountain lion, painter, and puma. The cougar (Puma concolor; see illustration) is a carnivorous member of the family…

The earliest representatives of people anatomically similar to living humans that evolved from more archaic humans approximately 150,000–300,000 years ago. The general process by which early modern humans (Homo sapiens) emerged from late archaic…

The biological sonar that bats, toothed whales, and certain other animals use to navigate without the visual system. Echolocation, or biosonar, is the physiological process that certain animals use to locate objects by reflected sound, primarily in…

The interaction of at least two organisms or species such that, for each, the birth or growth rates are depressed and the death rate increased by the presence of the other organisms or species. Ecological competition is the conflict that arises…

An obligate association formed between the roots of many plant species, especially trees, and a diverse range of soil fungi. The fungi and the finest, terminal root tips interact to form joint organs called ectomycorrhizas (Fig. 1). In…

A peculiar order of silk-spinning, orthopteroid insects, commonly called the embiids or web spinners, which are related to termites. The order Embioptera (also known as Embiidina or Embiodea) comprises about 300–400 described species, which are…

The sum of all external factors, both biotic (living) and abiotic (nonliving), to which an organism is exposed. All of the outside factors to which an organism is exposed comprise its environment (Fig. 1). The environment has a tremendous influence…

The name given to any of three carnivorous mammals in the genus Mustela (family Mustelidae); also known as the polecat. There are three species of ferrets, also termed polecats, belonging to the genus Mustela in the family Mustelidae of the order…

A group of grasses belonging to the genus Festuca used for both hay and pasture. There are approximately 100 species of fescue, and more than 30 are represented in the United States. Tall fescue (F. arundinacea; alternatively Lolium arundinaceum),…

A method of dating geological and archeological specimens by counting the radiation-damage tracks produced by spontaneous fission of uranium impurities in minerals and glasses. During fission two fragments of the uranium nucleus fly apart with high…

The trees, shrubs, herbs, bacteria, fungi, and animals, together with the surrounding air, soil, water, organic debris, and rocks (environmental substrate), interacting inside a defined boundary. Forests and woodlands occupy about 38% of the Earth's…

Fossil members of the group of primates constituting the apes. Apes and humans are closely related primates in the superfamily Hominoidea. The living hominoids are subdivided into the families Hylobatidae and Hominidae. The hylobatids, or lesser…

Extinct members of the order of mammals to which humans belong. All current classifications divide the living primates (order Primates) into two major groups (suborders) [Fig. 1]: the Strepsirhini (Strepsirrhini) or "lower" primates (lemurs,…

A physiologically interactive system within which growth, adaptation, species composition, nutrient cycling, biological productivity, and energy flows among inland aquatic microbial, plant, and animal communities are integrated with the environment.…

A large and diverse order of conspicuous brown algae (class Phaeophyceae), including such well-known seaweeds as Fucus and Sargassum. Definitive features of members of the Fucales include apical growth, production of sex organs in cavities, and a…

A group within the cnidarian subclass Octocorallia (class Anthozoa), comprising organisms known as gorgonians. Common names for members of the Gorgonacea (Figs. 1–5) include sea rods (Fig. 4a), sea fans (Fig. 4b), sea feathers (Fig. 4c), bamboo…

A biological community that contains few trees or shrubs, is characterized by mixed herbaceous (nonwoody) vegetation cover, and is dominated by grasses or grasslike plants. Grasslands are areas of herbaceous terrestrial vegetation dominated by…

A desert plant, Parthenium argentatum, cultivated as a source of rubber. Guayule belongs to the aster family (Asteraceae). It is a native perennial shrub that grows in the Chihuahuan Desert of north-central Mexico and southwestern Texas. The plant…

A group of species that utilize the same kinds of resources, such as food, nesting sites, or places to live, in a similar manner. Emphasis is on ecologically associated groups that are most likely to compete because of similarity in ecological…

The requirement of high salt (NaCl) concentrations for growth of microorganisms. Microorganisms (mainly bacteria) can be classified by their physiological tolerance to salt (Fig. 1). Most normal bacteria, such as Escherichia coli, and most…

The consumption of living plant tissue by animals. Plants and the animals that consume them constitute roughly one-half of the scientifically described species. Herbivorous species occur in most of the major taxonomic groups of animals, including…

The largest subclass in the class Bivalvia, phylum Mollusca. The subclass Heterodonta contains some of the most ecologically important bivalves (Fig. 1). For example, marine clams, cockles, and shipworms are heterodonts. Formerly, the class Bivalvia…

A species of fossil human from the Pleistocene representing a specialized side branch in human evolution in Africa and Eurasia. Homo erectus (Fig. 1) was a common, widespread, and long-surviving ancestor of modern humans (H. sapiens). Fossil remains…

The diversity of biological and genetic differences observed in the human population. Anthropologists study human biology to better understand the extent of human biological variability, to explain the mechanisms that create and pattern this…

The branch of ecology that considers the relations of individual persons and human communities with their particular environment. Human ecology is concerned with learning how the distributions and numbers of humans are determined by interactions…

The study of the establishment, spread, and ecological impact of species translocated from one region or continent to another outside their normal range, particularly when the translocation is the result of human activity (intentional or otherwise).…

Alien species whose introduction does or is likely to cause environmental or economic harm to forests. Nonnative organisms that cause a major change to native ecosystems are generally referred to as invasive species or invasives; they also are…

The distribution of plants and animals on islands. Islands harbor the greatest number of endemic species. The relative isolation of many islands has allowed populations to evolve in the absence of competitors and predators, leading to the evolution…

A predatory, cosmopolitan cetacean mammal, Orcinus orca, found typically in cold ocean waters. Killer whales (Orcinus orca) [Fig. 1] are top (apex) predators in the marine ecosystem, with no natural enemies other than humans. These carnivorous…

An order of large brown algae (class Phaeophyceae) commonly called kelps. Definitive features of members of the Laminariales include a life history in which microscopic, filamentous, dioecious gametophytes alternate with a massive, parenchymatous…

The process by which seriously disturbed land surfaces are stabilized against the hazards of water and wind erosion. All seriously disturbed land areas are in need of reclamation and should be stabilized and reclaimed as quickly as possible after…