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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…

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…

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…

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…

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…

Plants occupying sand dunes and the slacks, or swales, and flats between them. The density and diversity of dune vegetation are greater on coastal dunes than on desert dunes. Dune Plant geography Sand Zonation A zonation pattern is evident in the…

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…

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 study of insects that have a direct influence on humanity. Though this includes beneficial as well as harmful species, most attention is devoted to the latter and how they become pests and are controlled. The emphasis on managing harmful insects…

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 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),…

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…

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…

The subdiscipline in mycology and ecology that examines community composition and structure; responses, activities, and interactions of single species; and the functions of fungi in ecosystems. The fungi, as they have been historically classified,…

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…

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 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…

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…

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,…

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…

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…

Categories of land resources that provide information about uses and characteristics. In combination with geographic location systems, measurements of the amount of land in use, the amount available for development, and the changes in use over time,…

The long-term development or conservation of an area and the establishment of a relationship between local objectives and regional goals. Land-use planning is often guided by laws and regulations. The legal basis of land-use regulation in the United…

Symbiotic associations of fungi (mycobionts) and photosynthetic partners (photobionts). Lichens (Fig. 1) consist of fungi and algae or cyanobacteria growing together symbiotically. Lichen associations always result in a distinct morphological body…

Any of the taxonomically diverse trees and shrubs that form the dominant plant communities in tidal, saline wetlands along sheltered tropical and subtropical coasts. The various species of mangrove trees and shrubs are important ecological community…

The management of marine species and ecosystems to prevent their decline and extinction. As in terrestrial conservation, the goal of marine conservation is to protect biodiversity and ecosystem function through the preservation of species,…

An integrative science that studies the basic structural and functional relationships within and among living populations and their physical–chemical environments in marine ecosystems. Although an outgrowth of natural history and the life sciences,…

The harvest of animals and plants from the ocean to provide food for people and animals. Marine fisheries are places or industries engaged in the harvesting of aquatic life in seawaters. Important products in marine capture fisheries include fish…

The study of interrelationships between microorganisms and their environments. Microbial ecology is a scientific discipline concerned with how microorganisms (microbes) interact with each other and the environment. Microbial populations are able to…

Regularly occurring, oriented seasonal movements of individuals of many animal species. The study of animal behavior, or ethology, often includes analyses of migratory behavior (Fig. 1). The term migration can refer to a diversity of animal…

An isolated fertile area, usually limited in extent and surrounded by desert. The term was initially applied to small areas in Africa and Asia typically supporting trees and cultivated crops with a water supply from springs and from seepage of water…

Ecology of prehistoric times, extending from about 10,000 to about 3.5 × 109 years ago. Although the principles of paleoecology are the same as those underlying modern ecology, the two fields actually differ greatly. Paleoecology is a historical…

A substance that acts as a molecular messenger, transmitting information from one member of a species to another member of the same species. A pheromone is a chemical substance secreted by an individual that influences the behavior of other…

The study of the spatial distributions of plants and vegetation and of the environmental relationships which may influence these distributions. Plant geography (or certain aspects of it) is also known as phytogeography, phytochorology, geobotany,…

The study of spatial and temporal patterns in the abundance and distribution of organisms and of the mechanisms that produce those patterns. Population ecology investigates how and why populations change over time (Fig. 1). In general, species…

The interrelationships between two animals (most often of unlike species) whereby one acts as a predator that ensnares and eats the other (the prey). Predation occurs when one animal (the predator) kills and then eats another living animal (the…

A strategy that organisms use to avoid or deflect the attacks of predators by misleading the latter's visual senses. Protective coloration is an organism's color pattern that blends with the environment (Fig. 1) and increases that organism's…

An alpine biological community in the central portion of the Andes Mountains of South America characterized by low-growing, widely spaced plants that lack much green color for most of the year. Sparsely vegetated, treeless stretches of the puna…

The study of the fate and effects of radioactive materials in the environment. As a hybrid field of scientific endeavor, it is founded upon, and derives its basic principles from, both of its parent disciplines, that is, basic ecology and radiation…

A rigid and wave-resistant marine structure that stands above its surroundings. To navigators, a reef is any rocky structure that poses a threat to navigation. Marine biologists and geologists specify that reefs are constructed by organisms that…

A field in the science of conservation that is concerned with the application of ecological principles to restoring degraded, derelict, or fragmented ecosystems. The primary goal of restoration ecology, also known as ecological restoration, is to…

The common name for a number of fish in the family Salmonidae that live in coastal waters of the North Atlantic and North Pacific and breed in rivers tributary to the oceans. Salmon (Fig. 1) are large, predatory fish belonging to the genera…

The cultivation and harvesting (aquaculture) of salmon species. Salmon is the common name assigned to various fish belonging to the genera Oncorhynchus and Salmo (Fig. 1) in the order Salmoniformes. These relatively large, predatory fish live in…

A maritime habitat characterized by grasses, sedges, and other plants that have adapted to continual, periodic flooding. Salt marshes (Figs. 1 and 2) are found primarily throughout the temperate and subarctic regions of the world. The tide is the…

The term savanna was originally used to describe a tropical grassland with more or less scattered dense tree areas. This vegetation type is very abundant in tropical and subtropical areas, primarily because of climatic factors. The modern definition…

A fundamental aspect of social organization that is established by fighting or display behavior and results in a ranking of the animals in a group. Social hierarchies, or dominance hierarchies, are foundational facets of social organization and…

Insects that share resources and reproduce cooperatively. Social insects live in large, cooperative colonies and have evolved in various ways to maximize their fitness. In general, social insects adhere to social hierarchies, interacting and…

A scientific discipline that applies principles of evolutionary biology to the study of animal and human social behavior. Sociobiology is a synthesis of ethology (the study of animal behavior), ecology, and evolutionary theory in which social…

A harmonious balance of human needs with resource consumption over an extended period of time. Sustainable development is a closely related term to sustainability, described in the 1987 Brundtland Report—issued by the United Nations (UN) World…

A zone of forest vegetation encircling the Northern Hemisphere between the arctic-subarctic tundras in the north and the steppes, hardwood forests, and prairies in the south. The taiga is the largest terrestrial biome (a major community of plants…

A pattern of behavior in which an animal actively defends a space or some other resource. Territoriality is an important aspect of the behavior of many animals (see illustration). It is observed throughout the animal kingdom and is particularly…

An irreversible increase in the size of a tree. Trees grow to a larger size at maturity than other woody perennials (Fig. 1), have a comparatively long period of development to maturity, and live a long time in the mature state. Trees, like other…

One of the orders of the class Amphibia, comprising the salamanders. The taxon class Amphibia comprises the Lissamphibia (all modern amphibians, including frogs, toads, salamanders, and caecilians) and their more distant extinct relatives. The…

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…

Animals that live all or part of their life suspended and drifting in large aquatic environments. Zooplankton are animals that inhabit the water column of oceans and large freshwater systems, and they lack the means to counteract transport currents.…

An approach to management of natural resources that emphasizes how little is known about the dynamics of ecosystems and that, as more is learned, management will evolve and improve. Adaptive management is a systematic strategy that seeks to improve…

A model for the functioning of an agricultural system, with all inputs and outputs. An ecosystem may be as small as a set of microbial interactions that take place on the surface of roots, or as large as the globe. An agroecosystem may be at the…

Plant growth forms characteristic of upper reaches of forests on mountain slopes. In such an environment, trees undergo gradual changes that, though subtle at first, may become dramatic beyond the dense forest as the zone of transition leads into…

Intergrading regions on mountain slopes 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 physiognomy…