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The Joshua tree (Yucca brevifolia) is a remarkable evergreen, treelike plant found only in the southwestern United States. It was named by Mormon settlers in the early 1800s. Upon seeing the limbs of this plant branching upwards to heaven, the…

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…

Collectively, members of the class Amphibia are facing massive reductions in total numbers, and the overall biodiversity of amphibians across the globe is under threat. Scientists have determined that global climate change and habitat destruction…

A method used by animals to conceal themselves from an enemy by appearing to be a section of the natural background. Animal camouflage is a strategy that animal organisms use to avoid or deflect the attacks of predators by misleading the latter's…

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 application of ecological principles to the solution of human problems and the maintenance of a quality life. It is assumed that humans are an integral part of ecological systems and that they depend upon healthy, well-operating, and productive…

The cultivation of freshwater and marine species for human purposes. Aquaculture, or aquatic farming, is concerned with the raising of animals and the harvesting of plants in freshwater and marine environments (Fig. 1). In other words, it is the…

A parasitic disease caused by a roundworm typically found in raccoons that is transmissible to humans, other mammals, and birds. Baylisascaris procyonis is a parasitic roundworm of raccoons (Procyon lotor) and belongs to the order Ascaridida in…

The branch of ecology that focuses on the evolutionary causes of variation in behavior among populations and species. The scientific study of behavioral ecology investigates how changes of behavior are influenced by ecological factors (Fig. 1).…

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…

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),…

The biological diversity of different plant and animal species living on the island of Borneo. Borneo is the third largest island in the world. Located in Southeast Asia and straddling the Equator, it is divided among three countries: Indonesia,…

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…

A synthetic discipline that describes the distributions of living and fossil species of plants and animals across the Earth's surface as consequences of ecological and evolutionary processes. Biogeography overlaps and complements many biological…

The use of parasitoids, predators, and pathogens to reduce injurious pest insect populations and consequently the damage they cause. Viruses and bacteria are the most commonly used pathogens, but fungi, protozoa, and nematodes may also be important…

The amount and rate of production which occur in a given ecosystem over a given time period. Biological productivity may apply to a single organism, a population, or entire communities and ecosystems. Productivity can be expressed in terms of dry…

Organic materials or wastes produced by plants and animals that can be used as energy sources or fuels. Biomass is a collective term used to describe renewable materials that are derived from plants and animals. In some cases, microbial metabolic…

A major community of plants and animals having similar life forms or morphological features and existing under similar environmental conditions. A biome (see illustration) is a complex biotic community covering a large geographic area and…

A branch of meteorology and ecology that deals with the effects of weather and climate on plants, animals, and humans. Thermal equilibrium The principal problem for living organisms is maintaining an acceptable thermal equilibrium with their…

The method of introducing microorganisms (native or genetically engineered) into a contaminated site to consume and break down environmental pollutants. Bioremediation is a form of biodegradation. Specifically, bioremediation is the use of…

The thin zone of living organisms and their environments at the surface of the Earth. The biosphere is the layer of life of the Earth (Fig. 1). Included in the biosphere are all environments capable of sustaining life above, on, and beneath the…

The use of telemetry methods for sending signals from a living organism over some distance to a receiver. Usually, biotelemetry is used for gathering data about the physiology, behavior, or location of the organism. Generally, the signals are…

Terrestrial and aquatic animals that are 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…

The name given to two species of mammals that are members of the family Camelidae in the order Artiodactyla. The two camel species are the Bactrian camel (Camelus bactrianus) and the Arabian or dromedary camel (C. dromedarius). Both species are…

Charles Robert Darwin (February 12, 1809 – April 19, 1882) is one of the most celebrated and eminent scientists of the past few centuries, with his broadest and most notable influence arising from his theory of evolution by means of natural…

A large homopteran insect of the superfamily Cicadoidea generally having long transparent wings and with the male typically producing a loud, droning noise. Cicadas are a large and diverse group of insects belonging to the superfamily Cicadoidea…

It has been a long-held belief that, as a result of hunting habits, early humans were partly or even primarily responsible for the decline and eventual extinction of most of the largest mammalian species that inhabited ancient Africa. These large…

Biodiverse ecosystem characterized by frequent to persistent clouds at the vegetation level. Relative to lowland tropical rainforests, cloud forests are shorter in stature and exhibit a denser understory (see illustration). Located in tropical and…

A detrimental condition in honeybee colonies characterized by a rapid loss of the adult bee population, with an absence of dead bees in and around affected colonies. Colony collapse disorder (CCD) first came to light in the fall of 2006 and is…

The critically endangered northern white rhinoceros (Ceratotherium simum cottoni) is a subspecies of white rhino that is on the brink of complete extinction, with only two individuals left in captivity and no known members reported in the wild. The…

The collective measures and actions concerned with the preservation and restoration of animal and plant species and their habitats. To conserve an endangered species, an adequate number of populations must be maintained within a sufficient amount of…

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 science of restoring an extinct animal or plant using advanced genetic and reproductive technologies. The concept of de-extinction was science fiction until the recent advent of advanced genome sequencing platforms. The technological…

The International Union for Conservation of Nature (IUCN)—the global authority on the status of the natural world—estimates that approximately 5–10% of the world's insect species (class Insecta, phylum Arthropoda) are threatened and facing…

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…

A wide, open, comparatively barren tract of land with little rainfall and, consequently, few forms of life. Deserts (Fig. 1) comprise about one-fifth of the land surface on Earth. From an ecological viewpoint, the scarcity of rainfall in deserts is…

A process by which human activities contribute to reductions in the biological productivity of semiarid lands. The term was made popular by André Aubreville’s 1949 book, Climats, forêts et desertification de l’Afrique tropicale (Climates, Forests…

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…

Assemblages of living organisms that occur 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 subdiscipline of biology that concentrates on the relationships between organisms and their environments. Ecology, also called environmental biology, is concerned with patterns of distribution (where organisms occur) and with patterns of…

A functional system that includes an ecological community of organisms together with the physical environment, interacting as a unit. Ecosystems involve both biotic (living) components and abiotic (nonliving, physical) components (Fig. 1). Also…

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 development of strategies to allocate and conserve resources, with the ultimate goal of regulating the impact of human activities on the surrounding environment. Environmental management is a mixture of science, policy, and socioeconomic…

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…

The branch of ecology that studies the environmental changes that occur in ecosystems in relation to fire. Disturbance is a major environmental influence in many of Earth's ecosystems. Vital to the healthy functioning of forests, savannas,…

The study of ecological processes that affect exploited aquatic organisms in marine and freshwater environments. Because the field of fisheries ecology is primarily motivated by an attempt to harvest populations (Fig. 1), special attention has been…

A diagram depicting those organisms that eat other organisms in the same ecosystem. A food web (Fig. 1) is a graphical model that illustrates feeding relationships at various, changing trophic levels. In some cases, the organisms that are consumed…

A plant community consisting predominantly of trees and other woody vegetation growing closely together. Forests are complex ecosystems comprising plants, animals, and their environment, with trees as the dominant form of vegetation (Fig. 1). Trees…

Uncontrolled combustion of forest fuels or vegetation. Forest fire, bushfire, wildland fire, and wildfire are terms that are used interchangeably and refer to all unplanned fires that burn surface fuels or vegetation (such as grasses, weeds, brush,…

All freshwater comes from precipitation over land, which is distributed on Earth as blue and green water. Blue water—that is, surface and groundwater—is stored as freshwater in lakes, streams, ice, and snow, as well as below ground. Green water is…

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 harvest of animals and plants from the ocean to provide food for people and animals. Important products in marine capture fisheries include fish (Fig. 1); mollusks such as oysters, clams, and squid; and crustaceans such as crabs and shrimps.…

The pattern of care given an offspring by its mother. Maternal behavior constitutes the various aspects of behavior displayed by the female parent in the course of raising its offspring. In most species that care for their young after birth, the…

Bipartite, intimate, and mutualistic symbioses that are formed by soil-inhabiting fungi and plants. Mycorrhizae (mycorrhizas) can be formed between different groups of fungi and the roots, rhizomes (underground horizontal shoots), or thalli (plant…

The natural biological and chemical processes through which inorganic and organic nitrogen are interconverted. It includes the processes of ammonification, ammonia assimilation, nitrification, nitrate assimilation, nitrogen fixation, and…

A report by a team of conservation biologists concludes that the total number of birds in North America has dropped precipitously since 1970. Annual surveys monitoring the biodiversity and abundance of bird populations across the North American…

A biological community, essentially a grassland, covering extensive high areas in the equatorial mountains of the Western Hemisphere; also spelled páramo. Paramos (Fig. 1) occur in alpine (high-altitude) regions above the timberline and are…

The scientific study of parasites and of parasitism. Parasitism is a type of symbiosis and is defined as an intimate association between an organism (parasite) and another, larger species of organism (host) upon which the parasite is metabolically…

The biological, physical, and chemical processes involved in the cycling of phosphorus in the environment. The cycle comprises a geological (long-term) cycle and a biological (short-term) cycle, the latter with both terrestrial and aquatic…

A discipline that combines the study of physiological processes (the functions of living organisms and their parts) with ecological processes that connect the individual organism with population dynamics and community structure. Physiological…

The branch of plant science that seeks physiological (mechanistic) explanations for ecological observations. Physiological ecology is the study of biophysical, biochemical, and physiological processes used by organisms to cope with factors of their…

An organism that belongs to the kingdom Plantae in biological classification. A plant (see illustration) is a member of the taxonomic kingdom Plantae and is generally distinguished by the presence of chlorophyll, a rigid cell wall, and abundant,…

The extent to which a plant, or plant ecosystem, is susceptible to, or unable to cope with, the adverse effects of climate change. Plants are constantly changing their ecophysiology and distributions over different timescales as they respond to…