Ecology (redirected from environmental science)

ecology, study of the relationships of organisms to their physical environment and to one another. The study of an individual organism or a single species is termed autecology; the study of groups of organisms is called synecology.

The Ecosystem

Within the biosphere—the total expanse of water, land, and atmosphere able to sustain life—the basic ecological unit is the ecosystem. An ecosystem may be as small as a tidal pool or a rotting log or as large as an ocean or a continent-spanning forest. Each ecosystem consists of a community of plants and animals in an environment that supplies them with raw materials for life, i.e., chemical elements and water. The ecosystem is delimited by the climate, altitude, water and soil characteristics, and other physical conditions of the environment.

The Food Web and Other Vital Cycles

The energy necessary for all life processes reaches the earth in the form of sunlight. By photosynthesis green plants convert the light energy into chemical energy, and carbon dioxide and water are transformed into sugar and stored in the plant. Herbivorous animals acquire some of the stored energy by eating the plants; those animals in turn serve as food for, and so pass the energy to, predatory animals. Such sequences, called food chains, overlap at many points, forming so-called food webs. For example, insects are food for reptiles, which are food for hawks. But hawks also feed directly on insects and on other birds that feed on insects, while some reptiles prey on birds. Since a severe loss of the original energy occurs with each transfer from species to species, the ecologist views the food (energy) structure as a pyramid: Each level supports a smaller number and mass of organisms. Thus in a year's time it would take millions of plants weighing tons to feed the several steer weighing a few tons that could support one or two people. The ecological conclusion is that if human beings would eat more plants and fewer animals, food resources would stretch much further. Once the energy for life is spent, it cannot be replenished except by the further exposure of green plants to sunlight.

The chemical materials extracted from the environment and elaborated into living tissue by plants and animals are continually recycled within the ecosystem by such processes as photosynthesis, respiration, nitrogen fixation, and nitrification. These natural processes of withdrawing and returning materials are variously called the carbon cycle, the oxygen cycle, and the nitrogen cycle. Water is also cycled. Evaporation from lakes and oceans forms clouds; the clouds release rain that is taken up by the soil, absorbed by plants, and passed on to feeding animals—which also drink directly from pools and lakes that catch the rain. The water in plant and animal wastes and dead tissue then evaporates and can be recycled. Interference with these vital cycles by disturbance of the environment—for example, by pollution of the air and water—may disrupt the workings of the entire ecosystem. The cycles are facilitated when an ecosystem has a sufficient biological diversity of species to fill its so-called ecological niches, the different functional sites in the environment where organisms can act as producers of energy, consumers of energy, or decomposers of wastes. Such diversity tends to make a community stable and self-perpetuating.

Climax Communities

A climax community is one that has reached the stable stage. When extensive and well defined, the climax community is called a biome. Examples are tundra, grassland, desert, and the deciduous, coniferous, and tropical rain forests. Stability is attained through a process known as succession, whereby relatively simple communities are replaced by those more complex. Thus, on a lakefront, grass may invade a build-up of sand. Humus formed by the grass then gives root to oaks and pines and lesser vegetation, which displaces the grass and forms a further altered humus. That soil eventually nourishes maple and beech trees, which gradually crowd out the pines and oaks and form a climax community. In addition to trees, each successive community harbors many other life forms, with the greatest diversity populating the climax community.

Similar ecological zonings occur among marine flora and fauna, dependent on such environmental factors as bottom composition, availability of light, and degree of salinity. In other respects, the capture by aquatic plants of solar energy and inorganic materials, as well as their transfer through food chains and cycling by means of microorganisms, parallels those processes on land.

The early 20th-century belief that the climax community could endure indefinitely is now rejected because climatic stability cannot be assumed over long periods of time. In addition nonclimatic factors, such as soil limitation, can influence the rate of development. It is clear that stable climax communities in most areas can coexist with human pressures on the ecosystem, such as deforestation, grazing, and urbanization. Polyclimax theories stress that plant development does not follow predictable outlines and that the evolution of ecosystems is subject to many variables.

Bibliography

See E. P. Odum, Fundamentals of Ecology (3d ed. 1971); R. L. Smith, ed., The Ecology of Man: An Ecosystem Approach (1971); P. A. Colinvaux, Introduction to Ecology (1973); R. M. Darnell, Ecology and Man (1973); T. C. Emmel, An Introduction to Ecology and Population Biology (1973); D. B. Sutton and N. P. Harman, Ecology: Selected Concepts (1973); K. E. F. Watt, Principles of Environmental Science (1973); D. Worster, Nature's Economy (1977); R. Brewer, The Science of Ecology (1988).

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ecology

Study of the relationships between organisms and their environment. Physiological ecology focuses on the relationships between individual organisms and the physical and chemical features of their environment. Behavioral ecologists study the behaviours of individual organisms as they react to their environment. Population ecology is the study of processes that affect the distribution and abundance of animal and plant populations. Community ecology studies how communities of plant and animal populations function and are organized; it frequently concentrates on particular subsets of organisms such as plant communities or insect communities. Ecosystem ecology examines large-scale ecological issues, ones that often are framed in terms of measures such as biomass, energy flow, and nutrient cycling. Applied ecology applies ecological principles to the management of populations of crops and animals. Theoretical ecologists provide simulations of particular practical problems and develop models of general ecological relevance. See also systems ecology.

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Ecology

The subdiscipline of biology that concentrates on the relationships between organisms and their environments; it is also called environmental biology. Ecology is concerned with patterns of distribution (where organisms occur) and with patterns of abundance (how many organisms occur) in space and time. It seeks to explain the factors that determine the range of environments that organisms occupy and that determine how abundant organisms are within those ranges. It also emphasizes functional interactions between co-occurring organisms. In addition to being a unique component of the biological sciences, ecology is both a synthetic and an integrative science since it often draws upon information and concepts in other sciences, ranging from physiology to meteorology, to explain the complex organization of nature.

Environment is all of those factors external to an organism that affect its survival, growth, development, and reproduction. It can be subdivided into physical, or abiotic, factors, and biological, or biotic, factors. The physical components of the environment include all nonbiological constituents, such as temperature, wind, inorganic chemicals, and radiation. The biological components of the environment include the organisms. A somewhat more general term is habitat, which refers in a general way to where an organism occurs and the environmental factors present there. See Environment

A recognition of the unitary coupling of an organism and its environment is fundamental to ecology; in fact, the definitions of organism and environment are not separate. Environment is organism-centered since the environmental properties of a habitat are determined by the requirements of the organisms that occupy that habitat. For example, the amount of inorganic nitrogen dissolved in lake water is of little immediate significance to zooplankton in the lake because they are incapable of utilizing inorganic nitrogen directly. However, because phytoplankton are capable of utilizing inorganic nitrogen directly, it is a component of their environment. Any effect of inorganic nitrogen upon the zooplankton, then, will occur indirectly through its effect on the abundance of the phytoplankton that the zooplankton feed upon. See Phytoplankton, Zooplankton

Just as the environment affects the organism, so the organism affects its environment. Growth of phytoplankton may be nitrogen-limited if the number of individuals has become so great that there is no more nitrogen available in the environment. Zooplankton, not limited by inorganic nitrogen themselves, can promote the growth of additional phytoplankton by consuming some individuals, digesting them, and returning part of the nitrogen to the environment.

Ecology is concerned with the processes involved in the interactions between organisms and their environments, with the mechanisms responsible for those processes, and with the origin, through evolution, of those mechanisms. It is distinguished from such closely related biological subdisciplines as physiology and morphology because it is not intrinsically concerned with the operation of a physiological process or the function of a structure, but with how a process or structure interacts with the environment to influence survival, growth, development, and reproduction.

Major subdivisions of ecology by organism include plant ecology, animal ecology, and microbial ecology. Subdivisions by habitat include terrestrial ecology, the study of organisms on land; limnology, the study of fresh-water organisms and habitats; and oceanography, the study of marine organisms and habitats.

The levels of organization studied range from the individual organism to the whole complex of organisms in a large area. Autecology is the study of individuals, population ecology is the study of groups of individuals of a single species or a limited number of species, synecology is the study of communities of several populations, and ecosystem, or simply systems, ecology is the study of communities of organisms and their environments in a specific time and place. See Population ecology, Systems ecology

Higher levels of organization include biomes and the biosphere. Biomes are collections of ecosystems with similar organisms and environments and, therefore, similar ecological properties. All of Earth's coniferous forests are elements in the coniferous forest biome. Although united by similar dynamic relationships and structural properties, the biome itself is more abstract than a specific ecosystem. The biosphere is the most inclusive category possible, including all regions of Earth inhabited by living things. It extends from the lower reaches of the atmosphere to the depths of the oceans. See Biome, Biosphere

The principal methodological approaches to ecology are descriptive, experimental, and theoretical. Descriptive ecology concentrates on the variety of populations, communities, and habitats throughout Earth. Experimental ecology involves manipulating organisms or their environments to discover the underlying mechanisms governing distribution and abundance. Theoretical ecology uses mathematical equations based on assumptions about the properties of organisms and environments to make predictions about patterns of distribution and abundance. See Theoretical ecology