Some Comparative Perspectives on the Ecology and Habitats of Sarcodina
The attached sarcodines, living on terrestrial or aquatic surfaces, are especially favorable subjects for the study of ecological niches. The organisms are sufficiently restricted in their movement, and the environmental surfaces are adequately stable to
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Some Comparative Perspectives on the Ecology and Habitats of Sarcodina
General Ecological Concepts The attached sarcodines, living on terrestrial or aquatic surfaces, are especially favorable subjects for the study of ecological niches. The organisms are sufficiently restricted in their movement, and the environmental surfaces are adequately stable to permit periodic observations of the same group of organisms and their response to changes in the environment. Planktonic organisms, carried by currents, are less easily periodically examined due to their constantly changing location. Moreover, the possibility of mixing with other groups of planktonic organisms due to changes in current and turbulence effects must be taken into account when analyzing niches. The concept of niche is widely used by ecologists, but not always with the same meaning. We will use niche to mean the biological response and accommodation of an organism to the range of environmental and biotic factors that determine its distribution within an ecosystem. In broader perspective, the niche of an organism includes its biological activity (eg, diversity of prey, efficiency of food assimilation, tolerance to variations in temperature, salinity, pH, and Eh ) in response to environmental constraints and potentials that determine the geographical range and success of an organism in space and time. In practical terms, one can seldom assess all potential parameters that define a species' niche. Typically, several key factors are identified (as for example, temperature, pH, salinity, oxygen abundance, and available carbon for nourishment) and their range for a species is determined. This composite set of ranges is used to operationally define the niche of the species. Clearly, species that are capable of adapting to and utilizing a wide range of environmental resources are likely to have broader niches than those that require a very specialized environment. The historical development and some current thought on niche theory are described more fully by Vandermeer (1972), Lee (1974, 1980a,b), and Austin (1985). Vandermeer divides the concept of niche into three subcategories: (1) fundamental niche; ie, the potential range of habitats that an organism can exploit when no other competing organisms are present including those of the same species; (2) partial niche; ie, the part of the fundamental niche that can be occupied when a species is competing for resources; and (3) realized niche; ie, the niche range occupied when a species is in equilibrium with other O. R. Anderson, Comparative Protozoology © Springer Science+Business Media New York 1988
General Ecological Concepts
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organisms occupying the habitat. A partial niche is determined in part by constraints arising either by intraspecific competition or interspecific competition. Thus, when a niche is first occupied by a species, there is likely to be little interspecific competition, but as the individuals multiply, one of the first likely effects is a restriction on the exploitation ofthe habitat due
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