Showing papers on "Indicator species published in 1972"

Biological criteria of environmental change in the Chesapeake Bay

Abstract: ecosystems. In order to prevent or control these modifications, it is necessary to monitor the biota so that changes can be detected before they reach irreversible limits. Although knowledge of the dynamics of estuarine communities, especially those under stress, is limited, ecologists must provide managers with the best possible analysis of the direction and rate of change of biological conditions. This review will examine and evaluate analytical methods which seem most appropriate for use in the Bay, and, when necessary, will recommend research programs to develop better techniques. Biological measures of environmental change can be divided into five categories: bioassays, condition indices, population dynamics, community structure, and community metabolism. Bioassays measure the relative toxicity of a pollutant or polluted environment in terms of lethal or sublethal effects on test species. Condition indices measure the biological or physiological state of organisms living at a given location. Criteria based on population dynamics involve the relative abundance and distribution patterns of selected indicator species in nature. Biological indices of community structure concern the composition and relative abundance of species within a trophic level, phylogenetic group or entire community. Indicators of community metabolism measure the fixation and transfer of energy within ecosystems. Each of these approaches to biological monitoring necessitates assumptions and extrapolations which can be made only with considerable uncertainty. Thus it is not now possible to identify standard methods for biotic surveys. However, some of the techniques outlined below seem more appropriate than others. For the immediate future it seems desirable to rely upon several different procedures to document biological changes. The methods selected will depend upon the habitat, season, and nature of the environmental alteration.

The vegetation of remnant shale- limestone prairies in western kansas

Abstract: Floristics, vegetation indices and soils were studied on 65 remnant stands within the shale-limestone region of western Kansas. An environmental gradient, consisting of five moisture classes, was established to study species distributions and community structure. Most species exhibited con- tinuous distributional patterns in response to the moisture gradient. Mesic habitats were low in species numbers while drier sites exhibited a greater species diversity. The dominant grasses, Andropogon gerardi, Andropogon scoparius and Bouteloua gracilis were too ubiquitous in their distribution to be used in community delinea- tion; therefore, four communities based on indicator species were established within the study area. These communities were: very-dry (Lesquerella-Tetraneuris), dry-mesic (Salvia-Sporobolus), mesic (Amorplha-Euphorbia) and wet-mesic (Poa-- Rosa-Euphorbia). Grassland studies in Kansas have historically been concerned with the impact of drought and grazing upon the vegetation (Weaver and Albertson, 1956). The study of ungrazed grasslands has received less attention although such areas provide a theoretical reference point upon which grassland management decisions can be based. The term "prairie remnants" as used herein refers to areas of native prairie vegetation that have not been grazed by domestic livestock or that have been disturbed very little since the advent of European man in the region. The vegetation found on these prairie remnants should represent an adaptation to the total environment, but not necessarily be pristine in structure. The project was initiated to collect quantitative data from remnant grasslands and to provide information for further research on grass- land communities in the Mixed Prairie. Remnant grasslands are usually the result of man's inability to use them in the past due to the lack of water for grazing animals, poor location for farming or pecu- liarities of road construction. However, in recent years, land owners have found numerous ways to utilize these areas and these grasslands are rapidly disappearing.