Date of Award:

5-1-1988

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Biology Ecology

Committee Chair(s)

James A. MacMahon

Committee

James A. MacMahon

Committee

Ivan Palmblad

Committee

Vincent Tepidino

Abstract

The practice of describing and mapping communities as community types assumes that all the organisms of a community have similar distributions. This assumption is counter to the hypothesis that organisms are distributed by their individualistic environmental tolerances and requirement (Gleason, 1926, 1939). Three major North American systems used to describe community-types are the biome (Clements and Shelford, 1939), the biotic area (Dice, 1943) and the life zone (sensu Holdridge, 1949). While these systems differ in the bases for community classification, they all use the distributions of 'key' species to predict the distributions of the remaining species in a community. How well do maps of community types compare with maps of abiotic factors when both are compared to the distribution of a taxonomic assemblage that was not considered in the creation of any of the community classification systems? Grasshoppers (Order: Orthoptera, Family: Acrididae) of Utah were chosen as the taxonomic assemblage to test this question. Nineteen maps representing community-type and abiotic factor maps were tested for correlation with the grasshoppers. The primary method of analysis was Reciprocal Averaging, an indirect gradient analysis technique. The results of this analysis were validated using two secondary methods, cluster analysis, a hierarchical classification technique and Principal Coordinate Analysis, a type of factor analysis. Additionally, for each Principal Coordinate axis the factor loadings for every site was plotted on a map of Utah. Isolines were drawn to connect areas of equal factor loading. Those areas with factor loadings of 0.40 or greater were considered grasshopper biotic areas. The grasshopper distributions were more correlated with the distributions of abiotic factors than with the community-type maps. The Holdridge's Life Zones map had a higher degree of correlation than any of the other community-type maps, but it did not correlate as well as the abiotic factors. Possible biological influences of the abiotic factors on the grasshoppers that would cause the correlations of distribution were also discussed. Grasshopper species appear to be distributed independently of each other rather than in distinct assemblages. This may account for the poor correlations with the community-type maps. The characteristics of maps that the grasshoppers were most highly correlated with had map classes that were repeatable, non-hierarchical and reflected environmental gradients.

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