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Another theory, the "response theory" is considered by some researchers to be a <br />. better method of indexing diversity. The "response theory" is based on the reac- <br />tion of indices along a response curve to changes in importance (i.e. abundance) <br />of one or more members of a community. These changes may be expressed then as an <br />index of dominance of heterogeneity. In this concept, there are several criteria <br />an index must satisfy to be accepted as a viable measure of diversity. Specifi- <br />cally, these are as follows (Peet, 1974): <br />1. Rare species not actually sampled should not contribute to an index <br />response. <br />2. The response curve must start at the origin. <br />3. A shift of two species towards more nearly equal importance results in a <br />condition of greater evenness (Figures 3.6-1 and 3.6-2). <br />4. Decreased evenness results when two species diverge from equal importance <br />( Figure 3.6-1). <br />5. An increase in dominance occurs with the divergence in importance of <br />equally important species (Figure 3.6-2). <br />• According to Peet (1974), in choosing an index one should determine if the index <br />is most sensitive to changes in rare (type I) or common species (type II). Type <br />I indices are exemplified by the Shannon -Weiner (Weaver) index while McIntosh's <br />index is typical of type II indices (Peet, 1974). Type II indices may be consi- <br />dered preferable to type I since type II will describe the most important species <br />in terms of dominance. <br />Bonham (1974) devised a method of measuring diversity based on relative cover and <br />calculated diversity by modifying the Type II heterogeneity index of McIntosh <br />(1967). McIntosh's index is based on the distance between two or more stands in <br />an n -dimensional hyperspace. McIntosh maintains that since distance measures the <br />ecological similarity (or dissimilarity) between two communities, it is a ration- <br />al basis for defining existing diversity relationships between communities. <br />Specifically, "... the relative distance between two communities is the square <br />root of the sun of the squared difference between the measures of each species" <br />• 3-62 <br />