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Comparison of Species Richness for Stream-Inhabiting Insects in Tropical and Mid-Latitude Streams

Jean Stout and John Vandermeer
The American Naturalist
Vol. 109, No. 967 (May - Jun., 1975), pp. 263-280
Stable URL: http://www.jstor.org/stable/2459693
Page Count: 18
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Abstract

A quantitative comparison based on statistically smooth species-sample curves between tropical and mid-latitude species richness for rheophile insects from seven mid-latitude and nine tropical stream samples is presented. Actual data in the form of accumulated numbers of species compared with numbers of rocks taken from riffle sites are applied to a mathematical model in order to estimate numbers of species that should be present in a given area. Species-sample curves show that species richness of rheophile insects is significantly higher at a theoretical sample size of 100 rocks for tropical streams than it is for mid-latitude streams. This trend is not obvious until 20 or 25 rocks have been sampled. The results suggest to us that earlier studies indicating no differences in species richness between the two latitudinal regimes were based on inadequate sampling. Altitudinal trends exist between lowland and mid-elevation tropical sites. Seasonal differences were also observed for a tropical stream sampled at two locations, both in the wet and the dry season. It appears from manipulation of the parameters of the theoretical model, based on the data, that in general mid-latitude streams contain more regionally controlled rheophile species and that those species have the effect of being able to rapidly exploit the resources to the temporary exclusion of some locally controlled species.

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