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FIGURE 1 Relationship between insect size (body volume) and (A) species richness and (B) number of individuals for five insect orders. [Redrawn from Fig. 2 in Siemann, E., Tilman, D., and Haarstad, J. (1996). Insect species diversity, abundance, and body size relationships. Nature 380, 704-706, with permission from Nature.]

Biovolume (mm3)

0.1 1 10 100 1000 Biovolume (mm3)

FIGURE 1 Relationship between insect size (body volume) and (A) species richness and (B) number of individuals for five insect orders. [Redrawn from Fig. 2 in Siemann, E., Tilman, D., and Haarstad, J. (1996). Insect species diversity, abundance, and body size relationships. Nature 380, 704-706, with permission from Nature.]

Insect assemblages are thought to be structured by competition, with most of the insects found in medium-sized classes. Thus, the size of a particular insect is governed by its living habits and its feeding guild, in which competition with similar insects has forced some to evolve a larger or smaller body size. Empirical data show that species diversity in any taxonomic group of insects peaks at some intermediate body size (Fig. 1). For some authors, this implies that there may be fewer undescribed small insect species than previously suggested, which in turn, suggests that global biodiversity probably is lower than the highest estimates (30-50 million species). However, it is not clear whether such a pattern results from biological processes or from statistical or sampling properties. The size distribution of cars parked at Heathrow Airport also shows a peak in diversity at an intermediate size. Nevertheless, more knowledge about the causes behind size distribution patterns among insects and other organisms may provide key information in the effort to preserve biodiversity.

See Also the Following Articles

Biogeographical Patterns • Growth, Individual • Tracheal System

Further Reading

Conner, J., and Via, S. (1992). Natural selection on body size in Tribolium:

Possible genetic constraints on adaptive evolution. Heredity 69, 73-83. Dudley, R. (1998). Atmospheric oxygen, giant Paleozoic insects and the evolution of aerial locomotor performance. J. Exp. Biol. 201, 1043-1050. Gaston, K. J., Blackburn, T. M., and Lawton, J. H. (1993). Comparing animals and automobiles: A vehicle for understanding body size and abundance relationships in species assemblages. Oikos 66, 172-179. Mousseau, T. A. (1997). Ectotherms follow the converse to Bergmann's rule.

Evolution 51, 630-632. Price, P. W. (1984). "Insect Ecology." Wiley-Interscience, New York. Siemann, E., Tilman, D., and Haarstad, J. (1996). Insect species diversity, abundance and body size relationships. Nature 380, 704-706. van Voorhies, W. A. (1997). On the adaptive nature of Bergmann size clines: A reply to Mousseau, Partridge and Coyne. Evolution 51, 635-640.

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