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Science 17 February 2006:
Vol. 311. no. 5763, p. 913
DOI: 10.1126/science.311.5763.913n
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This Week in Science

Power laws apply to many patterns in ecological systems, yet mechanistic understanding of the factors behind power law distributions in populations have proved largely elusive. Vandermeer and Perfecto (p. 1000) studied the biology and the spatial population dynamics of a green scale insect on 40 hectares of shade-grown coffee in Mexico. The scales have several natural enemies (parasitoid wasps and predatory leaf-beetles), but some groups are guarded from these enemies by honeydew-seeking Azteca ants. The frequency distribution of scale cluster sizes among coffee plants generally follows the power-function distribution expected for exponentially growing populations founded at random previous times. The basic power function is a result of exponential population growth operating at the individual bush level; deviations from the power function are the result of incomplete migration patterns of the scale and protection from its ant mutualist.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)