IUCN / SSC Cat Specialist Group - Digital Cat Library |
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| Blackburn, T.M.; Gaston, K.J. | |
| Density, survey area, and the perfection (or otherwise) of ecologists | |
| 1999 Oikos (85): 1-6 | |
Species are not all equally abundant. Attempts to understand why have frequently involved comparative studies of a range of species. with the aim of identifying associated variation in other traits. While a number of characteristics have been linked with rare-common differences among species. the most frequently cited association is with body size. Specifically, a negative interspecific relationship has been observed between body size and population density (both logarithmically transformed) in a number of animal assemblages. Several explanations for this pattern exist, although most studies consider only that based on the amount of energy available to species of different body sizes. Unfortunately, the interpretation of comparisons between population densities is complicated by a negative relationship between densities and the size of the study areas over which they have been calculated. Population studies carried out over small areas tend to generate high density estimates. while estimates from large areas tend to be low. This density-area relationship implies that interspecific density- body size relationships may be confounded by differences in survey area among studies from which density estimates are compiled. Two lines of evidence support this argument. First, when density estimates derive from different studies. the survey area of the study is a better predictor of the density of a species than is its body size. Second, density and body size seldom show a simple negative relationship when the densities of all species are estimated from a single survey area. The density-area relationship is a problem for comparative studies because it is unclear to what extent density differences among species are genuine and derive from biological differences. or are artefacts of differences in survey effort and methodology at different spatial scales. |
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