The diversity of Linnaean communities: a way of detecting invertebrate groups at risk of extinction

Summary

As ecologists use changes in the relative abundances of species to detect environmental stress in ecological communities, it is possible to do the same for higher taxa (‘Linnaean communities’) by examining the distribution of species between genera. Using an adaptation of Simpson’s diversity index (D), we predict that, like ecological communities, mature Linnaean communities have D values >0.8 and developing and relictual communities have D values <0.8. We show that D values for seven Australian weevil taxa, three indicated to be mature (Amycterini, Aterpini, Leptopiina), two relictual (Nemonychidae, Belinae) and two actively radiating groups (Gonipterini, Cyphicerina), are as predicted. Apparently subdivision of niche space has the same statistical effects in stressed Linnaean communities as it does in ecological communities, with firstly the loss of species in genera with intermediate numbers of species followed by the loss of monotypic genera. Clearly therefore, the protection of monotypic genera in Linnaean communities with low D values should be the highest conservation priority as these are at the highest risk of extinction, while monotypic genera in high-D communities are not at such high risk. Similarly, the geographical distribution of monotypic genera in Linnaean communities with low D values, rather than that of rare species (most of which will be in genera with many species), may constitute a useful way of identifying areas of conservation concern.