As degradation of wetlands continues to occur as a result of human activities, it is important to identify aquatic and amphibious species' extinction risks and the relative hospitalities of sites to support intact biotic communities; one such technique involves comparing the nestedness of assemblages as an assay of predictability and stability. We measured the degree of nestedness of odonate communities (Odonata: dragonflies and damselflies) in the playa wetland complex of the Texas panhandle (data from 23 species in 73 playas in the summers of 2003–05) under current conditions as well as four simulations of future socioeconomic and climate change. Compared to randomized (null model) assemblages, significant nestedness was found for the system as a whole as well as for each year separately and for playas within each of the two dominant regional forms of land cover (cropland and grassland). Cropland and grassland playas were further split into three size categories, based on natural size breaks. Although departures from nestedness (idiosyncrasy) were unrelated to playa size or surrounding land use, larger playas surrounded by cropland displayed lower nestedness than did smaller ones whereas grassland playas showed the opposite pattern. This relationship between playa area and surrounding land-use type showed that there is lower stability in odonate community composition in even large playas if those playas are surrounded by agriculture. Departures from nestedness mainly consisted of unexpected species presences rather than absences, with idiosyncratic species being larger in total body length and including two range extensions. Under simulations of playa losses, community patterns were similar to contemporary data, suggesting that the ephemeral and dynamic nature of playas may already expose the odonate community to selective pressures possible under future land conversion.
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Vol. 28 • No. 4