Many wetland complexes around the world are highly influenced by human activity (chiefly land conversion for agriculture). Measuring the impact of such activity hinges not only upon using appropriate wetland indicator taxa but also upon metrics that are sensitive enough to capture subtle effects.Over a 5-year period, we quantified the distribution and community structure of odonates (dragonflies and damselflies) occupying a wetland complex in Texas. When using traditional community metrics, there were no significant differences in diversity or evenness in the odonate assemblages in wetlands surrounded by the two dominant regional forms of land use (tilled cropland and grassland). Similarity analyses likewise failed to detect any significant differences in odonate community composition with land use.Discriminant function analysis, however, revealed that species co-occurrences could be distinguished on the basis of surrounding land use, which indicates that odonate assemblages in these wetlands are structured in a manner that typical community metrics fail to adequately describe.Differences between the approaches are discussed, particularly with regard to the use of presence-absence data.

Playas represent the only natural source of above-ground freshwater in the southern High Plains of North America; there are >20,000 such wetlands in the Panhandle of Texas (area of the highest. concentration of playas). Many organisms use these small, ephemeral ponds during some stage of then, life histories; e.g., dragonflies and damselflies (class Insecta, order Odonata, and suborders Anisoptera and Zygoptera, respectively) Of this Otherwise semi-arid region require these aquatic habitats for larval development. Relatively few distributional records have been established for Odonata ill this region, so we conducted a baseline survey to assess distributional patterns of odonates ill playas. Five seasons of observation and collection yielded important presence-absence data, resulting in 110 Country records for the 16 countries in the study area.

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.