Relative importance of dynamic and static environmental variables as predictors of amphibian diversity patterns

Abstract

In this study, we evaluated whether static approaches, such as including only habitat characteristics that do not change over time, are adequate for the assessment of diversity–habitat relationships. We assessed the contribution of habitat characteristics that change over time to the spatial pattern of diversity (variation in species richness and in assemblage composition) in comparison to those characteristics that do not change. We have also provided an integral analysis to evaluate the role of the hydroperiod in structuring amphibian assemblages at any diversity level, including variation in species richness, variation in assemblage composition (i.e., nested pattern or species turnover) and variation in beta diversity. We monitored 19 amphibian assemblages from 2003 to 2006 in a highly fluctuating ecosystem, the temporary ponds in Doñana National Park. Both sets of habitat variables (temporally fixed and temporally variable) were necessary to develop a realistic understanding of amphibian diversity patterns, both when considering data collected in particular years or over several years. We found that environmental attributes that are irrelevant for pond species richness (alpha diversity) might be responsible for the variation in assemblage composition among ponds (beta diversity) and, hence, contribute to species diversity in the entire study area (gamma diversity). Therefore, we illustrate the need for an integral analysis of diversity in order not to disregard any relevant habitat factor. Alternatively, the relevance of the hydroperiod was not constant across time and was negligible in the wet year, while, in the dry year, we observed a strong nested pattern along the hydroperiod gradient and small differences in species predominance among assemblages. Therefore, our results show two conservation priorities in the study area: the preservation of ponds along the wide hydroperiod gradient; and a particular concern for the preservation of ponds with a long duration because they will provide a breeding habitat for most species in unfavourable years.