Reduction in odonate phylogenetic diversity associated with dam impoundment is revealed using taxonomic distinctness

Abstract

Taxonomic distinctness is a highly useful index combining species richness and taxonomic (phylogenetic) diversity to detect changes in the taxonomic structure of communities and assemblages. While analysis of an odonate assemblage before and after construction of a hydroelectric impoundment in the state of Hidalgo, Mexico, revealed no significant increase in average monthly species richness (although annual counts were slightly higher for the latter survey), taxonomic distinctness and its variation were reduced. The impoundment converted natural lotic conditions into lentic habitat with more littoral vegetation. Such conditions favored plant-dependent species (mostly in the Zygoptera) with more species per genus and genera per family relative to those not dependent (mostly in the Anisoptera). High ratios reduce the average risk of losing higher taxonomic structure with loss of a species. Reduced taxonomic distinctness and its variation occurred at the expense of the Gomphidae and Corduliidae, and several genera in the Libellulidae having non-plant dependent species that favor inorganic substrate in flowing waters. The results contrast with the common assumption that higher odonate diversity occurs in lentic habitats. Seasonal patterns of taxonomic distinctness appeared similar between surveys and may reflect reproductive and emergence cycles. The results support the use of taxonomic distinctness and its variation over species richness in ecological assessments and its application in further freshwater research. We encourage its use with aquatic insects, but recommend frequent sampling intervals to account for effects from emergence and reproductive behaviors. These results suggest new and added breadth to the value of taxonomic distinctness in ecological research regarding habitat change.