CHANGEs iN THE COMMuNiTy COMpOsiTiON OF RiVERiNE sNAkEs (sQuAMATA: sERpENTEs) OVER FiVE DECADEs

Biodiversity has been rapidly declining worldwide for over 175 y, and there do not appear to be any particular ecosystems or taxonomic clades that are exempt from this trend. Habitat alteration is an ongoing threat to the quality of the upper-middle Brazos River in Texas, USA, and changes associated with impoundments have been especially persistent over the past century. We examined data from four discrete surveys that spanned a 53-y period to determine changes in the snake community along the upper-middle Brazos River. Community structure changed since 1968, with the numbers of species and individuals per species both fluctuating over time. Values for & alpha;-diversity (number of species) over time indicate that, after declining, species richness has recently increased. & beta;-diversity (community composition over a region) estimates, however, indicate that species turnover (80%), rather than nestedness (20%) within a richer community, was primarily responsible for changes in community diversity. High values of turnover indicate that species experiencing a bottleneck are unlikely to recover via dispersal events from adjacent communities. Temporal & beta;-diversity indices reveal that the species still present in the surveyed section of the watershed have increased in abundance, indicative of potential homogenization of the community. Based on the estimated values for & alpha;- and & beta;-diversity, we suggest that the landscape of the upper-middle Brazos River needs management to sustain the richness of the snake community. Because diversity in this community is influenced primarily by species turnover, preservation of remaining riverine habitat and multiple protected sites along the river are needed to prevent the likely loss of additional species.