Diversity loss and homogenization in snake communities in a deforestation hotspot

Abstract

Aim: Agricultural expansion into tropical forests causes massive biodiversity loss. However, existing knowledge about these losses is heavily biased towards rainforests, as well as towards birds and mammals. Focusing on the South American Chaco, a global hotspot of deforestation and defaunation, we assessed how agriculture-driven deforestation impacted snake distribution and, thereby, snake communities. Location: Chaco ecoregion. Methods: We compiled a rich snake occurrence dataset and used it together with satellite-based, annual land-cover maps for 1985–2020 to build time-calibrated species distribution models. This yielded temporally and spatially detailed reconstructions of snake distributions, allowing us to identify winners (increase in suitable habitat) and losers (habitat decline) of land-use change. Further, we assessed changes in geographic patterns of taxonomic, functional, and phylogenetic diversity. Results: We could model 72 of 142 snake species occurring in the Chaco. Among these, surprisingly, we identified more winners (35) than losers (14). We caution, however, that we were unable to model many specialist species as these were data-deficient. Among functional guilds, semiarboreal and semifossorial species were among the most negatively affected, while most of the winning species were terrestrial, generalist species. Importantly, although some species gained habitat, our analyses revealed a general decline in taxonomic, functional, and phylogenetic snake diversity in the Chaco (more than 75% of all snake communities), suggesting biotic homogenisation. Main Conclusion: Our study uncovers an erosion of snake diversity due to agricultural expansion in the Chaco, with many snakes likely being more threatened than currently appreciated. At the community level, land-use changes and habitat loss are driving biotic homogenisation across snake communities, with potentially major knock-on effects on ecosystem functioning and integrity as key functional snakes are lost. Overall, our study underscores the urgency for conservation planning and action in the world's tropical dry forests, many of which are changing rapidly.