Global change explains the neotropical rattlesnake Crotalus durissus (Serpentes: Viperidae) range expansion in South America

Abstract

The neotropical rattlesnake Crotalus durissus occurs in South America, where it is generally associated to open areas in the dry diagonal of the continent, composed of xeric and savanna biomes. Since the 1950’s, however, the species started to be recorded in rainforest biomes. Land-use change, especially the conversion of forests to pasture, remains a widely believed but still untested hypothesis to explain this range expansion. An equally untested alternative hypothesis is ongoing climate change as a driver of this observed expansion. Here we modeled the current distribution of C. durissus using occurrence records prior to 1950 for model calibration. Model predictions were then evaluated using occurrence records post-1950. The sets of models considered (i) only bioclimatic predictors, (ii) only land-use land-cover predictors, and (iii) a combination of both. Our results indicated that since 1950’s the geographic range of C. durissus is expanding primarily due increase in pasture areas, and, secondarily due to ongoing changes in climate (changes in isothermality and precipitation). This range expansion encompasses the Argentinian Chaco and the arc of deforestation in the Amazon, which were unsuitable before the 1950’s. The ongoing range expansion of the neotropical rattlesnake can become a public health issue, given that it is a venomous snake of medical importance. The expansion of the neotropical rattlesnake range can be controlled through public policies aimed at restraining deforestation (especially in the Amazon and the Gran Chaco) and encouraging reforestation (especially in the Brazilian Atlantic Forest).