**The Western Amazonian Richness Gradient for Squamate Reptiles: Are There Really Fewer Snakes and Lizards in Southwestern Amazonian Lowlands?**

#### **Daniel L. Rabosky 1,\*, Rudolf von May 1,2, Michael C. Grundler 1 and Alison R. Davis Rabosky 1**


Received: 15 September 2019; Accepted: 14 October 2019; Published: 18 October 2019

**Abstract:** The lowland rainforests of the Amazon basin harbor some of the most species-rich reptile communities on Earth. However, there is considerable heterogeneity among climatically-similar sites across the Amazon basin, and faunal surveys for southwestern Amazonia in particular have revealed lower species diversity relative to sites in the northwestern and central Amazon. Here, we report a herpetofaunal inventory for Los Amigos Biological Station (LABS), a lowland site located in the Madre de Dios watershed of southern Peru. By combining active search and passive trapping methods with prior records for the site, we provide a comprehensive species list for squamate reptiles from LABS. We also estimate an "expected" list for LABS by tabulating additional taxa known from the regional species pool that we consider to have a high probability of detection with further sampling. The LABS total of 60 snake and 26 lizard taxa is perhaps the highest for any single site in the southern Amazon. Our estimate of the regional species pool for LABS suggests that the southwestern Amazonian lowlands harbor at least 25% fewer species of snakes relative to the western equatorial Amazon, a diversity reduction that is consistent with patterns observed in several other taxonomic groups. We discuss potential causes of this western Amazonian richness gradient and comment on the relationship between spatial diversity patterns in squamates and other taxa in the Amazon basin.

**Keywords:** species richness; diversity gradient; community structure; reptiles; neotropics; Amazon; rainforest; lizard; snake
