Regional Climate Drives Spatial Variation in Species Richness in the Most Diverse Family of Neotropical Snakes (Colubroidea: Dipsadidae)

TL;DR

The study finds that current climate factors, not evolutionary history, mainly explain the geographic patterns of snake species richness in Dipsadidae.

Contribution

The work provides new evidence that current climate seasonality and productivity directly drive species richness in Dipsadidae snakes.

Findings

Current climatic seasonality and productivity are the main drivers of species richness in Dipsadidae.

Macroevolutionary processes like speciation rates and evolutionary time have a limited role in explaining richness patterns.

High dispersal levels may obscure the influence of diversification and time on regional diversity.

Abstract

Species richness gradients are frequently associated with spatial variation of environmental conditions. However, understanding how the regional environment influences species assemblages is an ongoing topic of discussion, with three non‐exclusive explanations being proposed. Under these hypotheses, climate can determine the richness of regions in two main ways: (1) directly, by determining their carrying capacity, or (2) indirectly, through its effects on either (a) lineage diversification (i.e., the rates of speciation and/or extinction), or (b) the duration over which regions have been accumulating species. Recently, some studies have started to simultaneously evaluate and compare the role of these mechanisms in determining richness gradients. For this work, we set out to identify the factors that determine the spatial variation in richness of the hyperdiverse snake family Dipsadidae. To achieve this goal, we first calculated the number of species of the group in 100 × 100 km cells throughout its distribution. Then, using piecewise structural equations, we evaluated and compared the ability to predict the richness of these cells by several environmental (current climatic seasonality and past climatic stability) and evolutionary variables (speciation rates and time for speciation). We found that the richness gradient of Dipsadidae is directly explained by current seasonality and productivity, with a limited role of macroevolutionary processes. Therefore, our results support the idea that current climate has a primary role in determining the geographic patterns of the richness of the group, with the influence of diversification and time on regional diversity potentially obscured by the elevated levels of dispersal within the group. Such a possibility needs to be evaluated in future studies that explicitly assess the impact of dispersal on regional richness, both for the Dipsadidae and other groups where similar results have been reported.

Our study investigated the relative importance of the macroecological and macroevolutionary factors driving the patterns of species richness of the hyperdiverse snake family Dipsadidae across the Americas. By utilizing piecewise structural equations, we discovered that current climatic seasonality and productivity are the main drivers of species richness, with macroevolutionary mechanisms such as regional speciation and evolutionary time playing a limited role. However, the influence of diversification and time on regional diversity may be obscured by the high dispersal levels within the group — a possibility that needs to be explored in future studies, although our ability to do so is constrained by the limitations of current methodological approaches.

Figures