Time and environment explain the current richness distribution of non‐marine turtles worldwide

Abstract

Ecological, historical, and evolutionary hypotheses are important to explain geographical diversity gradients in many clades, but few studies have combined them into a single analysis allowing a comparison of their relative importance. This study aimed to evaluate the relative importance of ecological, historical, and evolutionary hypotheses in explaining the current global distribution of non-marine turtles, a group whose distribution patterns are still poorly explored. We used data from distribution range maps of 336 species of non-marine turtles, environmental layers, and phylogeny to obtain richness estimates of these animals in 2°  2° cells and predictors related to ecological, evolutionary and historical hypotheses driving richness patterns. Then we used a path analysis to evaluate direct and indirect effects of the predictors on turtle richness. Ancestral area reconstruction was also performed in order to evaluate the influence of time-for-speciation in the current diversity of the group. We found that environmental variables had the highest direct effects on non-marine turtle richness, whereas diversification rates and area available in the last 55 million yr minimally influenced turtle distributions. We found evidence for the time-for-speciation effect, since regions colonized early were generally richer than recently colonized regions. In addition, regions with a high number of colonization events had a higher number of turtle species. Our results suggested that ecological processes may influence non-marine turtle richness independent of diversification rates, but they are probably related to dispersal abilities. However, colonization time was also an important component that must be taken into account. Finally, our study provided additional support for the importance of ecological (climate and productivity) and historical (time-for-speciation and dispersal) processes in shaping current biodiversity patterns.

Climatic niche evolution in turtles is characterized by phylogenetic conservatism for both aquatic and terrestrial species

“…Terrestrial turtles were mainly characterized by mesic niches (scores close to zero). Such mesic niches (and a lower richness when compared to aquatic turtles) help to explain why richness and biogeographic patterns of turtles as a whole are also strongly related to precipitation and thus similar to the patterns of aquatic species alone (Ennen, Agha, Matamoros, Hazzard, & Lovich, ; Ennen et al., ; Iverson, ; Rodrigues et al., ). Finally, previous studies have found that the ancestor of recent turtles was most likely aquatic (Jaffe et al., ; Joyce & Gauthier, ; Rodrigues & Diniz‐Filho, ).…”

“…We note that using temperature data from terrestrial conditions to describe species' aquatic niches may seem controversial, but recent studies have shown that water temperatures are highly correlated with terrestrial ones at the scale of species geographic distributions (Frederico, De Marco, & Zuanon, ; Livingstone & Lotter, ). In fact, several recent studies evaluating climatic niche and distribution patterns of aquatic organisms, such as fishes (Culumber & Tobler, ; Edeline, Lacroix, Delire, Poulet, & Legendre, ; Emmrich et al., ) and turtles (Fagundes, Vogt, & De Marco Júnior, ; Ihlow et al., ; Rödder et al., ; Rodrigues, Olalla‐Tárraga, Iverson, Akre, & Diniz‐Filho, ; Waterson et al., ), have been performed using data on terrestrial conditions. Furthermore, it is important to highlight that even aquatic turtles also depend on terrestrial environments for activities such as basking and nesting, which are in turn environmentally influenced, reinforcing the relevance of terrestrial environmental conditions on their niches.…”

Dispersal is more important than climate in structuring turtle communities across different biogeographical realms

“…We did not use a larger threshold because turtle richness is generally low, and higher thresholds would dramatically reduce our sample number (see Rodrigues et al . () and table S1.3 for general information regarding turtle richness in global and biogeographical scale).…”

Phylogenetic and spatial analyses suggest minimum temperature as an environmental filter for turtle communities

“…Cells encompassing communities phylogenetically clustered (SES values lower than −1.96) were mainly found in areas of high turtle species richness (Buhlmann et al., ; Rodrigues et al., ). This similarity is stronger for SESMNTD values, which describe the relationships for the most recently divergent species (i.e.…”