Environmental factors explain the spatial mismatches between species richness and phylogenetic diversity of terrestrial mammals

Abstract

Aim Explore the spatial variation of the relationships between species richness (SR), phylogenetic diversity (PD) and environmental factors to infer the possible mechanisms underlying patterns of diversity in different regions of the globe. Location Global. Time period Present day. Major taxa studied Terrestrial mammals. Methods We used a hexagonal grid to map SR and PD of mammals and four environmental factors (temperature, productivity, elevation and climate‐change velocity since the Last Glacial Maximum). We related those variables through direct and indirect pathways using a novel combination of path analysis and geographically weighted regression to account for spatial non‐stationarity of path coefficients. Results Species richness, PD and environmental factors relate differently across the geographical space, with most relationships varying in both magnitude and direction. Species richness is associated with lower PD in much of the tropics and in the Americas, which reflects the tropical origin and the recent diversification of some mammalian clades in these regions. Environmental effects on PD are predominantly mediated by their effects on SR. But once richness is controlled for, the relationships between environmental factors and PD (i.e. PDSR) highlight environmentally driven changes in species composition. Environmental–PDSR relationships suggest that the relative importance of different mechanisms driving biodiversity shifts spatially. Across most of the globe, temperature and productivity are the strongest predictors of richness, whereas PDSR is best predicted by temperature. Main conclusions Richness explains most spatial variation in PD, but both dimensions of biodiversity respond differently to environmental conditions across the globe, as indicated by the spatial mismatches in the relationships between environmental factors and these two types of diversity. We show that accounting for spatial non‐stationarity and environmental effects on PD while controlling for richness uncovers a more complex scenario of drivers of biodiversity than previously observed.

Spatial variation in direct and indirect effects of climate and productivity on species richness of terrestrial tetrapods

“…The direct effects of temperature, precipitation and productivity on species richness were mainly positive, in agreement with the metabolic theory and the physiological tolerance, the more individuals and the niche diversity hypotheses (Currie et al, 2004;Evans, Warren, et al, 2005). Nevertheless, by allowing relationships to vary geographically, without splitting data arbitrarily into geographical subregions, our analysis revealed spatially structured exceptions to the well-known positive relationships, consistent with a previous finding for tetrapods in Australia (Powney et al, 2010) and for mammals globally (Barreto et al, 2019;Davies et al, 2011). A negative productivity-richness relationship was found only for reptiles around the Tropic of Cancer, offering insights into the lower richness of this group relative to other tetrapods in this region (Roll et al, 2017).…”

Extreme environments filter functionally rich communities of Atlantic Forest treefrogs along altitudinal and latitudinal gradients

“…We illustrate how studies of the processes driving community assembly in the Atlantic Forest can benefit from the inclusion of all three dimensions of biodiversity and a broader characterization of environmental constraints that go beyond elevational gradients. Similar to other studies (Stevens and Tello 2014, Barreto et al 2019), we point to the complementarity of the different measures of biodiversity dimensions, and how the regions where they are not fully redundant help us understand the drivers of biological patterns. In the Atlantic Forest, we find that phylogenetic diversity is not always a good proxy for functional diversity; using the former to represent the latter can obscure the interplay of multiple ecological processes in community assembly, in agreement with previous experimental work in other ecosystems (Germain et al 2018).…”

Elevation patterns and critical environmental drivers of the taxonomic, functional, and phylogenetic diversity of small mammals in a karst mountain area

“…A negative relationship between higher temperature and PD has been detected in some tropical areas. The mechanism underlying this phenomenon suggests that temperature has a primary effect on the acceleration of mutation and metabolic rates, and thus, the rate of speciation can be more rapid (Barreto, Graham, Rangel, & Belmaker, 2019). Our results showed a negative relationship in the Wuling Mountains, supporting the notion that the acceleration of speciation rates is the predominant factor for small mammals in this karst area.…”