The origins and maintenance of global species endemism

Abstract

Aim We test macroecological hypotheses (H1: long‐term climate stability; H2: climate seasonality; H3: climate distinctiveness or rarity; and, H4: spatial heterogeneity in contemporary climate, topography or habitat) proposed to explain broad‐scale patterns of total species endemism. Location Continental areas worldwide and zoogeographical realms. Methods Using species distribution maps for mammals and amphibians, we calculated five metrics of species endemism, based on inverse and median range size, and range size cut‐offs. We performed multi‐model averaging. We tested the accuracy of fitted models using cross‐validation, comparing observed versus predicted values of endemism among zoogeographical realms. Results Model averaging showed that species endemism for amphibians and mammals was statistically related to all set of predictors (H1, H2, H4 and richness), except for climate distinctiveness (H3). Effect sizes for spatial heterogeneity were larger and more consistent among zoogeographical realms than the effect sizes of climate stability. The effect of species richness on species endemism varies widely and depends on the metric of endemism and taxonomic group used in the analysis. Cross‐validation across all zoogeographical realms showed that predictions of endemism systematically fail for both taxa. In most cases, low to moderate endemism is predicted reasonably well. However, areas with high numbers of endemic species are systematically under‐predicted. Main conclusions Our results are not consistent with any of the processes hypothesized to create and maintain global patterns of endemism. Although we found statistically significant relationships, they failed the stronger test of a causal relationship: accurate prediction in independent data. The inconsistent effect of richness in our models suggests that patterns of endemism are not driven by the same variables as total richness. Patterns of endemism have no consistent relationships with climatic stability among zoogeographical realms, so suggestions that endemism reflect climatic stability are likely due to collinearity with other factors, especially spatial heterogeneity.

Museums and cradles of diversity are geographically coincident for narrowly distributed Neotropical snakes

“…High spatial heterogeneity on small scales may also account for the presence of distinct conditions needed for the accumulation of both paleo-and neo-endemics (Zuloaga et al 2019). In this way, topographic roughness, a well-recognized correlate of low extinction rates for reptiles and a proxy for habitat heterogeneity (Araújo et al 2008), was the most important predictor of PE in our study.…”

“…selection of lineages with narrower niches in less seasonal environments, Slatyer et al 2013). As niche breadth and dispersal abilities are sometimes phylogenetically conserved (Wiens and Graham 2005), it is possible that even if the environmental conditions are similar, grid cells with phylogenetically distinct communities may display distinct patterns of endemism (Zuloaga et al 2019). In line with this, the high spatial autocorrelation in the residuals of the GLM models indicates that PE is also linked to more local factors, which could be related to the local history of diversification (Rosauer and Jetz 2015).…”

A short distance to the last glacial coast best explains a Tasmanian centre of endemism

“…To investigate spatial patterns in endemism, species are often weighted by the inverse of their range (1 / number of grid cells occupied by an organism; Crisp et al 2001, Kessler 2002, Christman et al 2005, Zuloaga et al 2019. When summed for all species in a cell of a defined area, the resulting metric is called weighted endemism (Crisp et al 2001).…”

“…When summed for all species in a cell of a defined area, the resulting metric is called weighted endemism (Crisp et al 2001). However, weighted endemism is strongly predicted by species richness (Crisp et al 2001, Zuloaga et al 2019. Thus, weighted endemism is often corrected for species richness within any given area to give corrected weighted endemism (Crisp et al 2001).…”

“…Hotspots of local endemic plant species have been shown to be concentrated in coastal areas and islands where temperatures are moderated by the sea (Crisp et al 2001, Linder 2001, Mittermeier et al 2005, Kier et al 2009. The importance of the capacity of refugia (Keppel et al 2015) to facilitate species persistence in an area to buffer climate shifts during the Pleistocene (2.58 -0.012 MYA) climatic oscillations is regarded as critical in understanding patterns of local endemism (Jansson 2003, Sandel et al 2011, Castellanos-Morales et al 2016, Harrison and Noss 2017, although support for the climatic stability hypothesis is not universal (e.g., Zuloaga et al 2019). Distinctive edaphic conditions have also been associated with concentrations of local endemic plants (e.g., Kirkpatrick and Brown 1984, Gibson et al 1992, Morat 1993, Bredenkamp et al 2001, Stevanović et al 2003, Molina-Venegas et al 2013Anacker & Strauss 2014, Molina-Venegas et al 2015.…”