Desert lizard diversity worldwide: Effects of environment, time, and evolutionary rate

Abstract

Aim: Biodiversity is not uniformly distributed across the Earth's surface, even among physiographically comparable biomes in different biogeographic regions. For lizards, the world's large desert regions are characterized by extreme heterogeneity in species richness, spanning some of the most species-rich (arid Australia) and species-poor (central Asia) biomes overall. Regional differences in species diversity may arise as a consequence of the interplay of several factors (e.g., evolutionary time, diversification rate, environment), but their relative importance for biogeographic patterns remains poorly known. Here we use distributional and phylogenetic data to assess the evolutionary and ecological drivers of large-scale variation in desert lizard diversity.Location: Deserts worldwide.Major taxa studied: Lizards (non-snake squamates). Methods:We specifically test whether diversity patterns are best explained by differences in the ages of arid-adapted lineages (evolutionary time hypothesis), by regional variation in speciation rate, by geographic area of the arid systems, and by spatial variation related to environment (climate, topography, and productivity). Results:We found no effect of recent speciation rate and geographic area on differences in desert lizard diversity. We demonstrate that the extreme species richness of the Australian deserts cannot be explained by greater evolutionary time, because species began accumulating more recently there than in more species-poor arid regions. We found limited support for relationships between regional lizard richness and environmental variables, but these effects were inconsistent across deserts, showing a differential role of the environment in shaping the lizard diversity in different arid regions.Main conclusions: Our results provide evidence against several classic hypotheses for interregional variation in species richness, but also highlight the complexity of processes underlying vertebrate community richness in the world's great arid systems.

A global analysis of viviparity in squamates highlights its prevalence in cold climates

“…For instance, oviparous species richness declines much more rapidly towards lower temperatures than that of viviparous taxa, suggesting stronger selection against oviparity at cold temperatures (Figure 3). Productive environments, in turn, can contain enough vacant niches, food and shelter for the dispersing viviparous lineages to thrive (Tejero‐Cicuéndez et al, 2022). Therefore, such environments are not expected to impose significant costs on the gravid female.…”

“…Productive environments, in turn, can contain enough vacant niches, food and shelter for the dispersing viviparous lineages to thrive (Tejero-Cicuéndez et al, 2022). Therefore, such environments are not expected to impose significant costs on the gravid female.…”

Lizard richness in mainland China is more strongly correlated with energy and climatic stability than with diversification rates

“…We found negative relationships between richness and diversification rates in many cases. This counterintuitive result has been previously found in several taxa, including terrestrial vertebrates (Cerezer, Machac, et al, 2022;Hutter et al, 2017;Tejero-Cicuéndez et al, 2022) and fishes (Egan et al, 2022;Hortal et al, 2013). Such a negative relationship can stem from faster speciation being selected for in extreme environments, which do not allow enough time for biodiversity to accumulate (Harvey et al, 2020).…”

Same process, different patterns: pervasive effect of evolutionary time on species richness in freshwater fishes

“…However, some of these phylogenetic metrics could be biased by involving other evolutionary processes, thus not directly describing the time that a clade has had in a region. To overcome such potential bias, more recent studies have implemented ancestral area reconstruction analyses to directly estimate the colonization time of a clade within a region instead of using a proxy [19,49]. However, ancestral reconstruction at global scales can only estimate colonization time for the broad biogeographic regions that are previously defined, requiring additional regionalizations (and thus reconstructions) for different sets of taxa, including subsets such as those in a deconstruction approach.…”