Linking speciation to extinction: Diversification raises contemporary extinction risk in amphibians.

Dan A Greenberg,Arne Ø Mooers

doi:10.1002/evl3.4

Abstract

Many of the traits associated with elevated rates of speciation, including niche specialization and having small and isolated populations, are similarly linked with an elevated risk of extinction. This suggests that rapidly speciating lineages may also be more extinction prone. Empirical tests of a speciation‐extinction correlation are rare because assessing paleontological extinction rates is difficult. However, the modern biodiversity crisis allows us to observe patterns of extinction in real time, and if this hypothesis is true then we would expect young clades that have recently diversified to have high contemporary extinction risk. Here, we examine evolutionary patterns of modern extinction risk across over 300 genera within one of the most threatened vertebrate classes, the Amphibia. Consistent with predictions, rapidly diversifying amphibian clades also had a greater share of threatened species. Curiously, this pattern is not reflected in other tetrapod classes and may reflect a greater propensity to speciate through peripheral isolation in amphibians, which is partly supported by a negative correlation between diversification rate and mean geographic range size. This clustered threat in rapidly diversifying amphibian genera means that protecting a small number of species can achieve large gains in preserving amphibian phylogenetic diversity. Nonindependence between speciation and extinction rates has many consequences for patterns of biodiversity and how we may choose to conserve it.

Highlights

The evolutionary rates of speciation and extinction, their difference being diversification rate, shape current patterns of diversity across the tree of life
We delineated genera based on the taxonomy from the Amphibian Species of the World database v6.0 (Frost 2016) and included all monophyletic clades that (i) had at least one species assessed for threat status by the International Union for the Conservation of Nature (IUCN) Red List (IUCN 2016), (ii) that had both crown and stem group ages, and (iii) that had more than two representatives on the phylogeny for non-mono/ditypic genera
Extinction risk was distributed unevenly across the amphibian genera, with rapidly diversifying clades having a greater share of threatened species (Fig. 1); this holds true for diversification rates estimated from both stem ages

Summary

Introduction

The evolutionary rates of speciation and extinction, their difference being diversification rate, shape current patterns of diversity across the tree of life. Some biological characteristics that may increase speciation rates include poor dispersal capability (Claramunt et al 2012), specialization and narrow niche breadths (Rolland and Salamin 2016), large body size (Liow et al 2008; Monroe and Bokma 2009), or persistence at low population size (Stanley 1990) These characteristics are predicted to increase risk of extinction: poor dispersers have limited abilities to (re)colonize or move to suitable environments (Smith and Green 2005; Sandel et al 2011), specialists are vulnerable to environmental change (McKinney 1997; Colles et al 2009), large-bodied species typically have slow life histories (Cardillo et al 2005; Reynolds et al 2005), and small populations are subject to demographic stochasticity or extinction from local catastrophies (Lande et al 2003; Mace et al 2008). Clades that seem to have speciated both rapidly and recently have in turn a greater share of currently rare and threatened species

Methods

Results

Conclusion