Extinction Risk Escalates in the Tropics

Jana C Vamosi,Steven M Vamosi,Rob P Freckleton

doi:10.1371/journal.pone.0003886

Abstract

The latitudinal biodiversity gradient remains one of the most widely recognized yet puzzling patterns in nature [1]. Presently, the high level of extinction of tropical species, referred to as the “tropical biodiversity crisis”, has the potential to erode this pattern. While the connection between species richness, extinction, and speciation has long intrigued biologists [2], [3], these interactions have experienced increased poignancy due to their relevancy to where we should concentrate our conservation efforts. Natural extinction is a phenomenon thought to have its own latitudinal gradient, with lower extinction rates in the tropics being reported in beetles, birds, mammals, and bivalves [4]–[7]. Processes that have buffered ecosystems from high extinction rates in the past may also buffer ecosystems against disturbance of anthropogenic origin. While potential parallels between historical and present-day extinction patterns have been acknowledged, they remain only superficially explored and plant extinction patterns have been particularly neglected. Studies on the disappearances of animal species have reached conflicting conclusions, with the rate of extinction appearing either higher [8] or lower [9] in species richness hotspots. Our global study of extinction risk in vascular plants finds disproportionately higher extinction risk in tropical countries, even when indicators of human pressure (GDP, population density, forest cover change) are taken into account. Our results are at odds with the notion that the tropics represent a museum of plant biodiversity (places of historically lowered extinction) and we discuss mechanisms that may reconcile this apparent contradiction.

Highlights

The tropical biodiversity crisis has been escalating for decades
Tropical species may instead be more resilient to extinction, a factor that may have played an important role in the formation of the latitudinal biodiversity gradient [6,14]
Our findings indicate that species vary in their natural susceptibility to extinction via disturbance, with plant species inhabiting tropical countries being more sensitive to a given degree of human impact

Summary

Introduction

The tropical biodiversity crisis has been escalating for decades. We know that an ever-increasing percentage of threatened species of birds, mammals and conifers are found in the Neotropics [10]. While it is appreciated that this extinction has both natural and anthropogenic causes, disentangling the contribution of each to the demise of any particular species has proven immensely challenging [11,12,13]. Whether tropical species are more innately vulnerable to extinction can only be determined if we concurrently assess the confounding influences of human impact, which may exhibit a latitudinal gradient. Tropical species may instead be more resilient to extinction, a factor that may have played an important role in the formation of the latitudinal biodiversity gradient [6,14]. If human disturbance can be assumed roughly equivalent to natural catastrophes that have occurred over evolutionary time scales, knowledge of the distribution of susceptibility to extinction in the present may reveal important features of extinction rates that relate to latitudinal diversity

Methods

Results

Conclusion