The Threat of Disease Increases as Species Move Toward Extinction

Abstract

In the midst of global biodiversity loss and rising disease incidence in wildlife, there has been growing interest in the role of infectious disease in species extinction. At local scales infectious disease is a common driver of population declines but globally it is an infrequent driver of species extinction and endangerment. For those unfortunate species threatened by disease questions remain, including when, along the pathway to extinction, do pathogens become a threat? We used the 2011 IUCN Red List, focusing on amphibians, birds, and mammals to test the null hypothesis that the proportion of species threatened by disease is the same in each status category (least concern to extinct). Overall, we found that pathogens appear to increase in importance as species move towards extinction though this varies with host taxonomy. We compare this finding to other threats (e.g. land-use change and invasive species) and discuss the role of potential ecological and artifactual drivers. Furthermore, we identify what other threats most frequently co-occur with infectious disease to examine the specific role of disease in driving extinction. We determined that infectious disease is rarely the sole driver of extinction and that being affected by other threats increases the odds of infectious disease co-occurring as a driver of extinction. Ultimately, our conclusions echo previous calls for baseline data on the presence of pathogens in species when they show the first signs of extinction risk and arguably before.

Global patterns in threats to vertebrates by biological invasions

“…All the species assessments are reviewed and accepted by the IUCN and then published online (www.iucnredlist.org). The Red List process has been extensively described [17] and used in many other articles to provide guidelines regarding the conservation of species and habitats [9,18].…”

Distribution and Host Range of Ranaviruses

“…They may present a signifi cant threat to host species that are geographically isolated or exist at low abundance (Heard et al 2013 ;Price et al 2014 ;Earl and Gray 2014 ). Thus, highly susceptible host species that are rare may be at greatest risk (Earl and Gray 2014 ).…”

Ranaviruses

“…They may present a signifi cant threat to host species that are geographically isolated or exist at low abundance (Heard et al 2013 ;Price et al 2014 ;Earl and Gray 2014 ). Thus, highly susceptible host species that are rare may be at greatest risk (Earl and Gray 2014 ).…”