Chemical antipredator defence is linked to higher extinction risk

Abstract

Many attributes of species may be linked to contemporary extinction risk, though some such traits remain untested despite suggestions that they may be important. Here, I test whether a trait associated with higher background extinction rates, chemical antipredator defence, is also associated with current extinction risk, using amphibians as a model system—a group facing global population declines. I find that chemically defended species are approximately 60% more likely to be threatened than species without chemical defence, although the severity of the contemporary extinction risk may not relate to chemical defence. The results confirm that background and contemporary extinction rates can be predicted from the same traits, at least in certain cases. This suggests that associations between extinction risk and phenotypic traits can be temporally stable over long periods. The results also provide novel insights into the relevance of antipredator defences for species subject to conservation concerns.

Phylogenetic Comparative Methods can Provide Important Insights into the Evolution of Toxic Weaponry

“…In the course of a comparative study on the conservation status of poisonous amphibians [73], a relationship was found in which chemically-defended amphibians are more likely to be threatened than others. Since it is difficult to identify the direction of this relationship from the GLM-style analyses (see Section 2) which support the link, a one pathway model was created in which a non-poisonous and non-threatened amphibian lineage could evolve to be a chemically defended and threatened one by changing either trait first, and another model that constrained chemical defence to evolve first (so defence changes before threat status does).…”

“…In contrast, poisonous amphibians had lower diversification rates as a result of higher extinction rates than non-chemically-defended species [85]. The reasons for the increased extinction rate of poisonous amphibians over evolutionary time is still unknown, but persists into the present day as increased probability of having a threatened conservation status [73]. These results open up a new avenue for research to understand not just why poisonous amphibians suffer higher extinction risk, but why this differs from other toxic tetrapod groups.…”