Big brains reduce extinction risk in Carnivora
Why are some mammals more vulnerable to extinction than others? Past studies have explored many life history traits as correlates of extinction, but have not been successful at developing a unified understanding of why some species become extinct while other species persist despite living at the same time, under similar conditions, and facing equivalent challenges. I propose that the lens of wildlife behavior may bring into focus a more comprehensive view of why some species have gone extinct while others persist. The fossil record has recorded extinction events over carnivoran history; unfortunately, behavior is not well recorded in the fossil record. As a proxy for behavior, I examine relative encephalization (RE), brain size after controlling for body mass and phylogeny, as it has been found to be biologically relevant in understanding a wide variety of animal behavioral traits. I focus on the data-rich order Carnivora for which there are comprehensive data on brain size and extinction between 40 and 0.012 million years ago. I use Cox proportional-hazards models to assess the role that RE and body size have played on extinction risk for 224 species in the order Carnivora that existed between 40 and 0.012 million years ago. I show generally that carnivoran species with reduced RE had higher relative risks of extinction. Additionally, I find an interaction between RE and body size such that RE had the largest effects on relative extinction risk in the smallest-bodied species. These results suggest that RE is important for understanding extinction risk in Carnivora over geologic time frames.
KeywordsEvolution Brain size Relative encephalization Behavior Extinction risk Carnivora
I thank Rodolfo Dirzo, Lucia Jacobs, Deborah Gordon, Gretchen Daily, Amelia Wolf, Maria del Mar Sobral Bernal, Noah Simon, Reuben Youngblom, Stuart Abelson, Minh Chau N. Ho, Erin Kurten, Jonathan Payne, Rachel Vannette, Susumu Tomiya, Leonid Pekelis, Kristen Malinak, and George Michopoulos, for project discussion, manuscript review, and assistance on data processing. I thank Michael Abelson for his artwork in figure two. I also thank J. Finarelli and J. Flynn for collecting and making available brain size and body size used in this study (from their 2009 publication titled “Brain-size evolution and sociality in Carnivora”) and to those who worked to make the Paleobiology Database available and an incredible resource. I am appreciative of the patient and detailed review of this manuscript by Joerg Ganzhorn along with insightful comments from three anonymous reviewers.
Author contribution statement
ESA conceived, designed, and executed this study and wrote the manuscript. No other person is entitled to authorship.
This study was funded by the National Science Foundation Grant #1110332.
Compliance with ethical standards
Conflict of interest
The author declares that there is no conflict of interest.
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