Of the nearly 5,400 mammalian species alive today, a quarter of them are currently at risk of extinction due to loss of habitat, overexploitation, climate change and other human disturbances. Species not considered to be at risk of extinction are regularly added to the list of threatened species. Identifying species of greater conservation concern before their populations become critically threatened may be more effective and less expensive for protecting mammalian diversity than targeting species already known to have suffered population declines. In the fossil record, species of mammals that have gone extinct had significantly smaller relative brain sizes, (the size of the brain relative to body size), than species that are still alive today. Further, carnivore species listed currently as endangered have significantly smaller relative brain sizes as compared to carnivore species that are not threatened with extinction. Based on this preliminary data, this research project will examine more broadly the relationship between relative brain size and conservation status in order to test the hypothesis that species with larger relative brain sizes may be more successful in the face of environmental change, and thus more resistant to extinction. This project is unique in that it examines both modern mammalian species, using a more comprehensive methodology than has been employed to date, as well as mammalian species over the last 30 million years.

A goal of this research project is to produce tools that scientists, governments and conservation organizations can use to identify species that may be extinction-prone. By providing an inexpensive and readily deployable metric for proactively identifying species of concern, and guiding action to stem species loss, this work could provide important insights for conservation science and policy. This research will be disseminated through publications, conference presentations and continued communication with non-governmental organizations. Additionally, the substantial dataset that results from this work will be made available to other researchers and state and federal agencies. This research project will involved high school and undergraduate students in research methods and analysis, and supports the doctoral research of a graduate student.

Project Report

Background: Biological diversity is currently undergoing immense losses that rival extinction events found in the geological record. Conservation biology is focused on providing principles and tools for preserving that biological diversity. However, in his seminal 1985 paper, Michael Soulé describes conservation biology as a "crisis discipline." It remains, to this day, a crisis-oriented science due largely to the extreme complexity of the environment, variety of environmental perturbations and the relative lack of robust predictive tools. While there are a variety of tools targeted at mammal conservation (e.g. conservation breeding, spatial dispersal/use models, relocations, biological reserves and corridors) few of them are oriented toward predicting differential extinction-vulnerability in mammalian taxa. Tools that do offer predictive insights often require extensive life-history information, which can be expensive to obtain or otherwise unavailable and/or do not differentiate between animals of similar body sizes/trophic level. Relative encephalization, a biologically relevant trait, has been understudied in mammalian fauna with regard to wildlife persistence and could join the conservationist’s toolbox as a way to help identify at-risk mammalian species. Outcomes: This dissertation research examined the relationship between relative encephalization (RE; brain size corrected for the effects of body size and phylogenetic inertia) and risk of being endangered. A significant result from this work is, for modern mammalian species, a finding of strong correlation between RE, body size and species extinction risk. Our analyses have found that, for most mammalian species in the study, those with increased RE are more likely to be endangered than those with smaller levels of RE. Body size plays an important and interesting role in this relationship; unlike the majority of species for which increased RE is associated with increased risk, for those species in the largest quartile of body size there is little effect of RE on extinction risk. These findings are particularly interesting in light of other results from the same dissertation. In analyses of Carnivoran RE over the prior 40 million years we find a strikingly different result. Relative risk of extinction was generally higher for Carnivoran species that had smaller levels of RE over paleontological time frames. This effect, like the results from modern mammals, holds true for most species except for the very largest species. One interpretation, considering the results from both the paleontological time frame as well as the modern, is that human caused environmental changes may be responsible for changing the nature of threats to mammalian taxa and in turn have played a part in reversing the role of increased RE. Intellectual merit: this work has explicitly addressed the fundamental question of the importance of brain size on extinction risk in mammalian taxa. Many decades of interest and research have found that brain size is a trait that is important in understanding various aspects of wildlife life histories. However, the ultimate measure of how well a species’ behaviors and abilities are suited to its environment is its vulnerability to extinction. The research funded by this grant has directly tested this using a consistent methodology and has provided results that show that relative measures of brain size can be important in understanding a species’ risk of endangerment. Additionally, this work has resulted in a large dataset of brain sizes which can be used to address other morphological questions. Broader impacts: To date, there have been 21 undergraduates and community members who CO-PI Abelson has worked with on this project. These 21 included undergraduate students interested in research and wildlife conservation from Stanford University, UC Berkeley as well as recent undergraduates who sought experience in museum work and research. Those who assisted in the project learned skills including: -Working with museum specimens; how to measure endocranial capacity, proper/safe practices for working with museum specimens, mammal skull identification, how to discern the relative age of mammals by examining the prepared skull and general natural history museum processes for archiving mammalian specimens. -Database management; developing proficiency in working with excel, writing both simple and complicated formulas and writing computer code for macros (i.e. VBA scripts). Additionally, introductory experience was gained in using the statistical programming language R. -Exporting and working with natural history museum databases; systems designed for the user to query and export collection based data. -General discussions on research design, implementation and analysis to put specific experience in context of the larger project Scientific communication: To date, this work has been disseminated via presentations at three conferences. Additionally, the research had been published in the form of an article aimed at a general audience by Nature News and Scientific American.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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Alan James Tessier
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Stanford University
Palo Alto
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