Evolutionary theory as a tool for predicting extinction risk Austin J. Gallagher 1, 2 , Neil Hammerschlag 1, 3 , Steven J. Cooke 4 , Daniel P. Costa 5 , and Duncan J. Irschick 6, 7 1 Leonard and Jayne Abess Center for Ecosystem Science and Policy, University of Miami, Coral Gables, FL 33146, USA 2 Beneath the Waves, Inc., Syracuse, NY 13202, USA 3 Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA 4 Fish Ecology and Conservation Physiology Laboratory, Department of Biology and Institute of Environmental Science, Carleton University, Ottawa, ON K1S 5B6, Canada 5 Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060, USA 6 Organismic and Evolutionary Biology Program, 319 Morrill Science Center, University of Massachusetts at Amherst, Amherst, MA 01003, USA 7 Department of Biology, 221 Morrill Science Center, University of Massachusetts at Amherst, Amherst, MA 01003, USA Timely and proactive wildlife conservation requires strategies for determining which species are most at the greatest threat of extinction. Here, we suggest that evolutionary theory, particularly the concept of speciali- zation, can be a useful tool to inform such assessments and may greatly aid in our ability to predict the vulner- abilities of species to anthropogenic impacts. Predicting the fate of species in a changing world Species vary widely in how they are affected by environ- mental disturbance. Human-induced changes in the envi- ronment expose species to novel conditions that did not exist in their evolutionary past, and responses of species can impact their extinction risk [1]. Quantifying extinction risk is an important goal for conservation biologists and wildlife managers who must identify and prioritize species or popu- lations. However, quantifying this risk is challenging, be- cause populations can decline, stabilize, or even increase in the face of environmental change. Authors have discussed the importance of natural history and evolutionary infor- mation for assessing extinction risk [2,3]. These methods often require extensive life-history or detailed distributional data, which are optimized for r-selected terrestrial species (e.g., insects), but are less operational for larger and more- threatened k-selected consumers, especially those that are inherently rare, elusive, and difficult to study. A framework for integrating evolutionary concepts (i.e., specialization) into risk assessment that can be applied to identify which ecological mechanisms expose various spe- cies to extinction risk is warranted. Much of the discussion on specialization has focused on extreme (generalist and specialist) individual species; however, specialization is a continuum, with most species falling between extremes. Thus, we lack a comparative methodological perspective of how the vulnerability of species can be compared along this quantitative axis for evolutionary traits and how these traits might be integrated into assessments of extinction risk. Specialization as a tool for assessing ecological resistance An important principle in evolution is that of specializa- tion. As noted by others [4], ecologists have typically defined a specialist as a ‘species that occupies a relatively narrow niche or restricted range of habitats, or alterna- tively a species or population that selects resources out of proportion to availability.’ Specialization is a species-level phenomenon and can be measured in different ways (e.g., diet, temperature, morphology, etc.) and is tied to the concept of trade-offs [5]. The ‘jack-of-all-trades-master-of- none’ principle implies not only that lower levels of spe- cialization (i.e., generalist) enable species to access a wide array of resource niches with relatively equal effectiveness, but also that there are limitations on the ability to effi- ciently access certain resources. Specialists should be able to access a single resource more effectively, at the expense of accessing a wider range of resources. This suggests that highly specialized species can be disproportionately vulnerable to human-induced environmental change. Conversely, highly generalized species are likely to be less vulnerable to such pressures. Furthermore, the correlation between phenotypic value and fitness of traits might change between environments, in which specialized traits can become maladaptive under altered selective pressures (Box 1). Recent work on sharks has shown that evolution- arily unique species are suffering declines and becoming increasingly extinction prone at faster rates than their more-generalized counterparts [6]. Here, we discuss three examples that demonstrate how viewing specialization as a continuum can inform our understanding of extinction risk (Figure 1). Taxonomic case studies Migratory Pacific salmon Pacific salmon are notable for their remarkable long- distance migrations from freshwater habitats where they hatch (and return to reproduce) to ocean feeding grounds. Forum 0169-5347/ ß 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tree.2014.12.001 Corresponding author: Gallagher, A.J. (gallagher.austin@gmail.com). Keywords: conservation; physiology; specialization; ecology; plasticity; extinction. TREE-1891; No. of Pages 5 Trends in Ecology & Evolution xx (2015) 1–5 1