R E V I E W A N D S Y N T H E S I S Audrey Colles,1 Lee Hsiang Liow2 and Andreas Prinzing1* 1Unit ‘‘Ecobio’’, University Rennes 1, CNRS, Campus Beaulieu, B aˆtiment 14A, 35042 Rennes, France 2Centre for Ecological and Evolutionary Synthesis, Department of Biology, University of Oslo, PO BOX 1066, Blindern N-0316 Oslo, Norway *Correspondence: E-mail: andreas.prinzing@univ-rennes1.fr Ecology Letters, (2009) 12: 849–863 doi: 10.1111/j.1461-0248.2009.01336.x Are specialists at risk under environmental change? Neoecological, paleoecological and phylogenetic approaches Abstract The question what renders a species extinction prone is crucial to biologists. Ecological specialization has been suggested as a major constraint impeding the response of species to environmental changes. Most neoecological studies indicate that specialists suffer declines under recent environmental changes. This was conﬁrmed by many paleoeco- logical studies investigating longer-term survival. However, phylogeneticists, studying the entire histories of lineages, showed that specialists are not trapped in evolutionary dead ends and could even give rise to generalists. Conclusions from these approaches diverge possibly because (i) of approach-speciﬁc biases, such as lack of standardization for sampling efforts (neoecology), lack of direct observations of specialization (paleoeco- logy), or binary coding and prevalence of specialists (phylogenetics); (ii) neoecologists focus on habitat specialization; (iii) neoecologists focus on extinction of populations, phylogeneticists on persistence of entire clades through periods of varying extinction and speciation rates; (iv) many phylogeneticists study species in which specialization may result from a lack of constraints. We recommend integrating the three approaches by studying common datasets, and accounting for range-size variation among species, and we suggest novel hypotheses on why certain specialists may not be particularly at risk and consequently why certain generalists deserve no less attention from conservationists than specialists. Keywords Conservation biology, evolutionary dead-end, extinction and speciation, generalist-to- specialist, macroevolution, niche breadth, population decline, resource-use hypothesis, specialization-by-choice and specialization-by-constraint, species lifetime. Ecology Letters (2009) 12: 849–863 I N T R O D U C T I O N The identiﬁcation of species and populations at higher extinction risk is important for developing conservation strategies in the context of current and expected environ- mental change. Empirical estimation of extinction risk for an individual population or species is time and resource consuming and often unfeasible; hence much research has been devoted to ﬁnding general relationships between Re-use of this article is permitted in accordance with the Terms and Conditions set out at http://www3.interscience.wiley.com/ authorresources/onlineopen.html biological traits and response to environmental change. Such relationships could then be used to predict which popula- tions or species are at risk given environmental changes of varying magnitudes and durations. Specialization is thought to contribute strongly to extinction risk (e.g. McKinney 1997; Biesmeijer et al. 2006). Our operational deﬁnition of specialization is the use of a relatively restricted subset of resources or habitats in the ﬁeld by the focal species compared with other species. We use the binary categories specialization ⁄ generalization for conciseness but acknowledge that the underlying phenomena are usually continuous. We use a broad 2009 Blackwell Publishing Ltd/CNRS