860 A. Colles, L. H. Liow and A. Prinzing local communities: species that co-occur only with other species of the same niche position are likely highly specialized. (Ellenberg et al. 1992; Synbiosys, http:// www.synbiosys.alterra.nl). For organisms for which such databases do not exist, climate envelopes, phenological breadth or ecomorphological criteria may be suitable assessments of the geographical, local or fundamental niche respectively (Saﬁ & Kerth 2004; Jiguet et al. 2007). Use common datasets to integrate the three approaches and to circumvent approach-speciﬁc biases Applying phylogenetic approaches to neoecological or paleobiological datasets, particularly those involving spe- cies with living representatives or relatives, can facilitate illuminate some issues. Neocological and paleobiogical datasets often cover more lineages than normally used by most phylogeneticists (for instance all birds or all angiosperms in a region; e.g. Klotz et al. 2002). In using these datasets, less phylogenetic information, such as branch lengths, may be readily available, but sample sizes are high, and analyses such as sister-clade comparisons could lead to robust results (Oakley & Cunningham 2000; see Mitter et al. 1988 for an example of linking resource use to diversiﬁcation across sister clades). Neoecologists, on the other hand, may begin to understand how the present-day relationship between specialization and extinc- tion risk depends on the evolutionary history of species. Cross-disciplinary studies have already given us new insights, for instance when comparing basal and derived species within lineages (The neoecological approach- Limitations). Another example are tropical phytophages which may be more specialized across plant lineages (Dyer et al. 2007, but see Novotny et al. 2006), which, if conﬁrmed, might be an additional explanation of extinc- tion risks faced by tropical species. Finally, paleoecological studies can likewise beneﬁt from using phylogenetic information for clarifying the statistical non-independence of related taxa and from incorporating shorter time-scale mechanisms illuminated by neoecological studies. Account for range-size variation among species Analyses should account for the confounding effect of geographic range. Although broadly ranging species have a potentially large global niche breadth which possibly decreases extinction risk, simply having a large range also reduces extinction risk. After accounting for range size, the effect of ecological specialization on taxon longevity may disappear (Liow 2007a). Besides these confounding effects, local risks and global risks may also be different in nature and hence studies can beneﬁt from encompassing as many spatial scales as possible. 2009 Blackwell Publishing Ltd/CNRS Review and Synthesis Understand why some specialists may not be at risk We suggest two major hypotheses why specialists may not be at risk. The ﬁrst is that specialization on speciﬁc resources due to physiological or morphological constraints puts species at risk compared with generalists, while specialization due to lack of search-time constraints does not (because it is reversible, see above). Both types of specialization might be readily identiﬁable. For instance, organisms lacking protective structures (such as cuticles) and tolerance mechanisms might be specialized due to physical constraints, while organisms with slow life-histories may be specialized due to lack of search-time limitations (Prinzing 2003). The second hypothesis is that speciation may compensate for extinction in specialist lineages. Some higher-level taxa are not observed to suffer declines in paleoecological studies perhaps because speciation occurred over environmental changes. Recent methodological advances in separating the phylogenetic ﬁngerprints of extinction and speciation (e.g. Maddison et al. 2007 and references therein) may facilitate to test this scenario, but to our knowledge, have not been applied to studies involving specialization and decline. Encouragingly, even neoecologists may approach these potentially pertinent evolutionary mechanisms by studying the ﬁrst steps of speciation, e.g. in terms of subspecies formation. Both hypotheses have implications for evolutionary ecology. The ﬁrst suggests that for some species special- ization is not costly. The costs of being a generalist, such as inefﬁcient resource use, may thus be much more important than previously thought. The second suggests that the species level may sometimes not be the appropriate level of analysis. Specialization may persist throughout evolution not because it facilitates the survival of species having specializations but because it promotes speciation. The above recommendations will permit identiﬁcation of situations where specialists are indeed at risk: conser- vation efforts should be focalized on the particular resources and habitats of these specialists. Moreover, the ﬁnal recommendation will establish a bridge between conservation biologists studying correlates of being at risk and evolutionary biologists studying costs and beneﬁts of species niche use. A C K N O W L E D G E M E N T S Very insightful comments from Fre´de´ric Jiguet, Vojtech Novotny, John Wiens and four anonymous referees improved the manuscript. AP is supported by an ATIP fellowship by the Central National de la Recherche Scientiﬁque.