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ing habitat loss and fragmentation, drastic shifts in species abundances and distributions, and climate change (see above) (Myers and Knoll, 2001; Barraclough and Davies, 2005). Changes in the biotic and abiotic composition of the environment (including extinctions) may restructure niche space and moderate constraints on diversification imposed by niche saturation. Major turnovers in species composition may therefore be expected (Tilman and Lehman, 2001). Unfortunately, we lack detailed information on the past states of these attributes in geological history and so cannot easily construct quantitative empirical models that can be projected forward. Predicting the evolutionary future is hampered by large uncertainty about the magnitude and form of environmental change and by lineage-specific responses. If we wished to safeguard the evolutionary future, a sensible strategy would be to maintain a set of species that is overdispersed with respect to their ecological adaptations and (as a simple proxy) their phylogeny, maximizing the possibility of having the right set of features in an uncertain future (Crozier, 1997).

Returning to our original question, should conservation goals consider the long-term evolutionary future? We sound two notes of caution. First, although we have restricted our focus to mammals, they are only a tiny branch on the Tree of Life, and many of the major limbs, from ciliates to Chlamydia, may be better insulated from anthropogenic disturbances (Nee, 2005). The evolutionary future of life on Earth is therefore unlikely to be in serious jeopardy. Second, anthropogenic environmental change and extinctions are occurring on the order of tens to hundreds of years, but times to speciation are frequently estimated in thousands to millions of years (Barraclough and Davies, 2005), and recovery times after previous mass extinction events were perhaps 5–10 million years (Erwin, 2001). These timescales are too great for practical management. Diversity will almost certainly rebound after the current extinction event; however, it may be composed of species descended from a different, as yet unknown, subset of lineages from those that dominate now, and humans will likely not be included among them. Practical conservation should retain its focus on minimizing declines and extinctions in the present day.

ACKNOWLEDGMENTS

We thank Natalie Cooper, Lynsey McInnes, Jim Regetz, Gavin Thomas, and Nicola Toomey for discussion and John Avise and Doug Erwin for comments on the manuscript. This work was supported by the Natural Environment Research Council (U.K.), the National Science Foundation (U.S.), the European Union HOTSPOTS Early Stage Training Network, a Deutsche Forschungsgemeinschaft Heisenberg Scholarship, and the Leverhulme Trust.



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