Mammalian Response to Cenozoic Climatic Change

Multiple episodes of rapid and gradual climatic changes influenced the evolution and ecology of mammalian species and communities throughout the Cenozoic. Climatic change influenced the abundance, genetic diversity, morphology, and geographic ranges of individual species. Within communities these responses interacted to catalyze immigration, speciation, and extinction. Combined they affected long-term patterns of community stability, functional turnover, biotic turnover, and diversity. Although the relative influence of climate on particular evolutionary processes is oft-debated, an understanding of processes at the root of biotic change yields important insights into the complexity of mammalian response. Ultimately, all responses trace to events experienced by populations. However, many such processes emerge as patterns above the species level, where shared life history traits and evolutionary history allow us to generalize about mammalian response to climatic change. These generalizations provide the greatest power to understand and predict mammalian responses to current and future global change. 8.1 Review in Advance first posted online on February 5, 2009. (Minor changes may still occur before final publication online and in print.) A nn u. R ev . E ar th P la ne t. Sc i. 20 09 .3 7. D ow nl oa de d fr om a rjo ur na ls .a nn ua lre vi ew s.o rg by S ta nf or d U ni ve rs ity R ob er t C ro w n La w L ib . o n 03 /0 9/ 09 . F or p er so na l u se o nl y. ANRV374-EA37-09 ARI 18 January 2009 14:6 Population: group of interbreeding individuals within a species Abiotic: nonliving physical factors in the environment mya: million years ago INTRODUCTION As we grapple with the consequences of anthropogenic climatic change, understanding the biological response of species is one of our primary defenses in forestalling future biodiversity collapse. Anticipating that response, however, is hindered by three complicating issues: (a) We have little understanding about which species will be most sensitive, and what kinds of responses will be most common; (b) the full biological response to climatic change will operate over evolutionary time scales, but much of our knowledge of species dynamics has been gleaned from just a short time span—at best over a century, and often just a few years; and (c) extinction directly induced by habitat loss, habitat fragmentation, and overexploitation of populations is already proceeding at rates unparalleled in the Cenozoic (the past 65 million years), or perhaps the history of life. A longer-term perspective that encompasses how global warming interacts with species biology, extinction, and habitat loss is thus critical if we hope to understand how remaining species and communities will cope with ongoing global warming. Organisms are obviously affected by their environment; what is less obvious is the extent to which the abiotic environment sculpts different hierarchical levels of life, and the influence of climate on interactions between processes at different levels. Parmesan et al. (2006) recently reviewed the influence of climatic change on extant species (including mammals) over annual to century timescales. Here, we complement this review by using the fossil record to illustrate how mammals reacted to climatic change through geologic time in order to establish the full spectrum of mammalian responses to climatic change and the extent to which the responses of the past century appear unusual.