Abstract
Phenotypic plasticity and microevolution are the two primary means by which organisms respond adaptively to local conditions. While these mechanisms are not mutually exclusive, their relative magnitudes will influence both the rate of, and ability to sustain, phenotypic responses to climate change. We review accounts of recent phenotypic changes in wild mammal populations with the purpose of critically evaluating the following: (i) whether climate change has been identified as the causal mechanism producing the observed change; (ii) whether the change is adaptive; and (iii) the relative influences of evolution and/or phenotypic plasticity underlying the change. The available data for mammals are scant. We found twelve studies that report changes in phenology, body weight or litter size. In all cases, the observed response was primarily due to plasticity. Only one study (of advancing parturition dates in American red squirrels) provided convincing evidence of contemporary evolution. Subsequently, however, climate change has been shown to not be the causal mechanism underlying this shift. We also summarize studies that have shown evolutionary potential (i.e. the trait is heritable and/or under selection) in traits with putative associations with climate change and discuss future directions that need to be undertaken before a conclusive demonstration of plastic or evolutionary responses to climate change in wild mammals can be made.
Highlights
There can be little doubt that climate has acted as a strong selective force in the past, but rapid contemporary climate change is affording evolutionary ecologists the opportunity to study its influence first hand
We review the documented phenotypic changes observed in mammals that have been assumed to be associated with recent climate change, and assess the evidence that these changes are due to climate rather than some other environmental factor, that the observed changes are adaptive, and that the changes are a result of phenotypic plasticity and/or evolution
We have studied American red squirrels (Tamiasciurus hudsonicus) in Yukon, Canada since 1989 and during the first 10 years of study we found that first parturition dates advanced by 18 days (1.80 day yearÀ1; Reale et al 2003a)
Summary
There can be little doubt that climate has acted as a strong selective force in the past, but rapid contemporary climate change is affording evolutionary ecologists the opportunity to study its influence first hand. This, in turn, has led to increased over-winter survival and fitness and a threefold increase in population size In this case, increasing body mass in response to climate change can be considered an adaptive response. Parturition dates are phenotypically plastic in American red squirrels (Reale et al 2003a,b) and individual Columbian ground squirrels (Lane et al 2012) terminate hibernation earlier in response to warmer spring temperatures. We include energetic traits here because, little studied, they could have important ramifications both for the adaptation of wild mammal populations to their environment and the predictive ability of species distribution models (sensu Humphries et al 2002) With respect to the former, mammalian metabolic rates exhibit significant variation across zoogeographical zones, potentially due to differences in mean climatic variables or climatic variability (Lovegrove 2000).
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