Small Mammal Response to Climate Change

            Research on the period of climate change between the Pleistocene and Holocene eras has revealed that small mammals are not as resilient to changes in climate as had previously been assumed. The data suggest that rapidly changing climates negatively influence the richness and evenness of small mammals living in an ecosystem.  It is possible that these past trends can be used to predict animal populations’ survival response to our currently warming climate.  Blois et al. (2010) examined northern California’s small mammal populations during a warming climate and they concluded that small mammals have a direct relation to climate change which decreases their populations. — Leah Kahn
Blois J., McGuire J., Hadly E., 2010. Small mammal diversity loss in response to late-Pleistocene climatic change. Nature 771–774

            The species groupings of animals living in communities are shaped and influenced in numerous ways. This paper focuses on how the change from a glacial to interglacial climate influenced the survival of all species of small mammals.  The shift from the Pleistocene epoch to the Holocene epoch took place between 15,000 and 12,000 years ago, and significantly warmed the planet.  The average global temperature during the Pleistocene was 5 ºC which warmed to 7 ºC during the Holocene. The researchers excavated small mammal fossils surrounding the Samwell Cave Popcorn Dome in northern California.  They studied the remains of two pocket gopher species, as well as mountain beavers, ground squirrels, chipmunks and voles.  Significant loss from local communities is a pattern mirrored across North America during glacial-interglacial change, and the trends of fauna observed at this northern California cave can be used to broadly represent this diversity loss.
            Scientists were able to determine how old the fossils were by using radiocarbon dating and ancient DNA testing from specimens’ molars.  They examined the evenness of species composition throughout the shift to a warmer climate.  Evenness is a way to measure the balance of individuals.  For example, an ecosystem with 40 dogs and 42 foxes is much more even than one with 40 dogs and 100 foxes.  This is neither good nor bad but it allows scientists to more closely examine changes in taxa fitness.  Richness fell from 12 to 8 taxa.  Richness is simply the number of different kinds of animals in any given region or ecosystem.  The Amazon rainforest is, for example, much richer in species than the Southern California desert.  Blois et al. analyzed the change in evenness and richness during the rapidly warming climate. The data demonstrate a significant decline in species evenness and richness as the global temperature warms.
This aids our understanding of how small mammals may react to our current swiftly warming climate.  This decline in evenness and richness may occur in modern small mammal communities.  Small mammals are often viewed as unaffected and impervious to altered ecosystems due to their fast growth rate and high population densities.  However, these data illustrate that they are at risk for diversity loss.  This is most likely due to small mammals being directly affected by climate change.  Many animals in the region preferred cooler forests but small mammals were found unlikely to migrate to cooler regions and therefore became locally extinct.  Trends across North America confirm this lack of migration.  Some species may not have been able to keep up with climate change evolutionarily.
An alternative theory which could explain the changes in the small animal population include the extinction of megafauna, which may have altered predation and vegetation patterns.  Human impact is also unlikely because humans did not populate the region until about 3,000 years later.  There is currently a lack of support for either of these two theories.  The data in this study strongly suggest that a quickly warming climate will negatively impact the diversity of small animal populations.

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