Recent evidence suggests that some organisms are already undergoing phenotypic changes as a result of climate change. Researchers Nicholas M. Caruso et al. compared historical and contemporary size measurements for 15 salamander species in genus Plethodon from 102 populations, discovering that six of the species have shrunk significantly in body size over 55 years. The greatest reduction in body size occurred at southern latitudes that experienced the greatest amount of drying and warming (1).
Warmer environmental temperatures can limit foraging and activity. In turn, changes in body size are often associated with changes in foraging, behavior, diet, and activity patterns–increases in metabolic expenditures might result in reduced growth, if food and foraging time are limited. These factors together affect reproduction and predator-prey relationships, which all in turn affect survival rates and community composition. Thus, climate change can result in significant phenotypic shifts (1).
The researchers gathered and measured 1193 Plethodon salamanders from 102 populations and 15 species at 64 sites. 8257 measurements from preserved adult specimens from the same sites were also included, for a total of 9450 individual measurements. To determine whether the changes in body size resulted from climate change, biophysical models were used to analyze annual metabolic expenditure and annual activity duration (1).
The study found an overall 8% reduction in body size across all of the examined species over the 55-year period. Four potential causes for reduction in body size were investigated: latitude, elevation, climate change, and average species size. Average species size, elevation, change in temperature, and change in precipitation all failed to explain the change in body size. However, populations at lower latitudes, that experienced an increase in temperature and decrease in precipitation, showed the greatest reductions in body size. Overall, body size reductions were spatially and temporally correlated with documented climate change patterns (1).
This study is significant because few studies have definitively shown that phenotypic changes associated with climate change are genetically based–most studies didn’t rule out the possibility that the responses were instead environmentally-caused (1).
It also observed an approximate 1% reduction in body size per generation across the six species that exhibited significant trends. This rate of phenotypic change is among the largest observed among contemporary populations. This observation leads credence to the idea that human-caused environmental disturbances result in some of the most rapid and drastic phenotypic responses. This study thus provides evidence that organisms are already adapting on a wide scale to the changes that climate change has created on the environment (1).
1. N. M. Caruso et al, Glob. Change Biol. Widespread rapid reductions in body size of adult salamanders in response to climate change. (2014). Available at http://onlinelibrary.wiley.com/doi/10.1111/gcb.12550/full (3 April 2014).