Red Squirrel Responses to Regional Warming: Plastic or Genetic?
Reale, D., McAdam, A.G., Boutin, S. and Berteaux, D. 2003. Genetic and plastic responses of a northern mammal to climate change. Proceedings of the Royal Society B 270: 591-596.
Working with the entire population of about 325 red squirrels (Tamiasciurus hudsonicus) near Kluane Lake, Yukon (Canada), Reale et al. ear-tagged and monitored the reproductive activity of all females each and every year from 1989 to 2001, while identifying and similarly dealing with most of their young from birth to adulthood, during which period weather data were collected at a monitoring station located 50 km from their study site. In addition, noting that "spruce cones stored in the autumn of a given year are an important source of food for reproductive females in the spring of the following year," they counted the number of cones on the top 3 meters of about 300 trees every August.
Over the course of their study, the four Canadian researchers report that spring temperature rose by nearly 2°C, but they say there was "no particular trend for precipitation." Nevertheless, with just the increase in temperature, they found that over the ten full years of their observations, the mean number of spruce cones available over a female's lifetime rose more than 35%, which they describe as "a large increase in the abundance of food experienced by female squirrels." And they report that the squirrels responded to these environmental changes by advancing breeding by 18 days over the course of the 10-year study period, which represents an advancement of six days per squirrel generation.
Quoting Reale et al., "this dramatic advancement in breeding comprised a plastic response to increased food abundance as well as a microevolutionary response to selection." Or as they write in the concluding sentence of their paper, "the combination of phenotypic changes within generations and microevolutionary changes among generations resulted in large phenotypic responses to rapid changes in environmental conditions experienced by this population of squirrels over the past ten years [italics added]."