Christy McCain and Sarah King examined 1050 papers that took a look at the ways in which human-caused climate change is affecting mammals in North America. They took pains to include only works that could exclude other factors that might be causing changes, such as habitat destruction
The first thing to note about this study is that the authors sought, and found no publication bias. Science deniers often claim that there is a bias toward “popular” results, that is, studies that seem tilted to support mainstream opinion.. McCain and King found that out of all the studies they looked at, 52% - only slightly more than half - of mammalian populations responded to climate change as researchers expected. Of the remaining 48%, 7% had reacted opposite to expectations, and 41% had no detectable response at all.
Because this was such a broad study, covering species of all types with body sizes ranging from 2.5g (0.09oz) to 338kg (745lbs), its results have significance for species across the continent, and most likely across the world.
The researchers drew two main conclusions about likelihood of response to climate change.
The first is body size. The larger the animal, the more likely it is to change. Detectable changes started at around 100g (3.5oz), and went up from there to the point where the largest animals (polar bear and elk), were 27 times more likely to show responses to climate change.
The second major indicator is activity over the course of a 24 hour period. Species that are rigidly confined to activity at a certain time of day are far more likely to show significant changes due to the warming climate than species that can change their activity periods in response to changing conditions. Flexibility is key.
Eighty-two percent of the studies focused on changes to range, or to population size, leaving only 18% examining local extinction, seasonal behavior change, morphological change, or genetic change, so more research may be needed in the latter categories.
In the coming weeks, we’ll list the species covered in this review that live in New England, but the breadth of the study means that it forms a pretty reliable picture of what has been happening with mammals in general as the climate has changed.