Climate change and temporal trends in body size: the case of rodents.

2 February 2018

Villar, Carlos; Naya, Daniel

A reduction in body size has been proposed as the third universal ecological response to global warming, after species distributional shifts and phenological changes. However, some recent studies raise doubts about the validity of this pattern, in particular for endotherms. Within this context, here we analyzed data on body mass (mb) for 17 rodent species, covering (at least) the last 6 decades, together with data on temperature change and basal metabolic rate (BMR) for each species. We found that: (i) ten species (58.8%) showed no significant changes in mb, while the remaining seven species (41.2%) decreased their size during the 20th century; (ii) phylogenetic generalized linear mixed models indicate that there is a significant and negative effect of the year of collection on mb; (iii) the correlation coefficient between mb and the year of collection (ryear) was not correlated with species mean mb, species distributional range, the length of the time series, or the change in ambient temperature; and (iv) the correlation between ryear and (residual) BMR was significant (and negative) only for species that do not use torpor. In summary, our results suggest that reductions in mb are common among rodents, but we were unable to identify a clear cause behind these changes (e.g., some results support the energetic argument behind the Bergmann rule but other does not). We concluded that with less than 0.5% of the extant (known) rodent species analyzed to date, we still are far from reaching a clear understanding of current patterns of variation in body size that are associated with global environmental change for this group.