Abstract
Simple SummaryAnimal body size varies in response to many environmental factors and may be influenced by climate change, food availability, habitat alterations or species interactions. Here, we use a specimen collection of Italian rhinolophid bats (Rhinolophus hipposideros) covering a long historical period (1869–2016) and looked at their body and skull size to see whether these changed over time and space. Although no temporal responses were recorded, which rules out an effect of climate change or urbanization, we found an increase in body size from south to north along the Italian territory which is best explained according to Bergmann’s rule. The latter postulates that larger individuals retain heat more effectively, so their presence in northern, colder climates is favoured, whereas, smaller ones dissipate heat more easily and are best adapted to cope with southern, warmer climates.Body size in animals commonly shows geographic and temporal variations that may depend upon several environmental drivers, including climatic conditions, productivity, geography and species interactions. The topic of body size trends across time has gained momentum in recent years since this has been proposed as a third universal response to climate change along with changes in distribution and phenology. However, disentangling the genuine effects of climate change from those of other environmental factors is often far from trivial. In this study, we tested a set of hypotheses concerning body size variation across time and space in Italian populations of a rhinolophid bat, the lesser horseshoe bat Rhinolophus hipposideros. We examined forearm length (FAL) and cranial linear traits in a unique historical collection of this species covering years from 1869 to 2016, representing, to the best of our knowledge, the longest time series ever considered in a morphological assessment of a bat species. No temporal changes occurred, rejecting the hypotheses that body size varied in response to climate change or urbanization (light pollution). We found that FAL increased with latitude following a Bergmann’s rule trend, whereas the width of upper incisors, likely a diet-related trait, showed an opposite pattern which awaits explanation. We also confirmed that FAL is sexually dimorphic in this species and ruled out that insularity has any detectable effect on the linear traits we considered. This suggests that positive responses of body size to latitude do not mean per se that concurring temporal responses to climate change are also expected. Further investigations should explore the occurrence of these patterns over larger spatial scales and more species in order to detect the existence of general patterns across time and space.
Highlights
Climate change is one of the main threats to biodiversity and is well-known to exert several effects on the biota (e.g., [1])
We provide a unique example of morphological analysis done on mammals over almost 150 years, and employ linear morphology to test alternative hypotheses about body size change over space and time in Italian populations of this bat species, as follows
We found no temporal variation in forearm length and cranial size over ca. one century and a half in a rhinolophid bat species that is sensitive to human alteration of landscapes, including light pollution
Summary
Climate change is one of the main threats to biodiversity and is well-known to exert several effects on the biota (e.g., [1]). A main hypothesis regarding the latter, at least for terrestrial endotherms, is that body size will decrease in response to a warming climate. The rationale behind this hypothesis is provided by the so-called Bergmann’s rule [7], according to which animal species, or, within species, individuals in warmer climates show a smaller body size than those living in colder climates. When projected along a temporal gradient of increasing temperature such as that generated by climate change, this pattern would consist of a progressive reduction in body size, because smaller individuals will radiate heat more effectively, and would be better adapted to an increasing temperature scenario [8]. Studies have shown either pattern, as well as cases where no apparent body size trend was detected in response to climate change (reviewed in [8])
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