Body Size Variation in Italian Lesser Horseshoe Bats Rhinolophus hipposideros over 147 Years: Exploring the Effects of Climate Change, Urbanization and Geography

In-situ responses of temperate-zone bats to climate change

There is growing evidence that human-induced climate change poses a major threat to bats. As climate change progresses, we can only hope to mitigate its negative effects on bat populations by gaining a more comprehensive understanding of the complex interactions of all the factors involved. Drawing on recent evidence, largely from long-term field studies of individually marked bats, we discuss the multiple impacts-positive and negative-of climate change on temperate heterothermic bats and their responses to climate change in situ. For example, there is increasing evidence that warmer summers and milder winters are leading to changes in the seasonal phenology of bats, which in turn may lead to species-specific changes in demography, morphology, physiology, food availability, and roost use. We also highlight open research questions on the responses of bats to climate change. This includes better data on population trends and the underlying direct and indirect climate-related causes for changes in mortality and reproductive success. In order to assess the long-term impacts of climate change on bats, more information is needed about the relative importance of phenotypic plasticity and evolutionary adaptation in the responses of bats to climate change.

Climate is changing, are European bats too? A multispecies analysis of trends in body size

Animal size, a trait sensitive to spatial and temporal variables, is a key element in ecological and evolutionary dynamics. In the context of climate change, there is evidence that some bat species are increasing their body size via phenotypic responses to higher temperatures at maternity roosts. To test the generality of this response, we conducted a >20-year study examining body size changes in 15 bat species in Italy, analysing data from 4393 individual bats captured since 1995. In addition to examining the temporal effect, we considered the potential influence of sexual dimorphism and, where relevant, included latitude and altitude as potential drivers of body size change. Contrary to initial predictions of a widespread increase in size, our findings challenge this assumption, revealing a nuanced interplay of factors contributing to the complexity of bat body size dynamics. Specifically, only three species (Myotis daubentonii, Nyctalus leisleri, and Pipistrellus pygmaeus) out of the 15 exhibited a discernible increase in body size over the studied period, prompting a reassessment of bats as reliable indicators of climate change based on alterations in body size. Our investigation into influencing factors highlighted the significance of temperature-related variables, with latitude and altitude emerging as crucial drivers. In some cases, this mirrored patterns consistent with Bergmann's rule, revealing larger bats recorded at progressively higher latitudes (Plecotus auritus, Myotis mystacinus, and Miniopterus schreibersii) or altitudes (Pipistrellus kuhlii). We also observed a clear sexual dimorphism effect in most species, with females consistently larger than males. The observed increase in size over time in three species suggests the occurrence of phenotypic plasticity, raising questions about potential long-term selective pressures on larger individuals. The unresolved question of whether temperature-related changes in body size reflect microevolutionary processes or phenotypic plastic responses adds further complexity to our understanding of body size patterns in bats over time and space.

Variability in bat morphology is influenced by temperature and forest cover and their interactions

Multiple climatic and landscape drivers have been linked to variations in bat body size and wing functional traits. Most previous studies used proxies rather than actual climate and land-use data, and their interactions are rarely explored. We investigate whether higher summer average temperatures are driving decreasing bat body size as predicted by Bergmann's rule or increasing appendage size as per Allen's rule. We also explore whether temperature or resource availability (namely forest cover) is responsible for changes in wing functional traits. Using land-use data from historical maps and national statistics combined with climatic data, we assessed the effect of temperature and resource availability on bat morphology. We used 464 museum specimens of three bat species (Eptesicus nilssonii, Pipistrellus pygmaeus, and Plecotus auritus), spanning 180 years, across a 1200 km latitudinal gradient. We found no evidence of higher summer average temperatures driving decreases in body size in bats. Jaw sizes of P. auritus and P. pygmaeus changed over time but in different directions. The geographical variation of forest cover was also related to differences in wing functional traits in two species. Crucially, there was a significant antagonistic interactive effect of forest and temperature on tip index in P. pygmaeus whereby above 14.5°C the relationship between forest and tip index actually reversed. This could indicate that higher temperatures promote more pointed wings, which may provide energetic benefits. Our results show the importance of including both climatic and land-use variables when assessing trends in bat morphology and exploring interactions. Encouragingly, all three species have shown an ability to adapt their body size and functional traits to different conditions, and it could demonstrate their potential to overcome future negative impacts of climate and land-use change.

Landscape composition drives the impacts of artificial light at night on insectivorous bats

Among the most prevalent sources of biodiversity declines, Artificial Light At Night (ALAN) is an emerging threat to global biodiversity. Much knowledge has already been gained to reduce impacts. However, the spatial variation of ALAN effects on biodiversity in interaction with landscape composition remains little studied, though it is of the utmost importance to identify lightscapes most in need of action. Several studies have shown that, at local scale, tree cover can intensify positive or negative effects of ALAN on biodiversity, but none have - at landscape scale - studied a wider range of landscape compositions around lit sites. We hypothesized that the magnitude of ALAN effects will depend on landscape composition and species' tolerance to light. Taking the case of insectivorous bats because of their varying sensitivity to ALAN, we investigated the species-specific activity response to ALAN. Bat activity was recorded along a gradient of light radiance. We ensured a large variability in landscape composition around 253 sampling sites. Among the 13 bat taxa studied, radiance decreased the activity of two groups of the slow-flying gleaner guild (Myotis and Plecotus spp.) and one species of the aerial-hawking guild (Pipistrellus pipistrellus), and increased the activity of two species of the aerial-hawking guild (Pipistrellus kuhlii and Pipistrellus pygmaeus). Among these five effects, the magnitude of four of them was driven by landscape composition. For five other species, ALAN effects were only detectable in particular landscape compositions, making the main effect of radiance undetectable without account for interactions with landscape. Specifically, effects were strongest in non-urban habitats, for both guilds. Results highlight the importance to prioritize ALAN reduction efforts in non-urban habitats, and how important is to account for landscape composition when studying ALAN effects on bats to avoid missing effects.