Beyond the models: exploring the real-world responses of bats to climate change
Climate change poses a significant threat to global biodiversity, with impacts predicted to become much more severe by 2100. However, up to now, research has largely failed to provide representative overviews of wildlife responses to these threats.
More than anything, it can be hard to predict how wildlife will respond to the array of challenges that climate change will bring, especially for groups of animals that are diverse and globally distributed.
Bats are one such animal, accounting for 20% of global mammalian diversity with over 1430 species. They live in a variety of habitats, including tropical rainforests, oceanic islands and arid regions. Their diverse dietary adaptations play a crucial role in ecosystem services such as seed dispersal and pest population suppression.
Given their diversity, bats serve as excellent subjects for studying the impacts of climate change on vertebrates, offering valuable insights for conservation efforts at both local and global levels.
A systematic review in 2022 addressed this issue by discussing current knowledge of bat responses to climate change, identifying research gaps, and suggesting future directions.
Climate change responses in bats
When faced with climate change, animals have the option of moving to a new location, adapting to the new conditions or becoming extinct. The study identified a variety of positive, neutral and negative responses that bats were taking to new environmental changes.
Range changes, particularly expansions and shifts to new areas, are common, potentially indicating bats’ ability to adapt, especially in more ecologically plastic species.
In fact, range expansions have generally been observed in bat species with greater ecological plasticity, where ranges have generally shifted to higher latitudes in recent decades. On the other hand, evidence for range losses has generally been derived from species distribution modelling rather than from direct observations.
It can be difficult to quantify evolutionary changes made by wildlife in response to climate change because it’s hard to separate short-term seasonal adjustments — known as phenotypic plasticity — from lasting genetic changes — evolution — and as such, data is hard to collect.
Some bat species have been observed altering their phenology to adapt to changing conditions.
For example, the Brazilian free-tailed bat has brought forward its summer migration by approximately two weeks and is overwintering in areas previously only occupied in the summer.
These changes have been attributed to rising temperatures associated with climate change and are common in other vertebrates, including amphibians, birds and reptiles, especially in regions where climatic conditions are generally more unstable.
Phenological changes that may appear to be adaptations to changing conditions may prove to be problematic in the future, especially if there are temporal and spatial mismatches between bats and their resources (water, insects, fruit, etc.), the consequences of which will be hard to predict.
Similarly, a new study spanning 24 years of observations has noticed changes in Daubenton’s bats, a species found in Europe and Asia, which have also been attributed to climate change.
These bats live along rivers and live at slightly different altitudes based on sex. The altitude limit was found to have shifted upwards by 157m, probably as a result of increases in temperature over the 24-year period. Body size also increased as the calorific cost of regulating body temperature decreased, favouring an increase in the mass of newborn bats.
Changes in altitude may result in increased competition for food sources, which may lead to difficulties when coupled with the general decline of insect populations.
A bat hangs upside down in a tree (Riizz/Unsplash)
The most extreme response to climate change is extinction, either of a population in a specific region or of an entire species.
Models can be useful for predicting how a species’ range might change by looking at the environmental conditions they live in now and using climate models to map where these suitable conditions will be in the future.
Several of these models have predicted range contractions for different species of bats, such as the African fruit bat, which will increase their extinction risk.
Unusually high death rates have been reported in eight other bat species as a direct result of climate change-induced weather events, including wildfires and heatwaves. While extreme events are not a new hazard for bats, their frequency is increasing, putting particular strain on species with narrow habitat ranges.
Evidence suggests that extreme weather events associated with climate change have been responsible for local extinctions in other species, such as bumblebees, generating concerns about declining bat populations.
Research gaps and the future
So far, a lot of work done to predict how bats will respond to future climate changes has been based, at least in part, on modelling outputs. For example, from species distribution models,
“Models inevitably simplify the real world because they cannot incorporate all possible variables,” said Dr. Danilo Russo of the University of Naples Federico II, who co-authored the review. “Yet they offer insights into natural processes and make it possible to some extent to predict responses, carry out sensitivity analysis, etc. Species Distribution Models (SDMs) are no exception, and predicting not only spatial but also temporal patterns poses a particularly challenging task.”
So, while such models can be extremely useful, they do not currently provide detailed information about phenological, genetic, physiological and behavioural responses to climate change.
Therefore, collecting more genetic data on bat responses to climate change will greatly improve the ability of models to accurately predict future changes in the abundance and distribution of bat populations.
While there is currently little research into genetic responses to climate change, integrating genetic tools into assessing whether species will be viable long-term will provide valuable insights into genetic diversity, population size and adaptive responses, ultimately guiding conservation efforts.
More information is also needed to discover how climate change is impacting bat physiology. Current trends suggest that bats are reducing torpor — a period of short, involuntary hibernation some bat species exhibit — and increasing metabolic rates to cope with rising temperatures. The effects such changes might have are, as of yet, unclear.
It is important to have a good understanding of physiological capacities when predicting responses to climate change since these limit the range of places a species can survive and reproduce successfully.
Changes to how bats interact with other species, such as predators, may be affected by climate change, or new interactions may arise between species that had not previously interacted with bats. In particular, bats could have a ripple effect on entire ecosystems as they play such an integral role in them.
Currently, longitudinal studies that have generated live field data account for only about 12% of total studies into bats, according to the review, but provide vital information on the effects of both short- and long-term changes in environmental conditions.
Observing actual changes in phenology or distribution, rather than just predicting them via modelling, requires long-term field studies to be conducted, ideally lasting at least a decade.
Establishing thorough and ongoing monitoring of species abundance and distribution is crucial to confirm assessments of their vulnerability to climate change. Monitoring should be focused on areas where the impacts of climate change are predicted to be the most severe, to improve knowledge of climate change impacts on wildlife in general and thus improve future projections.