Vulnerability of Nordic bat species to climate change: identifying seasonal bottlenecks across latitudes (NordBats)

Species worldwide have adjusted their behaviours and migration patterns in response to climate change, and globally we see a surge in biodiversity loss. Despite the fact that bats belong to the second largest mammalian order in the world, we know relatively little about how individuals and populations are affected by climate change. Bats have low reproductive rates and high energetic demands. Scientists therefore believe they are particularly sensitive to climate change. But in order to inform conservation strategies, we need to know which traits make a bat species more vulnerable, and which seasons are most challenging for them to overcome across latitudes; although the Nordic winter is long and cold, the summer might prove to be a greater challenge for nocturnal animals, with the light and short summer nights restricting the time bats have to find food. Through this project, we try to identify the drivers of behavioural, physiological, or seasonal responses to climate change in Nordic bats across Fennoscandia. We also attempt to identify potential bottlenecks for survival in Nordic bats in light of climate change, given the seasonal energetic dilemmas that Nordic bats must overcome to survive. This project is a theoretical modelling project and a 3-year research cooperation between BatLab Norway (NMBU) and BatLab Finland (University of Helsinki).

Climate change will continue to alter weather conditions, food webs and energy requirements for species globally over the next decades, with escalating rates of warming especially predicted in the north. Bats belong to the second most species-rich mammal group in the world and are believed to be particularly sensitive to future climate change; however, we still have little knowledge on the mechanisms behind behavioral, physiological, and phenological responses to climate change in bats. Nordic bats live in seasonal environments and face particular energetic dilemmas each season, that ultimately impact their survival- or reproductive chances. Common for these energetic dilemmas is that Nordic bats can use energy-saving behaviours (torpor and hibernation) throughout the annual cycle, but face certain costs in return. However, the costs and benefits of using these behaviours depend on individual state and on current and future environmental conditions, which demands a certain level of environmental predictability in order for bats to optimise their decisions. With prospects of the weather becoming more unpredictable in the north, it has never been more urgent to identify potential bottlenecks for species living close to the border of their distribution limits, and to identify the traits that make them vulnerable to climate change. In this project I will use stochastic dynamic state-dependent optimization models to identify the mechanisms behind responses to climate change in different Nordic bat species across seasons and latitudes. Such models evaluate costs and benefits of different behaviors, calculates the optimal decision under various conditions, and predicts the consequences of each choice, finally allowing us to simulate long-term population survival. By combining the expertise of BatLab Finland and BatLab Norway I will be able to detect the seasonal limitations for survival and reproduction in Nordic bats across a latitudinal gradient.