Modelling the potential efficacy of treatments for white-nose syndrome in bats

The fungal disease white-nose syndrome (WNS) has caused mass mortality in some species of North American bats during hibernation. We use population viability models to test if a hypothetical WNS treatment or management action could facilitate the recovery of WNS-affected little brown myotis Myotis lucifugus populations. We modelled scenarios altering three parameters: (a) WNS severity (population growth rate of WNS-affected populations; lambda(WNS)); (b) proportion of population treated; and (c) treatment improvement in winter survival (TIWS). Our models predict that a treatment or management action that targets an entire population with a TIWS of 40% (the average TIWS in bat trials to date) will cause a population to stabilize or increase if WNS causes an annual decline of less than 70% (i.e. lambda(WNS) > 0.30). However, for severe WNS (lambda(WNS) = 0.10), the TIWS must be at least 54% to cause a population to stabilize or increase. Where only a proportion of a WNS-affected population is treated, population stability is much harder to achieve unless the impact of WNS attenuates over time. Our models suggest that a treatment or management action only facilitates the recovery of WNS-affected populations if WNS is mild, TIWS is high, and a large proportion of the population can be treated. If a small proportion of the population is treated, it is easier to facilitate recovery if WNS severity attenuates over time. Synthesis and applications. We modelled the predicted abundance trajectory of white-nose syndrome-affected little brown myotis Myotis lucifugus populations in response to a hypothetical treatment or management action. Our two types of models incorporate the complete range of possible scenarios varying three parameters: (a) population growth rate of the white-nose syndrome-affected population, (b) the improvement in winter survival associated with the treatment or management action, and (c) the proportion of the population treated. We suggest that our models, which can be explored using online Shiny applications, should be used in the planning phase of treatment or management action programmes for white-nose syndrome.