Overwinter hibernation survival
Overall, our energetic model predicted nearly ubiquitous survival of
uninfected bats throughout the range of M. lucifugus with
< 0.0001% of cells falling below the threshold for
survival. Our results found that 95% of all uninfected bats
roosting at \(4\)˚C and 98% relative humidity during hibernation would
only require 0.21 g–0.60 g of fat to survive the duration of
hibernation (median = 0.48 g, mean = 0.45 g, sd =
0.12 g, Figure S2). When considering the amount of fat bats had
pre-hibernation, the median bat emerged with 1.85 g of body fat
remaining (mean = 2.16 g, sd = 1.01 g) and the heaviest
95th percentile of bats had up to 4.05 g of fat
remaining. Considering these residual fat values in the terms of days
spent in hibernation, the median bat would have sufficient fat resources
to survive an additional 181 days (mean = 190.83 days, sd= 45.35 days) and those bats with < 4 g of fat remaining could
be capable of surviving another 280 days in those optimal roosting
conditions.
When P. destructans infection was included into the optimal
roosting conditions, the median value of fat required to survive
hibernation was increased by 0.7 g to 1.21 g (mean = 1.16 g,sd = 0.45) and the residual fat values dropped to a median of
1.22 g (mean = 1.45 g, sd = 0.76). In total, 95% of bats
were predicted to emerge with between 0.61 g and 2.93 g of fat remaining
after the hibernation. Translating the fat values into days, the median
value was reduced ~ 135 days to 45.63 days (mean= 55.41 days, sd = 45.35 days). Mortality of bats prior to the
end of the hibernation period was predicted in 4.82 % of the cells
where the survival of hibernating bats fell < 0, visible in
the northeastern provinces of Canada (Figure S2).
Most of the predicted best available subterranean hibernacula were
expected to have available temperatures at or above 4°C. Despite this,
32.64% of cells fell below that temperature and 6.44% of cells fell
below the lower critical temperature of 2°C that M. lucifugusdefends during hibernation (Figure S3). Despite these lower than optimal
temperatures, M. lucifugus was predicted to survive across most
of its distribution, with only 0.5% of cells predicted to fall below
the survival threshold—primarily around Denali National Park in
Alaska. Median fat required to survive hibernation as an uninfected bat
dropped 0.71 g to 1.11 g (mean = 1.41 g, sd = 0.93) with a
nearly identical 95% interior range. When including infection withP. destructans, the hibernation energetics model predicted the
median fat required for hibernation increased 0.72 g to 1.21g,
(mean = 1.20 g, sd = 0.40g). Like optimal roosting
conditions, infection resulted in 4.74% of cells falling below the
survival threshold.
While neither of the considered hibernation conditions predict large
areas to result in mortality, the increased percent of fat needed to
hibernate with P. destructans highlights the metabolic
consequences of infection (Figure S4). At \(4\)˚C and 98% relative
humidity, bats were predicted to expend a median of 154% more body fat
resources to hibernate while infected for the same winter duration
(Table S4). Overall, 95% of infected bats are predicted to increase
their metabolic expenditure between~66% and 195%
compared to their healthy counterparts. Hibernating at the predicted
best available temperature suggested similar increases in the energy
expended; however, the geographic distribution of where the greatest
increases occurred were different than those observed under static
preferred conditions.