Climate-induced physiological stress drives rainforest mammal population declines

Climate change is a major driver of global biodiversity loss, yet the
precise mechanisms linking climate change to population declines remain
poorly understood. We developed a novel, broadly applicable framework that
integrates biophysical, nutritional and population modelling to capture
fundamental physiological constraints on mammalian herbivores and applied
it to investigate the causes of declines in ringtail possums of the
Australian Wet Tropics (Pseudochirops archeri and Hemibelideus
lemuroides). Our approach bridges the gap between mechanistic
("bottom-up") models, which simulate species’ responses based
solely on their traits and local microclimates, and the more common
("top-down") statistical models, which infer species’ responses
from occurrence or abundance data and standard environmental variables. We
quantified population dynamics over a 30-year period by generating
species-specific estimates of temperature and water stress, foraging
limitations, and linking these with annual monitoring and nutritional
quality within an open population model. Our findings demonstrate that
climate change has impacted populations through physiological stress, but
in a species-specific manner. Both species have experienced population
collapses at lower elevations and in low-nutritional sites. For P.
archeri, we found evidence that population changes were driven by reduced
survival due to overheating and dehydration, alongside diminished
recruitment from limited foraging. In contrast, our model suggests that H.
lemuroides populations were primarily affected by foraging constraints,
emphasising the importance of considering climate-driven limitations on
foraging activity in addition to direct physiological stress. These
mechanistic insights offer a foundation for targeted conservation
strategies to mitigate the impacts of climate pressures on wild
populations.