The vulnerability of overwintering insects to loss of the subnivium

Aim: Winter climate change threatens the subnivium (i.e., the microhabitat
that exists between the snowpack and the ground), and the community of
species that depends on it for overwintering survival. One group of
species that will likely exhibit an array of responses to subnivium loss
are overwintering insects because they vary in their cold tolerance
strategies and lower thermal limits. For an assemblage of eight insect
species that range in their cold tolerance strategies and include both
pollinators and pests, we investigated species-specific vulnerabilities to
shifting subnivium conditions. Location: Great Lakes region of North
America Methods: We applied information on each insect’s supercooling
point to spatially- and temporally-explicit models of minimum subnivium
temperatures generated from active-warming experiments and comprising
three scenarios: current conditions (i.e., control), +3°C, and +5°C.
Results: Although species varied in their vulnerabilities, our predictions
indicated that exposure to lethal temperatures generally decreased under
warming of 3°C, but increased under warming of 5°C, indicating that once
enough warming happens, a tipping point is reached. We also found that
freeze-tolerant species (i.e., species that can survive at temperatures
below their supercooling point) possess a more cryptic vulnerability to
winter climate change because sustained below-freezing temperatures were
sufficient to induce vulnerability (i.e., predicted mortality), even when
temperatures were above the supercooling point. Main conclusions: This
work provides a better understanding of the vulnerability of different
insect species to winter climate change, which is critical because
overwintering survival and the fitness consequences incurred during
overwintering likely represent important bottlenecks for the population
dynamics of subnivium-dependent species.