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Dryad

Data from: Soilscapes of mortality risk suggest a Goldilocks effect for overwintering ectotherms

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Oct 04, 2024 version files 2.37 GB

Abstract

Changing climates are driving population declines in diverse animals worldwide. Winter conditions may play an important role in these declines but are often overlooked. Animals must not only survive winter but must also preserve body condition which is a key determinant of growing season success. We hypothesized that ectotherms overwintering in soil face a tradeoff between the risks of cold damage (including freezing) near the surface and of elevated energy use at deeper depths. To test this hypothesis, we developed landscapes of mortality risk across depth for overwintering bumble bee queens. These critical pollinators are in decline in part due to climate change, but little is known about how climate effects their overwintering mortality. We developed a mechanistic modeling approach combining measurements of freezing points and the temperature dependence of metabolic rates with hourly soil temperatures from across the US to estimate mortality risk across depth under historic conditions and under several climate change scenarios. We found that, under current climate conditions, overwintering queens face a Goldilocks effect: temperatures can be too cold at shallow depths due to substantial freezing risk, but too hot at deep depths where they risk prematurely exhausting lipid stores. Models suggest that increases in mean temperatures and in seasonal and daily temperature variation will increase risk of overwinter mortality. Our work suggests that ectotherms overwintering in the soil must select depths that balance competing risks of temperatures that are too cold or too hot. Better predictions of effects of changing climate on dormant ectotherms will require more measurements of physiological responses to temperature during dormancy across diverse taxa.