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Data and code from: Extreme heat drives opposing patterns of size-dependent survival across microhabitats

Litle, Jack1; Fales, Robin1; Murie, Kindall1; Carrington, Emily1

Published Sep 21, 2026 on Dryad. https://doi.org/10.5061/dryad.1zcrjdg6j

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Sep 21, 2026 version files 85.30 MB

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Abstract

Increasingly frequent and severe heatwaves threaten the persistence of species on earth. Survival under extreme heat is often attributed to organismal traits, such as body size, yet realized heat exposure also depends on microhabitat. We show that an historic heatwave – which killed over a billion coastal organisms – drove size-dependent survival in an intertidal mussel population, favoring opposite extremes of the size distribution. The direction of size-dependent survival shifted across metre-scale habitat, with small mussels favored on the high shore but large mussels favored on the low shore. Dynamic heat flux simulations revealed that body size and microhabitat interact to determine available cooling behaviors, driving the direction of size-dependent survival. On the high shore, greater desiccation risk limited evaporative cooling, advantaging small individuals that cool rapidly via convection (wind-cooling). On the low shore, lower desiccation risk enabled prolonged evaporative cooling, advantaging large-bodied individuals with greater water stores. Climate impact projections focusing primarily on species’ traits may systematically miss predictable, generalizable trait–microhabitat interactions that drive demographic filtering under extreme heat.