The consequences of climate change for biogeographic range dynamics
depend on the spatial scales at which climate influences focal species directly
and indirectly via biotic interactions. An overlooked question concerns the
extent to which microclimates modify specialist biotic interactions, with
emergent properties for communities and range dynamics. Here, we use
an in-field experiment to assess egg-laying behaviour of a range-expanding
herbivore across a range of natural microclimatic conditions. We show that
variation in microclimate, resource condition and individual fecundity can
generate differences in egg-laying rates of almost two orders of magnitude
in an exemplar species, the brown argus butterfly (Aricia agestis). This
within-site variation in fecundity dwarfs variation resulting from differences
in average ambient temperatures among populations. Although higher temperatures did not reduce female selection for host plants in good condition, the
thermal sensitivities of egg-laying behaviours have the potential to accelerate
climate-driven range expansion by increasing egg-laying encounters with
novel hosts in increasingly suitable microclimates. Understanding the sensitivity of specialist biotic interactions to microclimatic variation is, therefore,
critical to predict the outcomes of climate change across species’ geographical
ranges, and the resilience of ecological communities