Climate-driven variation in biotic interactions provides a narrow and variable window of opportunity for an insect herbivore at its ecological margin

Abstract

Climate-driven geographic range shifts have been associated with transitions between dietary specialism and generalism at range margins. The mechanisms underpinning these often transient niche breadth modifications are poorly known, but utilisation of novel resources likely depends on phenological synchrony between the consumer and resource. We use a climate-driven range and host shift by the butterfly Aricia agestis to test how climate-driven changes in host phenology and condition affect phenological synchrony, and consider implications for host use.Our data suggest that the perennial plant which was the primary host before range expansion is a more reliable resource than the annual Geraniaceae upon which the butterfly has become specialised in newly colonised parts of its range. In particular, climate-driven phenological variation in the novel host Geranium dissectum generates a narrow and variable ‘window of opportunity’ for larval productivity in summer. Therefore, although climatic change may allow species to shift hosts and colonise novel environments, specialisation on phenologically-limited hosts may not persist at ecological margins as climate change continues. We highlight the potential role for phenological (a)synchrony in determining lability of consumer-resource associations at range margins, and the importance of considering causes of synchrony and success in biotic interactions when predicting range shifts.

Understanding the biology of species' ranges: when and how does evolution change the rules of ecological engagement?

“…Models by Alexander et al [55] support the idea that trade-offs with biotic factors in particular decrease the evolutionary potential of populations at range limits, especially limits that are determined by climate. Also, Stewart et al [73] consider the butterfly Aricia agestis that has undergone a host shift that has reduced its host plant repertoire at its UK range margin. This host shift has allowed its spread to warming sites further north, probably through the evolution of novel genotypes at the range edge, and the loss of ancestral polyphagy.…”