Shifting daylength regimes associated with range shifts alter aphid-parasitoid community dynamics

Miss Rachel Kehoe1, Mr David Cruse1, Dr Dirk Sanders1, Prof Kevin Gaston1, Dr Frank van Veen1

1University Of Exeter, Halvasso, United Kingdom

With climate change leading to poleward range expansion of species, populations are exposed to new daylength regimes along latitudinal gradients. Daylength is a major factor affecting insect life cycles and activity patterns, so a range shift leading to new daylength regimes is likely to affect population dynamics and species interactions; however, the impact of daylength in isolation on ecological communities has not been studied so far. Here, we tested for the direct and indirect effects of two different daylengths on the dynamics of experimental multitrophic insect communities. We compared the community dynamics under “southern” summer conditions of 14.5‐hr daylight to “northern” summer conditions of 22‐hr daylight. We show that food web dynamics indeed respond to daylength with one aphid species (Acyrthosiphon pisum) reaching much lower population sizes at the northern daylength regime compared to under southern conditions. In contrast, in the same communities, another aphid species (Megoura viciae) reached higher population densities under northern conditions. This effect at the aphid level was driven by an indirect effect of daylength causing a change in competitive interaction strengths, with the different aphid species being more competitive at different daylength regimes. Additionally, increasing daylength also increased growth rates in M. viciae making it more competitive under summer long days. As such, the shift in daylength affected aphid population sizes by both direct and indirect effects, propagating through species interactions. Our results demonstrate that range expansion of whole communities can indeed change interaction strengths between species within ecological communities with consequences for community dynamics.


I use aphids and their natural enemies as a model system to research community dynamics, including vulnerability to extinctions and extinction cascades. Within my PhD work I use this same system to investigate the impact that global change including range expansion, and therefore day length changes, has on impacts on ecological communities by changing interactions between species

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