Topographical variation reduces phenological mismatch between a butterfly and its nectar source

The timing of many biological events, including butterfly imago emergence, has advanced under climate change, with the rate of these phenological changes often differing among taxonomic groups. Such inter-taxa variability can lead to phenological mismatches. For example, the timing of a butterfly’s flight period may become misaligned with a key nectar resource, potentially increasing the extinction risk to both species. Here we fit statistical models to field data to determine how the phenology of the marbled white butterfly, Melanargia galathea, and its main nectar source, greater knapweed, Centaurea scabiosa, have changed over recent years at three sites across the UK. We also consider whether topographical diversity affects C. scabiosa’s flowering period. At our focal site, on the species’ northern range limit, we find that over a 13-year period the onset of C. scabiosa’s flowering period has become later whilst there is no obvious trend over time in the onset of M. galathea’s flight period. In recent years, butterflies have started to emerge before their key nectar source was available across most of the site. This raises the intriguing possibility that phenological mismatch could be an unrecognised determinant of range limits for some species. However, the presence of topographical diversity within the site decreased the chance of a mismatch occurring by increasing the length of the flowering period by up to 14 days. We suggest that topographical diversity could be an important component in minimising phenological mismatches under future climate change.