Micro-climate determines oviposition site selection and abundance in the butterfly Pyrgus armoricanus at its northern range margin
- Knowledge about species habitat requirements is important when designing conservation strategies as well as for predicting species distributions. For herbivorous insects, insights in oviposition preferences can provide important information on their habitat requirements.
- The oviposition preferences of Oberthür's Grizzled Skipper butterfly Pyrgus armoricanus Oberthür at its northern range boundary in southern Sweden were studied and it was also tested to what extent oviposition preferences can predict variation in population size among monitored sites.
- Oviposition behaviour was observed and analysed using a two-step approach. First the characteristics of host plant ramets that female butterflies inspected for oviposition (including both ramets that were rejected and ramets used for oviposition) were compared with with control ramets. Second, ramets on which female butterflies oviposited were compared with ramets that butterflies inspected but rejected.
- The preferred plant species for oviposition was Filipendula vulgaris Moench. Filipendula vulgaris ramets inspected for oviposition by P. armoricanus females were situated in warm microclimates, primarily on south facing slopes, surrounded by lower vegetation and a higher percentage cover of bare ground compared with random control ramets.
- Among the inspected ramets, females chose to oviposit those situated in the warmest micro-climates and those surrounded by the largest percentage cover of bare ground.
- Together with habitat patch area, oviposition preferences explained 65% of the variation in butterfly population size.
- These results reveal the importance of a microclimate as a component of habitat quality for insect populations at the margins of their geographical range.