Microhabitat selection in a grassland butterfly: a trade-off between microclimate and food availability

Abstract

Understanding the factors that determine habitat quality is vital to ensuring appropriate habitat management. The main objective of this study was to assess the microhabitat preferences of egg-depositing females of the Grizzled Skipper (Pyrgus malvae) in calcareous grasslands of the Diemel Valley (Central Germany) for defining habitat quality. Based on this knowledge, we make management recommendations for the conservation of this threatened species. P. malvae generally preferred open and warm oviposition sites. However, there were considerable differences in the environmental conditions, depending on the selected host plant. On the small Potentilla tabernaemontani plants that grew in sparse vegetation with low-growing turf, mostly only one egg was found per plant. In contrast, occupied Agrimonia eupatoria host plants were larger and more prominent, regularly having more than one egg, and grew at sites with a taller and denser vegetation. The observed oviposition pattern reflects a trade-off between microclimate and food availability: Usually, occupied P. tabernaemontani plants grow under favourable microclimatic conditions. However, during hot years the risk of desiccation is high, leading to food shortage. In contrast, A. eupatoria generally provides more biomass, thrives on deeper soils and the vegetation has a cooler microclimate: hence, food shortage is somewhat unlikely. To meet the described habitat requirements of P. malvae, traditional rough grazing by sheep and goats seemed to be the most appropriate land management strategy. The re-introduction of coppicing in woodlands, particularly adjacent to calcareous grasslands, would also be beneficial.