Effects of food availability on butterfly diversity and network specialization across altitudinal levels in a Mediterranean landscape

Abstract

Altitudinal gradients, which involve diverse biotic and abiotic variables in small-scale spaces, provide a good opportunity to investigate the local and regional patterns that influence species assemblages, including those of pollinators and the plants with which they interact him. Here, we studied the variation in butterfly assemblages and their interactions with flowering plants across different altitudes in a Mediterranean mountain system. Moreover, considering the different vegetation (i.e. grassland, forest, shrubland)at each altitudinal level (i.e. lowland, mid-mountain, high-mountain), we examined the effects of food availability on butterfly assemblages.

We found butterfly richness and number of interactions between butterflies and flowering plants to be mainly influenced by the altitudinal level, with the mid-mountain region exhibiting the highest levels of both variables. Flower abundance positively correlated with butterfly richness on the lowland and high-mountain levels, while vegetation was a key factor impacting both butterfly richness and butterfly-flower interactions. Network modularity was highest at the mid-mountain level, while species specialization increased with the altitudinal levels. Species composition varied significantly across the altitudinal gradient, occurring at each specific altitudinal level and between different habitats, driven primarily by species turnover rather than a nested decline in species as altitude increases.

Our findings suggest that even though topoclimate may shape species composition at a regional scale, resource availability is key to explaining the differences among habitats with similar climatic conditions. This underscores the importance of promoting and maintaining diverse food resources for butterflies, particularly in the challenging environmental conditions found at both high and low altitudinal levels in Mediterranean mountain regions. Furthermore, a multiscale approach to butterfly conservation is imperative, considering the interplay of regional and local factors that influence community composition and diversity.