Micro-moth communities mirror environmental stress gradients within a Mediterranean nature reserve

Isolated conservation areas embedded in a hemerobic landscape matrix run the risk of losing their functionality through stress impacts from their surroundings. We studied insects in one of the last remaining coastal forest reserves in northern Italy, viz. the Pineta san Vitale near Ravenna, to assess whether local assemblages are shaped by gradients of external environmental stressors. Specifically, we asked whether proximity to the nearest sources of aerially transported pollutants and extent of soil salinity affect communities. We used nocturnal micro-moths as target group since their usually high degree of host-plant specificity and often small body size lead us to expect these insects to reveal community differentiation at very small spatial scales within the reserve. We sampled 6085 moths representing 157 species at 16 light-trap sites during the vegetation period in 2013. We then assembled a matrix of 37 traits relating to larval niche, body size, phenology, migration behavior and habitat preferences from literature sources. With these data we established that species composition and overall functional diversity of local micro-moth assemblages was strongly influenced by the distance to pollution sources, and less so by soil salinity. In contrast, species richness and species diversity were not effective in depicting influences of these two enviromental gradients. Our results show that micro-moth communities respond sensitively to environmental conditions on small spatial scales, yet not all community attributes are equally suitable to uncover such relationships. Species composition and functional diversity emerged as far more informative than measures of local species diversity.