How are arthopod communities structured and why are they so diverse? Answers from Mediterranean mountains using hierarchical additive partitioning

Mountains are complex ecosystems supporting a great variety of taxa. Here, we explored the diversity patterns of arthropods in two mountains, pinpointing the spatial scale that accounts most for overall diversity variation, using an additive partitioning framework. Butterflies and Orthoptera were sampled in Rodopi (2012) and Grammos (2013) mountains. Diversity was partitioned into five hierarchical levels (mountain, elevational zone, habitat, transect and plot). We compared the estimated diversity values for each level to the respective permuted values expected by chance, for all species, as well as for species identified as “rare” or “common”. At broader spatial levels, the variation in total diversity was attributed to the beta diversity component: mountains accounted for 20.94 and 26.25% of butterfly and Orthoptera diversity, and elevational zones accounted for 28.94 and 35.87% respectively. At finer spatial scales, beta diversity was higher than expected by chance in terms of the Shannon index. The type of habitat was found to play a significant role only for rare orthopterans. Finally, common species were recognized for shaping overall species diversity. We highlight the importance of the spatial levels of elevation zone and then mountain position in conservation planning, due to the greater beta diversity recorded at this scale as compared to habitat or more finite scales. Monitoring programs might need to adapt different strategies with respect to the focal organisms, and consider patterns of common rather than rare species that found to drive the patterns of the entire community.