On commonness and rarity of insect pollinators: patterns of species abundance and diversity in a hyperdiverse Mediterranean assemblage

This paper presents a comprehensive analysis of patterns of species abundance and diversity in a hyperdiverse insect pollinator assemblage from Mediterranean montane habitats of southeastern Spain. Data on pollinator visitation to flowers of the community of entomophilous plants (288 species) were gathered over a 29-year period, and ∼95% of individual pollinators recorded were identified to species, totalling 46,401 individuals in 845 species. Shapes of species abundance distributions (SADs) were virtually identical at the regional ( N = 56 sites) and local (one intensively studied site) scales, remained invariant over the study period, and were best predicted by the log-series distribution. Pollinator diversity estimates corresponding to the first three Hill numbers (Species richness, Shannon diversity and Simpson diversity; 0 D, 1 D and 2 D, respectively) were obtained for each plant species x site x year combinations ( N = 472 "sampling occasions"). Pollinator diversity measures varied widely among plant species; their frequency distributions were unimodal and strongly right-skewed; and interspecific variation was related to plant phylogeny, floral features and pollinator visitation rates. Pollinator diversity of individual plant species depended on habitat type, with dolomitic outcrops, rock cliffs and forest interior harboring the least diverse pollinator assemblages. Variation of 0 D, 1 D and 2 D among habitats and years was largely decoupled, revealing a complex patterning of pollinator species richness and dominance. Estimated proportions of undetected pollinator diversity ("dark diversity") varied with insect order (lowest for Lepidoptera, highest for Diptera). The adoption of community ecology tools for assessing pollinator diversity improves our ability to elucidate pollinator responses to natural and anthropogenic environmental change, and permits hitherto unexplored questions in pollination ecology.