Print PagePollinators are essential to the earth’s life support systems but how pollinator communities change with increasing human land use remains poorly understood. Here we investigate patterns of pollinator community disassembly across land use gradients, asking whether species abundance and floral specialization predict the order in which species are lost. Parallel analyses were performed on two data sets from contrasting ecoregions. In New Jersey, we collected pollinators at 20 sites for a total of 5132 specimens; in California, we collected pollinators at 27 sites for a total of 11,636 specimens. In each region, we first characterized plant-pollinator networks in extensive areas of high-quality habitat. We used these networks to measure two traits for each pollinator species: abundance, and the number of plant species visited. For the latter trait we used both observed values, and estimated asymptotic values; asymptotic values correct for possible sample size biases. Second, we evaluated the order of species loss with regard to each of these traits, using a non-overlapping set of study sites that were arrayed across a gradient of increasing land-use change. The observed order of species loss was then compared to a null model based on random loss order.
Results/Conclusions
Floral specialization and rarity appear to be associated with extinction risk for native pollinators. In New Jersey, we found that the pollinator species that visit the fewest plant species were significantly more likely to be lost with increasing land-use change, as compared with the random null. This result held regardless of whether the observed or estimated asymptotic values were used. The least abundant pollinator species were also significantly more likely to be lost with increasing land-use change. Analyses of the California data set are ongoing.
