Pollinator distribution in patches of suitable habitat depends more on patch isolation than on floral abundance

Abstract

Intrinsic complexity of real-world systems makes particularly difficult to decipher which factors influence the dispersal of pollinators in the landscape matrix and their distribution amongst patches of suitable habitat. Saltmarshes are an ideal and naturally simplified landscape to study the ability of different groups of pollinators to disperse across a landscape matrix, as they consist of a matrix of flooded areas surrounding patches of suitable habitat with different degrees of isolation from the mainland and different levels of floral abundance. We hypothesise that pollinator distribution to flowering plants depends more on patch isolation than on floral abundance, with pollinator richness and visitation rates to flowering plants decreasing with increasing distance from the mainland. To this end, we established 60 permanent plots at varying distances from the mainland and monitored pollinator visitation to entomophilous plants. We also quantified the reproductive success of entomophilous species in the surveyed plots by calculating fruit set. We found that the pollinator community of saltmarshes consisted only of flying pollinators with good dispersal abilities, while we recorded no flightless pollinator species. Both pollinator richness and visitation rate decreased with increasing distance of patches of suitable habitat from the mainland, affecting reproductive success of a non-autogamous entomophilous species. Interestingly, floral abundance did not affect pollinator richness and visitation rate to flowering plants, nor did it affect reproductive success of target plant species. In saltmarshes, the pollinator distribution depends more on patch distance from the mainland than on floral abundance. Our results suggest that the presence of patches of suitable habitat in a landscape matrix does not necessarily ensure the maintenance of pollinators. Rather, our results suggest that suitable habitat isolation is the critical factor in pollinator dispersal and distribution that should be considered to improve landscape matrix permeability to pollinators.