Effects of habitat isolation on pollinator communities and seed set

I. Steffan-dewenter et T. Tscharntke, Effects of habitat isolation on pollinator communities and seed set, OECOLOGIA, 121(3), 1999, pp. 432-440
Citations number
Categorie Soggetti
Journal title
ISSN journal
0029-8549 → ACNP
Year of publication
432 - 440
SICI code
Destruction and fragmentation of natural habitats is the major reason for t he decreasing biodiversity in the agricultural landscape. Loss of populatio ns may negatively affect biotic interactions and ecosystem stability. Here we tested the hypothesis that habitat fragmentation affects bee populations and thereby disrupts plant-pollinator interactions. We experimentally esta blished small "habitat islands" of two self-incompatible, annual crucifers on eight calcareous grasslands and in the intensively managed agricultural landscape at increasing distances (up to 1000 m) from these species-rich gr asslands to measure effects of isolation on both pollinator guilds and seed set, independently from patch size and density, resource availability and genetic erosion of plant populations. Each habitat island consisted of four pots each with one plant of mustard (Sinapis arvensis) and radish (Raphanu s sativus). Increasing isolation of the small habitat islands resulted in b oth decreased abundance and species richness of flower-visiting bees (Hymen optera: Apoidea). Mean body size of flower-visiting wild bees was larger on isolated than on nonisolated habitat islands emphasizing the positive corr elation of body size and foraging distance. Abundance of flower-visiting ho neybees depended on the distance from the nearest apiary. Abundance of othe r flower visitors such as hover flies did not change with increasing isolat ion. Number of seeds per fruit and per plant decreased significantly with i ncreasing distance from the nearest grassland for both mustard and radish. Mean seed set per plant was halved at a distance of approximately 1000 m fo r mustard and at 250 m for radish. In accordance with expectations, seed se t per plant was positively correlated with the number of flower-visiting be es. We found no evidence for resource limitation in the case of mustard and only marginal effects for radish. We conclude that habitat connectivity is essential to maintain not only abundant and diverse bee communities, but a lso plant-pollinator interactions in economically important crops and endan gered wild plants.