Steffan-Dewenter I, Tscharntke Teja
Agroecology, University of Göttingen, Waldweg 26, D-37073 Göttingen, Germany e-mail:
Oecologia. 1999 Nov;121(3):432-440. doi: 10.1007/s004420050949.
Destruction and fragmentation of natural habitats is the major reason for the decreasing biodiversity in the agricultural landscape. Loss of populations 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 established 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 grasslands 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 (Raphanus sativus). Increasing isolation of the small habitat islands resulted in both decreased abundance and species richness of flower-visiting bees (Hymenoptera: Apoidea). Mean body size of flower-visiting wild bees was larger on isolated than on nonisolated habitat islands emphasizing the positive correlation of body size and foraging distance. Abundance of flower-visiting honeybees depended on the distance from the nearest apiary. Abundance of other flower visitors such as hover flies did not change with increasing isolation. Number of seeds per fruit and per plant decreased significantly with increasing distance from the nearest grassland for both mustard and radish. Mean seed set per plant was halved at a distance of approximately 1000 m for mustard and at 250 m for radish. In accordance with expectations, seed set per plant was positively correlated with the number of flower-visiting bees. 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 also plant-pollinator interactions in economically important crops and endangered wild plants.
自然栖息地的破坏和碎片化是农业景观中生物多样性下降的主要原因。种群数量的减少可能会对生物相互作用和生态系统稳定性产生负面影响。在此，我们检验了这样一个假设：栖息地碎片化会影响蜜蜂种群，进而破坏植物 - 传粉者之间的相互作用。我们在八个钙质草原以及集约化管理的农业景观中，通过实验建立了两个自交不亲和的一年生十字花科植物的小型“栖息地岛屿”，这些“栖息地岛屿”距离物种丰富的草原越来越远（最远达1000米），以测量隔离对传粉者类群和结实率的影响，该影响独立于斑块大小和密度、资源可用性以及植物种群的遗传侵蚀。每个栖息地岛屿由四个花盆组成，每个花盆中有一株芥菜（Sinapis arvensis）和萝卜（Raphanus sativus）。小型栖息地岛屿隔离程度的增加导致访花蜜蜂（膜翅目：蜜蜂总科）的数量和物种丰富度均下降。在隔离的栖息地岛屿上，访花野生蜜蜂的平均体型比未隔离的栖息地岛屿上的更大，这强调了体型与觅食距离之间的正相关关系。访花蜜蜂的数量取决于与最近蜂房的距离。其他访花者（如食蚜蝇）的数量并未随着隔离程度的增加而改变。对于芥菜和萝卜而言，每个果实和每株植物的种子数量均随着与最近草原距离的增加而显著减少。芥菜在距离约1000米处，每株植物的平均结实率减半；萝卜在距离250米处，每株植物的平均结实率减半。正如预期的那样，每株植物的结实率与访花蜜蜂的数量呈正相关。我们没有发现芥菜存在资源限制的证据，而萝卜仅有边际效应。我们得出结论，栖息地连通性不仅对于维持丰富多样的蜜蜂群落至关重要，对于维持经济上重要的作物和濒危野生植物的植物 - 传粉者相互作用也至关重要。
