Abstract
Understanding biodiversity distribution is a primary goal of community ecology. At a landscape scale, bee communities are affected by habitat composition, anthropogenic land use, and fragmentation. However, little information is available on local-scale spatial distribution of bee communities within habitats that are uniform at the landscape scale. We studied a bee community along with floral and nesting resources over a 32 km2 area of uninterrupted Mediterranean scrubland. Our objectives were (i) to analyze floral and nesting resource composition at the habitat scale. We ask whether these resources follow a geographical pattern across the scrubland at bee-foraging relevant distances; (ii) to analyze the distribution of bee composition across the scrubland. Bees being highly mobile organisms, we ask whether bee composition shows a homogeneous distribution or else varies spatially. If so, we ask whether this variation is irregular or follows a geographical pattern and whether bees respond primarily to flower or to nesting resources; and (iii) to establish whether body size influences the response to local resource availability and ultimately spatial distribution. We obtained 6580 specimens belonging to 98 species. Despite bee mobility and the absence of environmental barriers, our bee community shows a clear geographical pattern. This pattern is mostly attributable to heterogeneous distribution of small (<55 mg) species (with presumed smaller foraging ranges), and is mostly explained by flower resources rather than nesting substrates. Even then, a large proportion (54.8%) of spatial variability remains unexplained by flower or nesting resources. We conclude that bee communities are strongly conditioned by local effects and may exhibit spatial heterogeneity patterns at a scale as low as 500–1000 m in patches of homogeneous habitat. These results have important implications for local pollination dynamics and spatial variation of plant-pollinator networks.
Highlights
From a strictly theoretical perspective, a community may be defined as the assemblage of species occupying an area within which all individuals are likely to interact, hindering spatial heterogeneity in distribution or abundance [1]
Rosmarinus officinalis was more or less evenly distributed throughout the park, whereas D. pentaphyllum was most abundant in the north-western edge
The Garraf bee community shows a clear spatial pattern at the habitat scale, with different species dominating in different plots separated by as few as 500–1000 m
Summary
From a strictly theoretical perspective, a community may be defined as the assemblage of species occupying an area within which all individuals are likely to interact, hindering spatial heterogeneity in distribution or abundance [1]. From a more deterministic perspective, species composition is expected to be closely related to this within-habitat heterogeneity, for example in resource availability [2]. Different species may respond to resource distribution at different scales. Local community structure is further shaped by species’ functional traits, such as dispersal ability, and by interactions between species resulting in either avoidance or attraction [5]. Community structure may be historically contingent, so that even under similar environmental conditions, different species assemblages may arise as a result of different immigration history or disturbance events [6]
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