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Keywords:

  • Distribution;
  • habitat mosaic;
  • suitability;
  • climate;
  • energy economics;
  • community structure;
  • Bombus.

ABSTRACT.

  • 1
    Analysis of surveys of bumble bee distribution among 2 km grid-squares in Kent revealed that some species are nearly ubiquitous among localities and abundant within each. For these ubiquitous species, Kent is near the middle of their latitudinal ranges.
  • 2
    The other species have very restricted distributions among localities and are less abundant where they occur. For each of these local species, Kent is near the margin of its latitudinal range.
  • 3
    The areas to which the local species are restricted are characterized by only a few of the many kinds of vegetation represented in Kent (shingle, sand dune, saltmarsh or old meadow). The ubiquitous species are also more abundant in areas with these kinds of vegetation.
  • 4
    A random model (Gause, 1936) and the core/satellite hypothesis (Hanski, 1982a) were proposed to explain similar patterns of distribution. I conclude that their assumptions are not well supported by the results of the present analysis.
  • 5
    A marginal mosaic model (after Andrewartha & Birch, 1954; Hengeveld & Haeck, 1981; Brown, 1984) is used to account for these patterns. This model depends on environmental factors (including resource levels and climate) affecting the economics of energy and, consequently, local persistence.
  • 6
    It follows from the marginal mosaic model that if the level of limiting resources in a habitat declines, then it is the species closest to their distribution limits that are most likely to face local extinction. These selective extinctions would result in a form of ‘community structure’.