The geographical range structure of the holly leaf-miner. II. Demographic rates

Summary

• 1
  Few studies have sought to document the variation in demographic rates exhibited by local populations across the geographical range of a species. None the less, such information has the potential to yield insights into the factors that determine the internal abundance structure of ranges.
• 2
  Major components of demographic rates are reported here for the holly leaf-miner Phytomyza ilicis Curtis across its natural geographical range in Europe, including areas at each of the extreme limits and at the core of its occurrence.
• 3
  Correlograms reveal that a number of these components exhibit significant spatial structure across the geographical range and, in conjunction with interpolated maps, suggest that some of these patterns are, in terms of broad trends, reasonably simple.
• 4
  Across the whole range, individual mortality components are largely independent of one another and of leaf-miner population densities, often exhibiting very different spatial patterns. Thus, P. ilicis populations experience markedly different mortality profiles across the range.
• 5
  While some correlations between broad-scale environmental variation and the components of demographic rates were found, it was not possible to separate these effects from shared spatial structure.
• 6
  In sum, the contribution of different components of demographic rates to local densities varies markedly across the geographical range of P. ilicis, and in isolation the pattern observed in any one locality provides limited information on what is occurring elsewhere, but these components none the less often exhibit systematic geographical patterns of variation.