Spatial variation in the magnitude and functional form of density-dependent processes on the large skipper butterfly Ochlodes sylvanus

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Abstract

  1. Understanding the underlying ecological processes that govern population dynamics is essential for identifying the risk of extinction faced by a population. Ecological processes are driven by a number of different density-dependent and density-independent factors. Influential factors may vary between species and are often classified for large areas of a species' geographical range.
  2. Here we test the hypothesis that these factors vary on a relatively small spatial scale across a species' range. The population dynamics of the large skipper butterfly Ochlodes sylvanus is investigated for each 100 km2 region within its British range.
  3. Different forms of density dependence, including Allee effects, and different density-independent factors are found to influence population change significantly in different regions. The possible underlying mechanisms responsible for each are discussed.
  4. In addition to this qualitative spatial variation in influencing factors, the relative contribution of density dependence and density-independent factors to temporal dynamics within each region is quantified. As the range of O. sylvanus is crossed from north-west to east, there appears to be a switch from density independence being more influential to density dependence having a greater impact on population change.

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