Annual and Long-Term Changes in a Population of the Wood White Butterfly Leptidea sinapis

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Abstract
(1) A life-table approach to the population ecology of the wood white butterfly is combined with a study of changes in its distribution amongst woodland rides (paths) over a period of 8 years. (2) Fecundity and early larval survial were the key factors determining annual fluctuations. Wet and cold weather during the flight period and early larval stages led to fewer adults in the following year. (3) Longer-term trends were associated with shading of the rides as the trees grew. Numbers were low in very open rides, peaked at 20-50% shade and were low in > 50% shade. (4) The suitability of rides was not a function of food-plant (Lathyrus pratensis) abundance. Structure of the food-plants in partially shaded areas increased oviposition. (5) Conventional life-tables using k factors may not always provide enough information for conservation. k-factor analysis elucidates annual flucutations but will rarely detect long-term trends caused by habitat changes. These may be of equal or greater interest, especially when they indicate a trend towards local extinction.