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Lycaena dispar is recorded as an early case of extinction and subsequent re-introduction in the UK. However, repeated establishment attempts have not resulted in self-sustaining populations, including those having taken place at Woodwalton Fen (Cambridgeshire, UK). Earlier studies at Woodwalton Fen showed that the highest mortalities occurred between the egg stage and resumption of larval feeding in spring. This study was designed; firstly, to investigate factors causing field mortality during different larval stages; secondly, to compare survival on Rumex hydrolapathum foodplants in different habitat situations; and thirdly, to compare survival in a natural population (Weerribben, The Netherlands) with the introduced Woodwalton Fen population. Experiments employed exclusion cages in order to examine the relative roles of vertebrate and invertebrate natural enemies, and survival on food-plants in open fen and waterside situations was compared. Results suggest invertebrate predation to be the dominant mortality factor acting upon pre-diapause larvae. Over the winter diapause natural enemies do not have a significant role. However during both these stages losses still occur that are unaccounted for. Extensive winter flooding appears to increase overwintering losses. Vertebrate predators cause significant mortality of post-diapause larvae. No significant difference was found between larval survival on open fen versus waterside plants. Comparison of introduced and native populations reveal that overwintering survival was significantly higher in the latter; potential reasons for this difference are discussed.
Ecography © 1996 Nordic Society Oikos