COEXISTENCE OF 2 LEAF-BEETLES IN THE SAME FUNDAMENTAL NICHE - DISTRIBUTION, ADULT PHENOLOGY AND OVIPOSITION

This study investigated the coexistence of two leaf-beetles, Galerucel la calmariensis and G. pusilla, on purple loosestrife (Lythrum salicar ia). G. pusilla and G. calmariensis share their distribution on a cont inental, regional, and local scale. Models of stable coexistence of tw o competitors assume access of inferior species to resources or refuge s that are temporarily or spatially unexploited by the superior specie s. Field and laboratory studies indicated that both species have inclu sive fundamental niches on their host plant. Cytological studies and c rossing experiments confirmed their status as true, reproductively iso lated species. G. calmariensis and G. pusilla showed no differences in adult phenology, winter mortality, colonization pattern nor ovipositi on, thus no temporal variation in resource use. Adults aggregated at t he same sites and on the same host plant individuals and their distrib utions are not independant. Aggregation or differences in resource use do not appear to play an important role in the coexistence of G. calm ariensis and G. pusilla. This study indicated that both species have i dentical competitive abilities.