Distribution, Abundance and Oviposition Patterns of Four Coexisting Chiastocheta Species (Diptera: Anthomyiidae)

Abstract

The distribution, abundance and oviposition pattern of four Chiastocheta species were investigated in relation to coexistence. The species occur sympatrically and are confined to patches of the perennial herb Trollius europaeus, on which the larvae act as seed predators. The relative abundances of the species were constant at large patch sizes, but fluctuating at small patch sizes. However, in all species the population sizes were correlated to patch size. Overall population sizes of C. dentifera and C. trollii were not different from each other, but significantly higher than that of C. inermella. All three had significantly higher overall population sizes than C. abruptiventris. All species were present in patches with more than 2000 flower heads. Chiastocheta dentifera was the species occurring at the fewest patches, followed by C. abruptiventris. Chiastocheta inermella and C. trollii were present in all but one patches. C. inermella was dominant at small patch sizes. At middle and large patch sizes C. trollii replaced C. inermella as the most abundant species. Within patches the relative abundance of C. dentifera became higher throughout the season, while that of C. trollii declined. Chiastocheta abruptiventris and C. inermella showed no seasonal pattern in relative abundances. Aggregated eggs distributions seemed only to influence coexistence of one species pair, C. dentifera - C. trollii. Covariance estimates of the egg distributions between species pairs showed that the estimate for C. dentifera/C. trollii was negative, C. dentifera/C. inermella was random and C. trollii/C. inermella was positive. Eggs of C. abruptiventris were spaced in a regular pattern with, on average, one egg on every second flower having no effect on the other species.