Distribution and density of larval fly population in pitcher plant leaves (Sarracenia purpurea L.): implication for competitive and commensal interactions.

Abstract

Populations of species are affected by other species or by individuals of their own species. This study examines the distribution and relationship of three different Diptera larvae (Wyeomyia smithii, Metriocnemus knabi, Bleasoxipha fletcheri) in the pitcher plant (Sarracenia purpurea) in Waldron Fen, Emmet County, Michigan. A total of 168 pitcher plants were sampled within a 30m x 40 m transect. A frequency of 0.63 for W. smithii, 0.35 for M. knabi, and 0.01 for B. fletcheri was reported. The meager occurrence of B. fletcheri let to its exclusion from any correlations done. A Mann-Whitney U test indicated that the difference between the means of average length of larvae/volume of pitcher of W. smithii alone and W. smithii in the presence of M. knabi was not statistically different. However, the difference between the means of M. knabi alone and M. knabi in the presence of W. smithii was statistically different. The mean larval density of the larvae and associations was calculated by dividing the larval number by plant content volume (ml). The difference between means of W. smithii alone and W. smithii in the presence of M. knabi was not significantly different. The difference between the means of M. knabi alone and M. knabi in the presence of W. smithii was also not significantly different. The volume of the leaves was significantly correlated to the occurrence of the species. A correlation also occurred between density and species occurrence. Based on these data there seemed to be evidence that competition may be taking place between larvae.