Variation in communities of dipterans in Nepenthes pitchers in Singapore: Predators increase prey community diversity

Abstract

Variation in 14 aquatic communities of dipterans in pitchers of 3 Nepenthes species was studied in Singapore. Communities in 3 clumps of Nepenthes ampullaria Jack included 3 large aquatic predators, Toxorhynchites acaudatus (Leicester), Nepenthosyrphus sp., and Nepenthomyia sp. In communities in 2 clumps of Nepenthes rafflesiana Jack, another large aquatic predator, Pierretia sp., occurred at low rates; but the remaining 9 communities (3 N. ampullaria, 2 N. rafflesiana, and 4 N. gracilis Korth. clumps) lacked large aquatic predators. In 3 N. ampullaria communities with large aquatic predators, phorid density was low and 4-5 filter-feeder mosquito species coexisted. There, filter feeder communities were dominated by Tripteroides nepenthis (Edwards) and Uranotaenia moultoni Edwards; Tripteroides tenax (Meijere) and Culex eminentia (Leicester) together occupied <10%. In contrast, 11 other filter feeder communities were monopolized by T. tenax (3 communities), inhabited only by T. tenax and C. eminentia (3 communities), or T. tenax or C. eminentia (or both), occupied >88% of 2-3 species (5 communities). Unique prey community structure in N. ampullaria clumps with large aquatic predators was attributed at least partly to selective removal of superior competitors by the predators and resultant colonization of inferior competitors more resistant to predation.