Do Predators Structure Wetland Macroinvertebrate Assemblages? Different Effects of Mudminnows and Dragonfly Nymphs in Field Experiments

Abstract

Predation by small fish and invertebrates has been shown to influence wetland macroinvertebrates in various ways and to various degrees in different types of wetlands. I sought to determine whether predation could be a significant factor causing invertebrate-community variation along an elevation gradient in a Lake Huron coastal wetland. I conducted three month-long predator exclusion/inclusion field experiments in the wet-meadow portion of the wetland, where the water was shallow (20–30 cm) and hypoxic, and mudminnows and dragonfly nymphs were the most-abundant predators. Experiment results showed that mudminnows caused a significant decrease in abundance and diversity, but did not substantially alter relative proportions of different macroinvertebrate taxa. NMDS ordination confirmed this result. Meanwhile, dragonfly nymphs, even at high density, had no significant effects on macroinvertebrate abundance, diversity, or relative abundances of different taxa. These results suggest that, while fish are capable of reducing prey abundance, neither they nor dragonfly nymphs played a significant role in causing the wet-meadow macroinvertebrate assemblage to differ from others in this wetland.