title: An acute trophic cascade among microorganisms in the tree hole ecosystem following removal of omnivorous mosquito larvae.
abstract: Results of two field experiments showed that selective removal of omnivorous mosquito larvae (Aedes triseriatus(Say)) functioning as top predators in the food web of a temperate, tree hole ecosystem resulted rapidly in increased abundance of flagellate and then ciliate populations. Flagellate density increased from <1 per ml to >103per ml within 4 days of omnivore removal, followed shortly thereafter by an increase in ciliate density from <1 per ml to >102per ml, after which flagellate density declined, and flagellate and ciliate densities stabilized. Rod-shaped bacteria increased slightly in density after removal of larval mosquitoes, then declined as protist density increased. Cocciform bacteria did not vary in density with these changes, thus the trophic cascade dampened at the remotest trophic level. Concomitant with the increase in protist densities, some bacteria formed elongated filaments >10 μm in length, likely an anti-predation, morphological response stimulated by suddenly intensified grazing as protozoan density rose. Results suggest that feeding by omnivorous mosquito larvae exhibited strong top-down effects on flagellate and ciliate populations, depressing them to below their equilibrium densities and nearly to extinction in tree hole ecosystems.
authors.affiliation: Department of Microbiology and Molecular Genetics, 2215 Biomedical and Physical Sciences Building, Michigan State University, East Lansing, MI 48824 USA ; Department of Entomology, Michigan State University, East Lansing MI 48824.
authors.forename: E D
authors.initials: ED
authors.lastname: Walker
authors.affiliation: Department of Entomology, Michigan State University, East Lansing MI 48824.
authors.forename: M G
authors.initials: MG
authors.lastname: Kaufman
authors.affiliation: Department of Entomology, Michigan State University, East Lansing MI 48824.
authors.forename: R W
authors.initials: RW
authors.lastname: Merritt
keywords: Food web; Omnivory; Tree holes; Trophic cascade