Date of Award

Spring 1992

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

First Advisor

James F Haney

Abstract

Littoral planktonic communities have rarely been included in food web dynamics and predator/prey behavior studies of planktonic communities of fresh water ecosystems. Polyphemus pediculus, a typically littoral predaceous cladoceran, is common in lakes and ponds throughout the northern temperate zone.

The patchy distribution of Polyphemus in littoral surface waters necessitates the use of a stratified random sampling regime to estimate and monitor Polyphemus populations. The population in Mirror Lake, NH, increased exponentially after the first appearance of parthenogenetic juveniles in late April. An abrupt decline in the population coincided with the movement of small Micropterus dolomieui fry into littoral areas in early June. Gut analyses indicated the small fry were eating Polyphemus but as they grew their diet changed to larger insect larvae and the Polyphemus population increased. Reproduction was entirely parthenogenetic until males appeared in late summer. Females carried resting eggs until the population disappeared in November.

Active aggregation behavior coincided with distinct horizontal movements toward shore over sunset, away from shore over sunrise. A comparison of diel movements of Polyphemus populations in two New Hampshire lakes supports the predator avoidance hypothesis.

Diel feeding rates of Polyphemus were studied in four-hour intervals with a differential count method. A multichambered predation trap accommodated three simultaneous feeding experiments and a control. Three different Polyphemus densities were used during each feeding experiment to represent the natural density range.

Polyphemus are diurnal feeders, more than 90% feeding occurring between sunrise and sunset. Polyphemus appear to select small, vulnerable prey (Polyarthra and individual Conochilus) over small prey with protective structures (Kellicottia). Feeding rates were highest for Vorticella that lived on Anabena colonies. Polyarthra and Conochilus constituted more than 70% of food ingested.

At patch densities feeding rates decreased and evidence of cannibalism was observed indicating that Polyphemus' aggregation behavior does not benefit feeding activities.

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