| Functionally similar species may reduce conflict with each other through habitat partitioning. Notonectids are voracious aquatic insect predators with overlapping diets and typically similar habitat preferences. I examined ecology and interactions of the genera Buenoa and Notonecta , to determine whether spatial segregation is their primary mechanism for coexistence.; Buenoa's ecology is less well known than that of Notonecta, so first I investigated Buenoa's relationship with potential prey in the open water where it spends more time than Notonecta (Chapter 1). In pond enclosures, Buenoa reduced populations of the largest of this relatively small-bodied community. Laboratory feeding experiments confirmed that declines were likely due to direct predation (Chapter 2).; To determine habitat preference, I examined interactions of the notonectids in mesocosms with vegetation filling half the container (Chapter 3). The presence of the other genus did not influence habitat choice by either notonectid. Segregation was only partial during the day, and overlap was almost complete at night, due to Notonecta's propensity to move into the open water at night. Buenoa's lack of Notonecta avoidance may be related to Notonecta's versatility as a predator, which reduces the possibility for Buenoa to find reliable spatial refuge.; In intensive sampling of Johnson Pond I was unable to detect habitat differences between notonectids, possibly because of great variation from day to day (Chapter 4). However, the animal community as a whole increased its use of surface waters at night. This result is interesting in a fishless pond, as increased nocturnal conspicuousness of pond animals is usually attributed to nighttime relaxation of predation pressure by visually feeding fish. This phenomenon also occurred in 2 other ponds (Chapter 5).; Buenoa may not suffer much from Notonecta competition, as it preys efficiently on small animals that Notonecta cannot utilize. Notonectids have potential for increased conflict at night due to Notonecta's nocturnal open water use. Spatial refuge from predation is a ‘moving target’ for Buenoa and does not account for the common co-occurrence of these insects. Coexistence may be facilitated by natural daily variation, variety of prey resources, and individual behaviors that help Buenoa reduce encounters or avoid capture. |
