Efeitos e mecanismos relacionados à redução do tamanho do habitat aquático sobre a interação predador-presa

Abstract

A reduction in aquatic habitat size facilitates encounters between predators and prey by reducing the height of the water column, which reduces the vertical space of prey displacement, and by reducing the volume of water, which concentrates prey. However, no study has determined the effects of these mechanisms on predator-prey interactions. The goal of this study was to evaluate the effects of reducing these mechanisms on the predation rates and on the parameters of functional response curves of predators with different foraging modes. We paired active-search predators (Buenoa sp., Hemiptera) or ambush predators (Pantala flavescens and Lestes sp., Odonata) with prey of different mobility types in the water column (Argyrodiaptomus paggi, Copepoda; Culex sp., Diptera). Each predator-prey interaction occurred under three different treatments: high water-column height and high water volume (H+V+), low water-column height and high water volume (H-V+) and low water-column height and low water volume (H-V-). In the first experiment, 1 predator interacted for 24 hours with a fixed abundance of prey of the same species, and predation rates were obtained. In the second, 1 predator interacted for 2 hours with different abundances of prey of the same species, and functional response curves were obtained. We used contrast analysis to separate the effects of the water-column height (H+, H-) and water volume (V+; V-). Predation rates were higher in V- than in V+ for Pantala and Buenoa consuming Argyrodiaptomus. We observed an increase in attack rates and a decrease in handling time in the functional response curves in V- in relation to V+ for Pantala and Lestes consuming Argyrodiaptomus. There was no significant difference between H+ and H- or V+ and V- with Culex. We concluded that the reduction in the water volume was the primary mechanism responsible for the changes in the interactions between predators and prey and that the effects of the reduction in the water volume depended on the behaviour of the prey and predator foraging modes. Of the predators, ambush predators were the most benefited, and of the prey, highly mobile prey were the most consumed under low water volume conditions. Thus, the reduction in aquatic habitat size can cause changes in the trophic structure of aquatic environments.