Cascata trófica e respostas fisiológicas de Astyanax (Characiformes) quando ameaçados por piscívoros de diferentes estratégias de caça.

Abstract

Predation is an important modulator interaction of populations and aquatic communities. Assuming that hunting modes of piscivores fish (sit-and-wait and active pursuit) result in different anti-predation behavior by prey. We aimed to investigate how behavior changes affect the survival of aquatic invertebrates and the selectivity of these fish for invertivores, and possible physiological changes that can occur in invertivores fish when confronted with different predators. To this end, we develop two experiments. The first evaluates the survival of two different types of aquatic invertebrates (Chironomus sancticaroli - benthic and Daphnia magna - planktonic) in a chain composed by invertivore Astyanax altiparanae end with piscivores Hoplias aff. malabaricus (sit-and-wait) and Astronotus crassipinnis (active pursuit), combined in environments with and without aquatic plants. The second experiment evaluates the physiological changes (cortisol and glucose levels) of Astyanax bimaculatus in response to same piscivores, and the role of underwater visibility condition that interaction. We showed that proportion of invertebrates consumed was dependent on the hunting modes type of piscivores. The presence of aquatic plants increased the survival of aquatic invertebrates, except in the treatments with A. crassipinnis. Considering physiological responses of fish invertivores, we showed that the presence of piscivores caused an increase in plasma levels of cortisol in A. bimaculatus, however, there was no significant difference between treatments with two types of piscivores. On the other hand, no significant change was observed for the plasma glucose levels, as well as no changes were found between clear and turbid water treatments. We conclude that hunting modes of piscivores affect differently the food chain, however plasma levels of cortisol and glucose by invertivores for both piscivores are similar and independent of anti-predation behavior.