Influence of different chemical signal on habitat selection of three zooplankters of Andean Patagonian ponds

TROCHINE, C.; MODENUTTI, B.; BALSEIRO, E.

Punta del Este Uruguay

Congreso; Shallow Lakes Congress; 2008

Univ. Rep.

Prey may react to chemical stimuli produced by macrophytes, as they can be used as refuge against predation though, submerged macrophytes may have a repellent effect (i.e. they are habitat for numerous invertebrate predators). In fishless Patagonian wetlands, the structural complexity provided by macrophytes modulates the rate of predation of the invertebrate predator Mesostoma ehrenbergii.We perform a field study to analyze the coexistence of M. ehrenbergii and three selected prey (two copepods, the calanoid Boeckella gracilis and the cyclopoid Acanthocyclops rubustus and the cladoceran Ceriodahnia dubia) and the influence of macrophytes stands in the horizontal distribution of these zooplankters. Also, through an experimental design we analyzed the response of these zooplankters to the signals produced by macrophytes (the emergent Juncus pallescens and the submerged Myriophyllum quitense), the predator M. ehrenbergii and the alarm signal provided by a homogenate of conspecifics.We established the coexistence of M. ehrenbergii and the selected prey and that B gracilis adult choose the vegetated area over the non-vegetated one in natural habitats. The habitat choice experiments indicated that the presence of M. ehrenbergii may directly affect the habitat selection of B. gracilis since this zooplankter swam away from the predator. Besides, M. ehrenbergii may indirectly affect the habitat selection of the cyclopoid copepod A. robustus and the cladoceran C. dubia since both zooplankters had a negative response to the alarm signal produced by crushed conspecifics.The presence of the submerged M. quitense did not affect the horizontal movements of any of the studied zooplankters. Contrary, the experiments with the emergent macrophyte J. pallescens showed that this aquatic plant may act as refuge for B. gracilis.This current work suggests that a predator-avoidance behavior such as horizontal migration may be observed in fishless environments in response to a tactile invertebrate predator like Mesostoma. Besides, the refuge effect of emergent macrophytes, enhancing the survival of pelagic copepods as B. gracilis, may act as a key factor stabilizing the predator-prey interactions and may have an evolutionary background.