MODENUTTI Beatriz Estela
Influence of different chemical signals on the habitat selection of three zooplankters of Andean Patagonian ponds.
Wiley Interscience
Año: 2009 vol. 54 p. 480 - 494
1. Zooplankton may react differently to chemical signals produced by macrophytes inshallow systems. They may be attracted by macrophytes, as the plants may be used as arefuge against predators, or the plants may have a repellent effect (e.g. when the plants area habitat for numerous invertebrate predators or fish). In fishless Patagonian ponds, thestructural complexity provided by macrophytes modulates the rate of predation onzooplankton by the invertebrate predator Mesostoma ehrenbergii (Turbellaria).2. We performed a field study to analyse the coexistence of M. ehrenbergii and three of itsprey (two copepods, the calanoid Boeckella gracilis and the cyclopoid Acanthocyclopsrobustus, and the cladoceran Ceriodaphnia dubia) in four ponds. In two of the ponds, wecarried out day and night sampling to evaluate the influence of macrophytes on thedistribution of these zooplankters.3. In laboratory experiments, we analysed the response of the zooplankters to the chemicalsignals produced by macrophytes (the emergent Juncus pallescens and the submergedMyriophyllum quitense), the predator M. ehrenbergii and the ‘alarm signal’ provided by ahomogenate of conspecifics.4. Our field studies demonstrated the coexistence of M. ehrenbergii and the selected preyin different seasons and that A. robustus and C. dubia choose the vegetated area (a mixedbed of J. pallescens and M. quitense) over the non-vegetated area. The habitat choiceexperiments indicated that the presence of M. ehrenbergii may directly affect the habitatselection of B. gracilis, because this zooplankter swam away from the predator. In addition,Mesostoma may indirectly affect the habitat selection of the cyclopoid copepod A. robustusand the cladoceran C. dubia as both zooplankters exhibited a negative response to thealarm signal produced by crushed conspecifics.5. The presence of the submerged M. quitense did not affect the horizontal movementsof any of the zooplankters studied. In contrast, the emergent macrophyte J. pallescenselicited a positive response of B. gracilis, suggesting that this aquatic plant may act as apredation refuge.6. Our results suggest that predator avoidance behaviour can occur in fishless environmentsin response to a tactile invertebrate predator like Mesostoma. In addition, therefuge effect of emergent macrophytes, enhancing the survival of pelagic zooplankters,may act as a key factor in stabilizing predator–prey interactions in fishless Patagonianponds, as has been widely recorded in northern temperate lakes with fish.