Drought alters the trophic role of an opportunistic generalist in an aquatic ecosystem
Abiotic change can alter species interactions by modifying species’ trophic roles, but this has not been well studied. Until now, bromeliad-dwelling tipulid larvae were thought to positively affect other macroinvertebrates via a facilitative processing chain. However, under drought, we found the opposite. We performed two microcosm experiments in which we factorially manipulated water level and predation by tipulids, and measured the effects on mosquito and chironomid larvae. The experiments differed in whether high water was contrasted with low or no water, allowing us to distinguish between the effects of desiccation stress (no water) and increased encounter rates due to compression of habitat or reductions in prey mobility (low and no water). We also included a caged tipulid treatment to measure any non-consumptive effects. As well as directly reducing prey survival, reductions in water level indirectly decreased chironomid and mosquito survival by altering the trophic role of tipulids. Our results suggest that increased encounter rates with prey led to tipulids becoming predatory under simulated drought, as tipulids consumed prey under both low and no water. When water level was high, tipulids exerted negative non-consumptive effects on prey survival. Because opportunistic predators are common throughout aquatic ecosystems, the effects of drought on the trophic roles of species may be widespread. Such restructuring of food webs should be considered when attempting to predict the ecological effects of environmental change.
KeywordsInsects Microcosm experiment Precipitation Tank bromeliad Trophic plasticity
We thank the Monteverde Cloud Forest Reserve, the Children’s Eternal Rain Forest Reserve, and the University of Georgia (Costa Rica Campus) for providing us with collection sites and offering logistical support. Thank you to Nestor Guevara and Randall Zamora Castro for helping with field work, and to Bill Haber, Alan Pounds, Frank Joyce, and Mary and Elias Newswanger for advice and logistical support. Comments from Rachel Germain, Angie Nicolas, and Natalie Westwood improved this manuscript. Funding was provided by a Natural Sciences and Engineering Research Council of Canada (NSERC) CGS-D Grant and a NSERC MSFSS Grant to S. L. Amundrud, a NSERC Discovery Grant to D. S. Srivastava, and by the Agence Nationale de la Recherche (ANR) through the Rainwebs project to Régis Céréghino, Céline Leroy, Bruno Corbara, Jean-François Carrias and D. S. Srivastava. All work was performed under MINAE research permits (034-2015-INV-ACAT and 041-2016-INV-ACAT). This is a publication of the Bromeliad Working Group.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable institutional and/or national guidelines for the care and use of animals were followed.
Data are available from the KNB Digital Repository: https://doi.org/10.5063/F1ZC8145
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