Predator effects on prey population dynamics in open systems |
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Authors: | Barbara L Peckarsky Billie L Kerans Brad W Taylor Angus R McIntosh |
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Institution: | (1) Department of Zoology and Entomology, University of Wisconsin, Madison, WI 53706, USA;(2) Rocky Mountain Biological Laboratory, P.O. Box 519, Crested Butte, CO 81224, USA;(3) Department of Ecology, Montana State University, Bozeman, MT 59717, USA;(4) Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA;(5) School of Biological Sciences, University of Canterbury, Christchurch, New Zealand |
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Abstract: | Animal population dynamics in open systems are affected not only by agents of mortality and the influence of species interactions
on behavior and life histories, but also by dispersal and recruitment. We used an extensive data set to compare natural loss
rates of two mayfly species that co-occur in high-elevation streams varying in predation risk, and experience different abiotic
conditions during larval development. Our goals were to generate hypotheses relating predation to variation in prey population
dynamics and to evaluate alternative mechanisms to explain such variation. While neither loss rates nor abundance of the species
that develops during snowmelt (Baetis bicaudatus) varied systematically with fish, loss rates of the species that develops during baseflow (Baetis B) were higher in streams containing brook trout than streams without fish; and surprisingly, larvae of this species were
most abundant in trout streams. This counter-intuitive pattern could not be explained by a trophic cascade, because densities
of intermediate predators (stoneflies) did not differ between fish and fishless streams and predation by trout on stoneflies
was negligible. A statistical model estimated that higher recruitment and accelerated development enables Baetis B to maintain larger populations in trout streams despite higher mortality from predation. Experimental estimates suggested
that predation by trout potentially accounts for natural losses of Baetis B, but not Baetis bicaudatus. Predation by stoneflies on Baetis is negligible in fish streams, but could make an important contribution to observed losses of both species in fishless streams.
Non-predatory sources of loss were higher for B. bicaudatus in trout streams, and for Baetis B in fishless streams. We conclude that predation alone cannot explain variation in population dynamics of either species;
and the relative importance of predation is species- and environment-specific compared to non-predatory losses, such as other
agents of mortality and non-consumptive effects of predators.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Mortality Non-consumptive effects Open systems Predation Recruitment |
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