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Abstract The capacity of an apex predator to produce nonconsumptive effects (NCEs) in multiple prey trophic levels can create considerable complexity in nonconsumptive cascading interactions, but these effects are poorly studied. We examined such effects in a model food web where the apex predator (blue crabs) releases chemical cues in urine that affect both the intermediate consumer (mud crabs seek shelter) and the basal prey (oysters are induced to grow stronger shells). Shelter availability and predator presence were manipulated in a laboratory experiment to identify patterns in species interactions. Then, experimentally induced and uninduced oysters were planted across high‐quality and low‐quality habitats with varying levels of shelter availability and habitat heterogeneity to determine the consistency of these patterns in the field. Oyster shell thickening in response to blue crab chemical cues generally protected oysters from mud crab predation in both the laboratory and in field environments that differed in predation intensity, structural complexity, habitat heterogeneity, and predator composition. However, NCEs on the intermediate predator (greater use of refugia) opposed the NCEs on oyster prey in the interior of oyster reefs while still providing survival advantages to basal prey on reef edges and bare substrates. Thus, the combined effects of changing movement patterns of intermediate predators and morphological defenses of basal prey create complex, but predictable, patterns of NCEs across landscapes and ecotones that vary in structural complexity. Generalist predators that feed on multiple trophic levels are ubiquitous, and their potential effects on NCEs propagating simultaneously to different trophic levels must be quantified to understand the role of NCEs in food webs.
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Environmental forcing and predator consumption outweigh the nonconsumptive effects of multiple predators on oyster reefs
Abstract The ability to predict how predators structure ecosystems has been shown to depend on identifying both consumptive effects (CEs) and nonconsumptive effects (NCEs) of predators on prey fitness. Prey populations may also be affected by interactions between multiple predators across life stages of the prey and by environmental factors such as disturbance. However, the intersection of these multiple drivers of prey dynamics has yet to be empirically evaluated. We addressed this knowledge gap using eastern oysters (Crassostrea virginica), a species known to suffer NCEs, as the focal prey. Over 4 months, we manipulated orthogonally the life stage (none, juvenile, adult, or both) at which oysters experienced simulated predation (CE) and exposure to olfactory cues of a juvenile oyster predator (crab), adult predator (conch), sequentially the crab and then the conch, or none. We replicated this experiment at three sites along an environmental gradient in a Florida (USA) estuary. For both juvenile and adult oysters, survival was reduced solely by CEs, and variation in growth was best explained by among‐site variation in water flow, with a much smaller and negative effect of predator cue. Adults exposed to conch cue exhibited reduced growth (an NCE), but this effect was outweighed by a positive CE on growth: Surviving oysters grew faster at lower densities. Finally, conch cue reduced larval settlement (another NCE), but this was swamped by among‐site variation in larval supply. This research highlights how strong environmental gradients and predator CEs may outweigh the influence of NCEs, even in prey known to respond to predator cues. These findings serve as a cautionary tale for the importance of evaluating NCE processes over temporal scales and across environmental gradients relevant to prey demography.
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- PAR ID:
- 10443052
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology
- Volume:
- 101
- Issue:
- 7
- ISSN:
- 0012-9658
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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