An Invasive Whelk As Predator And Prey

Author : Christopher Kent Kwan
Publisher :
ISBN 13 : 9781339825908
Total Pages : pages
Book Rating : 4.8/5 (259 download)

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Download or read book Impact of Copper Pollutants and Environmental Factors on Predator-prey Interactions in Marine Food Chains written by Christopher Kent Kwan and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Predators scare and eat prey, and the consequences of predators on community structure and ecosystem function depend largely on the relative importance of these two activities. An increasing trend in recent ecological research is a focus on fear, the predator non-consumptive effects on prey. A single predator may scare off many more prey than it can eat, especially if many prey individuals can detect it from far away. Predator non-consumptive effects often alter prey physiology, behavior, and morphology. These effects may translate into changes in community structure and ecosystem function. Although there is an emerging appreciation for the context-dependency of these interactions, we lack an understanding about how these interactions change with increasing anthropogenic stress--particularly chemical pollution. The prevalence of chemical pollution in coastal habitats combined with its potential to disrupt predator-prey interactions suggest that we must better understand how these stressors impact species interactions and in turn, ecosystem function. The consequences of sublethal pollutant levels on a single species may manifest themselves throughout the community. I addressed these issues by conducting laboratory and field experiments studying the impacts of sub-lethal copper levels and environmental factors on the species interactions in marine food chains. In Chapter 1, I tested the influence of chemical pollutants on predator-prey interactions because recent evidence suggests that pollutants may shift the role of consumptive and non-consumptive effects of predators. However, this hypothesis has not been tested directly by comparing predator consumptive and non-consumptive effects in polluted versus non-polluted settings. I used laboratory mesocosms to examine the influence of elevated copper pollution on the effects of crab predators in an estuarine food chain with intermediate whelk prey and basal barnacle resources. I examined predator consumptive effects (prey culled without predator chemical cues), non-consumptive effects (prey not culled and received predator chemical cues), and total effects (prey culled and received predator chemical cues). Although copper switched the relative importance of these effect types, the nature of this switch contrasted with our original prediction. Rather than decreasing whelk response to predator cues, copper compromised whelk responses to changes in conspecific density caused by simulated lethal predation. Specifically, reductions in conspecific density occurring in elevated copper levels did not trigger the normal increase in whelk consumption rates. Because intermediate copper concentrations did not change the effects of fear, these data suggest that copper decreased the relative importance of predator consumptive effects. However, this shift was not apparent at extremely high copper levels where non-consumptive effects also diminished. Given the prevalence of conspecific interactions among prey, disruption of these interactions at sublethal pollution levels may commonly influence predator impacts on their communities. In Chapter 2, I examined the extent to which pollutant effects are generalizable across food chains, since the increase of these anthropogenic stressors poses immense threats to the marine environment. Recent work indicates sublethal pollutant levels change organism behavior and species interactions. However, we have limited understanding of these pollutant impacts in terms of how long these effects last and whether different organisms are affected in similar ways. To address these gaps, I studied copper pollutant effects on the species interactions of two different marine food chains for extended durations. Both food chains consisted of predatory crabs, whelks, and barnacles. I examined the long-term impact of copper pollution on crab non-consumptive effects on whelk consumption of barnacles. For both food chains, in the absence of copper, crab cues induced predator avoidance behaviors in whelks and reduced their consumption on barnacles. In the food chain consisting of whelks from the open coast with lower exposure to pollutants, there were no effects of copper on whelks. For the food chain consisting of whelks from enclosed estuaries with greater exposure to pollutants, copper influenced whelk responses to crabs initially by increasing whelk consumption during exposure to crab cues. But this antagonistic effect between copper and crab cues on whelks attenuated after two weeks. My results show chemical contaminants may impact food chains differently, perhaps due to the evolutionary history of the component species, or their prior exposure to pollutants. In Chapter 3, I investigated the context-dependency of predator non-consumptive effects in the field, in light of the growing awareness that species interactions can be highly dependent on the environmental conditions in which they occur. The strength and direction of these interactions are often impacted by abiotic factors and human-caused stressors. However, there have been few studies conducted in the field to examine the influence of these variables on predator non-consumptive effects on prey. I conducted two field experiments investigating whether environmental conditions influence the strength of predator-non-consumptive effects in two different food chains. I tested the influence of ambient conditions on the non-consumptive effects of predatory crabs on whelk prey, which in turn feed on a basal resource of barnacles. I conducted a field experiment in San Francisco Bay to investigate whether differences in abiotic factors and pollutant levels among three sites would influence predator non-consumptive effects of crabs on their invasive whelk prey which feeds on barnacles. My data suggest the strength of predator non-consumptive effects varied among San Francisco Bay sites. Specifically, crab cues reduced whelk consumption of barnacles at two sites but did not have an effect at a third site. I found slightly warmer water at this one site, which may have weakened the predation risk caused by crab cues. Although whelks at this warmer site consumed more barnacles, they had a low growth efficiency that may be due to the higher metabolic demands of coping with warmer temperatures and relatively high pollution at this site. In another field experiment, I quantified the effects of predatory crab cues on whelk predation and growth rates at two sites in Bodega Harbor, CA. I found vastly different results between both Bodega Harbor sites. Namely, the presence of crabs lowered whelk consumption rates of barnacles at one site, but had no effect at the other site. Collectively, the results from all of our laboratory and field studies underscore the notion that predator-prey interactions are often context-dependent, and may especially be influenced by a highly variable, human-impacted environment. Understanding the relative effects of consumptive effects and non-consumptive effects in structuring ecological communities improves our abilities to predict and manage changes to species distributions in the face of anthropogenic stressors such as climate change, overfishing, species invasions, habitat alterations, and pollution. More specifically, a better understanding of how organisms affect each other and how those relationships are altered by a changing environment is critical in preparing and implementing conservation measures.