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Hay,
Mark E.
Hay,
Mark E.
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ItemHerbivore vs. nutrient control of marine primary producers: context-dependent effects(Georgia Institute of Technology, 2006-12) Burkepile, Deron E. ; Hay, Mark E.Pervasive overharvesting of consumers and anthropogenic nutrient loading are changing the strengths of top-down and bottom-up forces in ecosystems worldwide. Thus, identifying the relative and synergistic roles of these forces and how they differ across habitats, ecosystems, or primary-producer types is increasingly important for understanding how communities are structured. We used factorial meta-analysis of 54 field experiments that orthogonally manipulated herbivore pressure and nutrient loading to quantify consumer and nutrient effects on primary producers in benthic marine habitats. Across all experiments and producer types, herbivory and nutrient enrichment both significantly affected primary-producer abundance. They also interacted to create greater nutrient enrichment effects in the absence of herbivores, suggesting that loss of herbivores produces more dramatic effects of nutrient loading. Herbivores consistently had stronger effects than did nutrient enrichment for both tropical macroalgae and seagrasses. The strong effects of herbivory but limited effects of nutrient enrichment on tropical macroalgae suggest that suppression of herbivore populations has played a larger role than eutrophication in driving the phase shift from coral- to macroalgal-dominated reefs in many areas, especially the Caribbean. For temperate macroalgae and benthic microalgae, the effects of top-down and bottom-up forces varied as a function of the inherent productivity of the ecosystem. For these algal groups, nutrient enrichment appeared to have stronger effects in high- vs. low-productivity systems, while herbivores exerted a stronger top-down effect in low-productivity systems. Effects of herbivores vs. nutrients also varied among algal functional groups (crustose algae, upright macroalgae, and filamentous algae), within a functional group between temperate and tropical systems, and according to the metric used to measure producer abundance. These analyses suggest that human alteration of food webs and nutrient availability have significant effects on primary producers but that the effects vary among latitudes and primary producers, and with the inherent productivity of ecosystems.
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ItemReefer Madness: Drugs and Coral Reefs(Georgia Institute of Technology, 2006-11-11) Ludovice, Peter J. ; Hunt, William D. ; Hay, Mark E.Dr. Mark Hay of the Georgia Tech School of Biology will discuss the ecology of coral reefs and their connection to pharmaceuticals from the sea
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ItemChemically mediated competition between microbes and animals: microbes as consumers in food webs(Georgia Institute of Technology, 2006-11) Burkepile, Deron E. ; Parker, John D. ; Woodson, Clifton Brock ; Mills, Heath Jordan ; Kubanek, Julia ; Sobecky, Patricia A. ; Hay, Mark E.Microbes are known to affect ecosystems and communities as decomposers, pathogens, and mutualists. However, they also may function as classic consumers and competitors with animals if they chemically deter larger consumers from using rich food-falls such as carrion, fruits, and seeds that can represent critical windfalls to both microbes and animals. Microbes often use chemicals (i.e., antibiotics) to compete against other microbes. Thus using chemicals against larger competitors might be expected and could redirect significant energy subsidies from upper trophic levels to the detrital pathway. When we baited traps in a coastal marine ecosystem with fresh vs. microbe-laden fish carrion, fresh carrion attracted 2.6 times as many animals per trap as microbe-laden carrion. This resulted from fresh carrion being found more frequently and from attracting more animals when found. Microbe-laden carrion was four times more likely to be uncolonized by large consumers than was fresh carrion. In the lab, the most common animal found in our traps (the stone crab Menippe mercenaria) ate fresh carrion 2.4 times more frequently than microbe-laden carrion. Bacteria-removal experiments and feeding bioassays using organic extracts of microbe-laden carrion showed that bacteria produced noxious chemicals that deterred animal consumers. Thus bacteria compete with large animal scavengers by rendering carcasses chemically repugnant. Because food-fall resources such as carrion are major food subsidies in many ecosystems, chemically mediated competition between microbes and animals could be an important, common, but underappreciated interaction within many communities.
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ItemIntegrating prey defensive traits: contrasts of marine worms from temperate and tropical habitats(Georgia Institute of Technology, 2006-05) Kicklighter, Cynthia Ellen ; Hay, Mark E.Marine worms are speciose and numerically prominent members of marine communities where they play critical roles in trophic interactions and in affecting biogeochemical cycles. Despite the ecological importance of this group, little is known about their palatability to, and defenses against, consumers. In addition, most studies of prey defenses in marine organisms have focused on overt, sessile species: few studies have investigated more mobile and behaviorally complex species that could potentially be integrating predator deterrents with refuge use and other escape behaviors. To increase our understanding of consequences of defensive traits among mobile marine prey, we surveyed the palatability of 81 species of worms from the Caribbean and warm-temperate western Atlantic. Thirty-seven percent of the species were unpalatable. Worms with differentially exposed body portions commonly defended exposed feeding appendages with chemical or structural deterrents, while palatable and undefended bodies remained sheltered within structural refuges. Unpalatable worms tended to be brightly colored and sedentary, exposed to epibenthic predators, and to occupy hard substrates. Palatable worms tended to be drab, to live in structural refuges from consumers, to be mobile, and to inhabit unconsolidated sediments. Overall, taxonomy (Sabellidae and Terebellidae) and color were the traits most strongly associated with unpalatability. Unpalatable species appeared less constrained by predation and freer to forage for long periods on higher quality surface sediments or on other invertebrates at the sediment surface (thus, potentially influencing the distribution and abundance of other species). In contrast, palatable species appeared more constrained by predation risk. They fed on lower quality subsurface sediments and foraged at times or locations where consumers were less active. These ecological patterns may be generalized to other soft-bodied prey, such as caterpillars, which show similar trends regarding palatability and lifestyle.
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ItemFishes learn aversions to a nudibranch’s chemical defense(Georgia Institute of Technology, 2006-01-24) Long, Jeremy D. ; Hay, Mark E.The nudibranch Doriopsilla pharpa was rejected as food when tethered in the field and when offered to 2 species of co-occurring crabs (the lesser blue crab Callinectes similus and the mud crab Panopeus herbstii) and 2 species of co-occurring fishes (the mummichog Fundulus heteroclitus and the striped blenny Chasmodes bosquianus) in the laboratory. When the fishes were offered squid-based artificial food containing nudibranch extracts (i.e. defended food), both species initially consumed this food, but rapidly developed aversions in subsequent feedings. Although both fishes rapidly learned to reject the food, they learned using different cues. The striped blenny Chasmodes bosquianus regurgitated following the initial feeding and then avoided all food made of squid regardless of whether or not it contained the extract. In contrast, the mummichog Fundulus heteroclitus did not regurgitate, and learned to avoid only food containing the extract; it still consumed squid-based food without the extract. Thus, the mummichog detected the deterrent chemical and avoided only defended food while the striped blenny was a less effective feeder, avoiding both defended and undefended food that tasted like squid. Bioassay-guided separation using the mummichog demonstrated that the sesquiterpene polygodial was responsible for the deterrent effects of the nudibranch extract. This metabolite also resulted in the striped blenny avoiding either squid- or tuna-based food treated with this metabolite.