The loss of large-bodied herbivores and/or top predators has been associated with large-scale changes in terrestrial, freshwater, and marine ecosystems around the world. Understanding the consequences of these declines has been hampered by a lack of studies in relatively pristine systems. To fill this gap, I investigated the dynamics of the relatively pristine seagrass ecosystem of Shark Bay, Australia. I began by examining the seagrass species distributions, stoichiometry, and patterns of nutrient limitation across the whole of Shark Bay. Large areas were N-limited, P-limited, or limited by factors other than nutrients. Phosphorus-limitation was centered in areas of restricted water exchange with the ocean. Nutrient content of seagrasses varied seasonally, but the strength of seasonal responses were species-specific. Using a cafeteria-style experiment, I found that fast-growing seagrass species, which had higher nutrient content experienced higher rates of herbivory than slow-growing species that are dominant in the bay but have low nutrient content. Although removal rates correlated well with nutrient content at a broad scale, within fast-growing species removal rates were not closely tied to N or P content. Using a combination of stable isotope analysis and animal borne video, I found that green turtles (Chelonia mydas) – one of the most abundant large-bodied herbivores in Shark Bay – appear to assimilate little energy from seagrasses at the population level. There was, however, evidence of individual specialization in turtle diets with some individuals foraging largely on seagrasses and others feeding primarily on macroalgae and gelatinous macroplankton. Finally, I used exclusion cages, to examine whether predation-sensitive habitat shifts by megagrazers (green turtles, dugongs) transmitted a behavior-mediated trophic cascade (BMTC) between sharks and seagrasses. In general, data were consistent with predictions of a behavior-mediated trophic cascade. Megaherbivore impacts on seagrasses were large only in the microhabitat where megaherbivores congregate to reduce predation risk. My study highlights the importance of large herbivores in structuring seagrass communities and, more generally, suggests that roving top predators likely are important in structuring communities - and possibly ecosystems - through non-consumptive pathways.

As sustainability becomes a more prominent part of people’s lives, firms that embrace sustainability can create more value for customers. Value has traditionally been seen as being determined by the provider. However, recent theorisations have conceptualised value as being created by the customer with interactions as a key component. The primary way for customers to interact with firms is through indirect interaction – such as when reading labels on product packaging or taking part in advertising. In extant literature, there is a lack of research on how customers’ value creation is affected by interactions with firms – and more specifically – by indirect interaction. The purpose of this study has been to explore how customers’ value creation is affected by providers’ communication of sustainability efforts through indirect interaction. To gain this insight, 12 interviews with customers have been conducted and analysed in four dimensions – general, sustainability, communication and the value creation process. The study found that sustainability efforts were mainly communicated through indirect interactions. Sustainability efforts affected all respondents’ lives and consumption process. Customers valued communication of sustainability efforts that they perceived as being honest, could understand and was presented to them at an appropriate time.

Biological invasion has become a major threat to economy, ecology, global biodiversity and ecosystem function of aquatic ecosystems. The main aim of the thesis was to study the effects of the zebra mussel (Dreissena polymorpha), a versatile invasive species, on phytoplankton dynamics and ecosystem function of lakes. In a first attempt, I compared the density of Dreissena and the physicochemical data of ecosystems that it invaded among North American and European lakes to identify important factors in its invasion success. Secondly, I investigated the impact of zebra mussels on phytoplankton community composition in a natural lake. Thirdly, I evaluated whether zebra mussel feeding behavior were affected by the presence of predatory waterborne cues. Finally, I examined the effect of Dreissena on seston stoichiometry. A Generalized Additive Model revealed that a joint effect of surface area, mean depth, total phosphorus and calcium concentrations can explain the variability in Dreissena density. Selective grazing by zebra mussels varied in relation to seasonal phytoplankton dynamics. Risk cues released by predators affected both feeding rate and prey selection of the mussels and had cascading indirect effects on phytoplankton biomass and community structure. I found that the flux in nutrients caused by differences in zebra mussel consumption lead to a variation in phytoplankton nutrient limitation. The flexibility of zebra mussel feeding behavior and variation in susceptibility among phytoplankton groups to mussel ingestion indicate that invading zebra mussels could alter phytoplankton community composition of lakes and have important ecosystem consequences. The results of this thesis contribute to the growing evidence that predators indirectly affect resource dynamics and food web structure through their non-lethal effects on consumers. The results suggested that zebra mussel can indirectly both reduce and increase the energy transfer efficiency from primary producers to upper trophic levels in the pelagic and benthic food webs, respectively.

<p>Biological invasion has become a major threat to economy, ecology, global biodiversity and ecosystem function of aquatic ecosystems. The main aim of the thesis was to study the effects of the zebra mussel <i>(Dreissena polymorpha)</i>, a versatile invasive species, on phytoplankton dynamics and ecosystem function of lakes. </p><p>In a first attempt, I compared the density of <i>Dreissena</i> and the physicochemical data of ecosystems that it invaded among North American and European lakes to identify important factors in its invasion success. Secondly, I investigated the impact of zebra mussels on phytoplankton community composition in a natural lake. Thirdly, I evaluated whether zebra mussel feeding behavior were affected by the presence of predatory waterborne cues. Finally, I examined the effect of <i>Dreissena</i> on seston stoichiometry.</p><p>A Generalized Additive Model revealed that a joint effect of surface area, mean depth, total phosphorus and calcium concentrations can explain the variability in <i>Dreissena</i> density. Selective grazing by zebra mussels varied in relation to seasonal phytoplankton dynamics. Risk cues released by predators affected both feeding rate and prey selection of the mussels and had cascading indirect effects on phytoplankton biomass and community structure. I found that the flux in nutrients caused by differences in zebra mussel consumption lead to a variation in phytoplankton nutrient limitation.</p><p>The flexibility of zebra mussel feeding behavior and variation in susceptibility among phytoplankton groups to mussel ingestion indicate that invading zebra mussels could alter phytoplankton community composition of lakes and have important ecosystem consequences. The results of this thesis contribute to the growing evidence that predators indirectly affect resource dynamics and food web structure through their non-lethal effects on consumers. The results suggested that zebra mussel can indirectly both reduce and increase the energy transfer efficiency from primary producers to upper trophic levels in the pelagic and benthic food webs, respectively. </p>

Hard clams, Mercenaria mercenaria, are slow-moving organisms that are heavily preyed upon by both blue crabs and knobbed whelks in coastal Georgia. Hard clams are unable to escape from these predators, and when found, are commonly injured and/or consumed. Thus, their best survival strategy is to avoid their predators. In this study, we compared changes in clam behavior when exposed to blue crab and knobbed whelk predators. Clams reduced their feeding time when exposed to crabs and whelks, exudates from these predators, and to injured conspecifics. In a field experiment, we compared clam survival when caged predators where near clam beds vs. controls with empty cages. Clam survival was significantly higher when caged crabs or whelks were near, suggesting that clams detected these predators, reduced their feeding time, and were less apparent to ambient consumers. In lab behavioral assays, clams were less responsive to blue crabs in turbulent flows, and in the field, turbulence reduced the distance clams reacted to blue crabs. Previous studies have shown that blue crabs turbulence also diminishes blue crab foraging efficiency, and we conducted a field experiment to determine how turbulence affected clam-crab interactions. Our results suggest that predation intensity is greatest at intermediate turbulence levels, and lowest in flows with low and high turbulence levels. We attribute this pattern of predation intensity to differential effects of turbulence on the sensory abilities of crabs and clams. That is, in low turbulent flows, clams have a sensory advantage over crabs, and initiate avoidance behaviors before they are detected. However, as turbulence increases, clam perception diminishes faster than crabs, switching the sensory advantage to crabs, and making clams more vulnerable to consumers. In highly turbulent flows, crab perception declines at a rate faster than clams, and the sensory advantage returns to clams.

Cavity-nesting communities are structured by the creation of and competition for cavities as nest-sites. Viewing these communities as interconnected webs can help identify species interactions that influence community structure. This study examines cavity-nesting bird community interactions within the fire-maintained longleaf pine (Pinus palustris) ecosystem at Eglin Air Force Base, Florida. In chapter 1, I provide a background review of the ecology of my study system. In chapter 2, I use nest webs to depict the flow of cavity-creation and use at Eglin. I identified 2 webs into which most species could be placed. One web contained 6 species associated with pines. The second web contained 5 species associated with hardwoods. Red-cockaded woodpeckers (Picoides borealis) and northern flickers (Colaptes auratus) created most cavities used by other species within this community. In chapter 3, I describe snag densities and nest-site selection of the cavity-nesting bird community at Eglin. Large, mature pine snags were abundant, exceeding other reported densities for southern pine forests. Pine snags were heavily-used, despite the abundance of available red-cockaded woodpecker cavities in living pine. Hardwood snags accounted for 10% of nests found, and were used by 12 of 14 species. Diameters of nest-trees and available snags were below the range of optimal nest-snag diameters reported in other studies, indicating the need for site-specific snag management guidelines. In chapter 4, I combine a study of basic ecological principles with endangered species management to examine interactions within the cavity-nesting bird community at Eglin. I used a nest web to identify a potential indirect interaction between the red-cockaded woodpecker and large secondary cavity-nesters, mediated by the northern flicker. I used structural equation modeling to test a path model of this interaction. By experimentally manipulating cavity availability, I blocked links described in the model, confirming cavity creation and enlargement as mechanisms that influence this indirect relationship. I demonstrated that a red-cockaded woodpecker cavity-management technique could disrupt this indirect relationship by affecting northern flicker behavior, and provided an empirical example of how, in interactive ecological communities, single-species management can have indirect effects on non-target species. / Ph. D.

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