Top down control in a relatively pristine seagrass ecosystem

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.

Traducci?n comentada del ingl?s al espa?ol y an?lisis de elementos culturales en la obra teatral de derek walcott ?dream on monkey mountain? [sueno en la monta?a del mono]. [recurso electr?nico]

Este es un estudio descriptivo, en el cual se analizaron elementos culturales y marcas coloniales y anticoloniales en la traducci?n de ingl?s a espa?ol de la obra teatral ?Dream on Monkey Mountain? [Sue?o en la Monta?a del Mono] de Derek Walcott. Para llevarlo a cabo se utiliz? el m?todo cualitativo, aunque varios datos son presentados de forma cuantitativa. Parte de la informaci?n fue recogida a trav?s de observaci?n participante en los ensayos de los estudiantes de Arte Dram?tico de la Escuela de Artes Integradas de la Universidad del Valle (Cali, Colombia). Otros datos fueron obtenidos a partir del texto objeto de la traducci?n y la traducci?n misma. En cuanto al proceso de traducci?n, ?ste se sirvi? del m?todo filol?gico o traducci?n cr?tica anotada, m?todo libre y m?todo interpretativo-comunicativo; y se utilizaron t?cnicas tanto de la traducci?n directa como de la traducci?n oblicua. Se identificaron los elementos culturales, elementos coloniales y anticoloniales en el texto de partida y se usaron las t?cnicas de traducci?n que permitieron transferir o no transferir estos elementos a la cultura receptora. Mediante el an?lisis hecho se identificaron 24 diferentes categor?as de culturemas en la obra. Para traducir el texto y procesar los culturemas identificados se utilizaron 19 tipos de t?cnicas de traducci?n. Las t?cnicas utilizadas revelan que la estrategia principal usada por el traductor es domesticaci?n, es decir, en la mayor?a de los casos se opt? por adaptar los culturemas a la cultura receptora con el prop?sito de crear ?en ?sta?el mismo efecto que el texto de partida busc? crear en esa cultura.

Top Down Control in a Relatively Pristine Seagrass Ecosystem

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.