June 13 2017

2:00 pm LSB 2320

Sarah Joy Bittick
Department of Ecology and Evolutionary Biology, UCLA

Human manipulations of bottom-up and top-down controls cause degradation of primary and facilitation of secondary foundation species


Doctoral Dissertation Seminar
As human-induced global change impacts nearly every ecosystem worldwide, there is increasing concern for the degradation of foundation species. These species play key roles in ecosystem functioning by facilitating other species and supporting community structure through amelioration of harsh conditions and/or provision of habitat structure. Human alteration of forces controlling foundation species’ abundance and dominance, such as nutrient limitation and herbivory, can result in not only the decline of foundation species, but also a shift in spatial dominance to other, often less desirable species. However, some replacement species can also provide habitat structure or other ecological roles as more persistent, secondary foundation species.
Through a combination of in situ and mesocosm experiments, I investigated the influence human manipulation of nutrients has on dominance of a primary (a temperate seagrass) and secondary (a coral reef macroalga) foundation species, and the possible consequences to trophic structure in two of the most threatened marine systems worldwide. Chapter 1, demonstrates the decline of a primary foundation species due to anthropogenic increases in nutrients. Both the shoot density of the seagrass, Zostera marina, and the abundance of its epiphytes declined when macroalgal abundance was used as a proxy for nutrient enrichment. Reduced epiphyte load suggests that not only the habitat structure afforded by Z. marina is degraded by enrichment, but that there will be trophic consequences through a decrease in resources. In contrast, I determined in chapter 2 that anthropogenic increases of nutrients can facilitate dominance by a secondary foundation species of brown algae, Turbinaria ornata, on reefs in the South Pacific. Increases in T. ornata density also resulted in increased epiphyte loading and consequential foraging by herbivorous fishes as shown in chapter 3. Overall, my results demonstrated that human alterations of nutrient supplies can cause both degradation of primary and facilitation of secondary foundation species with drastic consequences to the trophic relationships they support.











































































































































































































































































































































































































































































































































































































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