Graduate Thesis Or Dissertation


Aquatic Plant Community Changes in Freshwater Ponds Recently Invaded by Elodea canadensis on the Western Copper River Delta, Alaska Public Deposited

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  • Establishment of a non-native plant species in new habitats beyond their native range is associated with inherent changes in ecosystem properties. These changes may be dramatic or subdued, and consequences may be positive or negative depending on characteristics and response of the resident ecosystem. Non-native aquatic plant species in the genus Elodea have demonstrated several adaptive characteristics which have led to a propensity for dominance where introduced. Species Elodea canadensis, Elodea nutallii, and their hybrid have recently become invasive in several waterbodies throughout the state of Alaska where this genus is the only documented non-native aquatic plant. In freshwater ponds of the Copper River Delta (CRD), the largest wetland complex in North America and critical habitat for fish and wildlife, infestation of E. canadensis has not homogenized all macrophyte communities over the last decade. Recent studies have described mechanisms of invasion of Elodea in other geographies; though, response of native plant species and native plant community dynamics in recipient habitats is still poorly understood. Wetland pond habitats on the CRD have undergone shifts in macrophyte community assemblage and rapid succession resulting from a major tectonic event and include freshwater species tolerant of subarctic climatic conditions. Aquatic plants play an important role in structure and function of habitat. The purpose of this thesis is to advance the knowledge of aquatic plant community characteristics and patterns of variability to describe change which may influence higher trophic levels directly or indirectly. Species cover abundance, a population characteristic closely related to biomass, was utilized to assess changes in community structure, composition, and diversity by potential displacement of species due to recent occurrence of a non-native invasive species. Further, I investigated variability of species abundances at the resolution of the growing season and investigated how water temperature may mediate species interaction. This information was collected in five freshwater ponds, some with established populations of Elodea canadensis, positioned adjacent to two different drainages in the West CRD and analyzed then as individual cases to determine trends and identify patterns over a four-year snapshot of time in the species invasion. Results of a community analysis employing non-parametric techniques for a multivariate dataset revealed no significant shift in community structure or composition in ponds where E. canadensis was present, never present, or eradicated among the four-year sample period. A pattern among ponds illustrating lack of trends at a yearly resolution suggested little influence exerted by the non-native species on the resident native assemblage at the levels of abundance in which E. canadensis has maintained over the time period. Investigation of temporal diversity at a yearly resolution revealed significant changes in individual species abundance and captured a pattern of shifts in species richness, evenness, and ordering of dominance. These results indicated a high level of variability within each growing season which may be explained by environmental parameters and their influence on species interactions. I concluded that, where there no overwhelming change in community characteristics has occurred over the study period, further investigation is needed to describe relationships between variability among species and physiochemical variables that may mediate the species interactions which structure aquatic plant communities. Establishment of these associations will allow further discernment of trends and aid in forecasting of community level changes.
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