Toft, Jason D.2011-08-162011-08-162000http://hdl.handle.net/1773/17065Biological invaders are widespread and can alter population dynamics and community structure of native ecosystems. Substantial habitat alteration by nonindigenous species can additionally affect the surrounding community. Aquatic plants are particularly invasive, especially in areas that are modified by humans. Water hyacinth (Eichhornia crassipes) is a floating aquatic plant that is non-indigenous to the Sacramento/San Joaquin Delta, California. A common native that functionally occupies similar habitats as hyacinth is pennywort (Hydrocotyle umbellata). Based on the utilization of such habitats by invertebrates and fish, my main scientific question was: Has hyacinth modified the invertebrate assemblage structure and fish-invertebrate food web as compared to pennywort? To assess this, I sampled invertebrates in hyacinth and pennywort and analyzed fish diets in the surrounding area at three sites in the Delta during 1998 and 1999. I also took measurements of leaf density, root structure, dissolved oxygen and temperature. Ecological differences between hyacinth and pennywort were linked to habitat architecture. Coupled with the management challenges of hyacinth, its ecological modifications make it an even more influential invader.en-USCopyright is held by the individual authors.invasive speciesEichhornia crassipesnoxious weedsHydrocotylepopulation dynamicsfood websaquatic invertebratesaquatic habitatfishfeeding behaviorlimnologydeltasfree-floating plantsdietCaliforniaSacramento RiverSan Joaquin RiverriversThesis