Changes In Community Structure And Ecosystem Processes In Response To Armored Catfish (Siluriformes: Loricariidae) Invasion

Abstract

Species invasions provide a n excellent opportunity to ask important ecological questions and test the effects of individual species on ecosystem structure and function. In both terrestrial and aquatic ecosystems, non-native grazing organisms alter the quality and quantity of food resources and affect nutrient storage and cycling. Low-trophic position species, such as herbivorous and detritivorous fishes, have been introduced and become established in aquatic ecosystems throughout the globe and these species can fundamentally change community st ructure and ecosystem processes. In Chiapas, Mexico I quantified the effects of non-native armored catfishes (Siluriformes: Loricariidae) on ecosystem structure and function. Loricariids are grazing fishes that have been introduced to many freshwater ecosystems outside of their native range due to their popularity in the aquarium trade. The purposes of this study were threefold. Initially, I examined the effects of loricariid grazing on the quality and quantity of basal food resources. Secondly, I investigated the top-down and bottom-up pathways by which loricariids affect algal biomass and gross primary productivity by quantifying the net effects of grazing and nutrient remineralization. Lastly, I examined whether loricariids are important drivers of nutrient dynamics and estimated whether they function as a source or sink of nutrients in invaded stream reaches. The results from this study indicate grazing by loricariids reduces the quality and quantity of benthic resources and this negatively influences higher trophic levels. Additionally, intensive grazing by high-densities of loricariids result s in a negative net-effect on algal biomass and primary productivity in the Chacamax River. At a larger spatial scale, my findings suggest loricariids dramatically increase the amount of nutrients stored in fish tissue and the rate at which nutrients are remineralized via fish excretion, thereby converting the river to a system where fishes are primary drivers of nutrient dynamics. This study also demonstrated invasive organisms can simultaneously function as sources and sinks of nutrients and these effects are element-dependent. Finally, this investigation highlights the importance of quantifying the consumptive and remineralization effects of invaders to develop a comprehensive understanding of how non-native organisms influence ecosystem structure and function in invaded ecosystems.