The Effects of Multiple Predtors as Nested Biotic Filters on Ecosystem Function in Streams. Seifert, Rebecca
Predators have been documented to reduce biodiversity and variability between communities by acting as biotic filters to local community membership. Biodiversity improves and stabilizes important ecosystem functions such as decomposition, but little is known about the effect of predators on these functions. This study hypothesized that if two predators, cutthroat trout (Oncorhynchus clarkii) and a predatory stonefly (Calineuria sp.), are acting as biotic filters, then their presence should cause lower diversity and greater similarity in stream invertebrate communities and leaf decomposition rates. Alder leaf packs with and without Calineuria were installed for 5 weeks in 10 streams, half with trout, near Vancouver, British Columbia. Invertebrates were identified to the lowest taxonomic level and leaf decomposition was estimated by determining the ash-free dry mass of each leaf pack. Nested ANOVAs suggest that trout may act as a weak filter on invertebrate diversity but conflicting results from multiple diversity measures make this uncertain. Neither predator produced a significant difference in total invertebrate or shredder abundance and community composition. Mean decomposition was lower in the presence of trout but there were no differences in the variation of leaf decomposition due to either predator. Calineuria did not affect any of the measured variables and is not a strong biotic filter in these streams. It appears that biotic filtering by predators and the relationships between biodiversity and ecosystem function are complex in these communities or may not apply in this system.
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