Notes

Outline

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Armored invertebrate grazers Snails or caddisflies Common in temperate streams Reduce standing crops and alter of algae Compete with other grazers Prevent trophic transfer to predators

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Conclusions from Glossosoma removal in Fox Creek Glossosoma suppress algal biomass in Fox Creek, despite low primary productivity. Competition with Glossosoma reduces abundance of primary consumers that are easy prey. Gut analysis and d13C data suggest Heptageniid nymphs consumed more algae where Glossosoma density reduced. At least one herbivore uses less algae and more terrestrial food as a result of competition with Glossosoma. This effect did not transfer up to the predator trophic level, at least within the spatial and temporal scale of this experiment. Algae support a substantial fraction of the stream biota.

How do the effects of armored grazing caddisflies vary with stream size within the watershed?

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Conclusions from watershed herbivory survey: Grazing caddisfly species differed in their phenology and their distribution among sites.  Species with a single generation per year dominated in larger streams. Species with multiple, overlapping generations dominated in smaller streams. We observed a strong decline in caddisfly biomass over summer at most sites, with one exception (Fox Creek, d.a. 2.5 km2). Variation caddisfly persistence among sites was mostly attributable to differences in species present . In early summer, herbivory was important in all but smallest streams. The importance of herbivory declined over summer as caddisflies completed development.