Macroinvertebrate Community Responses to Catastrophic Amphibian Declines in Neotropical Streams: Potential for Functional Redundancy Among Tadpoles and Grazing Mayflies

Amphibian populations are declining catastrophically around the world, in part due to a chytrid fungus pathogen. These declines offer the rare opportunity to quantify the consequences of a sudden, dramatic decline in consumer biodiversity in a natural system. As part of the Tropical Amphibian Declines in Streams (TADS) project, we examined stream macroinvertebrate assemblage structure and production for two years in two stream reaches in Panama. Both reaches initially had healthy stream-breeding amphibian communities, which declined during our study. As tadpoles declined precipitously during year 2, macroinvertebrate biomass and production declined significantly in one reach compared to year 1. Functional structure differed between years, with biomass and production of shredders and predators generally lower in both reaches during the second year. Some grazing mayflies responded positively to declining tadpole densities and concomitant increases in periphyton biomass, indicating a potential for some degree of functional redundancy. Our results indicate that responses of remaining consumers to these declines may not be evident at some coarser scales (e.g., total abundance), but functional and assemblage structure responses were evident, with some individual taxa responding quickly. Long-term studies at these sites may reveal further ecological consequences of the functional and taxonomic shifts that we observed.