Food Web Structure and Energy Flow in Panamanian Headwater Streams: Assessing Responses to Catastrophic Amphibian Declines

As part of the TADS (Tropical Amphibian Declines in Streams) project, we quantified energy flow and food web structure in four headwater stream reaches in the Panamanian uplands, two that had experienced massive amphibian declines and two with healthy amphibian populations. Our calculations were based on estimates of primary production, macroinvertebrate production, litter inputs, organic matter standing stocks, and seston export.  Total macroinvertebrate production varied little across the study reaches, ranging from 2.8 – 4.4 g AFDM m-2 y-1.  However, macroinvertebrate functional structure differed between pre- and post-decline sites, with shredder production consistently higher in pre-decline sites and scrapers and filterers consistently higher in post-decline sites.  Quantitative food webs indicated detrital pathways were dominant in all reaches, with shredders and collectors accounting for most energy flow through primary consumers.  However, scrapers were well-represented and consumed >100% (post-decline sites) and >400% (pre-decline sites) of available 1º production, indicating they are food-limited in these systems, particularly when tadpoles are present.  This study provides one of the first quantitative assessments of the impacts of amphibian declines on stream food webs and energy flow.