Date of Award
Master of Science
Tropical habitats have high taxonomic and ecological diversity, but they are currently subject to high rates of extinction. Amphibian populations are declining globally and while we have some understanding of the causes of these declines, it is unclear how these losses will influence ecosystem structure and function. Secondary production and trophic basis of production analyses link consumers to energy flow and reflect the relative importance of various energy sources and energy flow pathways in food webs. These techniques can yield valuable information on the roles of individual consumers in ecosystem function, and thus the ecological consequences of extinction and extirpation events. I estimated the trophic basis of production in a Panamanian headwater stream to identify major sources of energy, measure energy flow through consumers, and characterize interactions among trophic levels and functional feeding groups. I examined gut contents of 19 dominant macroinvertebrate and two dominant tadpole taxa collected during dry and wet seasons before an amphibian decline. I used previously published estimates of secondary production, assimilation efficiencies, and net production efficiencies, along with gut content data, to quantify food web structure and energy flow pathways. Overall consumption of allochthonous materials was greater than autochthonous (p < 0.001), and the dominant food sources were non-algal biofilm and vascular plant detritus. Autochthonous materials were consumed at higher rates during the dry season (p = 0.012). Total consumption rates varied within and among shredders (0.85 - 12.10 g/m2/yr), scrapers (0.46 - 0.91 g/m2/yr), filterers (1.20 - 4.67 g/m2/yr), gatherers (0.43 - 2.44 g/m2/yr) and predators (0.05 - 0.95 g/m2/yr). Overall consumption rates in pool habitats were higher compared to riffles. The degree of omnivory in the food web was much higher than has been observed in similar temperate streams. Omnivory was prevalent across all functional feeding groups, but more pronounced in predators, especially Anacroneuria (55% animal and 45% plant materials in guts). There was also an ontogenetic shift among most dominant macroinvertebrates from smaller, energy rich food sources (e.g., non-algal biofilm) to larger, less nutritious materials (e.g., vascular plant material) with increase in size. My research is the first to provide quantitative estimates of energy flow through a neotropical headwater stream food web. Information from this study is central to understanding and conserving tropical headwater streams. Further, my results, along with post-amphibian decline analyses from the same stream, will allow for a comprehensive assessment of the ecological consequences of amphibian declines.
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