Microbial Ecology

, Volume 49, Issue 4, pp 536–546 | Cite as

Relative Importance of Bacteria and Fungi in a Tropical Headwater Stream: Leaf Decomposition and Invertebrate Feeding Preference



Bacteria and fungi provide critical links between leaf detritus and higher trophic levels in forested headwater food webs, but these links in tropical streams are not well understood. We compared the roles of bacteria and fungi in the leaf decomposition process and determining feeding preference for two species of freshwater shrimp found in the Luquillo Experimental Forest, Puerto Rico, using experimental microcosms. We first tested the effects of four treatments on decomposition rates for leaves from two common riparian species, Cecropia scheberiana (Moraceae) and Dacryodes excelsa (Burseraceae), in laboratory microcosms. Treatments were designed to alter the microbial community by minimizing the presence of bacteria or fungi. The fastest decay rate was the control treatment for D. excelsa where both bacteria and fungi were present (k = −0.0073 day−1) compared to the next fastest rate of k = −0.0063 day−1 for the bacterial-conditioned D. excelsa leaves. The fastest decay rate for C. scheberiana was also the control treatment (k = −0.0035 day−1), while the next fastest rate was for fungal-conditioned leaves (k = −0.0029 day−1). The nonadditive effect for leaf decomposition rates observed in the control treatments where both fungi and bacteria were present indicate that bacteria and fungi perform different functions in processing leaf litter. Additionally, leaf types differed in microbial colonization patterns. We next tested feeding preference for leaf type and microbe treatment in microcosms using two species of freshwater shrimp: Xiphocaris elongata, a shredder, and Atya lanipes, a scraper/filterer. To estimate feeding preferences of individual shrimp, we measured change in leaf surface area and the amount of particles generated during 5-day trials in 16 different two-choice combinations. X. elongata preferred D. excelsa over C. scheberiana, and leaves with microbial conditioning over leaves without conditioning. There was no clear preference for fungal-conditioned leaves over bacterial-conditioned leaves. This lack of preference for which microbes were responsible for the conditioning demonstrates the importance of both bacterial and fungal resources in these tropical stream food web studies.


Lignin Microbial Biomass Leaf Disk Headwater Stream Leaf Type 



We are indebted to our research assistant, Anthony Cappa, and thank D. Jean Lodge and Stephanie Rohan for their assistance. We are also grateful to Alonso Ramirez and Angela Bobeldyk for providing useful data. We thank William H. Clements, F. Brent Reeves, and anonymous reviewers for helpful comments on earlier manuscripts. This research was supported by grant DEB-9411973 from the National Science Foundation to the University of Puerto Rico and the International Institute of Tropical Forestry, USDA, as part of the Long-Term Ecological Research Program in the Luquillo Experimental Forest. Additional support was provided by the Forest Service (USDA), the University of Puerto Rico, and Colorado State University.


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Copyright information

© Springer Science+Business Media, Inc. 2005

Authors and Affiliations

  1. 1.Institute of EcologyUniversity of GeorgiaAthensUSA

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