Are leaf litter secondary compounds responsible for the paucity of invertebrate shredders in lowland tropical streams?

M. Ardón and C.M. Pringle.Institute of Ecology, University of Georgia, Athens, GA 30602 USA

Recent work suggests that invertebrate shredders are scarce and species-poor in tropical streams. One prevailing hypothesis to explain this pattern is that the high diversity and concentrations of secondary compounds in leaves of tropical species inhibit invertebrate shredders. However, our work in Costa Rica suggests that secondary compounds decrease rapidly in early stages of breakdown and do not affect breakdown rate or invertebrate shredder colonization. Direct comparisons of effects of leaf chemical quality on breakdown rates in tropical versus temperate streams is hindered by the diversity of chemical parameters measured in different studies and the lack of standardized analytical methods. As a first step towards making tropical-temperate comparisons, we used standardized analytical techniques to measure initial litter chemistry of common riparian species from Coweeta Hydrological Laboratory, N.C. and La Selva Biological Station, Costa Rica. We are currently in the process of comparing effects of leaf chemistry on breakdown rate and invertebrate shredder biomass between La Selva and Coweeta streams. Preliminary analyses suggest that leaf litter from La Selva species exhibit a wider range of chemical parameters than Coweeta species. We will continue to add to this database by including analyses of common riparian trees from additional tropical and temperate sites.