Abstract
High species richness of tropical riparian trees influences the diversity of organic detritus entering streams, creating temporal variability in litter quantity and quality. We examined the influence of species of riparian plants and macroinvertebrate exclusion on leaf-litter breakdown in a headwater stream in the Luquillo Mountains of Puerto Rico. Leaf litter of Dacryodes excelsa (Burseraceae), Guarea guidonia (Meliaceae), Cecropia scheberiana (Moraceae), Manilkara bidentata (Sapotaceae), and Prestoea acuminata (Palmae) were incubated in litter bags in a pool of Quebrada Prieta. Fine mesh bags were used to exclude macroinvertebrates during leaf breakdown, and coarse mesh bags allowed access to decapod crustaceans (juvenile shrimps and crabs) and aquatic insects (mainly mayflies, chironomids, and caddisflies). D. excelsa and G. guidonia (in coarse- and fine-mesh bags) had significantly higher breakdown rates than C. scheberiana, M. bidentata, and P. acuminata. Breakdown rates were significantly faster in coarse-mesh bag treatments for all leaf types, thus indicating a positive contribution of macroinvertebrates in leaf litter breakdown in this headwater stream. After 42 days of incubation, densities of total invertebrates, mayflies and caddisflies, were higher in bags with D. excelsa and G. guidonia, and lower in P. acuminata, C. scheberiana y M. bidentata. Decay rates were positively correlated to insect densities. Our study highlights the importance of leaf identity and macroinvertebrate exclusion on the process of leaf litter breakdown in tropical headwater streams.
Highlights
Riparian plants provide essential inputs of organic detritus that alter food-web dynamics in streams by determining the quantity and quality of organic litter inputs (Naiman & Décamps, 1997; Wallace, Eggert, Meyer & Webster, 1999)
During the 42 days of incubation D. excelsa and G. guidonia showed the fastest breakdown rates in coarse-mesh bags (k=0.01747±0.0010 and k=-0.01199±0.00033, 40% and 60% of mass remaining, respectively), whereas P. acuminata and C. shreberiana presented the slowest rates (k=-0.00636±0.00087 and k=-0.00627±0.00033; 80% and 74% of mass remaining, respectively; Fig. 1, Table 1)
In fine-mesh bags D. excelsa and G. guidonia exhibited the fastest rates (k=0.007813±0.00030 and k=-0.007122±0.00076; 70% and 81% of mass remaining, respectively) in contrast with the slowest rates showed by C. shreberiana and P. acuminata (k=0.0035±0.00030 and k=0.0026±0.00015)
Summary
Riparian plants provide essential inputs of organic detritus that alter food-web dynamics in streams by determining the quantity and quality of organic litter inputs (Naiman & Décamps, 1997; Wallace, Eggert, Meyer & Webster, 1999). Tropical riparian tree species differ greatly in terms of the thickness, fiber content, and secondary chemistry (e.g., Stout, 1989; Irons et al, 1994; Campbell & Fuchshuber, 1995; Wantzen, Wagner, Suetfeld & Junk, 2002; Ardón & Pringle, 2008; Ardón, Pringle & Eggert, 2009) and nutrient content (Gonçalves, Graça & Callisto, 2006) of their leaves. These chemical and physical differences may partially explain the observed species-specific differences in litter processing rates for tropical streams (Ardón et al, 2009). Previous field and lab studies on Luquillo headwater streams and their food web have typically focused on the influence of either insects (Ramírez & Hernández-Cruz, 2004; Bobeldyk & Ramírez, 2007) or shrimps (Crowl et al, 2001; Crowl et al, 2006; March, Benstead, Pringle & Ruebel, 2001) but very few on leaf litter species effects (Wright & Covich, 2005)
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