Effects of litter patch area on macroinvertebrate assemblage structure and leaf breakdown in Central Amazonian streams

摘要

Leaf breakdown in streams is affected by several factors, such as leaf characteristics, water chemistry, microbial activity, and abundance of shredders. In turn, shredders may be resource-controlled. We hypothesized that the size of litter patches affects leaf breakdown, because large patches should be stable over time and therefore harbor high densities of shredders. We selected litter patches (area 0.25-10 m(2)) in 10 pools of three first-order streams (Manaus, Brazil). We installed 10 leaf packs of Mabea speciosa (Euphorbiaceae) in each patch, and sampled one after 1 day and three after 5, 19, and 28 days. The leaf packs were quickly colonized by the shredding caddisflies Triplectides and Phylloicus. The leaf breakdown rate (mean k = 0.026 +/- A 0.0015 SE) was high and similar to values reported for other tropical and temperate streams, although much higher than values reported for the adjacent Cerrado biome. Assemblage composition varied over time, but was not related to the size of litter patches. Contrary to our hypothesis, litter patch area did not affect breakdown rates (r (2) = 0.012, P = 0.766) or abundance of shredders after 5, 19, and 28 days (r (2) < 0.243, P > 0.147). We found, however, a positive relationship between the abundance of tropical shredders and leaf breakdown after 19 days (r (2) = 0.572, P = 0.011), suggesting that shredders play an important role in leaf breakdown in these headwater streams. Our study indicates that leaf breakdown rates in tropical streams are variable and can be as high as those of temperate streams.