The effect of large predators on the decomposition rate and the macroinvertebrate colonization pattern of leaves in a Mediterranean stream

The goal of this study is to experimentally assess the possible effect of macroinvertebrate predators on the decomposition rate of leaves in a Mediterranean stream and to analyze the pattern of colonization by macroinvertebrates of the litter bags through time. We designed a factorial experiment with three types of litter bags (allowing the entrance of no macroinvertebrates, only small macroinvertebrates and small and large, top-predators, macroinvertebrates). We measured the percentage of ash-free dry mass remaining after 15, 30, and 45 days, as well as the macroinvertebrate community composition of the two types of litter bags where they were allowed to enter. We did not find differences in the ash-free dry mass remaining between the two types that allowed the entrance of macroinvertebrates. The diversity of the community colonizing each type of litter bag was always relatively high and changed significantly with time and, in some cases, with the exclosure treatment studied. These results show the absence of important top-down control of macroinvertebrates and particularly in those involved in the leaf decomposition in the food web of this Mediterranean stream that could have repercussions on the leaf decomposition process.