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

Abstract

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. K E Y W O R D Scolonization, community diversity, litter breakdown, predation, shredders

Indirect control of decomposition by an invertebrate predator

“…Why predation has been found to have variable effects on decomposition is not fully understood but may be caused by differences in predator trophic guild -that is, predators that directly consume decomposer species may have negative cascading effects on decomposition (Lawrence & Wise, 2000;Wu et al, 2011;Wyman, 1998), whereas higher-trophic level predators that prey on the predators of decomposers, or on microbivores, may release decomposers from predation and, therefore, have positive cascading effects (Lawrence & Wise, 2004;McGlynn & Poirson, 2012;Melguizo-Ruiz et al, 2020). Moreover, a number of studies reported no predation effect on decomposition, which was attributed to high levels of functional redundancy within brown food webs (Cates et al, 2021), the complexity of food web pathways (Miyashita & Niwa, 2006;Namba & Ohdachi, 2016) and other biotic or abiotic factors overshadowing any predation effect (Denmead et al, 2017;Hocking & Babbitt, 2014;Homyack et al, 2010;López-Rodríguez et al, 2018). Notably, there is a lack of large-scale (>8 × 8 m), open plot experiments in previous literature (though see Parr et al, 2016 andCates et al, 2021), as the vast majority of studies employed mesocosms, which run the risk of artefacts arising due to small scales and enclosure of the study organisms (Petersen & Hastings, 2001).…”

Trophic ecology of Plecoptera (Insecta): a review

“…An example is the study by Malmqvist (1993), in which both direct and indirect effects of a stonefly predator, namely Diura nanseni (Kempny, 1900), reduced leaf litter decomposition rates. Additionally, the consumption of predator nymphs by fish seems to cascade to lower trophic levels (Buria et al 2010;Rodríguez-Lozano et al 2016), although this pattern is not widespread (López-Rodríguez et al 2018a). Additionally, stonefly predators may exert an indirect effect on the fitness of their prey.…”