Quality and quantity of leaf litter: Both are important for feeding preferences and growth of an aquatic shredder

Abstract

The study of leaf litter as a resource for shredders has emerged as a key topic in trophic links in ecology. However, thus far, most studies have emphasized the leaf quality as one of the main determinants of shredder behaviour and growth without simultaneously considering the leaf quantity availability. Nevertheless, the combined effects of leaf quantity and quality on shredder behaviour and growth is particularly crucial to further understand how ecosystem functioning may respond to the increasing flow intermittency due to climate change. In this study, we explore how changes in the leaf litter quality and quantity influence the feeding preferences and growth of an invertebrate shredder (Potamophylax latipennis). To do so, we used black poplar leaves conditioned in two streams with different flow regimens as a food resource. Afterwards, using a microcosm approach, we offered leaf discs that varied in terms of leaf quantity and quality to P. latipennis. Our results showed that flow intermittency had a negative effect on the quality of the food resource, and a lower quality had a negative effect on the consumption and growth rates of P. latipennis. Furthermore, we found that P. latipennis fed selectively on higher quality leaves even though the availability (quantity) of this resource was lower. In the context of climate change, with higher aridity/drier conditions/scenarios, our findings suggest that a decrease in the availability (quantity) of high-quality resources could potentially threaten links in global fluvial food webs and thus threaten ecosystem functioning.

Subsurface zones in intermittent streams are hotspots of microbial decomposition during the non-flow period

“…The results of our study show how the increase in the number of non-flow days that is related to lower OM decomposition in the surface zone could be due to the decrease in fungal biomass (Mustonen et al, 2016). As previous studies have pointed out, flow disruption constrains and retards fungal growth and colonization because sporulation requires flowing water (Arias-Real et al, 2018;Duarte et al, 2017;Gessner et al, 2010). Additionally, this reduction in fungal biomass and activity coupled to changes in the initial chemical composition of OM (leaf litter and woody debris), affects the palatability of OM (Suberkropp et al, 1983).…”

“…Microbes (fungi and bacteria) and invertebrates are the most important organisms that contribute to OM decomposition, but their activities may vary with local environmental conditions (Gessner et al, 2010). In freshwaters, fungi are the first colonisers and the main microbial decomposers during the early stages of decomposition, constituting an essential trophic link between OM and invertebrate consumers (Arias-Real et al, 2018;Gessner and Chauvet, 1994;Kuehn, 2016). Aquatic OM decomposition depends on environmental factors that affect biological activity and/or physical degradation (Krauss et al, 2011).…”

Leaf litter quality drives the feeding by invertebrate shredders in tropical streams

“…larvae selected softer leaf litter proportions in detriment to less palatable litter for feeding. Although I. laurina has higher nutritional content than M. guianensis, the processing of softer leaf litter appears to be more cost benefit for Phylloicus larvae metabolism (Arias-Real, Menéndez, Abril, Oliva, & Muñoz, 2018), corroborating our second hypothesis. We recorded a higher consumption in treatment with lower quantity compared with higher quantity just in Cerrado system.…”

Stochastic processes and ecological connectivity drive stream invertebrate community responses to short‐term drought

“…In contrast, cessation of flow completely stopped the input of suspended matter and suppressed algal and invertebrate biomass (Truchy et al., 2020), which may have reduced food availability for filter‐feeders, scrapers and predators (Bonada et al., 2007; Piano et al., 2019). Shredders did respond negatively to drought, suggesting their emigration, but only after a lag period which may reflect reduced palatability of leaves due to the drought‐driven reduction in fungal conditioning (Arias‐Real et al., 2018; Truchy et al., 2020). The stability of functional diversity may allow a rapid resumption of ecosystem functioning post‐drought, although strong reductions in certain trait abundances (e.g.…”