Strategies of shredders when feeding on low‐quality leaf‐litter: Local population adaptations or fixed species traits?

Abstract

The linkage between leaf-litter and macroinvertebrate shredders is pivotal for stream food webs. Global change is predicted to decrease the nutritional quality of litter inputs to streams. However, little is known about shredder's ability to develop local interpopulation adaptations to face nutrient-depleted leaf-litter. We hypothesized that this adaptation could be present in populations receiving low-quality leaf-litter. We performed feeding tests on three abundant shredders species from lowland (a snail) and mountain (two insects) streams. Two populations of each species were derived from two subregions contrasting in average quality of litter inputs. Individuals were fed on four diets of contrasting quality: two leaf-litter species with two qualities each, and their feeding rates, survivorship, growth, and energetic storage were evaluated. Results suggest that local population adaptation to low-quality litters is not common, being essentially a fixed species trait that varies across species, in particular among snails and insects. The ability of the snail to cope with low-quality litters suggests that ecosystem processes in lowland streams may resist reductions in litter quality. Conversely, potential alterations of riparian vegetation linked to global changes might disrupt mountain stream ecosystem functioning.

Dietary composition and fatty acid content of giant salmonflies (Pteronarcys californica) in two Rocky Mountain rivers

“…Maintaining habitat that meets the need of salmonflies will be key to conserving and restoring salmonfly populations in reaches where they are at risk of extirpation. Our research underscores the importance of a healthy riparian zone that provides allochthonous detritus for invertebrate nutrition as well as invertebrate habitat (Benke & Wallace, 2003;Fenoy et al, 2021). Understanding invertebrate diets and feeding ecology can guide future efforts to restore and conserve imperiled freshwater biodiversity.…”

Climate‐induced plasticity in leaf traits of riparian plants

“…Our second hypothesis of decreasing intraspecific leaf quality—linked to determinant traits of palatability and decomposability—with increasing aridity was partially supported, given that increasing temperature had negative effects on leaf quality of deciduous and semi‐deciduous species, but not on the evergreen Nerium , which displayed the opposite response. These results suggest potential effects on stream ecosystem functioning (Fenoy et al, 2021; Martínez et al, 2013), but with inverse sign depending on the identity of dominant species in the riparian vegetation. Moreover, in support of our third hypothesis, we generally observed higher variation among species than plasticity within species, except for a few traits (e.g.…”

“…These results suggest potential effects on stream ecosystem functioning (Fenoy et al, 2021;Martínez et al, 2013), but with inverse sign depending on the identity of dominant species in the riparian vegetation. Moreover, in support of our third hypothesis, we generally observed higher variation among species than plasticity within F I G U R E 4 Box-and-whisker plots for selected leaf trait variables of the four plant species studied: nitrogen (N), phosphorus (P), calcium (Ca) and magnesium (Mg) concentrations (% DM), molar elemental ratios (C:N and C:P), lignin concentrations (% DM), condensed tannins concentrations (mg Catechin Hydrate Equivalent g DM −1 ) and toughness (g) of each plant species.…”

“…Elevated litter concentrations of Ca and Mg—reported to be important for fungal decomposers (Jenkins & Suberkropp, 1995) and macroinvertebrates (Makkonen et al, 2012; National Research Council, 2005)—can also accelerate decomposition (Santonja et al, 2019). Moreover, tannins (Coq et al, 2010; Irons et al, 1988), lignin (Ferreira et al, 2016; Ramos et al, 2021; Schindler & Gessner, 2009) and toughness (Fenoy et al, 2021; Li et al, 2009) primarily tend to reduce litter consumption by detritivores. Our results point to a general decrease in leaf quality as a response to aridification in the three deciduous/semi‐deciduous species.…”

Elevated temperature may reduce functional but not taxonomic diversity of fungal assemblages on decomposing leaf litter in streams

“…This was further supported by the highest values for LCBD (local contribution to β-diversity) found in streams from the Semiarid lowland and Alcornocales, the two warmest and distant subregions in our study. Despite this, the influence of riparian vegetation cannot be ruled out (Bärlocher & Graça, 2002;Ferreira et al, 2006), since species composition of riparian forest in Alcornocales appeared to be evolved from tropical-like environments (pre-Mediterranean lineages; Salinas et al, 2018), and riparian corridors in the Semiarid lowland subregion are dominated by giant graminoids (Fenoy et al, 2021;Salinas et al, 2018). However, leaf-litter species did not significantly affect fungal assemblage composition, as reported in laboratory studies based on fungal spore morphology (Bärlocher et al, 2011), strengthening the prime role of stream-water characteristics in structuring fungal species assemblages.…”