Detritivore stoichiometric diversity alters litter processing efficiency in a freshwater ecosystem

Abstract

Many studies have estimated relationships between biodiversity and ecosystem functioning, and observed generally positive effects. Because detritus is a major food resource in stream ecosystems, decomposition of leaf litter is an important ecosystem process and many studies report the full range of positive, negative and no effects of diversity on decomposition. However, the mechanisms underlying decomposition processes in fresh water remain poorly understood. Organism body stoichiometry relates to consumption rates and tendencies, and decomposition processes of litter may therefore be affected by diversity in detritivore body stoichiometry. We predicted that the stoichiometric diversity of detritivores (differences in C: nutrient ratios among species) would increase the litter processing efficiency (litter mass loss per total capita metabolic capacity) in fresh water through complementation regarding different nutrient requirements. To test this prediction, we conducted a microcosm experiment wherein we manipulated the stoichiometric diversity of detritivores and quantified mass loss of leaf litter mixtures. We compared litter processing efficiency among litter species in each microcosm with single species detritivores, and observed detritivores with nutrient-rich bodies tended to prefer litter with lower C: nutrient ratios over litter with higher C: nutrient ratios. Furthermore, litter processing efficiencies were significantly higher in the microcosms containing species of detritivores with both nutrient-rich and -poor bodies than microcosms containing species of detritivores including only nutrient-rich or -poor bodies. This might mean a higher stoichiometric diversity of detritivores increased litter processing efficiency. Our results suggest that ecological stoichiometry may improve understanding of links between biodiversity and ecosystem function in freshwater ecosystems.

Litter P content drives consumer production in detritus‐based streams spanning an experimental N:P gradient

“…Previous measurements of benthic macroinvertebrate stoichiometry in CHL streams revealed that primary consumer body C:P ranged from 80 to 877 and that consumer C:N ratios were typically around 6 (Cross et al 2003). The range in C:N:P ratios of benthic macroinvertebrates in CHL streams is similar to that reported in other studies (Liess and Hillebrand 2006, Lauridsen et al 2012, Ohta et al 2016 and suggests a higher likelihood of P-limited growth in primary consumer taxa due to the greater relative imbalance between consumer and resource P content than in N content. Although consumer body C:P does not reflect elemental demand directly, it serves as a useful proxy for estimating elemental imbalances in the absence of estimates of C:P threshold elemental ratio (TER C:P ; Frost et al 2006).…”

“…, Ohta et al. ) and suggests a higher likelihood of P‐limited growth in primary consumer taxa due to the greater relative imbalance between consumer and resource P content than in N content. Although consumer body C:P does not reflect elemental demand directly, it serves as a useful proxy for estimating elemental imbalances in the absence of estimates of C:P threshold elemental ratio (TER C:P ; Frost et al.…”

Traits of litter‐dwelling forest arthropod predators and detritivores covary spatially with traits of their resources

“…100,No. Finally, traits related to stoichiometry were shown to be useful to describe herbivore/ plant interactions (Deraison et al 2015) and to be good predictors of detritivore-litter interactions in aquatic systems (Ohta et al 2016). As the amplitude of seasonal functional variation was never studied for feeding and palatability traits of litter-dwelling arthropods, it is unclear how seasonality, including phenology and developmental stages of arthropods, could influence our results.…”

“…As the amplitude of seasonal functional variation was never studied for feeding and palatability traits of litter-dwelling arthropods, it is unclear how seasonality, including phenology and developmental stages of arthropods, could influence our results. Finally, traits related to stoichiometry were shown to be useful to describe herbivore/ plant interactions (Deraison et al 2015) and to be good predictors of detritivore-litter interactions in aquatic systems (Ohta et al 2016). Including stoichiometry in future work will undoubtedly be interesting to explore, in addition to the physical aspects of feeding interactions studied here.…”

Differential resource consumption in leaf litter mixtures by native and non-native amphipods

“…These different taxa which can perform overlapping functions but also facilitate one another by performing complementary functions in processing detritus, hence, the identity of the species making up a diverse community can be more informative than their number. For example, organisms with different body stoichiometries sometimes preferentially process resources with different nutrient contents, leading to higher total decomposition rates in stoichiometrically-diverse communities (Ohta et al, 2016). As another example, larger shredding organisms can create fine particulate material which is then available for smaller organisms to further decompose (Tonin et al, 2018).…”