Detrital nutrient content and leaf species differentially affect growth and nutritional regulation of detritivores

Abstract

Resource nutrient content and identity are common bottom–up controls on organismal growth and nutritional regulation. One framework to study these factors, ecological stoichiometry theory, predicts that elevated resource nitrogen (N) and phosphorus (P) contents enhance organism growth by alleviating constraints on N and P acquisition. However, the regulatory mechanisms underlying this response – including whether responses depend on resource identity – remain poorly understood. In this study, we tested roles of detrital N and P contents and identity (leaf species) in constraining growth of aquatic invertebrate detritivores. We synthesized results from seven detritivore species fed wide nutrient gradients of oak and maple detritus in the laboratory. Across detritivore taxa, we used a meta‐analytic approach quantifying effects of detrital leaf species and N and P contents on growth, consumption, and N‐ and P‐specific assimilation and growth efficiencies. Detritivore growth rates increased on higher‐N and P detritus and on oak compared to maple detritus. Notably, the mechanisms of improved growth differed between the responses to detrital nutrients versus leaf species, with the former driven by greater consumption rates despite lower assimilation efficiencies on higher‐nutrient detritus, and the latter driven by improved N and P assimilation and N growth efficiencies on oak detritus. These findings suggest animal nutrient acquisition changes flexibly in response to resource changes, altering the fate of detrital N and P throughout regulation. We affirm resource identity and nutrients as important bottom–up controls, but suggest these factors act through separate pathways to affect organism growth and thereby change detrital ecosystems under anthropogenic forest compositional change and nutrient enrichment.

Land use alters trophic redundancy and resource flow through stream food webs

“…The changes in diets of primary consumers and predators in response to composition of resources across different land use indicate strong bottom‐up control of macroinvertebrate communities. Such bottom‐up control has been reported in various freshwater (Kiffney, Buhle, Naman, Pess, & Klett, ; Shurin, Clasen, Greig, Kratina, & Thompson, ), marine (Capuzzo et al., ) and terrestrial (Halvorson, Fuller, Entrekin, Scott, & Evans‐White, ; Lister & Garcia, ) ecosystems. Our results show that the bottom‐up effects of land use may extend beyond individual consumer–resource interactions and cascade to the structure of the entire food web.…”

The stoichiometric legacy of fire regime regulates the roles of micro‐organisms and invertebrates in decomposition

“…We suggest that this resilience is driven by the tendency of invertebrates to ingest multiple elemental resources in composite form and regulate resource assimilation internally (Behmer , Halvorson et al. ), such that the invertebrates in 4yB experimental plots might have consumed larger amounts of low‐quality litter to obtain the required amount of P (Suzuki‐Ohno et al. , Jochum et al.…”

“…However, they also reveal that invertebrate-driven decomposition at Peachester is more resilient to litter P depletion than to litter N depletion. We suggest that this resilience is driven by the tendency of invertebrates to ingest multiple elemental resources in composite form and regulate resource assimilation internally (Behmer 2009, Halvorson et al 2018, such that the invertebrates in 4yB experimental plots might have consumed larger amounts of low-quality litter to obtain the required amount of P (Suzuki-Ohno et al 2012, Jochum et al 2017). The prospect of such a mechanism is strengthened by the seemingly limited role of invertebrate community characteristics in determining ML invertebrates in our study (Appendix S1: Table S2, Fig.…”

“…Invertebrates, on the other hand, typically ingest multiple elemental resources simultaneously, in composite form, and regulate resource assimilation internally (Behmer , Halvorson et al. ). Thus, invertebrates may consume greater amounts of a low‐quality resource to obtain the required amount of a limiting nutrient (Suzuki‐Ohno et al.…”

“…Moreover, microbial decomposition is driven by the activities of extracellular ecoenzymes that are resource specific, and thus responsive to environmental cues and microbial demand for specific resources (Burns and Dick 2002). Invertebrates, on the other hand, typically ingest multiple elemental resources simultaneously, in composite form, and regulate resource assimilation internally (Behmer 2009, Halvorson et al 2018). Thus, invertebrates may consume greater amounts of a lowquality resource to obtain the required amount of a limiting nutrient (Suzuki-Ohno et al 2012, Jochum et al 2017).…”