Metabolic theory and taxonomic identity predict nutrient recycling in a diverse food web

Abstract

Reconciling the degree to which ecological processes are generalizable among taxa and ecosystems, or contingent on the identity of interacting species, remains a critical challenge in ecology. Ecological stoichiometry (EST) and metabolic theory of ecology (MTE) are theoretical approaches used to evaluate how consumers mediate nutrient dynamics and energy flow through ecosystems. Recent theoretical work has explored the utility of these theories, but empirical tests in species-rich ecological communities remain scarce. Here we use an unprecedented dataset collected from fishes and dominant invertebrates (n = 900) in a diverse subtropical coastal marine community (50 families, 72 genera, 102 species; body mass range: 0.04-2,597 g) to test the utility of EST and MTE in predicting excretion rates of nitrogen (E N ), phosphorus (E P ), and their ratio (E NP ). Body mass explained a large amount of the variation in E N and E P but not E NP . Strong evidence in support of the MTE 3/4 allometric scaling coefficient was found for E P, and for E N only after accounting for variation in excretion rates among taxa. In all cases, including taxonomy in models substantially improved model performance, highlighting the importance of species identity for this ecosystem function. Body nutrient content and trophic position explained little of the variation in E N , E P , or E NP , indicating limited applicability of basic predictors of EST. These results highlight the overriding importance of MTE for predicting nutrient flow through organisms, but emphasize that these relationships still fall short of explaining the unique effects certain species can have on ecological processes. ecological stoichiometry | consumer-mediated nutrient cycling | coastal ecosystems | nitrogen | phosphorus

Disentangling the influences of mean body size and size structure on ecosystem functioning: an example of nutrient recycling by a non‐native crayfish

“…2012), although this relationship can be isometric (e.g., Allgeier et al. 2015). Although details are not presented in full here, the N:P excretion ratio of O. virilis (mean = 200) was similar to other crayfish species (Lessard‐Pillon & McIntyre unpubl.…”

“…2008; Allgeier et al. 2015), although significant interspecific variability in this relationship may exist (Villeger et al. 2012; Allgeier et al.…”

“…2012; Allgeier et al. 2015). In aquatic systems, heterogeneous distributions of total consumer biomass can generate biogeochemical hotspots and hot moments – areas and times of elevated biogeochemical reaction rates (e.g., McClain et al.…”

Embracing general theory and taxon-level idiosyncrasies to explain nutrient recycling

“…This debate concerning the existence (or lack thereof) of general laws is as old as Ecology itself. Allgeier et al (4) lend support to both sides of this debate by statistically disentangling general trends and taxon-level idiosyncrasies in rates of nutrient recycling by individuals. Nutrient recycling is a process fundamental to ecosystem function because it entails the breakdown of organic molecules, thereby releasing dissolved nutrients back into the environment for reuse by plants (5).…”

“…Mass balance dictates that E x = C − E g − P for overall rates of nutrient gain and loss (5). Allgeier et al (4) show that, after statistically controlling for differences among taxa using mixed effects models (13), the dependencies of nitrogen and phosphorus recycling rates on body mass, M, are both well approximated by 3/4-power body mass scaling relations (i.e., ∝ M 3=4 ), implying that a species that is 2.5 times larger in adult mass recycles nitrogen and phosphorus at approximately double the rate (i.e., 2.5 3/4 ≈ 2), as illustrated above.…”