Resource composition mediates the effects of intraspecific variability in nutrient recycling on ecosystem processes

Abstract

Despite the growing evidence for individual variation in trophic niche within populations, its potential indirect effects on ecosystem processes remains poorly understood. In particular, few studies have investigated how intraspecific trophic variability can modulate the effects of consumers on ecosystems through potential changes in nutrient excretion rates.Here, we first quantified the level of intraspecific trophic variability in 11 wild populations of the omnivorous fish Lepomis gibbosus. Outputs from stomach content and stable isotope analyses revealed that the degree of trophic specialization and trophic positions were highly variable between and within these wild populations. There was intrapopulation variation in trophic position of more than one trophic level, suggesting that individuals consumed a range of plant and animal resources. We then experimentally manipulated intraspecific trophic variability to assess how it can modulate consumermediated nutrient effects on relevant processes of ecosystem functioning. Specifically, three food sources varying in nutrient quality (e.g. plant material, macro-invertebrate and fish meat) were used individually or in combination to simulate seven diet treatments. Results indicated that intraspecific variability in growth and nitrogen excretion rates were more related to the composition of the diet rather than the degree of specialization, and increased with the trophic position of the diet consumed. We subsequently used microcosms and showed that critical ecosystem functions, such as primary production and community respiration, were affected by the variability in excretory products, and this effect was biomass-dependent. These results highlight the importance of considering variation within species to better assess the effects of individuals on ecosystems and, more specifically, the effects of consumer-mediated nutrient recycling because the body size and the trophic ecology of individuals are affected by a large spectrum of natural and human-induced environmental changes.

Variability of functional traits and their syndromes in a freshwater fish species (Phoxinus phoxinus): The role of adaptive and nonadaptive processes

“…Nonetheless, we failed to detect the environmental pressures driving divergences in these two traits. The variability in excretion rate probably stands in trophic and stoichiometric factors, such as trophic niche, elemental composition of resources, or allochthonous nutrient inputs (El‐Sabaawi, Warbanski, Rudman, Hovel, & Matthews, ; Evangelista et al, ), which could be characteristic of each geographical site. Hence, measuring stoichiometric variability of individuals and populations would benefit to infer hypotheses regarding variability in excretion rate.…”

“…For instance, the variability in covariations involving excretion rate may have implications for the dynamics of nutrient recycling and ecological stoichiometry (Atkinson, Capps, Rugenski, & Vanni, 2017;Vanni, 2002); while in some populations, large individuals should excrete a high quantity of nitrogen, they should excrete a low quantity of nitrogen in other populations, with potential consequences for primary production (Evangelista et al, 2017;McIntyre et al, 2008).…”

“…Functional traits display variability both within and among populations (Helsen et al, 2017;Villéger, Brosse, Mouchet, Mouillot, & Vanni, 2017). For instance, the nutrient excretion rate (a trait potentially affecting nutrient availability in ecosystems, Vanni, 2002) can vary substantially among and within populations (Evangelista, Lecerf, Britton, & Cucherousset, 2017;Villéger, Grenouillet, Suc, & Brosse, 2012). Since functional traits determine the way organisms modulate the environment, it is important to investigate the spatial distribution of these traits (Funk et al, 2016;Villéger et al, 2017).…”

“…tors, such as trophic niche, elemental composition of resources, or allochthonous nutrient inputs(El-Sabaawi, Warbanski, Rudman, Hovel, & Matthews, 2016;Evangelista et al, 2017), which could be F I G U R E 4 Estimates of P ST for each trait (body mass, metabolic rate, excretion rate, and boldness) and for each covariation (body mass-metabolic rate, body mass-excretion rate, body massboldness, metabolic rate-excretion rate, metabolic rate-boldness, and excretion rate-boldness), and F ST (vertical straight line) on neutral microsatellite markers. Horizontal bars represent 95% confident interval of P ST , and vertical dotted line represents 95% confident interval of F ST that were calculated using cluster bootstrap procedure Syndromes of functional traits among populations of European minnow.…”

Stable resource polymorphism along the benthic littoral–pelagic axis in an invasive crayfish

“…Indeed, substantial trait and genetic variability among invasive individuals have been reported (Forsman, ; González‐Suárez, Bacher, & Jeschke, ), indicating that a high level of intraspecific variability can occur following the introduction stage (60–100 years after establishment, e.g., Hendry, Wenburg, Bentzen, Volk, & Quinn, ; Kinnison, Unwin, Boustead, & Quinn, ; Lankau, ). Because intraspecific variability can modulate the ecological effects of invasive individuals on ecosystem processes (Evangelista, Lecerf, Britton, & Cucherousset, ), quantifying the extent of intraspecific variability in invasive species, notably within populations and across the invasion landscape, is therefore relevant for both applied and theoretical perspectives.…”