An allometric niche model for species interactions in temperate freshwater ecosystems

Abstract

Trophic interactions are central in understanding ecosystem processes and the management of natural ecosystems but are frequently complex to estimate. To address this issue, body size has been shown to be a useful trait to reconstruct species interactions, particularly in aquatic ecosystems. An allometric niche model (aNM) considering body size as a niche trait is proposed to predict trophic interactions in temperate freshwater ecosystems. The aNM calibration was based on 26 ubiquitous freshwater species with known minimal and maximum prey body sizes that permitted the establishment of prey body size ranges for vertebrate and invertebrate consumers. The aNM inferences were validated for 13 empirical freshwater food webs, and the model was applied to an extensive inventory of 474 species (spanning six orders of body size magnitude) from the largest natural French lake (Lake Bourget). This application permitted to strengthen the aNM validation with predatorprey mass ratio comparisons, predicted diet analyses, and allowed the exploration of the lake food web structure. The aNM provided appreciable intrinsic validity (specificity = 87 AE 12%, sensitivity = 59 AE 29%, accuracy = 81 AE 10%), and departures among inferred and empirical trophic interactions were explained by foraging specificities or limited sampling of stomach contents. In Lake Bourget, 26,037 trophic links were inferred. Predatorprey mass ratios for vertebrates and invertebrates were consistent with those empirically established and were occasionally higher for invertebrates as the aNM considers small prey (e.g., bacteria) as possible resources for invertebrates. The inferred diets for three species selected for their well-known foraging ecology also revealed plausible outcomes of the aNM. The nested structure of the lake food web was determined by highlighting different topologies among the benthic and the pelagic food sub-webs and the role of top predator fish in the coupling of both food sub-webs. Due to the large number of species inventories available worldwide for freshwater ecosystems anchored in the ecological monitoring, the aNM may represent a valuable tool for both ecologists and managers to address complementary facets of applied biodiversity studies (e.g., reconstruct highly resolved food webs, predict pressures on important species or new interactions with invasive species).

Temperature, productivity, and habitat characteristics collectively drive lake food web structure

“…The parameters c and r were estimated using a linear model and 5%–95% quantile regressions, respectively (Gravel et al, 2013). The aNM was calibrated using a set of 26 consumers covering wide taxonomic and body size diversities (i.e., from protists to piscivorous fish) for which diets and/or feeding ranges were already documented (see Vagnon et al, 2021 for more details). Due to vertebrate and invertebrate consumers differing in their feeding ranges, the aNM parameters ( c and r ) were estimated independently for these two taxonomic groups.…”

“…Due to vertebrate and invertebrate consumers differing in their feeding ranges, the aNM parameters ( c and r ) were estimated independently for these two taxonomic groups. Vagnon et al (2021) validated the model using independent data and found that it predicts well empirical trophic links (accuracy = 81 ± 10%, equation 4 of Vagnon et al, 2021) (see also Supporting Information S4 for predator–prey mass ratio analysis and Supporting Information S5 for an analysis of the influence of fish body size on the niche attributes, trophic links, and food web metrics using either empirical body size measurements or body size estimates from the literature). Overall, the aNM provides integrative food webs including all realized trophic interactions although they are not necessarily realized simultaneously in nature.…”

Combining food web theory and population dynamics to assess the impact of invasive species

“…We used the aNM (Vagnon et al, 2021) to infer trophic interactions between SC included in the typical peri-Alpine lake food web and to reconstruct the "non-invaded" (i.e., without S. glanis) and "invaded" food webs (i.e., with S. glanis). This model relies on the niche model principles (Williams and Martinez, 2000) stating that the niche position of consumer j is given by its average body size bs j and that its resources fall within a body size range bs_r j centered on bs_c j .…”

“…This model relies on the niche model principles (Williams and Martinez, 2000) stating that the niche position of consumer j is given by its average body size bs j and that its resources fall within a body size range bs_r j centered on bs_c j . The range bounds were estimated using quantile regressions (i.e., bs_r jmin = QR at 5% and bs_r jmax = QR at 95%) as suggested by Gravel et al (2013) and are specifically fitted whether consumers are vertebrate or invertebrate (Vagnon et al, 2021).…”

“…In this study, we used an approach combining an allometric niche model with a population dynamic model, both allometrically scaled, to grasp the diversity of impacts (direct/indirect, negative/positive) that invasive species can exert on wide resident communities (from primary producers to the apex predator) in aquatic ecosystems. More precisely, we reconstructed a non-invaded and an invaded food web by inferring trophic interactions among multiple species clusters (S = 58) in presence and in absence of an invader using an allometric niche model (hereafter called aNM; Vagnon et al, 2021). These interactions were then included in a population dynamic model, based on the model from Brose et al (2006) that we modified by using alternative allometric parameterization, allowing to measure abundance changes of resident species over time in absence/presence of the invader with few empirical data inputs.…”