Abstract
Food web dynamics are vital in shaping the functional ecology of ecosystems. However, trophic ecology is still in its infancy in groundwater ecosystems due to the cryptic nature of these environments. To unravel trophic interactions between subterranean biota, we applied an interdisciplinary Bayesian mixing model design (multi‐factor BMM) based on the integration of faunal C and N bulk tissue stable isotope data (δ13C and δ15N) with radiocarbon data (Δ14C), and prior information from metagenomic analyses. We further compared outcomes from multi‐factor BMM with a conventional isotope double proxy mixing model (SIA BMM), triple proxy (δ13C, δ15N, and Δ14C, multi‐proxy BMM), and double proxy combined with DNA prior information (SIA + DNA BMM) designs. Three species of subterranean beetles (Paroster macrosturtensis, Paroster mesosturtensis, and Paroster microsturtensis) and their main prey items Chiltoniidae amphipods (AM1: Scutachiltonia axfordi and AM2: Yilgarniella sturtensis), cyclopoids and harpacticoids from a calcrete in Western Australia were targeted. Diet estimations from stable isotope only models (SIA BMM) indicated homogeneous patterns with modest preferences for amphipods as prey items. Multi‐proxy BMM suggested increased—and species‐specific—predatory pressures on amphipods coupled with high rates of scavenging/predation on sister species. SIA + DNA BMM showed marked preferences for amphipods AM1 and AM2, and reduced interspecific scavenging/predation on Paroster species. Multi‐factorial BMM revealed the most precise estimations (lower overall SD and very marginal beetles' interspecific interactions), indicating consistent preferences for amphipods AM1 in all the beetles' diets. Incorporation of genetic priors allowed crucial refining of the feeding preferences, while integration of more expensive radiocarbon data as a third proxy (when combined with genetic data) produced more precise outcomes but close dietary reconstruction to that from SIA + DNA BMM. Further multidisciplinary modeling from other groundwater environments will help elucidate the potential behind these designs and bring light to the feeding ecology of one the most vital ecosystems worldwide.
Highlights
Trophic dynamics provide vital information about ecological functioning (Lindeman, 1942; Polis & Winemiller, 2013; Start, 2018)
Our findings indicate that the four designs of BMM employed result in different predictions for the diet preferences of stygofaunal beetle species
The small negative Δ14C values for amphipod AM2 and copepods (C and H) suggested that the carbon involved in their biochemical cycles was formed before 1950, while the positive values detected for beetles revealed modern sources indicative of high positions in the trophic chain (Hyodo et al, 2008)
Summary
Trophic dynamics provide vital information about ecological functioning (Lindeman, 1942; Polis & Winemiller, 2013; Start, 2018). Over the last four decades, isotope mixing models, such as IsoSource (Phillips & Gregg, 2001) or Bayesian mixing models (BMM, Parnell et al, 2013), have been increasingly used for quantitative reconstruction of dietary preferences Both techniques aim to quantify unknown mixing contributions via measurement of the isotopic signals in consumers and food sources (Post, 2002). Dietary proxies based on bulk carbon (δ13C) and nitrogen (δ15N) stable isotope analysis (SIA) are a powerful tool for studying trophic preferences and food web interactions (Fry, 2006 and references therein). The work aims to (a) evaluate the use of multi-discipline and/or isotope only models in subterranean ecosystems and (b) provide recommendations on the use of isotopic techniques in groundwater ecology
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