Inferring species interactions from ecological survey data: a mechanistic approach to predict quantitative food webs of seed-feeding by carabid beetles

Abstract

Ecological networks are valuable for ecosystem analysis but their use is often limited by a lack of data because many types of ecological interaction, e.g. predation, are short-lived and difficult to observe or detect. There are different methods for inferring the presence of interactions, which we lack methods to predict interaction strengths and so use weighted network analysis.Here, we develop a trait-based approach suitable for creating quantitative networks, i.e. with varying interaction strengths. We developed the method for seed-feeding carabid ground beetles (Coleoptera: Carabidae) although the principles can be applied to other interactions.We used existing literature data from experimental seed-feeding trials to predict a per-individual interaction cost index based on carabid and seed size with frequency-dependent prey selection and assuming bottom up control. This was scaled up to the population level to create predicted inferred weighted networks using the abundance of carabids and seeds in samples from arable fields and energetic intake rates of carabids from the literature. From these weighted networks, we also calculated a novel measure of predation pressure.We applied it to existing ecological survey data from 255 arable fields with carabid data from pitfall traps and plant seeds from seed rain traps. Analysis of these inferred networks led to testable hypotheses about how networks and predation pressure varied amongst fields.Inferred networks are valuable because (i) they provide null models for the structuring of food webs to test against empirical species interaction data, e.g. DNA analysis of carabid gut regurgitates, and (ii) they allow weighted inferred networks to be constructed whenever we can estimate interactions between species and have ecological census data available. This would permit network analysis even at times and in places when interactions were not directly assessed.

Direct and indirect effects of landscape and field management intensity on carabids through trophic resources and weeds

“…Future research should extend this analysis by relaxing the implicit assumption we have made that all prey species, within each of the animal and seed prey components, have the same food value for carabids. Different scores might be assigned to the food resources depending on carabid feeding preferences evaluated in laboratory tests (Gaba et al, 2019), by molecular analysis (Frei (Gray et al, 2021;Pocock et al, 2020).…”

Combined effect of crop rotation and carabid beetles on weed dynamics in arable fields

“…Weed regulation through the action of natural predators not only reduces the number of weeds in the seedbank but can also reduce the use of synthetic herbicides and the risk of evolution of herbicide-resistance. Although carabid beetles do have preferences in their seed consumption (Honek et al, 2007; Petit et al, 2014), carabid diet is relatively broad and largely driven by seed:carabid size (Pocock et al 2020). Therefore, the regulation service provided by carabid beetles is likely to increase taxonomic and functional diversity and control the dominance of highly competitive weeds.…”

“…We quantified predation pressure as the number of seeds consumed by the assemblage of carabids present, taking into account carabid seed preferences, the community of seeds present, and carabid energetic requirements (Pocock et al, 2020). In their work, Pocock et al, (2020) derive a predation pressure index from an inferred carabid-seed food web.…”

“…We quantified predation pressure as the number of seeds consumed by the assemblage of carabids present, taking into account carabid seed preferences, the community of seeds present, and carabid energetic requirements (Pocock et al, 2020). In their work, Pocock et al, (2020) derive a predation pressure index from an inferred carabid-seed food web. In this food web, the interactions were inferred based on species frequency-dependent foraging and size-dependent preferences obtained from the literature (Gendron, 1987; Honek et al, 2013; Petit et al, 2014), and the interaction strengths were calculated by scaling up by carabid density and energetic requirements.…”

“…the indirect link between standing weed and seedbank t 1 . Fourthly, the effect of carabid beetles on the seedbank at t 1 by including the predation pressure index derived from the inferred carabid-seed food web in each field (see details in Pocock et al, 2020). With this last relationship, we accounts for the effectiveness of carabids in regulating arable weeds, based on their dietary preference and calorific requirement which are expected to have important implication in carabid seed consumption and contribution to weed management (Gaba et al, 2019; Honek et al, 2013; Petit et al, 2014).…”