Ecological network assembly: How the regional metaweb influences local food webs

Abstract

1. Local food webs result from a sequence of colonisations and extinctions by species from the regional pool or metaweb, that is, the assembly process. Assembly is theorised to be a selective process: whether or not certain species or network structures can persist is partly determined by local processes including habitat filtering and dynamical constraints. Consequently, local food web structure should reflect these processes.2. The goal of this study was to test evidence for these selective processes by comparing the structural properties of real food webs to the expected distribution given the metaweb. We were particularly interested in ecological dynamics; if the network properties commonly associated with dynamical stability are indeed the result of stability constraints, then they should deviate from expectation in the direction predicted by theory.3. To create a null expectation, we used the novel approach of randomly assembling model webs by drawing species and interactions from the empirical metaweb.The assembly model permitted colonisation and extinction, and required a consumer species to have at least one prey, but had no habitat type nor population dynamical constraints. Three datasets were used: (a) the marine Antarctic metaweb, with two local food webs; (b) the 50 lakes of the Adirondacks; and (c) the arthropod community from Florida Keys' classic defaunation experiment.4. Contrary to our expectations, we found that there were almost no differences between empirical webs and those resulting from the null assembly model. Few empirical food webs showed significant differences with network properties, motif representations and topological roles. Network properties associated with stability did not deviate from expectation in the direction predicted by theory. 5. Our results suggest that-for the commonly used metrics we considered-local food web structure is not strongly influenced by dynamical nor habitat restrictions. Instead, the structure is inherited from the metaweb. This suggests that the network properties typically attributed as causes or consequences of ecological stability are instead a by-product of the assembly process (i.e. spandrels), and may potentially be too coarse to detect the true signal of dynamical constraint.

Network analysis suggests changes in food web stability produced by bottom trawl fishery in Patagonia

“…We found that fishery activities in the San Jorge Gulf (SJG) could reduce the stability of the food web. Recent results suggest that unweighted topological metrics can not detect either alterations in fluxes 47 or changes in stability 19 . In our study, both the weighted and unweighted metrics showed the same pattern, with quasi sign-stability being the metric with the most straightforward interpretation that showed the lowering of stability.…”

“…To describe and compare food webs, a useful approach is through network metrics related to stability and resilience of the system, like the level of omnivory 13 , the mean trophic level 14 , modularity 15 and other metrics 16 . However, an accumulating body of evidence suggests that the relationship between structural properties and stability can only be understood if the strength of interactions are considered 17 – 19 .…”

Land‐use intensity affects the potential for apparent competition within and between habitats

“…Thus, these results support the notion that landscape scale management impacts invertebrate communities at the local level, and contribute to a growing realisation that the consideration of species interactions as being isolated and spatially explicit limits our understanding of the processes governing ecological communities (Guichard, 2017). Instead, networks of networks combined into a single ‘metaweb’ can provide a powerful tool for understanding landscape level deterministic processes (Saravia et al., 2019).…”

The structure of Lepidoptera-plant interaction networks across clades, life stages, and environmental gradients

“…We subsequently applied the “metaweb” approach (Ho et al, 2022; Saravia et al, 2022) to extrapolate local co-occurrences of Lepidoptera and plants to local interaction networks, taking our dietary matrices as the respective larval and adult metawebs. The approach assumes that a feeding interaction indicated in the metaweb will realise if the corresponding Lepidoptera-plant species pair co-occur locally, that is in the given grid cells looked at.…”