Non‐random interactions within and across guilds shape the potential to coexist in multi‐trophic ecological communities

Abstract

Theory posits that the persistence of species in ecological communities is shaped by their interactions within and across trophic guilds. However, we lack empirical evaluations of how the structure, strength and sign of biotic interactions drive the potential to coexist in diverse multi‐trophic communities. Here, we model community feasibility domains, a theoretically informed measure of multi‐species coexistence probability, from grassland communities comprising more than 45 species on average from three trophic guilds (plants, pollinators and herbivores). Contrary to our hypothesis, increasing community complexity, measured either as the number of guilds or community richness, did not decrease community feasibility. Rather, we observed that high degrees of species self‐regulation and niche partitioning allow for maintaining larger levels of community feasibility and higher species persistence in more diverse communities. Our results show that biotic interactions within and across guilds are not random in nature and both structures significantly contribute to maintaining multi‐trophic diversity.

Structural asymmetry in biotic interactions as a tool to understand and predict ecological persistence

“…Rather, our results emphasize that the interaction structure of the system, which varies from year to year, implying concomitant variations in the size and shape of the FD, is in itself ecologically relevant for predicting short-term demographic performance. As shown in Box 2, this framework can accommodate more complex communities considering not only plants but also several trophic levels, such as plant-pollinator systems or multi-trophic communities (García-Callejas et al, 2023). Empirically documenting all relevant competitive, mutualistic and trophic interactions of a community is the next step needed to percolate the use of theoreticallyinformed tools to better understand and predict the temporal dynamics of ecological systems.…”

“…This framework posits that the structure of species interactions determines the opportunities for species to coexist by conditioning the size of the feasibility domain. Particular structures of species interactions, such as intraspecific competition exceeding interspecific competition, promote larger sizes of the feasibility domains and, therefore, larger opportunities for species to coexist (Barabás et al, 2016;García-Callejas et al, 2023). In order to measure the size of the feasibility domain, we need to connect the structure of species interactions with a model describing the dynamics of interacting species.…”

“…We denote such quantity as the species exclusion ratio (García-Callejas et al, 2023) (see Suppl. Section 5 for a generalization of Equation ( 5)).…”

“…The larger these opportunities (measured as the size of the so-called feasibility domain), the larger the range of environmental conditions the community can withstand without losing any species. Among other insights, it has been predicted (Saavedra et al, 2017), and empirically shown (Bartomeus et al, 2021;García-Callejas et al, 2023) that this situation occurs when species experience strong selfregulation and niche differentiation. These insights are probabilistic in nature , coherent with the principle that is impossible to quantify the whole set of abiotic and biotic factors modulating community dynamics (Shoemaker et al, 2019).…”

Food web complexity modulates environmental impacts on food chain length

“…Our findings may also provide important insights into the stability-diversity debate (McCann, 2000). "May's paradox" of community stability has sparked a discussion of how complex webs of interacting species are maintained despite their inherent instability (Gardner and Ashby, 1970;May, 1972;Allesina and Tang, 2012), and previous studies suggest that the non-random species interaction is the key factor promoting stable coexistence (Thébault and Fontaine, 2010;Mougi and Kondoh, 2012;García-Callejas et al, 2023). The present study suggests another non-randomness related to community stability: expanding the "vertical" dimension of biodiversity (Wang and Brose, 2018), or increasing FCL, is more likely to lead to community collapse than increasing "horizontal" biodiversity or adding species to the already-occupied trophic positions.…”