Biology subjects

Thebault, E.

Publications and source records attributed to Thebault, E..

9 recordsLinked to original sources

bioRxiv2026

Correlated traits generate the structure and stability of multiplex ecological networks

Ecological stability and function emerge from the many and diverse types of interactions among species. Ecological networks represent the structure and strength of species interactions, but their study is often restricted to single interaction-types, likely due to an absence of models for plausibly (i.e., nonrandomly) structured 'multiplex networks' of multiple interaction types. Here, we present a general but mechanistic model that simulates multiplex networks using the different, but correlated, traits that determine different species interactions. We show that ecological stability varies systematically with these trait correlations by controlling the emergent complexity and positioning of strong interactions in the community. Our model provides a flexible but power tool to study multiplex networks under alternative trait-based hypotheses, offering new insights into the structure and stability of complex natural systems.

ecology↗

bioRxiv2026

Population and community variability deviate from stationary expectations during transient dynamics

Under complex perturbation regimes, biodiversity dynamics show temporal variability in species and community abundance around long-term population trends. Many species indeed show long-term declines while other species increase, putting natural communities far from stationary regimes, while variability is often studied near equilibrium. We contribute to bridging this gap by investigating population and community variability during long-term trends caused by press perturbations in stochastic models of population dynamics. By estimating the deterministic changes in mean and variance during the transient regime, we show that population variability deviates from stationary expectations. Moreover, the deviation strongly depends on the sign of the population trends: increases generate excesses of variability while declines generate deficits. Scaling up to community variability, we propose a decomposition of community variability deviation, allowing to highlight that community variability in the transient regime depends on how the press perturbation is distributed within species relative abundances and growth rates. These results challenge the equilibrium assumption and open new perspectives for the study of the variability of ecological systems under multiple perturbation types.

ecology↗

bioRxiv2025

Biodiversity temporal trends are reshaping food web structure and redundancy in riverine ecosystems

Biodiversity temporal changes are expected to profoundly impact ecosystem functioning and stability, yet large-scale empirical evidence remains limited. Bridging this gap requires aligning biodiversity temporal trends with food web theory and Biodiversity-Ecosystem Functioning research, both of which provide strong predictions about the ecological consequences of biodiversity loss. Most insights on those consequences currently rely on spatial comparisons of ecological communities, assuming they reflect temporal trends--a space-for-time substitution. Here, we analyze biodiversity and food web time series from over 400 riverine fish communities across France (1995-2018) to evaluate how biodiversity temporal trends reshape food web structure and community functioning. We examine relationships among species richness, community biomass, and three key food web metrics: connectance, weighted average trophic level, and trophic pathway redundancy. We also test the space-for-time hypothesis using spatial gradients and a theoretical food web model. Our structural equation models and robustness analysis reveal that declines in species richness strongly correlate with reduced community biomass, with top trophic-level species playing a disproportionate role in food web changes. Declining biomass is associated with the loss of top trophic levels and decreased connectance, while temporal changes in species richness negatively correlates with changes in connectance. Both biomass and species richness declines reduce trophic pathway redundancy, suggesting that biodiversity loss weakens community robustness to future perturbations. Our findings align with food web theory and Biodiversity-Ecosystem Functioning research, support the validity of space-for-time approaches for basic food web metrics, and demonstrate the relevance of food web metrics as indicators of ecosystem function and fragility. SignificanceRates of biodiversity loss raise urgent concerns about ecosystem functioning and stability, yet how biodiversity trends directly impact these critical processes remains unclear. For instance, food web & Biodiversity-Ecosystem Functioning research has delivered strong predictions about the ecological consequences of biodiversity loss but lack of empirical assessment. Using an extensive dataset of riverine fish communities, we link biodiversity trends to temporal changes in food web structure. We demonstrate that temporal changes in species richness and community biomass consistently associate with altered food web structure. We found that declining biodiversity reduces trophic pathway redundancy, likely increasing ecosystem vulnerability to perturbations. Our findings suggest that food web structure metrics could serve as valuable indicators for monitoring ecosystem health and guiding conservation strategies.

ecology↗

bioRxiv2024

Ecological networks across interaction types are modular and highly driven by sampling intensity at biogeographical scales

Understanding how the structure of ecological communities varies across biotic and abiotic dimensions is a fundamental goal in ecology. This challenge is now approachable due to the increasing availability of data on community structure across the globe. Ecological communities are often defined with respect to the guilds considered and the interactions they engage in, but it is unclear whether interactions of different types respond similarly to large-scale environmental gradients. Therefore, we lack a deeper understanding of how the emergent structure of interaction networks varies across biogeographical gradients, and how this effect may change depending on their constituent interaction types. Here, using a unique dataset of 952 networks across the globe, we provide a first comparison of network structural metrics and their large-scale variability for five overarching interaction types (feeding, frugivory, herbivory, parasitism and pollination). We show that degree distribution, but not connectance alone, helps us understand the observed network structures, and this pattern is maintained across interaction types (with the partial exception of food webs). Moreover, degree distribution descriptors are generally explained by differences across studies, which represent a proxy for variability in sampling and network construction methods. Environ-mental factors show weaker but robust effects on network degree distribution, and food webs are generally more sensitive to changes in environmental factors than networks of other interaction types. By analysing common descriptors of the degree distributions of ecological networks, this study underscores for the first time generalities and differences across networks of different interaction types and their response to environmental and anthropogenic factors.

ecology↗

bioRxiv2023

Bacterial pathogens dynamic during multi-species infections

Soft rot Pectobacteriacea (SRP) gathers more than 30 bacterial species that collectively rot a wide range of plants by producing and secreting a large set of plant cell wall degrading enzymes (PCWDEs). Worldwide potato field surveys identified 15 different SRP species on symptomatic plants and tubers. The abundance of each species observed during outbreaks varies over space and time and the mechanisms driving species shift during outbreak are unknown. Furthermore, multi-species infections are frequently observed and the dynamics of these coinfections are not well understood. To understand the dynamics of coinfections, we set up 16 different synthetic communities of 6 SRP strains to mimic coinfections. The bacteria present in each tested community were representative of 2 different species, with 3 strains per species. These communities were inoculated in potato tubers or on synthetic media and their outcome was followed by amplification and Illumina sequencing of the discriminatory housekeeping gene gapA. We also compared disease incidence and bacterial multiplication in potato tubers during mixed-species infection and single-species infection. A species that was unable to induce disease in potato was efficiently maintained and eventually became dominant in some of the communities tested, indicating that cheating can shape dominant species. Modeling indicates that the cost of PCWDEs production and secretion, the rate of potato degradation and the diffusion rate of degraded substrate could favor the cheater species. Interaction outcomes differed between potato tuber and synthetic medium, highlighting the driving effect of environmental conditions, with higher antagonistic interactions observed in potato tubers. Antagonistic interactions were strain specific and not species specific. Toxicity interference was also observed within some communities, allowing the maintenance of strains otherwise sensitive to toxic compounds. Overall, the results indicate that intraspecific competition, cooperation through trophic interaction and toxicity interference contribute to the maintenance of SRP diversity. The implications of these processes for epidemiological surveillance are discussed.

microbiology↗

bioRxiv2023

A general trait-based model for multiplex ecological networks

Ecological networks can represent the structure of food webs, energy flow, and the many and diverse types of interactions between species in ecosystems. Despite its tremendous importance for understanding biodiversity, stability, ecosystem functioning, research on ecological networks has traditionally been restricted to subsets of the species or interactions in ecosystems, i.e., "subnetworks" such as pollination networks or food webs. As a result, the structure of "multiplex" networks that include multiple interaction types is mostly unknown and there is no robust, underlying theory to support their study. Some ecological traits, such as body size or length of mouth parts, are well-known as key predictors of different species interactions. These traits are often strongly related to each other due to evolutionary history, allometry, and selection, and this relatedness may constrain the structure of ecological multiplex networks. We use this idea to develop a model that simulates multiplex ecological networks by interconnecting subnetworks using correlated traits. Our model predicts how multiplex network structure, measured as the overlaps between species functional roles, is affected by neutral processes, interaction rules, and trait constraints, while the structure of individual subnetworks is independent of these trait correlations. Additionally, our model accurately predicts the structure of an observed multiplex network using existing knowledge on species trait correlations and basic features of known ecological subnetworks. This work will stimulate new studies of the structure and dynamics of complex ecosystems by providing a null expectation for how multiplex ecological networks are structured under different ecological conditions.

ecology↗

bioRxiv2023

Quality matters: stoichiometry of resources modulates spatial feedbacks in aquatic-terrestrial meta-ecosystems

Species dispersal and resource spatial flows greatly affect the dynamics of connected ecosystems. So far, research on meta-ecosystems has mainly focused on the quantitative effect of subsidy flows. Yet, resource exchanges at heterotrophic-autotrophic (e.g., aquatic-terrestrial) ecotones display a stoichiometric asymmetry that likely matters for functioning. Here, we joined ecological stoichiometry and the meta-ecosystem framework to understand how subsidy stoichiometry mediates the response of the meta-ecosystem to subsidy flows. Our model results demonstrate that resource flows between ecosystems can induce a positive spatial feedback loop, leading to higher production at the meta-ecosystem scale by relaxing local ecosystem limitations ("spatial complementarity"). Furthermore, we show that spatial flows can also have an unexpected negative impact on production when accentuating the stoichiometric mismatch between local resources and basal species needs. This study paves the way for studies on the interdependancy of ecosystems at the landscape extent. Data: The code and the data, as well as a small tutorial to run the model are available on Github via Zenodo: https://doi.org/10.5281/zenodo.7733880

ecology↗

bioRxiv2018

Impact of nutrient cycling on food web stability

AO_SCPLOWBSTRACTC_SCPLOWNutrient cycling is fundamental to ecosystem functioning. Despite recent major advances in the understanding of complex food web dynamics, food web models have so far generally ignored nutrient cycling. However, nutrient cycling is expected to strongly impact food web stability and functioning. To make up for this gap, we built an allometric and size structured food web model including nutrient cycling. By releasing mineral nutrients, recycling increases the availability of limiting resources for primary producers and links each trophic level to the bottom of food webs. We found that nutrient cycling can provide a significant part of the total nutrient supply of the food web, leading to a strong enrichment effect that promotes species persistence in nutrient poor ecosystems but leads to a paradox of enrichment at high nutrient inputs. The presence of recycling loops linking each trophic level to the basal resources weakly affects species biomass temporal variability in the food web. Recycling loops tend to slightly dampen the destabilising effect of nutrient enrichment on consumer temporal variability while they have opposite effects for primary producers. By considering nutrient cycling, this new model improves our understanding of the response of food webs to nutrient availability and opens perspectives to better link studies on food web dynamics and ecosystem functioning.

ecology↗

bioRxiv2017

Selective effects of temperature on body mass depend on trophic interactions and network position

Body mass is a key trait constraining interspecific interactions in food webs through changes in metabolic requirements. Because climate warming affects metabolic rates, it creates direct selective effects on body mass. Many empirical studies suggest that body mass decreases under warming, although important exceptions have been noted. We first analyze the evolution of body mass in a simple consumer-resource model to provide conditions under which a body mass increase or decrease may be expected. We then extend our model to a multi-trophic food web context that allows for the coevolution of body mass and of feeding preferences. We focus here on how the trophic position of a consumer influences its evolutionary response to warming under different scenarios for the temperature dependence of attack rates. We observe that body masses can remain constant or increase with temperature when attack rates are constant or increasing with temperature, while body mass reductions in response to warming are only expected when attack rates have a thermal optimum and populations are initially locally adapted. We also found that body masses at lower trophic levels vary less under warming than body masses at higher trophic levels, which may be explained by decreasing levels of stabilizing selection along food chains.

ecology↗