The plant-ant Camponotus schmitzi helps its carnivorous host-plant Nepenthes bicalcarata to catch its prey

The Bornean climber, Nepenthes bicalcarata, is unique among plants because it is both carnivorous and myrmecophytic, bearing pitcher-shaped leaves and the ant Camponotus schmitzi within tendrils. We explored, in the peat swamp forests of Brunei, the hypothesis that these ants contribute to plant nutrition by catching and digesting its prey.Wefirst tested whether ants increasedplant's capture rate.Wefound that unlikemost plant-ants, C. schmitzidonot exhibit dissuasive leaf-patrolling behaviour (zero patrol on 67 pitchers of 10 plants) but lie concealed under pitcher rim (13 ± 6 ants per pitcher) allowing numerous insect visits. However, 47 out of 50 individuals of the largest visitor dropped into the pitchers of five plants were attacked by ants and the capture rate of the same pitchers deprived of their ambush hunting ants decreased three-fold.We then tested whether ants participated in plant's digestion.We showed in a 15-d long experiment that ants fed on prey and returned it in pieces in seven out of eight pitchers. The 40 prey deposited in ant-deprived pitchers remained intact indicating a weak digestive power of the fluid confirmed to be only weakly acidic (pH ?5, n = 67). The analysis of 10 pitcher contents revealed that prey, mainly ants and termites, was very numerous (?400 per pitcher per plant) and highly fragmented. Altogether, these data suggest a positive effect of C. schmitzi on both prey intake and breakdown. This ant-plant interaction could thus be a nutritional mutualism involving the unusual association of carnivory and myrmecotrophy

Metaecosystem dynamics drive community composition in experimental, multi‐layered spatial networks

Cross‐ecosystem subsidies are studied with a focus on resource exchange at local ecosystem boundaries. This perspective ignores regional dynamics that can emerge via constraints imposed by the landscape, potentially leading to spatially‐dependent effects of subsidies and spatial feedbacks. Using miniaturized landscape analogues of river dendritic and terrestrial lattice spatial networks, we manipulated and studied resource exchange between the two whole networks. We found community composition in dendritic networks depended on the resource pulse from the lattice network, with the strength of this effect declining in larger downstream patches. In turn, this spatially‐dependent effect imposed constraints on the lattice network with populations in that network reaching higher densities when connected to more central patches in the dendritic network. Consequently, localized cross‐ecosystem fluxes, and their respective effects on recipient ecosystems, must be studied in a perspective taking into account the explicit spatial configuration of the landscape

Seasonal dynamics of detritus flows and decomposition across ecosystem boundaries

Material fluxes are ubiquitous in nature within and across ecosystems, connecting habitats with vastly different characteristics, like forests to rivers and lakes.1–3 Although individual fluxes and their cascading effects are well known,4–6 very few studies address the intra-annual phenology of ecosystem processes, despite the pronounced seasonality of fluxes. Here, we empirically quantified and resolved fluxes of recalcitrant and labile types of leaf litter in temperate riparian forests and streams across a year, representing one of the most emblematic examples of seasonal systems. We quantified intra-annual variation in litter inputs from terrestrial plants to forest floors and streams and estimated aquatic and terrestrial decomposition rates across the year at 6-week intervals. Our data show that the autumn pulse of leaf litter is complemented by smaller magnitude but more constant-through-the-year lateral flows to the stream ecosystems. Decomposition of labile litter fluctuated seasonally, on a different phenology, with generally higher rates in summer, but rates of recalcitrant litter decomposition remained largely constant. Microorganisms were the main contributors to the decomposition process in both forests and streams. Overall, our work highlights the asynchronous and seasonally variable changes in decomposition rates between recalcitrant and labile detritus despite their initial synchronized availability and suggests that the dominating presence of recalcitrant litter buffers ecosystem responses to the concentrated temporal distribution of litter resources.7,8 Investigating such ecological processes both across ecosystem borders and at fine intra-annual resolutions is imperative to understand complex system responses in the context of species’ shifts in phenologies and resource quality.9–1

Deforestación y agroindustria en Bolivia: el comercio internacional como motor del “extractivismo” en la Ecología-Mundo

La Amazonía es una región de gran importancia socioecológica, además de un territorio de disputa política y discursiva. Los complejos procesos de la región demandan un análisis interdisciplinario. El presente trabajo se centra en la dinámica de la deforestación en Bolivia, identificando los motores próximos y ulteriores. La principal causa próxima de la deforestación en Bolivia es el cultivo agroindustrial de soya y la ganadería extensiva. En el bioma amazónico el principal motor posterior de la deforestación se relaciona con la demanda de mercancías. Dado que existe una fuerte dependencia del régimen de lluvias en la evapotranspiración de los árboles en la Amazonía boliviana, la conversión del uso de la tierra causada por este sector puede afectar profundamente el clima regional, a través de procesos de retroalimentación. La caracterización de la producción de soya en Bolivia como “extractivismo agrario” es insuficiente. Este concepto por sí solo, y sin ser vinculado a la Ecología-mundo, dificulta una crítica necesaria al capitalismo, así como abordar adecuadamente los problemas socioecológicos, frecuentemente originados en asimetrías históricas. Por lo tanto, es necesario considerar el “extractivismo” como una agregación de relaciones de intercambio desigual

La conservation à la croisée des chemins

Dans le contexte actuel de déclin impor- tant de la biodiversité et d’effritement constant des services écosystémiques qu’elle procure, les approches de conservation classiques semblent en partie inadéquates pour maintenir l’in- tégrité des écosystèmes dont les socié- tés humaines ont pourtant besoin, car les priorités de conservation sont d’abord établies en fonction de la rareté de l’espèce et non de son importance fonctionnelle dans l’écosystème. Dans un contexte de restriction budgétaire globale pour la conservation, cela crée un déséquilibre disproportionné entre les efforts mis en œuvre pour maintenir une espèce dans un écosystème donné et la nécessité de protéger le fonction- nement et la résilience de l’ensemble de l’écosystème. Nous suggérons qu’un changement d’objectif vers la protection des réseaux écologiques pourrait per- mettre, du même souffle, de protéger la biodiversité et l’intégrité écosystémique que celle-ci soutient

Interactions multi-échelles entre ressources abiotiques, réseaux trophiques et propriétés des écosystèmes : nouveaux jalons théoriques pour une écologie intégrative

RÉSUMÉ: Ce travail de thèse s'inscrit dans l'effort actuel de construction d'une écologie intégrative. J'y étudie les mécanismes d'interaction entre ressources abiotiques, réseaux trophiques et propriétés des écosystèmes, au moyen d'une expérience d'évolution, d'un modèle de méta-écosystème et d'un modèle bioénergétique d'assemblage d'écosystèmes. Les organismes modifient la disponibilité des ressources en les prélevant pour leur croissance. Inversement, la disponibilité des ressources influence la diversité et la composition en espèces du réseau trophique, en agissant comme force de sélection sur les traits d'acquisition des ressources (chap. 1,5). Les propriétés de l'écosystème, telles que stabilité et productivité, dérivent des interactions entre la dynamique des ressources et celle du réseau trophique (chap. 2). Enfin,le fonctionnement de l'écosystème rétroagit sur les ressources abiotiques via le recyclage de la biomasse (chap. 2, 5). Ces processus interviennent lors de I'assemblage des réseaux trophiques et structurent le développement des écosystèmes (chap. 3-5). Dans cette thèse, j'analyse ces mécanismes de rétroaction biotique-abiotique sur plusieurs échelles d'organisation, d'espace et de temps. Notamment, les modèles développés ici fournissent des outils novateurs pour étudier les mécanismes de construction des écosystèmes, en mettant en évidence les liens entre métabolisme des espèces, structure du réseau trophique et fonctionnement de l'écosystème, et leur variation au cours du temps. Ce travail ouvre de vastes perspectives de recherche en combinant les derniers progrès d'une écologie intégrative dans une conception mécaniste du développement des écosystèmes. -- Mot(s) clé(s) en français : biodiversité, développement des écosystèmes, assemblage des communautés, méta-écosystèmes, recyclage, nutriments inorganiques, modèle bioénergétique. -- ABSTRACT: This thesis participates to the current effort towards the construction of an integrative ecology. I study the feedback mechanisms between abiotic resources, food webs and ecosystem properties, through an evolution experiment, a model of metaecosystem, and a bioenergetic ecosystem assembly model. Organisms modify resource availability by consuming them for their growth. Conversely, resource availability influences the species diversity and composition of the food web, by acting as a selection pressure on traits for resource acquisition (chap. 1, 5). Ecosystem properties, such as stability and productivity, derive from the interactions between resource and food web dynamics (chap. 2). Finally, ecosystem functioning feeds back on abiotic resources through the recycling of biomass (chap. 2 and 5). These processes occur during the food web assembly and drive the development of ecosystems (chap. 3-5). In this thesis I analyze these biotic-abiotic feedback mechanisms on several scales of organization, space and time. The models developed here provide innovative tools to study the mechanisms of ecosystem construction by pointing out the links between species metabolism, food web structure and ecosystem functioning, and their variation through time. This work opens wide research perspectives, as it combines the most recent progress of an integrative ecology into a mechanistic framework of ecosystem development. -- Mot(s) clé(s) en anglais : biodiversity, ecosystem development, community assembly, metaecosystems, inorganic nutrients, recycling, bioenergetic model

MULTI-SCALE FEEDBACKS BETWEEN ABIOTIC RESSOURCES, FOOD WEBS AND ECOSYSTEM PROPERTIES : New theoretical milestones for an integrative ecology

Ce travail de thèse s'inscrit dans l'effort actuel de construction d'une écologie intégrative. J'y étudie les mécanismes d'interaction entre ressources abiotiques, réseaux trophiques et propriétés des écosystèmes, au moyen d'une expérience d'évolution, d'un modèle de méta-écosystème et d'un modèle bioénergétique d'assemblage d'écosystèmes. Les organismes modifient la disponibilité des ressources en les prélevant pour leur croissance. Inversement, la disponibilité des ressources influence la diversité et la composition en espèces du réseau trophique, en agissant comme force de sélection sur les traits d'acquisition des ressources (chap. 1, 5). Les propriétés de l'écosystème, telles que stabilité et productivité, dérivent des interactions entre la dynamique des ressources et celle du réseau trophique (chap. 2). Enfin, le fonctionnement de l'écosystème rétroagit sur les ressources abiotiques via le recyclage de la biomasse (chap. 2, 5). Ces processus interviennent lors de l'assemblage des réseaux trophiques et structurent le développement des écosystèmes (chap. 3-5). Dans cette thèse j'analyse ces mécanismes de rétroaction biotique-abiotique sur plusieurs échelles d'organisation, d'espace et de temps. Notamment, les modèles développés ici fournissent des outils novateurs pour étudier les mécanismes de construction des écosystèmes, en mettant en évidence les liens entre métabolisme des espèces, structure du réseau trophique et fonctionnement de l'écosystème, et leur variation au cours du temps. Ce travail ouvre de vastes perspectives de recherche en combinant les derniers progrès d'une écologie intégrative dans une conception mécaniste du développement des écosystèmes.This thesis participates to the current effort towards the construction of an integrative ecology. I study the feedback mechanisms between abiotic resources, food webs and ecosystem properties, through an evolution experiment, a model of metaecosystem, and a bioenergetic ecosystem assembly model. Organisms modify resource availability by consuming them for their growth. Conversely, resource availability influences the species diversity and composition of the food web, by acting as a selection pressure on traits for resource acquisition (chap. 1, 5). Ecosystem properties, such as stability and productivity, derive from the interactions between resource and food web dynamics (chap. 2). Finally, ecosystem functioning feeds back on abiotic resources through the recycling of biomass (chap. 2 and 5). These processes occur during the food web assembly and drive the development of ecosystems (chap. 3-5). In this thesis I analyze these biotic-abiotic feedback mechanisms on several scales of organization, space and time. The models developed here provide innovative tools to study the mechanisms of ecosystem construction by pointing out the links between species metabolism, food web structure and ecosystem functioning, and their variation through time. This work opens wide research perspectives, as it combines the most recent progress of an integrative ecology into a mechanistic framework of ecosystem development

How pulse disturbances shape size‐abundance pyramids

Ecological pyramids represent the distribution of abundance and biomass of living organisms across body-sizes. Our understanding of their expected shape relies on the assumption of invariant steady-state conditions. However, most of the world’s ecosystems experience disturbances that keep them far from such a steady state. Here, using the allometric scaling between population growth rate and body-size, we predict the response of size-abundance pyramids within a trophic guild to any combination of disturbance frequency and intensity affecting all species in a similar way. We show that disturbances narrow the base of size-abundance pyramids, lower their height and decrease total community biomass in a nonlinear way. An experimental test using microbial communities demonstrates that the model captures well the effect of disturbances on empirical pyramids. Overall, we demonstrate both theoretically and experimentally how disturbances that are not size-selective can nonetheless have disproportionate impacts on large species

Global quantitative synthesis of ecosystem functioning across climatic zones and ecosystem types

Aim Providing a quantitative overview of ecosystem functioning in a three‐dimensional space defined by ecosystem stocks, fluxes and rates, across major ecosystem types and climatic zones. Location Global. Time period 1966–2019. Major taxa studied Ecosystem‐level measurements (all organism types). Methods We conducted a global quantitative synthesis of a wide range of ecosystem variables related to carbon stocks and fluxes. We gathered a total of 4,479 values from 1,223 individual sites (unique geographical coordinates) reported in the literature (604 studies), covering ecosystem variables including biomass and detritus stocks, gross primary production, ecosystem respiration, detritus decomposition and carbon uptake rates, across eight major aquatic and terrestrial ecosystem types and five broad climatic zones (arctic, boreal, temperate, arid and tropical). We analysed the relationships among variables emerging from the comparisons of stocks, fluxes and rates across ecosystem types and climates. Results Within our three‐dimensional functioning space, average ecosystems align along a gradient from fast rates–low fluxes and stocks (freshwater and pelagic marine ecosystems) to low rates–high fluxes and stocks (forests), a gradient that we hypothesize results mainly from variation in primary producer characteristics. Moreover, fluxes and rates decrease from warm to colder climates, consistent with the metabolic theory of ecology. However, the strength of climatic effects differs among variables and ecosystem types, resulting, for instance, in opposing effects on net ecosystem production between terrestrial and freshwater ecosystems (positive versus negative effects). Main conclusions This large‐scale synthesis provides a first quantified cross‐ecosystem and cross‐climate comparison of multivariate ecosystem functioning. This gives a basis for a mechanistic understanding of the interdependency of different aspects of ecosystem functioning and their sensitivity to global change. To anticipate responses to change at the ecosystem level, further work should investigate potential feedbacks between ecosystem variables at finer scales, which involves site‐level quantifications of multivariate functioning and theoretical developments

Resource Flow Network Structure Drives Metaecosystem Function

International audienceNon-living resources frequently flow across ecosystem boundaries, which can yield networks of spatially-coupled ecosystems. Yet, the significance of resource flows for ecosystem function has predominantly been understood by studying two or a few coupled ecosystems, overlooking the broader resource flow network and its spatial structure. Here, we investigate how the spatial structure of larger resource flow networks influences ecosystem function at meta-ecosystem scales by analyzing meta-ecosystem models with homogeneously versus heterogeneously distributed resource flow networks, but otherwise identical characteristics. We show metaecosystem function can differ strongly between meta-ecosystems with contrasting resource flow networks. Differences in function generally arise through the scaling-up of nonlinear local processes interacting with spatial variation in local dynamics, the latter of which is influenced by network structure. However, we find that neither network structure guarantees the greatest metaecosystem function. Rather, biotic (organism traits) and abiotic (resource flow rates) properties interact with network structure to determine which yields greater meta-ecosystem function. Our findings suggest the spatial structure of resource flow networks coupling ecosystems can be a driver of ecosystem function at landscape scales. Further, our study demonstrates how modifications to the structural, biotic, or abiotic properties of meta-ecosystem networks can have non-trivial, large-scale effects on ecosystem function