Effet de la température sur les interactions trophiques et intraguildes au sein d'un système plante-herbivore-ennemis naturels : modélisation et approches expérimentales

Bien que les effets des changements climatiques sur les individus d'une espèce soient largement connus, les connaissances demeurent limitées quant aux conséquences sur les interactions trophiques. Notre étude s'intéresse aux effets de la température sur un système biologique plante-puceron-coccinelle. Nous avons modélisé les interactions trophiques et réalisé des expériences empiriques afin de caractériser l'effet de la température sur les composantes du système biologique étudié. Nos modèles et résultats mettent en évidence que le taux de prédation et la fréquence des interactions intraguildes augmentent avec la température, atteignent un maximum puis décroissent à température élevée. Conformément aux prédictions du modèle, la prédation intraguilde diminue lorsque la densité de puceron augmente. Nos résultats démontrent aussi que le système biologique résiste mieux aux pics de température en présence de coccinelles qu'en leur absence. Notre étude souligne l'importance de considérer la température dans les interactions trophiques puisqu'elle influence le comportement des organismes et la fréquence de leur interaction.Although the effects of climate change on individual organisms or populations have been well documented, our understanding about their consequences on trophic interactions remains limited. We investigated the effects of temperature on complex interactions in a plant-aphid-ladybeetle system. We combined models and laboratory experiments to characterize the effects of temperature on components of our biological system. We found that predation rate and intraguild interactions increase with temperature, reach a maximum, and then decrease at higher temperature. According to model predictions, intraguild predation decreases when aphid density increases. We also observed that the food chain is more resistant to temperature peaks when ladybeetles are included in the system than when they are absent. Our study highlights the importance of considering temperature in trophic and guild interactions since it influences the behavior of organisms as well as the frequency of interactions

Stratégie de ponte d'un prédateur furtif et conséquences pour la lutte biologique

Le comportement de ponte des insectes est un facteur déterminant de la survie de leurs oeufs et de leurs larves. Les caractéristiques environnementales, les besoins et l'écologie d'une espèce devraient alors influencer le choix de ponte d'une femelle. La cécidomyie Aphidoletes aphidimyza Rondani (Diptera : Cecidomyiidae), est un petit diptère dont les larves se nourrissent exclusivement de pucerons et adoptent un comportement furtif de prédation caractérisé par l'absence de réaction d'alarme des proies. Les larves d'A. aphidimyza ont une faible capacité de déplacement et sont très vulnérables face aux prédateurs intraguildes actifs ce qui peut influencer le choix de ponte d'A. aphidimyza. L'objectif du premier chapitre est de modéliser le comportement de ponte d'A. aphidimyza afin de mettre en évidence les facteurs biotiques déterminant ce comportement. Des expériences de terrain en verger de pommiers ont permis de tester les prédictions des modèles. En accord avec les prédictions de l'un des modèles, nos résultats démontrent que le nombre d'oeufs pondus par A. aphidimyza augmente avec l'abondance de pucerons. Cependant, les prédateurs intraguildes, les fourmis et les larves de conspécifiques n'ont pas d'influence significative sur la réponse de ponte d'A. aphidimyza. Le modèle validé révèle que le nombre optimal d'oeufs à pondre dans une colonie de pucerons dépend uniquement de l'abondance des pucerons et de la voracité des larves d'A. aphidimyza. L'objectif du deuxième chapitre est d'évaluer l'impact d'un lâcher inoculatif d'A. aphidimyza sur les populations du puceron vert du pommier: Aphis pomi De Geer et de déterminer les facteurs qui influencent cet impact. Suite aux lâchers, les populations de pucerons ont diminué significativement et nos résultats suggèrent que plus l'abondance des larves d'A. aphidimyza est importante, plus l'impact sur les colonies de pucerons est conséquent. Néanmoins, les larves d'A. aphidimyza n'ont pas la capacité de contrebalancer le taux d'accroissement très rapide des grandes colonies de pucerons. Pour la lutte biologique, ceci indique qu'A. aphidimyza devrait être utilisée comme un moyen de prévenir les grandes infestations de pucerons et non comme un moyen de lutter contre celles-ci. De plus, nos résultats suggèrent que les fourmis ont la capacité d'expulser les oeufs et les larves d'A. aphidimyza malgré leur caractère furtif. L'objectif du troisième chapitre est de décrire et de discuter d'un comportement de ponte atypique observé pour la première fois chez A. aphidimyza. Ce comportement consistant à pondre les oeufs en amas fut observé en laboratoire lors d'exposition de femelles A. aphidimyza à des températures froides (-18°) et lors d'un lâcher d'A. aphidimyza en verger de pommiers. Lors du lâcher, ce comportement fut probablement induit par l'intoxication des femelles à un insecticide (le GF 120 ©). Ce comportement atypique pourrait être une réponse à des conditions mortelles (températures très froides, insecticides) qui permettrait de maximiser l'aptitude phénotypique des femelles dans de telles circonstances. Finalement. notre étude permet d'approfondir les connaissances concernant le comportement de ponte d'A. aphidimyza et de déterminer son efficacité à contrôler les populations de pucerons en regard des facteurs qui peuvent influencer ce contrôle. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Aphidoletes aphidimyza, Comportement de ponte, Modèle d'optimisation, Prédation furtive, Prédation intraguilde, Lasius niger, Aphis pom, Coccinellidae

Warming indirectly increases invasion success in food webs

International audienceClimate warming and biological invasions are key drivers of biodiversity change. Their combined effects on ecological communities remain largely unexplored. We investigated the direct and indirect influences of temperature on invasion success, and their synergistic effects on community structure and dynamics. Using size-structured food web models, we found that higher temperatures increased invasion success. The direct physiological effects of temperature on invasions were minimal in comparison with indirect effects mediated by changes on food web structure and stability. Warmer communities with less connectivity, shortened food chains and reduced temporal variability were more susceptible to invasions. The directionality and magnitude of invasions effects on food webs varied across temperature regimes. When invaded, warmer communities became smaller, more connected and with more predator species than their colder counterparts. They were also less stable and their species more abundant. Considering food web structure is crucial to predict invasion success and its impacts along temperature gradients

Nine years of experimental warming did not influence the thermal sensitivity of metabolic rate in the medaka fish Oryzias latipes

A pressing challenge is to determine whether and how global-change drivers influence species physiology and survival. Recently, researchers have proposed the metabolic theory of ecology, defending the hypothesis of a universal thermal dependence of metabolic rate or, alternatively, the metabolic cold adaptation theory, stating that local adaptation can influence the thermal sensitivity of metabolic rate. However, the long-term (i.e. multigenerational) consequences of warming for the thermal sensitivity of metabolic rate remain largely unexplored although it determines energy use and is crucial for species response to climate change. In this study, we used an evolutionary experiment with medaka fishes Oryzias latipes maintained for more than 12 generations at warm and cold temperatures (30 and 20°C, respectively) to address this issue. Our objective was to investigate whether thermal adaptation influences the relationship between temperature and mass-corrected metabolic rate and how this may occur. In agreement with the universal thermal dependence hypothesis, we found that warming did not significantly influence the thermal sensitivity of mass-corrected metabolic rate: neither the intercept nor the slope of the temperature–metabolic rate relationship differed among fish lineages. Our small-scale laboratory experiment thus indicated that there is limited potential for evolutionary change in medaka fish metabolic rate in response to warmer temperatures. Overall, we provide evidence that 9 years of experimental warming did not influence the thermal sensitivity of metabolic rate. Our results highlight the invariability of the thermal dependence of metabolic rate, which has important implications for adaptation to climate warming. This finding suggests a limited potential for metabolic adaptations in response to long-term temperature changes, which may have negative consequences for the persistence of fish populations under climate change

Prey and predator density‐dependent interactions under different water volumes

Predation is a critical ecological process that directly and indirectly mediates population stabilities, as well as ecosystem structure and function. The strength of interactions between predators and prey may be mediated by multiple density dependences concerning numbers of predators and prey. In temporary wetland ecosystems in particular, fluctuating water volumes may alter predation rates through differing search space and prey encounter rates. Using a functional response approach, we examined the influence of predator and prey densities on interaction strengths of the temporary pond specialist copepod Lovenula raynerae preying on cladoceran prey, Daphnia pulex, under contrasting water volumes. Further, using a population dynamic modeling approach, we quantified multiple predator effects across differences in prey density and water volume. Predators exhibited type II functional responses under both water volumes, with significant antagonistic multiple predator effects (i.e., antagonisms) exhibited overall. The strengths of antagonistic interactions were, however, enhanced under reduced water volumes and at intermediate prey densities. These findings indicate important biotic and abiotic contexts that mediate predator–prey dynamics, whereby multiple predator effects are contingent on both prey density and search area characteristics. In particular, reduced search areas (i.e., water volumes) under intermediate prey densities could enhance antagonisms by heightening predator–predator interference effects

Influence of intra-and interspecific variation in predator–prey body size ratios on trophic interaction strengths:

Predation is a pervasive force that structures food webs and directly influences ecosystem functioning. The relative body sizes of predators and prey may be an important determinant of interaction strengths. However, studies quantifying the combined influence of intra‐ and interspecific variation in predator–prey body size ratios are lacking. We use a comparative functional response approach to examine interaction strengths between three size classes of invasive bluegill and largemouth bass toward three scaled size classes of their tilapia prey. We then quantify the influence of intra‐ and interspecific predator–prey body mass ratios on the scaling of attack rates and handling times

Scientists' warning on climate change and insects

Climate warming is considered to be among the most serious of anthropogenic stresses to the environment, because it not only has direct effects on biodiversity, but it also exacerbates the harmful effects of other human-mediated threats. The associated consequences are potentially severe, particularly in terms of threats to species preservation, as well as in the preservation of an array of ecosystem services provided by biodiversity. Among the most affected groups of animals are insects—central components of many ecosystems—for which climate change has pervasive effects from individuals to communities. In this contribution to the scientists' warning series, we summarize the effect of the gradual global surface temperature increase on insects, in terms of physiology, behavior, phenology, distribution, and species interactions, as well as the effect of increased frequency and duration of extreme events such as hot and cold spells, fires, droughts, and floods on these parameters. We warn that, if no action is taken to better understand and reduce the action of climate change on insects, we will drastically reduce our ability to build a sustainable future based on healthy, functional ecosystems. We discuss perspectives on relevant ways to conserve insects in the face of climate change, and we offer several key recommendations on management approaches that can be adopted, on policies that should be pursued, and on the involvement of the general public in the protection effort

Aperçu éditorial: Changement global: intégrer les conséquences écologiques et évolutives à travers le temps et l'espace

International audienceHuman activities have changed ecosystems at local and global scales. These changes include altered climate, habitat loss and fragmentation, species invasions, land use change, pollution, and pesticides [1]. These changes threatens many species and affects biodiversity and ecosystem functions and services through multiple side effects [2, 3, 4]. Insects are of major importance for ecology, economy, health, and alimentation and their populations are declining worldwide [5]. Understanding the impacts of global change drivers on the diversity, abundance, and functions of insect species is thus an urgent scientific and societal challenge. However, addressing this challenge is difficult for several reasons. First, species are embedded within communities and the effects of global change drivers on a single species thus depend on their direct and indirect effects mediated by species interactions [6,7]. Second, evolutionary, epigenetic and plastic phenotypic responses to environmental change affect the spatial and temporal distributions of phenotypes which can modulate the speed of evolutionary adaptation as well as species' functions and interactions [8, 9, 10]. Third, humans can strongly influence species dispersal by fragmenting natural habitats or mediating insect dispersal trough long distances [11,12]. Change in insect dispersal can have important consequences on, for instance, their meta-population dynamics or the establishment of exotic invasive species. Fourth, global change drivers can interact in space and time and their combined effects can be additive, synergistic or antagonist, which adds another layer of difficulty when addressing or predicting multiple driver effects on insects [13]. We propose that analysing issues of global change from a perspective addressing these fourth points will lead to a fully integrative understanding of the ecological and evolutionary consequences of global change across time and space. However, developing a comprehensive understanding of how all this plays out remains an important research frontier. We thus have assembled 12 contributions that each tackle a component of what we believe is needed to integrate the ecological and evolutionary consequences of global change across time and space. We hope that this issue will advance a new, concerted research effort that can help developing a more comprehensive perspective on how global change affects ecological systems. Such comprehensive perspective is certainly needed to preserve biodiversity, manage natural resources, and maintain key ecosystem services such as pollination and the control of agricultural pests and vector diseases

On the use of functional responses to quantify emergent multiple predator effects

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Stoichiometric constraints modulate the effects of temperature and nutrients on biomass distribution and community stability

International audienceTemperature and nutrients are two of the most important drivers of global change. Both can modify the elemental composition (i.e. stoichiometry) of primary producers and consumers. Yet their combined effect on the stoichiometry, dynamics, and stability of ecological communities remains largely unexplored. To fill this gap, we extended the Rosenzweig-MacArthur consumer-resource model by including thermal dependencies, nutrient dynamics, and stoichiometric constraints on both the primary producer and the consumer. We found that stoichiometric constraints dampen the paradox of enrichment and increased persistence at high nutrient levels. Nevertheless, they also reduced consumer persistence at extreme temperatures. Finally, we also found that stoichiometric constraints can strongly influence biomass distribution across trophic levels by modulating consumer assimilation efficiency and resource growth rates along the environmental gradients. In the Rosenzweig-MacArthur model, consumer biomass exceeded resource biomass for most parameter values whereas, in the stoichiometric model, consumer biomass was strongly reduced and sometimes lower than resource biomass. Our findings highlight the importance of accounting for stoichiometric constraints as they can mediate the temperature and nutrient impact on the dynamics and functioning of ecological communities