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Invasions by exotic species in areas already occupied by related species may lead to extinction or niche partitioning. Bactrocera dorsalis has invaded the Comoros archipelago in 2005 where other tephritids were already present. The host ranges of fruit flies in the Comoros were studied by conducting a seven-year survey on the three islands of the archipelago with a substantial sampling effort comprising 91 plant species from 37 families. The results showed that 45 fruit species in 16 families were infested by tephritid species. Eight fruit fly species were detected in the sampled fruits, but 78% of the individuals were identified as B. dorsalis, confirming its dominance and polyphagous status. More than ten years after its invasion, B. dorsalis has replaced Ceratitis capitata as the dominant fruit fly species on several species such as mango and citrus. The coexistence between B. dorsalis and C. capitata seems possible due to the capacity of the latter to exploit different niches, i.e. higher altitudinal ranges and a few host fruit species (among which, chillies and coffee berries) constituting a refuge niche. Information about coexistence between B. dorsalis and other tephritids is useful for the management and better estimates of invasion risks and associated biosecurity measures.

International audience; The aim of our review was to examine the cases of Tephritidae invasions across island systems in order to determine whether they follow a hierarchical mode of invasion. We reviewed the literature on factors and mechanisms driving invasion sequences in Pacific and Southwest Indian Ocean islands and gathered every record of invasion by a polyphagous tephritid in island groups. From invasion date or period, we defined an invasion link when a new fruit fly established on an island where another polyphagous tephritid is already resident (that was indigenous or a previous invader). Across surveyed islands, we documented 67 invasion links, involving 24 tephritid species. All invasion links were directional, i.e., they involved a series of invasions by invaders that were closely related to a resident species but were increasingly more competitive. These sequential establishments of species are driven by interspecific competition between resident and exotic species but are also influenced by history, routes, and flows of commercial exchanges and the bridgehead effect. This information should be used to improve biosecurity measures. Interactions between trade flow, invasive routes, and the presence of invasive and resident species should be integrated into large-scale studies.

All the environmental conditions necessary for natural forest regeneration constitute a favorable microsite for seed germination and seedling growth. Among these microsites, terricolous bryophytes represent an important support, present in almost all ecosystems. In addition, bryophytes have an important role in the recruitment of certain vascular plants in temperate forests. Terricolous bryophytes, through the expression of certain morphological traits such as density or mat thickness, can modify regeneration microsites by modulating soil temperatures; moisture and access to nutrients (filter theory). However, the interactions between tree forest regeneration and bryophytes remain poorly understood. In order to understand the interactions between bryophytes and regeneration, we studied the general effects of vegetation strata and bryophytes on natural forest regeneration in a causal system (Structural Equation Modelling) on a national network of observation plots. In a second step, we conducted a regeneration monitoring in mixed forest on a regional network of experimental plots to identify the effects of bryophytes on the growth and survival of sessile oak (Quercus petraea) and Scots pine (Pinus sylvestris) seedlings. We also tried to evaluate the effects of two functionally different bryophyte species on the abiotic conditions of the microsite by monitoring temperature, humidity and light in situ. Finally, we conducted a semi-controlled greenhouse experiment to monitor germination and growth of oak and pine on bryophyte mats as well as on bare soil as a function of two atmospheric and two edaphic humidities. We show and discuss that, depending on their functional traits; different bryophyte species do not have the same effect on seedling establishment, growth, or survival rates. Bryophytes may have a physical barrier effect but also play a role on moisture in regeneration microsites. Terricolous bryophytes would filter out different tree species depending on their seed size., L’ensemble des conditions environnementales nécessaires à la régénération forestière naturelle constitue un microsite favorable pour la germination des graines et la croissance des semis. Parmi ces microsites, les bryophytes terricoles représentent un support important, présent dans la quasi-totalité des écosystèmes. De plus, les bryophytes ont un rôle important sur le recrutement de certaines plantes vasculaires dans les forêts tempérées. Les bryophytes terricoles, par l’expression de certains traits morphologiques comme la densité ou l’épaisseur du tapis, peuvent modifier les microsites de régénération en modulant les températures, l'humidité et l’accès aux nutriments du sol (théorie des filtres). Cependant, les interactions entre la régénération forestière arborée et les bryophytes restent méconnues. Afin de mieux comprendre les interactions entre les bryophytes et la régénération, nous avons étudié les effets généraux des strates de végétation et des bryophytes sur la régénération forestière naturelle dans un système causal (Modèle d’Équations Structurelles) sur un réseau national de placettes d’observation. Dans un deuxième temps, nous avons réalisé un suivi de régénération en forêt mélangée sur un réseau régional de placettes expérimentales pour identifier les effets des bryophytes sur la croissance et la survie des semis de chêne sessile (Quercus petraea) et pin sylvestre (Pinus sylvestris). Nous avons également essayé d’évaluer les effets de deux espèces de bryophytes fonctionnellement différentes sur les conditions abiotiques du microsite en réalisant des suivis de température, d’humidité et de lumière in situ. Enfin, nous avons réalisé une expérimentation en conditions semi-contrôlées en serre pour suivre la germination et la croissance du chêne et du pin sur des tapis de bryophytes ainsi que sur le sol nu, en fonction de deux humidités atmosphériques et de deux humidités édaphiques. Nous montrons et discutons qu’en fonction de leurs traits fonctionnels, les différentes espèces de bryophytes n’ont pas le même effet sur l’installation, la croissance ou le taux de survie des semis. Les bryophytes peuvent avoir un effet de barrière physique mais jouent également un rôle sur l’humidité dans les microsites de régénération. Les bryophytes terricoles filtreraient différentes espèces arborées notamment selon la taille de leur graine.

International audience; Ensuring food security for a world population projected to reach over nine billion by 2050 while mitigating the environmental impacts and climate change represent the major agricultural challenges. Diversification of the cropping systems using notably cereal–legume mixtures is one key pathway for such agroecological intensification. Indeed, intercropping is recognised as a practice having the potential to increase and stabilise the yields in comparison with sole crops while limiting the use of inputs notably when species exploit resources in a complementary way. However, predicting intercropped species grain yield remains a challenge because the species respond to competition through complex genotype x cropping mode interactions. Here, we hypothesised that the grain yield achieved by a cultivar in low nitrogen input durum wheat–grain legume intercrops (ICs) could be estimated using a few simple variables. The present work is based on a 2-year field experiment carried out in southwestern France using two durum wheat ( Triticum turgidum L.), four winter pea ( Pisum sativum L.), and four winter faba bean ( Vicia faba L.) genotypes with contrasting characteristics, notably in terms of height and precocity, to explore a wide range of durum wheat–grain legume phenotypes combinations to generate variability in terms of yield and species proportion. The major result is that the yield of durum wheat–grain legume IC component in low nitrogen input conditions could be correctly estimated from only three variables: (i) wheat cultivar full density sole crop (SC) yield, (ii) legume cultivar half density sole crop (SC½) yield, and (iii) an indicator of legume cultivar response to interspecific competition. The latter variable, the interspecific interaction index (IE), reveals cultivars' competitive abilities and tolerance to competition. However, to propose generic IC design and management procedures, further mechanistic understanding is required to better understand the links between tolerance to interspecific competition and cultivar phenotype characteristics. In particular, a special emphasis on the grain legume is needed as their response to interspecific competition appears less predictable than that of durum wheat. Cultivar choice is a key element to optimise the functional complementarity and subsequent IC advantages. This work proposes a simple tool to assist the design of specific breeding programs for cultivars ideotypes adapted to intercropping.

This work is dedicated to Serge Quilici who has been leading prolific research on the tephritids of Reunion his whole career. This article has been reviewed and recommended by Peer Community in Ecology, https://doi.org/10.24072/pci.ecology.100080. The peer review history for this article is available at https://publo ns.com /publo n/10.1111/ele.13825.; International audience; The relative importance of ecological factors and species interactions for shaping species distributions is still debated. The realised niches of eight sympatric tephritid fruit flies were inferred from field abundance data using joint species distribution modelling and network inference, on the whole community and separately on three host plant groups. These estimates were then confronted the fundamental niches of seven fly species estimated through laboratory-measured fitnesses on host plants. Species abundances depended on host plants, followed by climatic factors, with a dose of competition between species sharing host plants. The relative importance of these factors mildly changed among the three host plant groups. Despite overlapping fundamental niches, specialists and generalists had almost distinct realised niches, with possible competitive exclusion of generalists by specialists on Cucurbitaceae. They had different assembly rules: Specialists were mainly influenced by their adaptation to host plants, while generalist abundances varied regardless of their fundamental host use.

Harbour seal (Phoca vitulina) and grey seal (Halichoerus grypus) are two sympatric marine mammal species that are increasingly considered as potential competitors, especially at their European core distributions. The objective of this PhD was to study the foraging strategies and trophic ecology of these species at the limit of their range (Baie de Somme, Eastern English Channel, France), and to investigate the hypothesis of potential interspecific competition. Biotelemetry devices were fitted on 49 individuals to document their movements and dives at sea.The analysis of surface locations and diving behaviour, completed recently by the detection of Prey Capture Attempts (accelerometry), allowed for a better understanding of the two seal species’ foraging strategies and improved the detection of their foraging areas. Trophic niches of the two seal species were then characterised with the analysis of diet, stable isotopes (in the whiskers of the same captured individuals), and foraging areas. A high interspecific trophic overlap was identified between these niches, resulting from the consumption of benthic flatfish in coastal areas, and we suggest that it provides here the basis for potential competition between both species. This study also showed the key role of individual foraging strategies on the ecological conclusions at the scale of the species/sub-population, including that the potential competition may be due to some individual grey seal strategies. Continuing these studies is essential to detect any potential ecological changes that could be trophically-induced., Le phoque veau-marin (Phoca vitulina) et le phoque gris (Halichoerus grypus), deux espèces sympatriques de mammifères marins, sont de plus en plus considérés comme des compétiteurs potentiels, et ce plus particulièrement au cœur de leur distribution européenne. L’objectif de cette thèse est d’étudier les stratégies de chasse et l’écologie trophique de ces espèces en limite de leur aire de distribution (baie de Somme, Manche Est, France), et d’explorer l’hypothèse de compétition interspécifique. Des outils de bio-télémétrie ont été déployés sur 49 individus afin d’obtenir des données sur leurs déplacements et plongées en mer. L’analyse des localisations en surface et du comportement en plongée, complétée plus récemment par la détection de tentatives de captures de proies (accélérométrie), a permis de mieux comprendre les stratégies de chasse de ces espèces, et d’améliorer la détection des zones de chasse. Les niches trophiques des deux espèces de phoques ont ensuite été caractérisées par analyse du régime alimentaire, des isotopes stables (vibrisses des mêmes individus capturés), et des zones de chasse. Un important chevauchement interspécifique a été identifié entre ces niches, résultant de la consommation de poissons plats benthiques en zone côtière, ce qui apporte ici le contexte informatif d’une potentielle compétition. Cette étude montre aussi le rôle clé des stratégies individuelles de chasse sur les conclusions écologiques à l’échelle de l’espèce/sous-population,dont la potentielle compétition qui serait induite par certains phoques gris. La poursuite des suivis est nécessaire pour détecter tout potentiel changement écologique dont l’origine serait trophique.

International audience; Modern agriculture needs to develop transition pathways toward agroecological, resilient and sustainable farming systems. One key pathway for such agroecological intensification is the diversification of cropping systems using intercropping and notably cereal-grain legume mixtures. Such mixtures or intercrops have the potential to increase and stabilize yields and improve cereal grain protein concentration in comparison to sole crops. Species mixtures are complex and the 4C approach is both a pedagogical and scientific way to represent the combination of four joint effects of Competition, Complementarity, Cooperation, and Compensation as processes or effects occurring simultaneously and dynamically between species over the whole cropping cycle. Competition is when plants have fairly similar requirements for abiotic resources in space and time, the result of all processes that occur when one species has a greater ability to use limiting resources (e.g., nutrients, water, space, light) than others. Complementarity is when plants grown together have different requirements for abiotic resources in space, time or form. Cooperation is when the modification of the environment by one species is beneficial to the other(s). Compensation is when the failure of one species is compensated by the other(s) because they differ in their sensitivity to abiotic stress. The 4C approach allows to assess the performance of arable intercropping versus classical sole cropping through understanding the use of abiotic resources.

Resilience of cocoa agroforestry vs. full sun under extreme climatic conditions. In the specific case of our study, the two shade tree species associated with cocoa resulted in strong competition for water and became a disadvantage to the cocoa plants contrary to expected positive effects.

1. Autoparasitoids are intraguild consumers that attack and kill heterospecific and conspecific parasitoids as well as immature stages of hemipteran hosts, such as aphids, whiteflies and soft scales. Field experiments assessing the importance of interspecific competition between autoparasitoids and primary parasitoids, as well as its impact on herbivore suppression, are scarcely found in the ecological literature. 2. Using field data from 40 olive orchards, this study examined the mechanisms that regulate: (i) the interspecific competition between primary parasitoids of the genus Metaphycus and the autoparasitoid Coccophagus lycimnia; and (ii) the density of their shared herbivore host, the soft scale Saissetia oleae. 3. Metaphycus parasitoids used smaller hosts than C. lycimnia, yet did not outcompete C. lycimnia. On the other hand, C. lycimnia preferred to use Metaphycus females as secondary hosts for producing males rather than their own females. This preference might explain why the autoparasitoid negatively affected the density of the primary parasitoids. 4. Parasitism by the autoparasitoid C. lycimnia at the beginning of the season was the sole variable positively related to host mortality throughout the season, showing its greater effect on herbivore suppression. 5. In this study, an autoparasitoid, inferior at resource exploitation, was shown to outcompete a primary parasitoid without disrupting herbivore suppression. info:eu-repo/semantics/publishedVersion

Habitat selection is a behavioural process in response to environmental stimuli as resource availability (food, shelter) and threats(competitors, predators). The understanding of the underlying mechanisms is crucial in ecology and allow to identify and consider factors limiting populations. The stake of this PhD thesis was to identify limiting factors (landscapes, game practices) and reponses of grey partridge (Perdix perdix) populations under mixed game management (annual releases of captive-reared birds, without shooting suspension). Habitat selection patterns have changed towards a lower avoidance of risky habitats, while habitat suitability has decreased and the proportion of captive-reared birds in the population has likely increased. Interspecific competition with red-legged partridge also affected habitat selection in grey partridge. Some individuals showed a behavioural capacity to adjust (in terms of rhythms of activity, habitat selection, space use) to the spatiotemporal structuration of risk along the diel cycle, potentially influenced by individual traits (personality, health status). Habitat suitability, predation and hunting pressures were identified as structuring factors of grey partridge populations. A game management based on releases of naïve birds and competing species, disturbances induced by shooting during the post-release period, and no preliminary assessement of habitat quality, could locally imperil the maintenance of grey partridge populations.; La sélection de l’habitat est définie comme un processus comportemental en réponse à des stimuli environnementaux tels que la disponibilité en ressources (alimentation, refuges)et la présence de menaces (compétiteurs, prédateurs). La compréhension des mécanismes sous-jacents est essentielle en écologie et permet d’identifier et d’appréhender les facteurs limitant les populations. L’enjeu de cette thèse était d’identifier les facteurs limitants (paysages, pratiques cynégétiques) et la réponse des populations de Perdrix grise (Perdix perdix) soumises à gestion cynégétique (apports annuels d’oiseaux d’élevage, sans arrêt de la chasse). Les patrons de sélection d’habitat ont varié vers un évitement moins prononcé des habitats associés à un fort risque de prédation, dans le même temps que la qualité d’habitat a diminué et que la prévalence d’oiseaux d’élevage a probablement augmenté dans la population. La compétition interspécifique avec la Perdrix rouge affecte également la sélection de l’habitat de la Perdrix grise. Certains individus démontrent une capacité d’ajustement comportemental (rythme d’activité,sélection de l’habitat, de l’espace) à la structuration du risque au cours du cycle circadien, possiblement influencée par des déterminants individuels (personnalité, état sanitaire). La qualité d’habitat, les pressions de prédation et de chasse sont des facteurs structurants des populations. Une gestion cynégétique basée sur l’apport d’oiseaux naïfs et d’espèces compétitrices, un dérangement lié à la chasse en phase post-lâcher et une non-évaluation préalable de la qualité de l’habitat, rendent le maintien des populations de Perdrix grise sur un territoire très incertain.

Habitat selection is a behavioural process in response to environmental stimuli as resource availability (food, shelter) and threats(competitors, predators). The understanding of the underlying mechanisms is crucial in ecology and allow to identify and consider factors limiting populations. The stake of this PhD thesis was to identify limiting factors (landscapes, game practices) and reponses of grey partridge (Perdix perdix) populations under mixed game management (annual releases of captive-reared birds, without shooting suspension). Habitat selection patterns have changed towards a lower avoidance of risky habitats, while habitat suitability has decreased and the proportion of captive-reared birds in the population has likely increased. Interspecific competition with red-legged partridge also affected habitat selection in grey partridge. Some individuals showed a behavioural capacity to adjust (in terms of rhythms of activity, habitat selection, space use) to the spatiotemporal structuration of risk along the diel cycle, potentially influenced by individual traits (personality, health status). Habitat suitability, predation and hunting pressures were identified as structuring factors of grey partridge populations. A game management based on releases of naïve birds and competing species, disturbances induced by shooting during the post-release period, and no preliminary assessement of habitat quality, could locally imperil the maintenance of grey partridge populations.; La sélection de l’habitat est définie comme un processus comportemental en réponse à des stimuli environnementaux tels que la disponibilité en ressources (alimentation, refuges)et la présence de menaces (compétiteurs, prédateurs). La compréhension des mécanismes sous-jacents est essentielle en écologie et permet d’identifier et d’appréhender les facteurs limitant les populations. L’enjeu de cette thèse était d’identifier les facteurs limitants (paysages, pratiques cynégétiques) et la réponse des populations de Perdrix grise (Perdix perdix) soumises à gestion cynégétique (apports annuels d’oiseaux d’élevage, sans arrêt de la chasse). Les patrons de sélection d’habitat ont varié vers un évitement moins prononcé des habitats associés à un fort risque de prédation, dans le même temps que la qualité d’habitat a diminué et que la prévalence d’oiseaux d’élevage a probablement augmenté dans la population. La compétition interspécifique avec la Perdrix rouge affecte également la sélection de l’habitat de la Perdrix grise. Certains individus démontrent une capacité d’ajustement comportemental (rythme d’activité,sélection de l’habitat, de l’espace) à la structuration du risque au cours du cycle circadien, possiblement influencée par des déterminants individuels (personnalité, état sanitaire). La qualité d’habitat, les pressions de prédation et de chasse sont des facteurs structurants des populations. Une gestion cynégétique basée sur l’apport d’oiseaux naïfs et d’espèces compétitrices, un dérangement lié à la chasse en phase post-lâcher et une non-évaluation préalable de la qualité de l’habitat, rendent le maintien des populations de Perdrix grise sur un territoire très incertain.

International audience; Individual interactions are crucial to many ecological processes but are difficult to quantify for long periods in aquatic animals. In this study, we applied a digital proximity logging device recently developed for terrestrial animals to a freshwater fish, the brown trout (Salmo trutta L.). After preliminary calibration and quantification of detection errors, we recorded the interactions occurring between five male and four female brown trout in an artificial channel during one week of the spawning season. The 55,637 logs recorded allowed us to describe the encounter network and its fine scale evolution. In particular, the time spent with females varied a lot across males, from two to 24 h in a five-day period, and the males, which spent the most time with females tended to mate more. At the individual level, the temporal distribution of encounters reflected shifts in dominance status, with males sequentially taking over exclusive proximity with females before spawning. Beyond sexual encounters, the method presented here could be applied to many processes interesting to fish ecologists, such as predator-prey interactions, intra and interspecific competition or disease transmission

International audience; Interspecific competition with native species during biological invasions can sometimes limit alien expansion. We aimed to determine the potential ecological effects of Limatus durhamii Theobald 1901, a native Neotropical mosquito (Diptera: Culicidae) species, on the invasive species Aedes (Stegomyia) aegypti (Linnaeus 1762) that breeds in the same artificial water containers. Development time and adult dry mass were measured in three rearing conditions: control (a single larva), intraspecific competition (two conspecific larvae), and interspecific competition (two heterospecific larvae). Food was provided ad libitum to eliminate exploitative competition. For Ae. aegypti, development time was not affected by interspecific interference competition (non-significant differences with the control) and the adult dry mass was significantly higher, meaning that individual fitness likely increased. Yet, because previous studies showed longer development time and lighter adults during competition with other invasive mosquitoes, it is likely that Ae. aegypti can express a different phenotype depending on the competing species. The similar pattern found for Li. durhamii females and the non-significant difference with the control for males explain in part why this species can compete with Ae. aegypti.

Relation entre les caractères morphologiques observés sur des plantes espacées et les indices de compétition intra et inter-spécifiques chez la luzerne. 2. Rencontres Francophones sur les Légumineuses (RFL2)

International audience; Nest-site selection is an important component of species socio-ecology, being a crucial factor in establishment of group living. Consequently, nest-site characteristics together with space-use proxies may reveal the social organization of species, which is critical when direct observation of social interactions is hindered in nature. Importantly, nest-site choice is expected to be under strong selective pressures and the object of intra- and inter-specific competition. Although the bulk of research on sociality focuses on its ecological drivers, our study introduces interspecific competition as a potential factor that could influence social evolution. We investigated the influence of habitat and interspecific competition on the social organization of two sister species of the African four striped mouse (Rhabdomys dilectus dilectus and Rhabdomys bechuanae) in a similar macroenvironment. These species diverged in allopatry and occupy distinct environmental niches. We radiotracked 140 adults to identify their nest-sites, determine nest characteristics and record groups that shared nest-sites. Group cohesion was estimated from nest-site fidelity, group association strength, and home range overlap within versus between group members. We compared the two species in sympatry versus parapatry to determine the impact of species interference on sociality. In parapatry, the two species selected distinct nest-site types, interpreted as different anti-predator strategies: R. bechuanae selected fewer, spaced, less concealed nest-sites whereas R. d. dilectus selected clumped and less visible nest-sites. Rhabdomys bechuanae also showed more cohesive and stable social groups than R. d. dilectus. In sympatry, compared to R. bechuanae, R. d. dilectus occupied similar nest-sites, however slightly more exposed and clumped, and displayed similar nest-site fidelity and group association strength. We conclude that although habitat selection may be an important driver of social divergence in Rhabdomys, species interference, by limiting R. d. dilectus movements and forcing nest-site sharing may induce new ecological pressures that could influence its social evolution.

Key message : In a mixed poplar/black locust plantation in central France, adverse conditions have led to a prevalence of interspecific competition, resulting in a poorer performance than monocultures.Context : In mixed tree plantations, the presence of woody N-2-fixing species is thought to reduce N needs by fertilization. However, benefits associated to soil nitrogen enrichment have to outweigh the negative effects of interspecific competition. To do so, co-occurring tree species have to be chosen carefully to promote niche sharing between species and reduce competition. Black locust and poplar mixtures therefore seem promising since both species are fast growing and have potentially complementary crown shapes.Aims : Our objective was to evaluate the impact of the poplar/black locust mixture on the growth, above-and belowground biomass production, and nitrogen allocation of the two species, as compared to their respective monocultures.Methods : An experimental plantation mixing poplar and black locust was set up in central France. For five growing seasons, growth, nitrogen allocation, and carbon allocation were monitored for the two species growing either in mixture or in monoculture.Results : After a couple of promising growing seasons, black locust growth and survival slowly declined, mainly in the mixture. At the stand level, biomass production in the mixed plots was nearly 50% below the most productive monoculture (poplar) by age 5 years.Conclusion : Under adverse conditions, interspecific competition in the mixture was the preponderant interaction, resulting in higher mortality and lower biomass production than the two monocultures.

Among plant-parasitic nematodes (PPNs), the species Meloidogyne chitwoodi constitutes an important agricultural issue and is listed as a quarantine species in the EU. This study investigated whether PPN communities can affect the establishment and expansion of M. chitwoodi during a simulated introduction. An original experimental design was developed on potato in the glasshouse involving four PPN communities derived from a single natural one that was initially grown on different host plants. Meloidogyne chitwoodi was inoculated at two different densities (50 or 1000 second-stage juveniles (J2) per pot). After 4 months, M. chitwoodi was more abundant in the community showing a low overall abundance of PPNs, decreased in the other PPN communities and failed to establish in five pots out of 80. Results showed that establishment - even starting from a very low inoculum - can occur in all communities even if indigenous PPNs in the community affect the expansion through interspecific competition. The reverse interaction was also observed as PPN taxa were generally less abundant in the 1000 M. chitwoodi J2 inoculation treatments. The proportion of M. chitwoodi males produced was higher in the community showing low overall PPN abundance, suggesting a strong sensitivity of M. chitwoodi to intraspecific competition. The presented results suggest that a low abundance of indigenous PPNs presents a higher risk of expansion of M. chitwoodi even if the introduced inoculum is low.

International audience; Optimal habitat selection is essential for species survival in ecosystems, and interspecific competition is a key ecological mechanism for many observed species association patterns. Specialized animal species are commonly affected by resource and interference competition with generalist and/or omnivorous competitors, so avoidance behavior could be expected. We hypothesize that specialist species may exploit broad range cues from such potential resource competitors (i.e., cues possibly common to various generalist and/or omnivorous predators) to avoid costly competition regarding food or reproduction, even in new species associations. We tested this hypothesis by studying short-term interactions between a native larval parasitoid and a native generalist omnivorous predator recently sharing the same invasive host/prey, the leaf miner Tuta absoluta. We observed a strong negative effect of kleptoparasitism (food resource stealing) instead of classical intraguild predation on immature parasitoids. There was no evidence that parasitoid females avoided the omnivorous predator when searching for oviposition sites, although we studied both long- and short-range known detection mechanisms. Therefore, we conclude that broad range cue avoidance may not exist in our biological system, probably because it would lead to too much oviposition site avoidance which would not be an efficient and, thus, beneficial strategy. If confirmed in other parasitoids or specialist predators, our findings may have implications for population dynamics, especially in the current context of increasing invasive species and the resulting creation of many new species associations.

Le temps nécessaire à l’évaluation et à l’acceptation d’une ressource est directement lié à sa qualité. Ainsi, les individus s’approvisionnant dans un milieu naturel font face à un compromis entre vitesse de prise de décision et qualité de la ressource (speed-accuracy trade-off). Si la qualité de la ressource est un élément important pour favoriser sa valeur adaptative (fitness), le temps nécessaire au processus de décision n’est plus disponible pour d’autres tâches essentielles comme la vigilance. De plus, une prise de décision trop longue expose aussi les individus à un risque plus important de compétition et de perte d’opportunités. On s’attend à ce que des animaux confrontés à un risque de prédation ou de compétition ajustent la durée de leur prise de décision, et ainsi leur sélectivité pour une ressource. Toutefois, la compétition représentant un risque moins important à court terme que la prédation, on s’attend à ce que l’ajustement de sélectivité ce fasse proportionnellement à l’intensité du risque rencontré. Pour tester ces attendus, nous avons analysés le comportement d’approvisionnement d’un coléoptère carabique granivore Harpalus affinis dans quatre situations de risque différentes : i) un risque de prédation, ii-iii) une compétition intra et inter spécifique et iv) un témoin sans risque. Nos résultats montrent que les individus confrontés à un risque de prédation ou de compétition réduisent leur sélectivité pour les graines consommées. L’effet du risque de prédation s’avère 3 fois plus important que celui de la compétition (qu’elle soit intra ou inter spécifique). H. affinis semble donc capable d’ajuster finement sa sélectivité en réponse au risque qu’il rencontre.

Description of the subject. The geographic distributions of a species, be it native or alien, is expected to be limited at some point by environmental conditions. In this situation, a range edge equilibrium (REE) takes place, i.e., populations occurring beyond the edge have a growth rate reduced below replacement. The occurrence of REE has never been tested for an invasive species. In Western Europe, the invasive weed Ambrosia artemisiifolia L. has spread in most parts of southern and central France, where it can be found in very high densities in sunflower fields, but seems to be limited in its northwards expansion. It is currently unknown whether the range has reached a limit or not. Information about how the species responds to sunflower competition is also lacking.Objectives. This work addressed two questions: Has the northern part of A. artemisiifolia invaded range in Western Europe reached REE? How is A. artemisiifolia performance influenced by sunflower competition?Method. Plots were established in an agricultural field ca. 250 km north to the current invaded range, in Belgium. We planted A. artemisiifolia seedlings with or without sunflower competition. The following year, the population growth rates and the soil seed bank were assessed. Results. The species established populations with relatively high growth rates and soil seed bank. Sunflower competition did not have a significant impact on plant performance. Conclusions. The results invalidate the hypothesis of equilibrium at the current margin of A. artemisiifolia invaded range, and suggest a significant potential for invasion northwards., L’équilibre en bordure d’aire nord n’est pas atteint pour l’invasion d’Ambrosia artemisiifolia L. en Europe de l’OuestDescription du sujet. La distribution géographique d’une espèce, indigène ou invasive, peut être limitée par l’environnement. Dans cette situation, le taux de croissance des populations au-delà de la bordure d’aire est inférieur au taux de remplacement, et un équilibre en bordure d’aire (Range edge equilibrium, REE) prend place. L’émergence d’un REE n’a jamais été spécifiquement testée chez une espèce invasive. En Europe de l’Ouest, l’espèce invasive Ambrosia artemisiifolia L. est très abondante dans les champs de tournesols du centre et du sud de la France, mais sa progression semble limitée vers le Nord. Actuellement, on ne sait pas si l’espèce a atteint un REE ou non. Des informations sur la réponse de l’espèce face à la compétition du tournesol sont également manquantes.Objectifs. Ce travail adresse deux questions : En Europe de l’Ouest, A. artemisiifolia a-t-elle atteint un REE au nord de son aire d’invasion ? Comment la compétition du tournesol influence-t-elle l’espèce ? Méthode. Des plantules d’A. artemisiifolia ont été plantées avec ou sans tournesols dans des quadrats installés dans un champ en Belgique, environ 250 km au nord du front d’invasion. L’année suivante, le taux de croissance des populations et la banque de graines ont été évalués.Résultats. Le taux de croissance des populations et la banque de graines ont été relativement importants. La compétition du tournesol n’a pas eu d’impact significatif sur les performances des plants.Conclusions. Les résultats réfutent l’hypothèse d’un équilibre au front d’invasion actuel et suggèrent un potentiel d’invasion significatif vers le Nord.

International audience; Can specialist natural enemies persist in ecosystems when competing with omnivorous natural enemies for their shared prey? The consequences of omnivory have been studied theoretically, but empirical studies are still lacking. Omnivory is nevertheless common in nature and omnivorous predators coexist with specialists in many ecosystems, even when they are intraguild predators. This type of association is also common in agroecosystems in which biological control strategies are used. Our study provides an example of the outcome of such an association in the context of biological control of the invasive pest Tuta absoluta (Lepidoptera) in a tomato agroecosystem. The two natural enemies involved, that is, a specialist (Stenomesius japonicus (Hymenoptera) parasitoid) and an omnivore (Macrolophus pygmaeus (Hemiptera) predator), were able to coexist for 3months in our experimental cages in the absence of metacommunity mechanisms (i.e., emigration and recolonization), contrary to theoretical expectations. However, they negatively affected each other's population dynamics. We found that spatial resource segregation was not a mechanism that promoted their coexistence. Regarding pest control, the specialist and omnivorous natural enemies were found to exhibit complementary functional traits, leading to the best control when together. Mechanisms that may have promoted the coexistence of the two species as well as consequences with regard to the inoculative biological control program are discussed.

Wood specific gravity is a key element in tropical forest ecology. It integrates many aspects of tree mechanical properties and functioning and is an important predictor of tree biomass. Wood specific gravity varies widely among and within species and also within individual trees. Notably, contrasted patterns of radial variation of wood specific gravity have been demonstrated and related to regeneration guilds (light demanding vs. shade-bearing). However, although being repeatedly invoked as a potential source of error when estimating the biomass of trees, both intraspecific and radial variations remain little studied. In this study we characterized detailed pith-to-bark wood specific gravity profiles among contrasted species prominently contributing to the biomass of the forest, i.e. the dominant species, and we quantified the consequences of such variations on the biomass. Wood specific gravity is a key element in tropical forest ecology. It integrates many aspects of tree mechanical properties and functioning and is an important predictor of tree biomass. Wood specific gravity varies widely among and within species and also within individual trees. Notably, contrasted patterns of radial variation of wood specific gravity have been demonstrated and related to regeneration guilds (light demanding vs. shade-bearing). However, although being repeatedly invoked as a potential source of error when estimating the biomass of trees, both intraspecific and radial variations remain little studied. In this study we characterized detailed pith-to-bark wood specific gravity profiles among contrasted species prominently contributing to the biomass of the forest, i.e. the dominant species, and we quantified the consequences of such variations on the biomass. Results Wood specific gravity profiles from pith-to-bark presented positive, neutral and negative trends. Positive trends mainly characterized light-demanding species, increasing up to 1.8 g.cm-3 per meter for Piptadeniastrum africanum, and negative trends characterized shadebearing species, decreasing up to 1 g.cm-3 per meter for Strombosia pustulata. The linear mixed model showed the greater part of wood specific gravity variance was explained by species only (45%) followed by a redundant part between species and regeneration guilds (36%). Despite substantial variation in wood specific gravity profiles among species and regeneration guilds, we found that values from the outer wood were strongly correlated to values from the whole profile, without any significant bias. In addition, we found that wood specific gravity from the DRYAD global repository may strongly differ depending on the species (up to 40% for Dialium pachyphyllum). Main Conclusion Therefore, when estimating forest biomass in specific sites, we recommend the systematic collection of outer wood samples on dominant species. This should prevent the main errors in biomass estimations resulting from wood specific gravity and allow for the collection of new information to explore the intraspecific variation of mechanical properties of trees., SCOPUS: ar.j, info:eu-repo/semantics/published

International audience; Coexistence often involves niche differentiation either as the result of environmental divergence, or in response to competition. Disentangling the causes of such divergence requires that environmental variation across space is taken into account, which is rarely done in empirical studies. We address the role of environmental variation versus competition in coexistence between two rodent species: Rhabdomys bechuanae (bechuanae) and Rhabdomys dilectus dilectus (dilectus) comparing their habitat preference and home range (HR) size in areas with similar climates, where their distributions abut (allopatry) or overlap (sympatry). Using Outlying Mean Index analyses, we test whether habitat characteristics of the species deviate significantly from a random sample of available habitats. In allopatry, results suggest habitat selection: dilectus preferring grasslands with little bare soil while bechuanae occurring in open shrublands. In sympatry, shrubland type habitats dominate and differences are less marked, yet dilectus selects habitats with more cover than bechuanae. Interestingly, bechuanae shows larger HRs than dilectus, and both species display larger HRs in sympatry. Further, HR overlaps between species are lower than expected. We discuss our results in light of data on the phylogeography of the genus and propose that evolution in allopatry resulted in adaptation leading to different habitat preferences, even at their distribution margins, a divergence expected to facilitate coexistence. However, since sympatry occurs in sites where environmental characteristics do not allow complete species separation, competition may explain reduced inter-species overlap and character displacement in HR size. This study reveals that both environmental variation and competition may shape species coexistence.

International audience; 1. Spatial patterns of freshwater fish species at regional and local scales were investigated to explore the possible role of interspecific interactions in influencing distribution and abundance within communities occupying coastal streams of North-Western France. 2. Nine sites from nine streams situated in the same biogeographical region were sampled annually over the 6-year period from 1990 to 1995. 3. Similar habitats (sites) with richer regional colonization pools exhibited proportionally richer local communities in terms of number of species, total density and total biomass of individuals. Furthermore, no negative relationships were found between density and biomass of each of the most common species and local species richness. 4. Results of dynamic regression models (applied to the above-mentioned species) suggest an absence of strong competition between all pairs of species. 5. The evidence on lack of density compensation for species-poor communities and absence of perceptible interspecific competition between species suggest that the communities studied are non-interactive. 6. Two main explanations can be advanced. First, the local abundance of species in the communities studied could be determined through differential responses to unpredictable environmental changes, rather than through biological interactions. Second, as a result of historical events, the communities studied are reduced in congeneric species which can limit, in turn, the influence of interspecific competition in structuring these communities. 7. These results underline the strong influence of regional processes in shaping local riverine fish communities and minimize the possible influence of species interactions in governing these communities.

Alfalfa is subjected to interspecific competition in two situations (i) intercropping with a forage grass, where the required long-lasting equilibrium between species is frequently threatened by excessive alfalfa competitive ability ; (ii) competition against weeds, which can be severe in monoculture and require shigh competitive ability to avoid any chemical weed control. In both cases, competition for light interception is the main mechanism that drives the species proportion. Vegetative vigour and plant architectural traits can affect the alfalfa competition dynamics across successive harvests. Once completely unveiled, these traits could be selected for new varieties with improved adaptation to competition.

International audience; By burrowing galleries and producing casts, earthworms are constantly changing the structure and properties of the soils in which they are living. These changes modify the costs and benefits for earthworms to stay in the environment they modify. In this paper, we measured experimentally how dispersal behaviour of endogeic and anecic earthworms responds to the cumulative changes they made in soil characteristics. The influence of earthworm activities on dispersal was studied in standardised mesocosms by comparing the influence of soils modified or not modified by earthworm activities on earthworm dispersal rates. The cumulative use of the soil by the earthworms strongly modified soil physical properties. The height of the soil decreased over time and the amount of aggregates smaller than 2 mm decreased in contrast to aggregates larger than 5 mm that increased. We found that: (i) earthworm activities significantly modified soil physical properties (such as bulk density, soil strength and soil aggregation) and decreased significantly the dispersal rates of the endogeic species, whatever the species that modified the soil; (ii) the decreasing in the dispersal proportion of the endogeic species suggests that the cost of engineering activities may be higher than the one of dispersal; (iii) the dispersal of the anecic species appeared to be not influenced by its own activities (intra-specific influences) or by the activities of the endogeic species (inter-specific influences). Overall these results suggest that the endogeic species is involved in a process of niche construction, which evolved jointly with its dispersal strategy.

Les interactions multi-trophiques jouent un rôle clé dans la structuration des agrosystèmes et régissent la dynamique des populations qui les composent. Dans le cadre de la lutte biologique, les populations de ravageurs sont contrôlées par ces interactions. Quand une espèce exotique envahit l'agrosystème, cela déstabilise l'équilibre préexistant et peut, via des interactions directes ou indirectes, modifier le contrôle biologique des espèces autochtones. D'autre part, l'efficacité des auxiliaires envisagés pour lutter contre l'espèce invasive va aussi dépendre des interactions au sein de l'agrosystème. En France, depuis 2008, l'agrosystème constitué par la culture de tomates sous serre est perturbé par l'arrivée d'une espèce invasive originaire d'Amérique latine : Tuta absoluta (Gelechiidae). La chenille mineuse provoque de graves défoliations des plants de tomate et attaque aussi les fruits. Les agents de lutte majoritairement utilisés en tomates sous serre en France sont un prédateur omnivore, Macrolophus pygmaeus (Miridae), initialement utilisé contre diverses espèces de ravageurs, notamment les aleurodes, ainsi que le parasitoïde oophage Trichogramma achaeae. Le prédateur M. pygmaeus s'est avéré capable de consommer les oeufs et, plus rarement, les jeunes stades larvaires de T. absoluta. L'objectif de cette thèse fut (i) d'étudier la perturbation des interactions liée à l'invasion, (ii) de rechercher de nouveaux auxiliaires autochtones, puis (iii) d'évaluer l'efficacité de ces auxiliaires lorsqu'ils sont intégrés dans l'agrosystème. Nous avons montré que de nouvelles interactions sont apparues suite à l'invasion, notamment la compétition apparente entre les aleurodes et T. absoluta en présence de M. pygmaeus. Dans un second temps, nous avons recherché de nouveaux auxiliaires, en se focalisant d'abord sur les trichogrammes, Trichogramma achaeae étant déjà commercialisé contre T. absoluta en France. Une souche de trichogramme plus efficace et ayant la capacité de se mettre en diapause ou en quiescence était recherchée. Les expérimentations de laboratoire et de terrain n'ont pas permis de mettre en évidence un trichogramme plus intéressant que celui déjà commercialisé. De plus, nous avons observé une prédation intra-guilde de M. pygmaeus sur les trichogrammes juvéniles i.e. oeufs parasités, et nous avons montré que T. absoluta n'était pas un hôte approprié pour ces parasitoïdes. Même si les oeufs de T. absoluta permettent la production de générations filles, l'impact de ces générations en serre dans des conditions réalistes était négligeable. Les trichogrammes ne s'installant pas sur la culture, les études concernant les parasitoïdes oophages se sont arrêtées là et nous nous sommes intéressés aux parasitoïdes larvaires. En partenariat avec une équipe espagnole (IRTA), la biologie de deux parasitoïdes larvaires a été étudiée et a souligné l'intérêt de Stenomesius japonicus (Eulophidae) en tant que potentiel agent de lutte biologique contre T. absoluta. Malgré les interactions négatives subies par le parasitoïde (compétition pour la ressource et cléptoparasitisme), des expérimentations sous serre en conditions réalistes ont montré que le prédateur et le parasitoïde larvaire pouvaient coexister pendant plusieurs mois. L'effet de l'addition dans l'agrosystème d'une proie alternative pour le prédateur omnivore sur l'exclusion du parasitoïde a ensuite été évalué. Cette étude a prouvé, elle aussi, que le parasitoïde était capable de se maintenir dans la culture, même en présence d'autres proies pour le prédateur. Ce travail de thèse a donné des pistes prometteuses pour le contrôle biologique de T. absoluta en Europe grâce à des espèces autochtones. Il a clarifié les interactions multi-trophiques en jeu dans l'agrosystème étudié et a mis en évidence le rôle des interactions dans le succès ou l'échec des programmes de lutte biologique.

The researches carried out on early stages of Cymothoe (J.-L. A.) and on systematics of Rinorea (G. A.) show that the 41 species of Cymothoe the hostplants of which are known feed either on various Flacourtiaceae (13 species) or on Violaceae belonging to the genus Rinorea (28 species). These last 28 species show a very high degree of trophic specialization : two thirds of them are monophagous, the others being stenophagous, with 2 to 6 species of host-Rinorea, usually closely related. The relations between the beographic distributions of Cymothoe and of Rinorea are analyzed. Various field observations of the laying behaviour of females are reported, as well as the results of choice experiments, which confirm the trophic specificity and show that, as soon as they hatch, larvae are able to recognize their food plant, even though they do not have to find it in nature. The ecological significance of this specialisation is discussed ; it does not seem to be related to a possible interspecific competition., Les recherches effectuées au Cameroun sur les premiers états des Cymothoe (J.-L. A.) et sur la systématique des Rinorea (G. A.) montrent que les espèces de Cymothoe dont les plantes-hôtes sont connues (41 espèces) se nourrissent soit de diverses Flacourtiacées (13 espèces), soit de Violacées du genre Rinorea (28 espèces). Dans le second cas, la spécialisation trophique est très étroite : les deux tiers des espèces sont strictement monophages, les autres sténophages (avec de 2 à 6 espèces de Rinorea-hôtes, en général étroitement affines). Les rapports entre la distribution géographique des Rinorea et celle des Cymothoe sont analysés. Diverses observations sur le comportement de ponte des femelles et quelques expériences de choix faites en laboratoire sont rapportées : elles confirment la spécificité trophique et montrent que, dès l'éclosion, les larves savent reconnaître leur plante nourricière, bien que dans la nature elles n'aient pas à trouver celle-ci. La signification écologique de cette spécialisation est discutée ; elle paraît sans rapport avec un éventuel phénomène de compétition interspécifique., Amiet Jean-Louis, Achoundong Gaston. Un exemple de spécialisation trophique chez les Lépidoptères : les Cymothoe camerounaises inféodées aux Rinorea (Violacées) (Lepidoptera, Nymphalidae). In: Bulletin de la Société entomologique de France, volume 101 (5), décembre 1996. pp. 449-466.