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International audience; Recent decline in abundance of Atlantic salmon (Salmo salar) and concomitant changes in life history may result from a decline in the growth conditions during marine migration. Available literature suggests the existence of a sex-specific reaction norm linking maturation with environmental growth conditions at sea. However, the extent to which this mechanism explains variations in age at maturity remains unclear. Using a historical collection of scales (1987–2017) from the Sélune River, France, we showed that marine growth declined over the first summer and remained stable during the subsequent periods at sea among returning salmon. Results support the hypothesis of a sex-specific probabilistic reaction norm, with individual probability to return after 1 year at sea increasing when growth increases. Females may require higher growth than males to attain their maturation threshold. This mechanism is a good candidate to explain temporal variability in sea-age at return at both the individual and population level in the Sélune population and in many other southern European populations.

Understanding the geographical scales at which environmental variables affect an individual's body size, and thus their mortality risk, can inform management strategies to help conserve wild populations under climate change. Yet, our current understanding of these relationships is based on studies done at different scales that report inconsistent findings. We predicted that temperature-related variables (e.g. winter temperature) influence body size at a regional scale, that is, affecting individuals in geographically independent catchments similarly, whereas non-temperature-related variables (e.g. conspecific competitor density) exert a local influence, that is, affecting individuals in geographically independent catchments differently. We developed statistical models to test our predictions using body length measures of a large and long-term sample of juvenile Atlantic salmon (Salmo salar) from three rivers in the U.K. and France. We developed mixture models to predict the individual juvenile salmon ages objectively from their body length. We then developed linear mixed models to describe inter-annual changes in mean length of the youngest (age 0) cohort of juvenile salmon from river-specific seasonal variables, and tested whether they exerted their influence at a local or regional scale. All models accounted for spatio-temporal differences in sampling protocols and individual reproductive strategy. We estimated and interpreted coefficients using Bayesian theory. Our findings supported our predictions. Juvenile salmon were longer in years of higher overwinter water temperature and this effect was best parameterised as a single regional coefficient applicable to all three rivers. Similarly, spring mean temperature was best parameterised with a single regional nonlinear coefficient. In contrast, juvenile salmon were shorter in years of high densities of competing conspecifics and their interaction with total mean discharge and these effects were represented by local river-specific coefficients. Summer droughts had a negative effect on juvenile salmon length but was best parameterised as a single regional coefficient, contrary to our expectations. We show that environmental variables affect biological processes at different but predictable geographical scales. Temperature-related variables affect body sizes of exothermic animals at a regional scale, whereas non-temperature variables, such as the density of conspecific competitors and water abstraction, exert their influence at a local scale. These findings highlight the importance of integrating local and regional management plans to mitigate the impacts of climate change on the body size, and ultimately the conservation, of exothermic species.

International audience; Allee effects have important implications for many aspects of basic and applied ecology. The benefits of aggregation of conspecific individuals are central to Allee effects, which have led to the widely held assumption that social species are more prone to Allee effects. Robust evidence for this assumption, however, remains rare. Furthermore, previous research on Allee effects has failed to adequately address the consequences of the different levels of organisation within social species’ populations. Here, we review available evidence of Allee effects and model the role of demographic and behavioural factors that may combine to dampen or strengthen Allee effects in social species. We use examples across various species with contrasting social structure, including carnivores, bats, primates and eusocial insects. Building on this, we provide a conceptual framework that allows for the integration of different Allee effects in social species. Social species are characterised by nested levels of organisation. The benefits of cooperation, measured by mean individual fitness, can be observed at both the population and group levels, giving rise to “population level” and “group level” Allee effects respectively. We also speculate on the possibility of a third level, reporting per capita benefits for different individuals within a group (e.g. castes in social insects). We show that group size heterogeneity and intergroup interactions affect the strength of population‐level demographic Allee effects. Populations with higher group size heterogeneity and in which individual social groups cooperate demonstrate the weakest Allee effects and may thus provide an explanation for why extinctions due to Allee effects are rare in social species. More adequately accounting for Allee effects in social species will improve our understanding of the ecological and evolutionary implications of cooperation in social species.

Pôle EcolDur Département SPE; International audience; Predators can provide a valuable ecosystem service by suppressing crop pests. However, intraguild predation, where predators compete for the same prey resource whilst consuming each other, may destabilize population dynamics and increase the risk of pest outbreaks. Very little is known about intraguild predation in open fields or the strengths of trophic links between predators which may negatively affect pest control. * We tested the null hypothesis that predation by the epigeal predator Pterostichus melanarius (Coleoptera: Carabidae) on different spiders is species-independent (proportional to density). A combination of population monitoring in winter wheat, molecular identification of juvenile spiders, molecular analysis of predator gut contents and a Monte Carlo simulation model were used to analyse prey choice. * Pterostichus melanarius were pitfall-trapped over three months, and 622 individuals were screened for the remains of four spider species. Predation rates on spiders were 43·6% in June and 33·3% in August and showed clear evidence of prey choice. * Predation on the web-dependent Tenuiphantes tenuis (Linyphiidae) was significantly greater than predicted from a random choice model, while predation on Bathyphantes gracilis (Linyphiidae) was significantly lower. The beetles may be selecting the most abundant species disproportionately (switching) or responding in some cases to spatial niche separation (T. tenuis locate their webs marginally lower than B. gracilis). However, two itinerant hunters, Erigone spp. (Linyphiidae) and Pachygnatha degeeri (Tetragnathidae), were consumed in proportion to their density. * Synthesis and applications. High levels of intraguild predation were revealed using molecular diagnostics. The gut analysis approach provided invaluable data that will inform the future design of appropriate pest management and integrated farming strategies that encourage these predators. The data showed strong evidence of prey choice. Managers can, however, probably encourage high densities of all these known aphid predators (spiders and carabids) because disproportionately high rates of predation on the most common spiders at our field sites (T. tenuis) were not sufficient to prevent strong growth in the density of this species between June and August (adults increased × 1·6 and juveniles × 8·6). Such work is essential if we are to reveal the processes behind functional biodiversity in crops.

Agricultural intensification and associated loss of high‐quality habitats are key drivers of insect pollinator declines. With the aim of decreasing the environmental impact of agriculture, the 2014 EU Common Agricultural Policy (CAP) defined a set of habitat and landscape features (Ecological Focus Areas: EFAs) farmers could select from as a requirement to receive basic farm payments. To inform the post‐2020 CAP, we performed a European‐scale evaluation to determine how different EFA options vary in their potential to support insect pollinators under standard and pollinator‐friendly management, as well as the extent of farmer uptake.A structured Delphi elicitation process engaged 22 experts from 18 European countries to evaluate EFAs options. By considering life cycle requirements of key pollinating taxa (i.e. bumble bees, solitary bees and hoverflies), each option was evaluated for its potential to provide forage, bee nesting sites and hoverfly larval resources.EFA options varied substantially in the resources they were perceived to provide and their effectiveness varied geographically and temporally. For example, field margins provide relatively good forage throughout the season in Southern and Eastern Europe but lacked early‐season forage in Northern and Western Europe. Under standard management, no single EFA option achieved high scores across resource categories and a scarcity of late season forage was perceived.Experts identified substantial opportunities to improve habitat quality by adopting pollinator‐friendly management. Improving management alone was, however, unlikely to ensure that all pollinator resource requirements were met. Our analyses suggest that a combination of poor management, differences in the inherent pollinator habitat quality and uptake bias towards catch crops and nitrogen‐fixing crops severely limit the potential of EFAs to support pollinators in European agricultural landscapes. Policy Implications. To conserve pollinators and help protect pollination services, our expert elicitation highlights the need to create a variety of interconnected, well‐managed habitats that complement each other in the resources they offer. To achieve this the Common Agricultural Policy post‐2020 should take a holistic view to implementation that integrates the different delivery vehicles aimed at protecting biodiversity (e.g. enhanced conditionality, eco‐schemes and agri‐environment and climate measures). To improve habitat quality we recommend an effective monitoring framework with target‐orientated indicators and to facilitate the spatial targeting of options collaboration between land managers should be incentivised., To conserve pollinators and help protect pollination services, our expert elicitation highlights the need to create a variety of interconnected, well‐managed habitats that complement each other in the resources they offer. To achieve this the Common Agricultural Policy post‐2020 should take a holistic view to implementation that integrates the different delivery vehicles aimed at protecting biodiversity (e.g. enhanced conditionality, eco‐schemes and agri‐environment and climate measures). To improve habitat quality we recommend an effective monitoring framework with target‐orientated indicators and to facilitate the spatial targeting of options collaboration between land managers should be incentivised.

International audience

International audience; Invertebrates perform many vital functions in agricultural production, but many taxa are in decline, including pest natural enemies. Action is needed to increase their abundance if more sustainable agricultural systems are to be achieved. Conservation biological control (CBC) is a key component of integrated pest management yet has failed to be widely adopted in mainstream agriculture. Approaches to improving conservation biological control have been largely ad hoc. Two approaches are described to improve this process, one based upon pest natural enemy ecology and resource provision while the other focusses on the ecosystem service delivery using the QuESSA (Quantification of Ecological Services for Sustainable Agriculture) project as an example. In this project, a predictive scoring system was developed to show the potential of five seminatural habitat categories to provide biological control, from which predictive maps were generated for Europe. Actual biological control was measured in a series of case studies using sentinel systems (insect or seed prey), trade-offs between ecosystem services were explored, and heatmaps of biological control were generated. The overall conclusion from the QuESSA project was that results were context specific, indicating that more targeted approaches to CBC are needed. This may include designing new habitats or modifying existing habitats to support the types of natural enemies required for specific crops or pests.

International audience; Electrofishing in streams of low water conductivity has technical limitations leading to the widespread use of poison fishing. In theory, provided a high enough voltage gradient can be created in water, electrofishing should be possible in all but the lowest of conductivities (

Recent declines in Atlantic salmon Salmo salar populations are generally attributed to factors in their marine life-phase. However, it is postulated that factors affecting their freshwater life-phase might impact their marine survival, such as the influence of body size. While larger smolts are widely hypothesized to have higher marine survival rates, empirical support remains scant, in part due to inadequate data and ambiguous statistical analyses. Here, we test the influence of smolt body size on marine return rates, a proxy for marine survival, using a 12-year dataset of 3688 smolts tagged with passive integrated transponders in the River Frome, Southern England. State-space models describe the probability of smolts surviving their marine phase to return as 1 sea-winter (1SW) or multi-sea-winter adults as a function of their length, while accounting for imperfect detection and missing data. Models predicted that larger smolts had higher return rates; the most parsimonious model included the effect of length on 1SW return rate. This prediction is concerning, as freshwater juvenile salmon are decreasing in size on the River Frome, and elsewhere. Thus, to maximize adult returns, restoration efforts should focus on freshwater life-stages, and maximize both the number and the size of emigrating smolts.

International audience; Numerous studies show that landscape simplification reduces abundance and diversity of natural enemies in agroecosystems, but its effect on natural pest control remains poorly quantified. Further, natural enemy impacts on pest populations have usually been estimated for a limited number of taxa and have not considered interactions among predator species. In a quantitative synthesis with data collected from several cropping systems in Europe and North America, we analyzed how the level and within-field spatial stability of natural pest control services was related to the simplification of the surrounding landscape. All studies used aphids as a model species and exclusion cages to measure aphid pest control. Landscape simplification was quantified by the proportion of cultivated land within a 1 km radius around each plot. We found a consistent negative effect of landscape simplification on the level of natural pest control, despite interactions among enemies. Average level of pest control was 46% lower in homogeneous landscapes dominated by cultivated land, as compared with more complex landscapes. Landscape simplification did not affect the amount of positive or negative interactions among ground-dwelling and vegetation-dwelling predators, or the within-field stability of pest control. Our synthesis demonstrates that agricultural intensification through landscape simplification has negative effects on the level of natural pest control with important implications for management to maintain and enhance ecosystem services in agricultural landscapes. Specifically, preserving and restoring semi-natural habitats emerges as a fundamental first step to maintain and enhance pest control services provided by predatory arthropods to agriculture.

Four British bumblebee species (Bombus terrestris, Bombus hortorum, Bombus ruderatus and Bombus subterraneus) became established in New Zealand following their introduction at the turn of the last century. Of these, two remain common in the United Kingdom (B. terrestris and B. hortorum), whilst two (B. ruderatus and B. subterraneus) have undergone marked declines, the latter being declared extinct in 2000. The presence of these bumblebees in New Zealand provides an unique system in which four related species have been isolated from their source population for over 100 years, providing a rare opportunity to examine the impacts of an initial bottleneck and introduction to a novel environment on their population genetics. We used microsatellite markers to compare modern populations of B. terrestris, B. hortorum and B. ruderatus in the United Kingdom and New Zealand and to compare museum specimens of British B. subterraneus with the current New Zealand population. We used approximate Bayesian computation to estimate demographic parameters of the introduction history, notably to estimate the number of founders involved in the initial introduction. Species-specific patterns derived from genetic analysis were consistent with the predictions based on the presumed history of these populations; demographic events have left a marked genetic signature on all four species. Approximate Bayesian analyses suggest that the New Zealand population of B. subterraneus may have been founded by as few as two individuals, giving rise to low genetic diversity and marked genetic divergence from the (now extinct) UK population.

Pheasant chicks, like many other farmland birds, require a large proportion of invertebrates in their diet for successful growth and development during their first few weeks. This study used human-imprinted pheasant chicks as a novel sampling tool to investigate which arable habitats provided the best foraging. Using human-imprinted chicks decreased sampling bias and allowed a biologically relevant method of assessing invertebrate availability within each habitat. Faecal analysis was used to identify which invertebrates were eaten and correction factors established to take into account the differing digestion rates of different fragments. The validity of using commercially farmed chicks for this study was confirmed by the comparison of wild and farmed strain chicks. The value of non-cropped areas, both long-term set-aside and crops planted for game cover, in terms of diet and cover is confirmed. Greater proportions of preferred prey groups were consumed in both types of set-aside than in the commercial crop fields. Interestingly, no difference was found between spring and winter sown cereals and non-cereal crops. The long-term set-aside areas were found to be particularly beneficial to foraging birds as their vegetation structure allowed easy access to potential prey items. As farming has intensified, many farmland birds, which also require invertebrates during their early stages, have declined. If the diet of imprinted pheasant chicks is comparable to those of other farmland birds this method could be used to accurately assess benefits to avian conservation on a wider scale. Human-imprinted grey partridge foraging with pheasant chicks showed similar behaviour and ate similar insects indicating that habitats benefiting one are likely to benefit the other. Faecal samples collected from wild broods of other farmland birds - the skylark, yellow wagtail and lapwing - showed certain similarities in dietary preference implying that careful comparisons may be made.

Many animal populations are threatened by human activity, including habitat loss and harvesting but recent advances in population ecology show that the age- and sex-structure are important when aiming to understand population dynamics. However, research on population dynamics often focuses on species that experience relatively little human disturbance and human caused mortality is often assumed not to affect population dynamics. An increasing number of studies shows short-term and long-term evolutionary and ecological consequences of harvesting. This has not only implications for the understanding of population dynamics but also for the management and conservation of species in human-dominated landscapes. This thesis aims to investigate the interaction between the demographic structure and harvesting in a fluctuating species, the red grouse (Lagopus lagopus scoticus) using a combination of empirical and theoretical approaches. The relative roles of age-related parasite burden, fecundity and shooting in driving population dynamics are assessed, and empirical data are used to parameterise a model examining the effect of harvesting on the population dynamics. The empirical part of the thesis starts with the investigation of the intensity and distribution of the parasitic nematode Trichostrongylus tenuis for three age-classes of red grouse before the breeding season. The intensity of the parasite increased with host age. Parasites in two-year-old grouse were more aggregated than in one-year-old and 3+-year-old grouse. This has implications for population dynamics because the aggregation of parasites within the host influences mortality rates. Females of the oldest age class (3+-years-old) were less fecund than younger grouse and interactions with nesting habitat and year were found to affect female fecundity. The age- and sex-structure of shot birds was compared with the age- and sex-structure of the population before shooting. More old birds were shot at small bag sizes but this bias decreased as more birds were shot. Old males were highly susceptible to shooting at the beginning of the season but susceptibility decreased with number of shooting events. A relationship between bag numbers and population density was found. An age- and sex-structured population model was used to examine the effect of harvesting on red grouse population dynamics. Selective harvest for or against a certain age class led to a skew in the sex ratio of the population and to a decrease in fecundity and therefore to a drop in population size and harvest yield. Parasites and the exclusion of young birds through aggressiveness affected the population dynamics and led to a skew in the harvest rate at which the maximum sustainable yield was attained. Shooting early in the season resulted in a higher yield because individuals were removed from the population before they contributed to the availability of free ranging stages of the parasite. The population model demonstrated that parasites, aggressiveness and harvesting interact and that harvesting is a significant factor in population dynamics. Overall, the current practice of shooting rarely more than 50% of the population seems to be a good precautionary principle. Uncertainty in the harvesting rate increased the probability of local extirpation of the population. Therefore, reliable estimates of the population, including the age and sex structure, are invaluable parts of red grouse management. This study showed that harvesting and the age and sex structure of the population are important drivers of red grouse population dynamics and an understanding of their interactions is important for sustainable management of red grouse.

For roughly the past 200 years land-managers have used the practice of “muirburning” to manipulate the structure of heather (Calluna vulgaris) to create a patchwork of habitat structures able to provide forage and nesting sites for red grouse (Lagopus lagopus scoticus) as well as grazing for sheep (Ovis aries) and red deer (Cervus elaphus). This thesis investigates both the behaviour and impact of management fires in recognition of the need to develop multi-aim land management practices that ensure both continued productivity and protection of biodiversity in the face of climatic and environmental change. Fuel structure and loading are crucial controlling factors on both fire behaviour and impact governing both rate of spread and heat release to the ground surface. A visual obstruction method is developed that estimates total and fine fuel loading as well as the structure of the heather canopy. In order to adequately understand fire impact a dimensional analysis approach is taken to estimating the mass of burnt heather stems. Experiments at a number of spatial and temporal scales relate variation in heather fuel moisture content to stand structure and variation in weather conditions. Monitoring shows moisture contents to be relatively stable temporally, but spatially variable. Periods of extreme low moisture contents in early spring are associated with frozen ground, winter cuticle damage and physiological drought. Such conditions may have contributed to the large number of wildfires in 2003. A replicated plot design was used to investigate the effect of weather conditions and fuel loading on fire behaviour. An empirical approach is taken to fire behaviour modelling with equations describing rate of spread and fireline intensity being developed on the basis of fuel structure descriptors and windspeed. The theoretical negative correlation between fuel bed density and rate of spread is demonstrated to hold true for heather stands, while the impact of heterogeneity in fuel bed structure is also investigated. Redundancy Analysis is used to investigate the influence of multiple predictors on a number of aspects of fire behaviour including: rate of spread, fireline intensity, flame length and ground surface heating. Data from this and previous studies are used to ground-truth a number of fire behaviour prediction systems including BehavePlus and the Canadian Fire Behaviour Prediction System. Finally linkages between fire behaviour, fire severity and heather regeneration are investigated. A number of proxy measures of ‘Immediate Severity’ are tested and used to examine the influence of fires on plant regeneration. The post-fire development of stands is shown to relate primarily to stand age and structure before burning, and to post-fire substrates rather than variation in fire behaviour and severity.