Showing papers by "Vincent Bretagnolle published in 2016"

Herbicides do not ensure for higher wheat yield, but eliminate rare plant species.

Abstract: Weed control is generally considered to be essential for crop production and herbicides have become the main method used for weed control in developed countries. However, concerns about harmful environmental consequences have led to strong pressure on farmers to reduce the use of herbicides. As food demand is forecast to increase by 50% over the next century, an in-depth quantitative analysis of crop yields, weeds and herbicides is required to balance economic and environmental issues. This study analysed the relationship between weeds, herbicides and winter wheat yields using data from 150 winter wheat fields in western France. A Bayesian hierarchical model was built to take account of farmers’ behaviour, including implicitly their perception of weeds and weed control practices, on the effectiveness of treatment. No relationship was detected between crop yields and herbicide use. Herbicides were found to be more effective at controlling rare plant species than abundant weed species. These results suggest that reducing the use of herbicides by up to 50% could maintain crop production, a result confirmed by previous studies, while encouraging weed biodiversity. Food security and biodiversity conservation may, therefore, be achieved simultaneously in intensive agriculture simply by reducing the use of herbicides.

Networking Our Way to Better Ecosystem Service Provision

Abstract: The ecosystem services (EcoS) concept is being used increasingly to attach values to natural systems and the multiple benefits they provide to human societies. Ecosystem processes or functions only become EcoS if they are shown to have social and/or economic value. This should assure an explicit connection between the natural and social sciences, but EcoS approaches have been criticized for retaining little natural science. Preserving the natural, ecological science context within EcoS research is challenging because the multiple disciplines involved have very different traditions and vocabularies (common-language challenge) and span many organizational levels and temporal and spatial scales (scale challenge) that define the relevant interacting entities (interaction challenge). We propose a network-based approach to transcend these discipline challenges and place the natural science context at the heart of EcoS research.

How individual Montagu's Harriers cope with Moreau's Paradox during the Sahelian winter

Abstract: 1. Hundreds of millions of Afro-Palaearctic migrants winter in the Sahel, a semi-arid belt south of the Sahara desert, where they experience deteriorating ecological conditions during their overwintering stay and have to prepare for spring migration when conditions are worst. This well-known phenomenon was first described by R.E. Moreau and is known ever since as Moreau's Paradox. However, empirical evidence of the deteriorating seasonal ecological conditions is limited and little is known on how birds respond. 2. Montagu's Harriers Circus pygargus spend 6 months of the year in their wintering areas in the Sahel. Within the wintering season, birds move gradually to the south, visiting several distinct sites to which they are site-faithful in consecutive years. At the last wintering site, birds find themselves at the southern edge of the Sahelian zone and have no other options than facing deteriorating conditions. 3. We tracked 36 Montagu's Harriers with GPS trackers to study their habitat use and behaviour during winter and collected data on the abundance of their main prey, grasshoppers, in Senegal. Since grasshopper abundance was positively related to vegetation greenness (measured as normalized difference vegetation index, NDVI), we used NDVI values as a proxy for prey abundance in areas where no field data were collected. Prey abundance (grasshopper counts and vegetation greenness) at wintering sites of Montagu's Harriers decreased during the wintering period. 4. Montagu's Harriers responded to decreasing food availability by increasing their flight time during the second half of the winter. Individuals increased flight time more in areas with stronger declines in NDVI values, suggesting that lower food abundance required more intense foraging to achieve energy requirements. The apparent consequence was that Montagu's Harriers departed later in spring when their final wintering site had lower NDVI values and presumably lower food abundance and consequently arrived later at their breeding site. 5. Our results confirmed the suggestions Moreau made 40 years ago: the late wintering period might be a bottleneck during the annual cycle with possible carry-over effects to the breeding season. Ongoing climate change with less rainfall in the Sahel region paired with increased human pressure on natural and agricultural habitats resulting in degradation and desertification is likely to make this period more demanding, which may negatively impact populations of migratory birds using the Sahel.

Niche partitioning by three Pterodroma petrel species during non-breeding in the equatorial Pacific Ocean

Abstract: Niche divergence is expected for species that compete for shared resources, including migrants that occupy similar regions during the non-breeding season. Studies of temperate seabirds indicate that both spatial and behavioural segregation can be important mechanisms for reducing competition, but there have been few investigations of resource partitioning by closely related taxa in low productivity, tropical environments. We investigated niche partitioning in 3 gadfly petrel taxa, Pterodroma leucoptera leucoptera (n = 22), P. leucoptera caledonica (n = 7) and P. pycrofti (n = 12), during their non-breeding season in the eastern tropical Pacific Ocean by combining tracking data from geolocator-immersion loggers with remotely sensed environmental data in species distribution models (SDMs), and by comparing feather stable isotope ratios. The 3 taxa showed spatial partitioning: two foraged in the North Equatorial Counter Current and one in the South Equatorial Current. This reflected differences in their realised habitat niches, with significant taxon-specific responses to thermocline depth, sea surface temperature and bathymetry. There were also differences among taxa in activity patterns, and all birds spent a much larger proportion of time in flight at night than during the day, suggesting predominance of nocturnal foraging behaviour. Comparison of stable isotope ratios in feathers suggests that P. l. leucoptera and P. pycrofti mainly consume vertically migrating mesopelagic fishes, whereas the diet of P. l. caledonica also includes some lower trophic levels including crustaceans and squid. Unique insights can be gained from studies of the foraging ecology of tropical pelagic seabirds, in comparison with temperate and polar waters, and are urgently required for understanding and protecting tropical avifauna in key marine habitats.

Density-dependent reproduction causes winter crashes in a common vole population

Abstract: Common voles in western France exhibit three-year population cycles with winter crashes after large outbreaks. During the winter of 2011–2012, we monitored survival, reproduction, recruitment and population growth rate of common voles at different densities (from low to outbreak densities) in natura to better understand density dependence of demographic parameters. Between October and April, the number of animals decreased irrespective of initial density. However, the decline was more pronounced when October density was higher (loss of ≈54 % of individuals at low density and 95 % at high density). Using capture-mark-recapture models with Pradel’s temporal symmetry approach, we found a negative effect of density on recruitment and reproduction. In contrast, density had a slightly positive effect on survival indicating that mortality did not drive the steeper declines in animal numbers at high density. We discuss these results in a population cycle framework, and suggest that crashes after outbreaks could reflect negative effects of density dependence on reproduction rather than changes in mortality rates.

Spatio‐temporal modelling of auk abundance after the Erika oil spill and implications for conservation

Abstract: 1. Species distribution models are widely used in applied ecology and conservation. While accounting for spatial dependences is now the rule, temporal dependences have rarely been dealt with explicitly. In this study, we analyse wintering auk distribution in the Bay of Biscay and English Channel and estimate changes in abundance within and between years while accounting for space–time dependencies. We then propose a retrospective estimate of the impact of the Erika oil spill that occurred in December 1999. 2. Two series of extensive aerial surveys, repeated at intervals of 1–2 months, were carried out at a 10-year interval off the French Atlantic coast (2001–2002 and 2011–2012). Spatially and temporally explicit Bayesian models were fitted to these data to provide spatio-temporal predictions of auk abundance. These were then used to compare abundances within the area affected by the Erika oil spill two and twelve years after the catastrophe. 3. The results showed that 1 55 million auks wintered in the study area in 2011–2012. The main wintering area was the English Channel (more than one million auks) but the Bay of Biscay also became an important area in the middle of winter (470 000 auks) owing to a strong southward shift in auk distribution. 4. Two years after the catastrophe (2001–2002), the area affected by the Erika oil spill hosted a small proportion of auks of the Bay of Biscay – about 80 000 individuals. This number increased by more than three times 10 years later and reached 270 000 individuals, whereas no significant change was detected elsewhere. We suggest that it could result from a recovery after the extra-mortality induced by the Erika oil spill. 5. Policy implications. This study identified major auk wintering areas, with abundances much higher than previously realized. Oil spills have occurred regularly in these areas, with major delayed impacts on auk breeding populations. The worst case scenario would be if a major oil spill occurred in the English Channel in February, when abundance reaches one million auks. Although such a disaster has not so far occurred, stricter policies on the transport of hydrocarbons should be implemented to prevent such a possibility.

Robust estimation of survival and contribution of captive‐bred Mallards Anas platyrhynchos to a wild population in a large‐scale release programme

Abstract: The survival of captive-bred individuals from release into the wild to their first breeding season is crucial to assess the success of reintroduction or translocation programmes, and to assess their potential impact of wild populations. However, assessing the survival of captive-bred individuals following their release is often complicated by immediate dispersal once in the wild. Here, we apply Lindberg's robust design model, a method that incorporates emigration from the study site, to obtain true estimates of survival of captive-bred Mallards Anas platyrhynchos, a common duck species released on a large scale in Europe since the 1970s. Overall survival rate from release in July until the onset of the next breeding season in April was low (0.18 ± 0.07 se) and equivalent to half the first-year survival of local wild Mallards. Higher overall detectability and temporary emigration during the hunting period revealed movements in response to hunting pressure. Such low survival of released Mallards during their first year may help prevent large-scale genetic mixing with the wild population. Nevertheless, by combining our results with regional waterfowl counts, we estimated that a minimum of 34% of the Mallards in the region were of captive origin at the onset of the breeding season. Although most released birds quickly die, restocking for hunting may be of sufficient magnitude to affect the wild population through genetic homogenization or loss of local adaptation. Robust design protocols allow for the estimation of true survival estimates by controlling for permanent and temporary emigration and may require only a moderate increase in fieldwork effort.

Cold Tolerance and Sex-Dependent Hypothermia May Explain Winter Sexual Segregation in a Farmland Bird.

Abstract: Migration is an important event in the life cycle of many organisms, but considerable intraspecific variation may occur in its timing and/or destination, resulting in sexual segregation during wintering periods. In this study, we tested the body size hypothesis, or cold tolerance hypothesis, which predicts that body size dimorphism modulates metabolic costs associated with cold climate. Using the Eurasian skylark, we first investigated whether this species showed sexual differential migration. Then we explored the body size hypothesis by experimentally testing the effect of low ambient temperature (Ta) on both metabolic rate (MR) and body temperature (Tb). We tested for sex-related differences in metabolism and in energy-saving mechanism (hypothermia). We found clear differential migration by sex in skylark wintering populations, with a male-biased sex ratio decreasing toward southern latitudes. Measurements on captive birds at 20°, 6°, and -5°C demonstrated a significant increase in MR when Ta decreased, but there is no difference between sexes. While both males and females reduced their Tb overnight, Tb reduction was more pronounced in females exposed to the coldest temperature treatment. In addition, we found that individuals with the most reduced Tb lost less body weight during the night, suggesting that Tb reduction may help minimize energy expenditure when conditions become constraining. Our study suggests that functional mechanisms may be involved in latitudinal segregation between sexes and supports the hypothesis that sex-specific physiological strategies and thermal tolerance may explain segregation between sexes.

Some like it hot: effect of environment on population dynamics of a small tropical seabird in the Caribbean region

Abstract: An understanding of how environmental changes affect life history traits and population dynamics is essential for predicting the effects of climate change, managing ecosystems, and determining how species and habitats can best be preserved. This applies particularly to seabirds, which, as top marine predators, are often considered as indicators of marine ecosystem changes. Most studies have so far been conducted in polar or temperate regions. However, important changes in the functioning of tropical marine ecosystems have been reported, but the responses of top predators remain poorly known. This study focused on a tropical seabird, Audubon's shearwater Puffinus lherminieri, analyzing the relationships between climate change and the survival of adults, nesting success, and population dynamics. The population studied breeds in Martinique, in the south of the Caribbean region, which is strongly influenced by the Amazon and Orinoco rivers. A data set for the period 1995 to 2014 was used to estimate the survival by age classes and breeding success and to determine which climate variables most affected demographic parameters. The population dynamics were modeled to predict the future population growth rates in response to climate change. The annual adult survival rate increased over the last 20 years, currently standing at 94% for adult birds more than 6 years old. Adult survival increased with sea surface temperature (SST) during the nonbreeding season as well as with Amazon River discharge, although the latter with a lag of 1 year. The effect of SST was explained by the positive relationship between SST and chlorophyll a during years of high discharge from the Amazon and Orinoco. The population decreased between 1995 and 2007 at a rate of 3% per year and then increased between 2008 and 2014 at a rate of 7% per year. The increase in adult survival observed should continue as temperatures increase in the future, and the population models predicted a stable or increasing population over the next 50 years (λ = 1.018). These results contrast with the negative effect of increasing SST on seabird populations found in temperate and polar regions, emphasizing the need to study the impact of climate change on tropical seabirds.

Corrigendum: Delivery of crop pollination services is an insufficient argument for wild pollinator conservation

Abstract: Author(s): Kleijn, David; Winfree, Rachael; Bartomeus, Ignasi; Carvalheiro, Luisa G; Henry, Mickael; Isaacs, Rufus; Klein, Alexandra-Maria; Kremen, Claire; M'Gonigle, Leithen K; Rader, Romina; Ricketts, Taylor H; Williams, Neal M; Adamson, Nancy Lee; Ascher, John S; Baldi, Andras; Batary, Peter; Benjamin, Faye; Biesmeijer, Jacobus C; Blitzer, Eleanor J; Bommarco, Riccardo; Brand, Mariette R; Bretagnolle, Vincent; Button, Lindsey; Cariveau, Daniel P; Chifflet, Remy; Colville, Jonathan F; Danforth, Bryan N; Elle, Elizabeth; Garratt, Michael PD; Herzog, Felix; Holzschuh, Andrea; Howlett, Brad G; Jauker, Frank; Jha, Shalene; Knop, Eva; Krewenka, Kristin M; Le Feon, Violette; Mandelik, Yael; May, Emily A; Park, Mia G; Pisanty, Gideon; Reemer, Menno; Riedinger, Verena; Rollin, Orianne; Rundlof, Maj; Sardinas, Hillary S; Scheper, Jeroen; Sciligo, Amber R; Smith, Henrik G; Steffan-Dewenter, Ingolf; Thorp, Robbin; Tscharntke, Teja; Verhulst, Jort; Viana, Blandina F; Vaissiere, Bernard E; Veldtman, Ruan; Ward, Kimiora L; Westphal, Catrin; Potts, Simon G

Contribution of released captive-bred Mallards to the dynamics of natural populations

Abstract: The consequences of releasing captive-bred game animals into the wild have received little attention, despite their potential demographic impact, as well as costs and/or benefits for recipient populations. If restocking aims at increasing harvest opportunities, increased hunting pressure is expected, which would then be supported by either wild or released individuals. On the other hand, the wild recipient population may benefit from the release of captive-bred conspecifics if this reduces hunting pressure on the former through dilution of risk or selective harvesting of captive-bred individuals. Here, we modelled a Mallard (Anas platyrhynchos) population consisting of wild individuals supplemented by captive-bred conspecifics, a very common practice in Europe over the last 40 years. The objective was to test the effect of an increase of harvest rate on released and wild individuals, respectively. Our results show that, due to the low reproductive value of the released Mal-lards, the population was hardly affected by a change in harvest of these low performance individuals. Conversely, a 15 percent increase in harvest rate of the wild individuals would lead to a quick decline of the population. We discuss these results in the context of the Camargue population, located in the South of France, which has experienced an increase in Mallard harvest without apparent reduction of population size. We suggest that this has only been possible due to the release of captive-bred Mallards.

Modélisation et analyse de données environnementales à travers une ontologie spatio-temporelle

Abstract: Cet article presente les travaux pour le projet interdisciplinaire GEMINAT (GeoConnaisances des milieux naturels) qui a pour but d'integrer et d'exploiter des donnees environnementales heterogenes par l'application du web semantique. A partir d'un cas d'etude mene sur un observatoire environnemental base a Chize, nous resumons les besoins d'analyse spatio-temporelle des experts biologistes et ecologues envers les bases de donnees de l'assolement et de la biodiversite. Nous montrons comment la mise en oeuvre d'un framework avec une ontologie spatio-temporelle jouant le role d'un mediateur semantique peut resoudre les difficultes d'analyse et de maintenance qu'induisent ces systemes, amenes a de constantes evolutions de leurs modeles. En particulier, la demonstration de la faisabilite d'un tel systeme est faite, et nous mesurons sa capacite a repondre a des requetes complexes melant plusieurs sources de donnees et les dimensions spatiales et temporelles.

Alimentation des abeilles domestiques et sauvages en système de grandes cultures

Abstract: Durant les 50 dernieres annees, l’intensification agricole a profondement modifie la physionomie des paysages en Europe. Pour satisfaire les demandes croissantes des populations humaines, les systemes de grandes cultures produisent aujourd’hui des cereales, mais et autres oleagineux sur des surfaces de plus en plus etendues, au detriment de la diversite des varietes culturales locales et des habitats semi-naturels comme les prairies et reseaux bocagers. Comme beaucoup d’autres organismes, les abeilles sont affectees par ces changements environnementaux. Bien que les cultures a floraison massive, telles que le colza ou le tournesol, offrent des ressources florales tres abondantes pour les abeilles, leur floraison reste temporaire et limitee dans le temps. En consequence, les apiculteurs ont desormais recours a des transhumances et au nourrissage artificiel pour faire face aux periodes de disette saisonniere recurrentes dans ces zones de grandes cultures. En outre, la diversite des abeilles sauvages est erodee et l’efficacite des mesures de compensation agro-environnementales destinees a semer des melanges floraux reste a demontrer. Nous proposons ici une revue des travaux de recherche recents entrepris par l’UMT PrADE pour documenter l’ecologie de l’alimentation des abeilles et caracteriser leurs interactions avec les surfaces cultivees et naturelles dans un systeme de grandes cultures.

Mobilizing ecology for the innovative design of sustainable agro-ecosystems

Abstract: There is a paradox between the constant increase of knowledge production in ecology and the limited impact of innovations aiming to improve agro-ecosystems’ sustainability. Drawing on recent design theories’ formalism, this paper shows how shifting from a ‘decision’ pathway (i.e., identify optimal decisions to implement within a set of pre-defined options) to a ‘design’ pathway (i.e., enlarge the range of decision alternatives) may help overcoming this paradox. Considering that the former pathway tends to set off conflicts between stakeholders, inefficient public spending and limited innovation, we propose a conceptual framework facilitating the mobilization of ecological knowledge in innovative design processes. The elaboration of the framework draws upon a three-year collaboration between a design scientist and a research team in ecology which is conducing a long-term research program on reconciling intensive crop production and biodiversity preservation in western France. The framework was then applied to two other contrasted empirical cases, wet grasslands and subalpine grasslands, to reveal its potential in various contexts. The framework proposed is the following: once ecologists identify a key regulation process to be maintained in the agro-ecosystem, which we name “key underlying property”, various configurations of the agro-ecosystem can be explored to meet this property. We introduce the notion of “ecological fund”, i.e., the subsystem in which the key underlying property needs to be maintained, and suggest that it can be the departure point of a design process. An ecological fund is identified on the basis of ecological knowledge, but it guides a design process that may involve various stakeholders, instead of proposing a turnkey solution. We thus show that, despite ecology is often considered either as a discipline of expertise, used to inform decision-making processes, or as a constraint for agricultural production, it provides key knowledge that opens innovative design opportunities for enhancing agro-ecosystems’ sustainability.