Phenological and meteorological determinants of spider ballooning in an agricultural landscape

International audienceSpiders are known to commonly use aerial dispersal, so-called ballooning, especially at juvenile stages. They produce a silk thread that allows them to rise up in the air to disperse, which serves as inbreeding avoidance or to find an optimal over-winter habitat. Studies of phenology, species and meteorological factors associated with aerial dispersal have been limited to laboratory settings, with few data obtained under natural settings and no studies to date executed in France. To understand aerial dispersal, we conducted daily sampling between 2000 and 2002 at a height of 12 m. For adults, high proportions of "ballooners'' were observed during four seasonal peaks, with dispersal most prevalent during summer, while for juveniles dispersal was protracted across summer and fall. Linyphiidae is the most abundant family among the 10,879 individuals caught. We show a significant and negative influence of high wind speeds on ballooning, an effect that increased even under low temperatures (< 19 degrees C). At wind speeds greater than 4 m.s (1) dispersal becomes difficult, and is almost impossible beyond 5.5 m.s (1). Ballooning ability is reported for the first time for several species. This study increases our knowledge on aerial dispersal in spiders in an agricultural context. Such behaviour can be seen as a survival strategy to escape from a disturbed and unstable landscape. (C) 2016 Academie des sciences. Published by Elsevier Masson SAS. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

3D tracking of animals in the field, using rotational stereo videography

International audienceWe describe a method for tracking the path of animals in the field, based on stereo videography and aiming-angle measurements, combined in a single, rotational device. In open environments, this technique has the potential to extract multiple 3D positions per second, with a spatial uncertainty of <1 m (rms) within 300 m of the observer, and <0.1 m (rms) within 100 m of the observer, in all directions. The tracking device is transportable and operated by a single observer, and does not involve any animal tagging. As a video of the moving animal is recorded, track data can easily be completed with behavioural data. We present a prototype device based on accessible components that achieves about 70% of the theoretical maximal range. We show examples of bird ground and flight tracks, and discuss the strengths and limits of the method, compared with existing fine-scale (e.g. fixed-camera stereo videography) and large-scale tracking methods (e.g. GPS tracking)

Holocene Erosion Patterns in European Alps Viewed from Lake Sediment

In this paper we review the scientific efforts that were led over the last decades to reconstruct erosion from continuous alpine lake sediment records. Whereas most available geological records of Holocene terrigenous input focused in climate we propose a regional approach without any a priori regarding erosion forcing factors. In that aim, we integrated a set of sediment sequences from various environment along an altitudinal gradient from 200 up to 2400m asl in Northern French Alps. Altogether our data point climate change as one of the main factor of erosion variability. In particular, the last two cold spells that occurred during the early middle age (Dark Age) and between the 14th and the 20th century AD (Little Ice Age) appear to be outstanding compared to any other periods of enhanced erosion along the Holocene. The climatic forcing of those erosion phases is supported by an increase in the contribution of glacier-eroded material at a regional scale. However, at local scales, our data point the growing importance, since at least the mid Bronze Age (ca. 3500 cal. BP) of human activities as a major erosion factor. This influence peaked during the late Iron Age and Antiquity periods (200 BC - 400 AD) when we record a regional generalised period of enhanced erosion in response to the development of pasturing activities. Thanks to provenance and weathering markers, we evidenced a strong relationship between the changes in ecosystems, soil development and erosion patterns. We hence showed the vegetal colonisation of bared soil led to a period of intense weathering while new soils were under formation between 11,000 and 8,000 cal. BP. Soils then knew an optimum until the onset of the Neoglacial at ca. 4,500 cal. BP prior to decline under both climate and human pressures. Altogether our data point the complexity of processes that affected the Earth critical zone along the Holocene and especially since humans became a major geologic agent. However, we highlight the interest of leading spatialized paleo-investigation in order to reconstruct those dynamics through and thus better understand the processes in play in critical zone dynamics over long time periods

Reconstructing geomorphic patterns and forcing factors from Alpine Lake Sediment

International audienceIn this paper we review the scientific efforts that were led over the last decades to reconstruct geomorphic patterns from continuous alpine lake sediment records. Whereas our results point a growing importance of humans as erosion forcing factors, we will focus here on climate-related processes. Our main dataset is made of a regional approach which was led without any a priori regarding erosion forcing factors. We hence integrated a set of sediment sequences from various environment along an altitudinal gradient from 200 up to 2400m asl in Northern French Alps. Altogether our data point climate change as one of the main factor of erosion variability. In particular, the last two cold spells that occurred during the early middle age (Dark Age) and between the 14th and the 20th century AD (Little Ice Age) appear to be outstanding compared to any other periods of enhanced erosion along the Holocene. The climatic forcing of those erosion phases is supported by an increase in the contribution of glacier-eroded material at a regional scale. At local scales, our data also point the growing importance, since at least the mid Bronze Age (ca. 3500 cal. BP) of human activities as a major erosion factor. This influence peaked during the late Iron Age and Antiquity periods (200 BC - 400 AD) when we record a regional generalised period of enhanced erosion in response to the development of pasturing activities. Thanks to provenance and weathering markers, we evidenced a strong relationship between the changes in ecosystems, soil development and erosion patterns. We hence showed the vegetal colonisation of bared soil led to a period of intense weathering while new soils were under formation between 11,000 and 8,000 cal. BP. Soils then knew an optimum until the onset of the Neoglacial at ca. 4,500 cal. BP prior to decline under both climate and human pressures. Altogether our data point the complexity of processes that affected the Earth critical zone along the Holocene. However, we highlight the interest of leading spatialized paleo-investigation in order to reconstruct those dynamics through and thus better understand the processes in play in critical zone dynamics over long time periods

Erosion under climate and human pressures: An alpine lake sediment perspective

International audienceWe review the scientific efforts over the last decades to reconstruct erosion from continuous alpine lake sediment records. We focused both on methodological issues, showing the growing importance of non-destructive high resolution approaches (XRF core-scanner) as well as progresses in the understanding of processes leading to the creation of an “erosion signal” in lakes. We distinguish “continuous records” from “event-records”. Both provide complementary information but need to be studied with different approaches. Continuous regionally-relevant records proved to be particularly pertinent to document regional erosion patterns throughout the Holocene, in particular applying the source to sink approach. Event-based approaches demonstrated and took advantage of the strong non-linearity of sediment transport in high altitude catchment areas. This led to flood frequency and intensity reconstructions, highlighting the influence of climate change upon flood dynamics in the mountain.The combination of different record types, both in terms of location (high vs. low elevation), sedimentology (high vs. low terrigenous contribution) and significance (local vs. regional) is one of the main outputs of this paper. It allows the establishment of comprehensive histories of NW French Alps erosion, but also and consequently, soil dynamics and hydrological patterns throughout the Holocene. We also discuss the influence of glacier dynamics, one of the major agents of erosion in the Alps.A major feature is the growing human influence upon erosion at a local scale since at least the middle of the Bronze Age (3500 cal. BP). However and according to the regional record from Lake Bourget, only few periods of rising erosion at local scales generated a regional record that can be discriminated from wetter climatic periods. Among them, the period between 200 BCE and 400 AD appeared to be marked by a generalised rise in human-triggered erosion at local scales in the northern French Alps.This review highlights the importance of modern high-resolution and interdisciplinary studies of lake sediments, in order to better understand the complex relationships between humans, climate and the Earth system in general. We strongly argue that regional integration of data is now required to move a step further. Such an integration is easier with cost- and time-effective methods as well as after a better definition of approaches and their limits. This should lead to a stronger collaboration between paleo-data producers and modellers in the near future

Reconstructing geomorphic patterns and forcing factors from Alpine Lake Sediment

International audienceIn this paper we review the scientific efforts that were led over the last decades to reconstruct geomorphic patterns from continuous alpine lake sediment records. Whereas our results point a growing importance of humans as erosion forcing factors, we will focus here on climate-related processes. Our main dataset is made of a regional approach which was led without any a priori regarding erosion forcing factors. We hence integrated a set of sediment sequences from various environment along an altitudinal gradient from 200 up to 2400m asl in Northern French Alps. Altogether our data point climate change as one of the main factor of erosion variability. In particular, the last two cold spells that occurred during the early middle age (Dark Age) and between the 14th and the 20th century AD (Little Ice Age) appear to be outstanding compared to any other periods of enhanced erosion along the Holocene. The climatic forcing of those erosion phases is supported by an increase in the contribution of glacier-eroded material at a regional scale. At local scales, our data also point the growing importance, since at least the mid Bronze Age (ca. 3500 cal. BP) of human activities as a major erosion factor. This influence peaked during the late Iron Age and Antiquity periods (200 BC - 400 AD) when we record a regional generalised period of enhanced erosion in response to the development of pasturing activities. Thanks to provenance and weathering markers, we evidenced a strong relationship between the changes in ecosystems, soil development and erosion patterns. We hence showed the vegetal colonisation of bared soil led to a period of intense weathering while new soils were under formation between 11,000 and 8,000 cal. BP. Soils then knew an optimum until the onset of the Neoglacial at ca. 4,500 cal. BP prior to decline under both climate and human pressures. Altogether our data point the complexity of processes that affected the Earth critical zone along the Holocene. However, we highlight the interest of leading spatialized paleo-investigation in order to reconstruct those dynamics through and thus better understand the processes in play in critical zone dynamics over long time periods

Diffusion et dynamique de la culture du millet dans les Alpes ouest-européennes sur la base des concentrations en miliacine dans les sédiments lacustres

International audienceDomestication and diffusion of cereals lead to major transformation in ancient civilizations. For broomcorn millet (Panicum miliaceum), initiatives from several research groups aim at precising the timing and pathways of its diffusion from its Asian cradle during the 6th millennium BC to Western Europe during the Bronze Age, mostly from charred seeds recovered in archaeological contexts. An alternative approach consists of detecting miliacin, a molecular biomarkers that is specific to millet in lake sediments. The first occurrence of miliacin in sediments attests to the beginning of millet cultivation in the catchment and the evolution of miliacin concentration helps unraveling the dynamics of millet cultivation and consumption. Here we provide a first regional synthesis of miliacin sedimentary records from six lakes in the European Western Alps (Ledro and Iseo; Italy, Le Bourget, La Thuile, Paladru and Aiguebelette; France). This allows us (1) providing additional milestones to the journey of millet diffusion in Europe; (3) identifying potential local differences in the dynamics of millet cultivation.La domestication et la diffusion des céréales furent deux étapes clé dans le développement des sociétés. Jusqu'à aujourd'hui, la diffusion du millet commun (Panicum miliaceum) depuis son foyer de domestication en Asie au 6ème millénaire av J.C. jusqu'en Europe de l'Ouest à l'âge du Bronze a été principalement étudiée par l'analyse de graines en contexte archéologique. Une approche alternative et complémentaire consiste à tracer la présence de la miliacine, biomarqueur moléculaire du millet, dans les sédiments lacustres afin non seulement de déterminer les dates de premières cultures et consommation dans le bassin versant des lacs, mais aussi d'évaluer les phases d'emprise et de déprise au moyen des variations de concentrations de miliacine dans les sédiments. Ici, nous proposons une première synthèse régionale des dates d'apparition de la miliacine et de l'évolution de ses concentrations dans les sédiments de six lacs des Alpes italiennes et françaises (lac de Ledro et lac d'Iseo en Italie et Le Bourget, La Thuile, Paladru et Aiguebelette en France). Cette synthèse nous permet de discuter le calendrier de diffusion du millet dans les Alpes au regard des travaux en contexte archéologique, et de cerner de potentielles hétérogénéités spatiales dans la dynamique de culture de cette céréale

A large-scale erosion anomaly (2nd c. BC- 4th c. AD) in NW Alps: a locally-defined onset of the Anthropocene

International audienceThe research program Pygmalion consisted in a 4-yearslong unprecedented scientific effort to investigate complexhuman-climate-environment interactions in NorthernFrench Alps. Thanks to a wide geographic cover, it ledto evidence an erosion anomaly that began in 200 BC,at the time of the Allobroges Gallic tribe, just prior theirembedment into the Roman Empire and ended at the endof the Roman period (around 400 AD). Indeed during thewhole Holocene period, a strong link has been evidencedbetween climate and erosion fluxes at a regional scale.This link was obviously broken at the end of Iron Age.At that time, huge erosion fluxes were recorded fromsedimentary records taken in lakes with small catchmentareas, both in high and low elevation sites. Even regionaldetrital fluxes in Lake Bourget, representative of a 4000km2 catchment area, present an anomaly, whereas noglacier advance nor temperature drop were recorded inthe area. Moreover paleovegetation and fire regime datapoint major changes in vegetation cover that pinpointsa drastic change in land-use practices at regional scalesuggesting a reinforcement of pasturing activities. In LakeAnterne high-altitude (2060 m asl) catchment area, thisis confirmed by DNA barcoding data acquired on fromlake sediment evidencing the unprecedented intensivepresence of both sheeps and cows as well as by thediscovery of a ruined shepherd caban, the first occupationof which being dated 2nd c. BC. Finally, based on themeasurement of molecular biomarker, we evidenced thisperiod as peak in broomcorn millet cultivation aroundLake Bourget and Lake Paladru.Based on above-mentioned field evidences we argue thatchanges in land-use practices between 200 BC and 400 ADhad such an important impact that it significantly affectedthe erosion budget at a regional scale. From our datasetcovering the whole Holocene, this was the first time, in theconsidered area, that human activities became intensiveenough to significantly alter an important geodynamicprocess such as erosion. Following various authors wehence wonder if this could not define a local onset of theAnthropocene period characterised by the emergence ofhumans as a major geologic agent