Dynafor au congrès international de la SFE² 2024 à Lyon

Dynafor a participé à la conférence SFE² GFO Joint meeting, International Conference on Ecological Sciences - Sciencesconf.org qui s'est tenue du 21 au 25 octobre 2024 à Lyon. Il y a eu 4 communications orales faites par des dynaforien.nes dans plusieurs sessions de ce colloque et un poster exposé. Voici les résumés de ces présentations.

1°) Using a stochastic movement simulator to estimate wild bee's pollination contribution in heterogeneous agricultural landscapes

Anouk Glad , Annie Ouin , Sylvain Moulherat, David Sheeren , Emilie Andrieu (communication orale)

Abstract : Insect pollinators are responsible for at least a part of the pollination of more than 90 % of wild flowering plants and 75% of food crops worldwide (IPBES, 2016). Among those, wild bees are known to participate in the pollination of a wide variety of flowering plants and are declining at alarming rates (Cameron et al., 2011; Potts et al., 2010). To predict the pollination potential in a landscape, a comprehensive knowledge of their foraging movement behavior is essential. Thus, in the majority of the models aiming to estimate pollination at a landscape scale, the probability of discovering a resource mainly depends on the distance to the nest without considering landscape heterogeneity.

Animal movement has been modeled by a large variety of algorithms. Among them, the stochastic movement simulator (SMS) presents better performances in estimating relative connectivity (Palmer et al., 2011). This method is based on a series of sequential movement decisions incorporating path memory, a directional parameter, a perceptual range and the movement cost, allowing to take into account the spatial arrangement of the landscape.

This study aims to evaluate the contribution of landscape heterogeneity (composition and configuration) on wild bee's pollination services estimates using a “central place forager” (CPF) model and SMS. First, the role of the landscape heterogeneity on the pollination estimates was investigated by performing simulations on a set of virtual landscapes to cover a gradient of fragmentation, patch isolation, and composition. The results obtained by the CPF-SMS model were compared to those obtained by a distance-weighted kernel model (InVEST Lonsdorf et al., 2009). In the second part, the model sensitivity to path memory, directional and perceptual range parameters was explored using a real agricultural landscape located in the long-term Socio-Ecological Research site PYGAR (Occitanie, France) and two species differing by their size and movement ability (Lasioglossum marginatum and Andrena flavipes). The preliminary results show large differences in pollination estimates for intermediate fragmented landscapes. CPF-SMS model is sensitive to the memory path by increasing the total number of passage whereas the perceptual parameter augmentation slightly decreases the number of passage. Finally, the model's estimates where compared to an abundance dataset containing wild bee's captured from three trapping sessions in April 2016 (30 traps), 2017 (10 traps) and 2019 (16 traps) in order to select the best parameters values for each model species. The results showed that a different set of parameters gives the best capture rates estimates for each study species.

2°) Detecting species neutral modules in co-occurrence data : principles and application to plant communities

Fabien Laroche (communication orale)

Abstract : Neutral theory of community ecology aims at providing a mechanistic null hypothesis to study biodiversity patterns. However, it has been little developped for the analysis of co-occurrence data, where it remained mostly focused on community-wide statistics about covariance among species occurrences, which proved little efficient at detecting deviation from neutrality. It has been repeatedly suggested that stronger neutrality tests may be obtained by moving towards a more analytical approach of species composition in communities. In particular, searching for groups of species that behave non-neutrally one with another - a structure reminiscent of the concept of 'guild' in community ecology - has proven successful in the analysis of spatio-temporal patterns of relative abundances, and may also generate new insights on co-occurrence patterns. However, an important obstacle is the lack of a tractable neutral sampling theory of species presence-absence to develop new tests with sound mathematical background and well undertood instrumental hypotheses.

Here, I propose a first step towards developping such a sampling theory. I show that a simple and general form of co-occurrence sampling formula can be derived from neutral theory first principles with limited instrumental assumption. This leads to the prediction that two species should show a constant ordination of their presence probability among sites, which opens the way to tests of the 'rank consistency' of species pairs. A systematic pairwise application of this test yields a species rank consistency network, the modules of which may reveal species groups where rank consistency holds within groups but ranks are unconsistent among groups. Such 'neutral modules' of species can be biologically interpreted by relating their composition to species traits and relating their spatial distribution to local environmental conditions. We validated our framework on virtual data generated from a metacommunity model with environmental filtering. We then used it to revisit two published examples of plant communities : (i) compositional changes in tropical tree communities along a rainfall gradient in Western Ghats, India; (ii) Thymus vulgaris effect on mediterranean herbaceous communities in Saint-Martin-de-Londres basin, France. In both cases, we retrieved important results from previous studies while using only presence-absence of plant species, hence illustrating the relevance of our approach.

3°) Forest soil microhabitats characterisation and relationships with ground-dwelling predatory arthropod communities (carabid beetles and spiders)

Amandine Acloque, Elsa Massé , Frédéric Revers (communication orale)

Abstract: In forest, the complexity and spatio-temporal heterogeneity of stands provide habitats for many arthropods, including soil arthropods known to play a key role in numerous ecosystem processes. The heterogeneity of forest habitats provides different ecological niches, and, consequently, a heterogeneous distribution of species. Arthropod abundance, for example, has been found to be higher in deciduous stands than in coniferous ones, and the current insect decline is more pronounced in production forest stands, and for insects of the upper stages of the food chain, i.e., predators such as carabid beetles and spiders. Carabid beetles and spiders are often used as bioindicators of habitat quality, since their distribution on a small scale is determined by strict ecological requirements and habitat and microhabitat properties. Numerous studies have highlighted the role of various habitat characteristics and microhabitats on invertebrate communities, but none of them has proposed a synthesis incorporating all the targeted characteristics that could lead to a standardised protocol.

In this study carried out in southwest France along the Ciron river, we aimed to characterise soil microhabitats associated to ground-dwelling arthropods in different forest types and explore their relationships with associated biodiversity, by monitoring carabid beetles and spiders. We studied gradients of forests, from deciduous riparian forest to monospecific plantation forest, with intermediate area with mix forests or coniferous ones. Soil invertebrates were sampled using pitfall traps from March to September in 2021 and 2022. Microhabitats were characterised on the basis of 1m²-quadrats around the pitfall traps in spring, summer and autumn. We characterised soil cover (leaf litter, needle litter, grass, bare ground) and micro-structure elements (e.g., vegetation height, litter thickness, deadwood debris). We also measured distances to different local structuring elements (e.g., living tree, dead tree, tree stump), estimated canopy openness using hemispherical pictures and realised vegetation surveys.

Preliminary results first reveal different structuration and composition of invertebrate communities in the different forest stands of the study area. Moreover, they show a significant effect of soil cover (litter type), micro-structure metrics and canopy openness on small-scale community structuring for both carabid beetle and spider communities. Finally, our preliminary results also support the importance of riparian forests and the habitats they provide, since they contribute to regional biodiversity by sheltering pools of species that are different from neighbouring environments.

4°) Landscape heterogeneity and pesticide reduction favor predation but also grape infestation by Lobesia botrana

Axelle Tortosa, Aude Vialatte, Fabien Laroche, Adrien Rusch, Martin Entling, Brice Giffard (communication orale)

Abstract : To date, there is a consensus that biological control, benefits from landscape heterogeneity but is context-dependent. While previous studies have highlighted the potential complementarity among natural enemy guilds for biological control, none has investigated such complementarity based on the life stage of predation. Hence, we aim to investigate if predation across multiple developmental stages of Lobesia botrana could exhibit complementarity over time, enhancing the effectiveness of biological control.

We investigated how landscape variables but also the intensity of farming practices affected the predation of Lobesia botrana at different stages and associated crop damage in French vineyards. We hypothesized that both top-down and bottom-up processes are at play suggesting that landscape heterogeneity through higher amount of semi-natural habitats or with smaller vineyards favor higher levels of predation, lower pest densities and higher complementarity across time resulting in reduced pest damage. We also expected consistent effects of biodiversity-friendly practices.

Our study involved 38 vineyards-landscapes, where semi-experimental sentinel approaches were used to quantify predation rates on pupae-, egg- and caterpillar-stages. Damage caused by the larvae of first and second generations were observed.

Results showed that landscapes with average smaller vineyards promoted egg and pupae predations, while the quantity of semi-natural habitats around the vineyards favored caterpillar predation. However, no complementary effects between predation rates across pest life stages on pest abundance were found. Only high pupae predation significantly reduced spring infestation despite pesticide use intensity. Our study highlights the substantial influence of farming practices on pest infestation levels. We showed that some local practices contribute to limit pest abundance, such as higher grassy area cover that limits grape perforations whereas pesticide use intensity hampered biological control by affecting negatively predation rates at several stages but also decreased directly grape damage. Our work reveals that landscape effects have potential to improve predation at multiple stages of development, whereas farming intensity tends to limit them. It also underlines the importance of understanding the specific stages of pest development targeted by natural enemies for effective biological control. This highlights the importance of adopting integrated pest management strategies that account for both landscape-scale factors and local farming practices. Therefore, efforts should be increased to replace chemical pest control with other measures to mitigate reliance on chemical pesticides.

5°) Restoring grasslands for pollinators in agricultural landscapes in southwestern France

Amandine Acloque, Annie Ouin et Emilie Andrieu (poster)

Abstract: Pollinators play a key role in terrestrial ecosystem functioning, being primarily essential to the reproduction of many wild plants and around 75% of the world’s food crops. The current pollinator decline is therefore at the root of an agricultural vulnerability that could severely impacts food security. Restoring pollinators and their habitats is thus a major issue for biodiversity conservation, agriculture sustainability and human health.

In agricultural landscapes, semi-natural habitats like permanent grasslands with extensive management harbour high biodiversity, support communities of pollinators and crop auxiliaries, and significantly contribute to ecological continuity at local and landscape scales. Nevertheless, 49% of the world’s grasslands area have been degraded, the greater part of European semi-natural grasslands has been lost since the 1940s, and their area continues to decrease. Restoring pollinator habitats such as grasslands seems to be a nature-based solution to deal with the increasing demand in pollination and an alternative to pesticide for pest regulation.

Based on recently restored grasslands (~ 2 years), we aim to study the effect of grassland restoration on pollinator communities at local and landscape scales. Grassland restoration involved implanting local seeds (or green hay), harvested from diversified grasslands (donor grasslands), on former crops or degraded plots. During 4 sessions in a year, we sampled three groups of pollinating insects (abundance and behaviour): wild bees, butterflies and hoverflies, with insect nets along 150m-long transects in restored grasslands, associated controls (previous crop) and donor grasslands. The cover of flowering plants was also recorded in each transect and for each session. Additionally, a full botanical survey was carried out for each transect.

Preliminary results from 2024 sampling campaign are expected to (i) reveal an increasing gradient of diversity in pollinator communities from control parcels, restored grasslands to donor grasslands but also (ii) show different pollinator behaviours between the different parcel types, with more nesting and flower visiting individuals in restored and donor grasslands than in controls. In the longer term, after several sampling campaigns (at least two years), restored grasslands are expected to increase pollinator communities not only on a local scale, but also on a landscape scale.