Biology subjects

Gaba, S.

Publications and source records attributed to Gaba, S..

7 recordsLinked to original sources

bioRxiv2025

Off target: herbicides applied in cereal fields exclude non-competitive species, while replacing them by competitive weeds.

Weed diversity plays an important role in maintaining resilient agroecosystems, yet agricultural practices, such as pesticide applications, significantly shape weed communities. Previous studies have primarily focused on comparing organic and conventional farming, with a particular emphasis on land-use intensification, with less attention on the impact of pesticides. Our study examined the impact of herbicide, fungicide, and insecticide use - both in terms of Treatment Frequency Index (TFI), i.e. intensity of application, and quantity - on weed communities in 96 non-organic cereal fields over 4 years. Interestingly, our results indicate that fungicide application intensity decreased weed abundance by 11.6% and species richness by 14.6% for each one-standard-deviation (1-SD) increase in TFI, whereas the total quantity applied (QA) did not. In contrast, for herbicides, QA had a stronger negative impact on weed communities than TFI, with a 14.3% decrease in weed abundance and a 12.4% decrease in species richness for each 1-SD increase in QA. This suggests that TFI of fungicide, which may reflect low-dose but frequent applications, could exert indirect and long-term effects on weed suppression, potentially by altering symbiotic arbuscular mycorrhizal fungi in the soil. In comparison, QA of herbicide more directly reflects the toxic load delivered to weeds and is therefore a better predictor of their suppression. Based on a combination of multivariate and univariate analyses and the study of underlying mechanisms in community changes, our results reveal that herbicides are the main factor shaping weed communities by decreasing the abundance of non-target/non-competitive species while replacing them by problematic, competitive to crops, weed species. These findings point out the potential ineffectiveness of herbicides application on problematic weeds and emphasize the need to reconsider the use of herbicides to maintain weed diversity in agricultural landscapes.

ecology↗

bioRxiv2023

Environmental variables and species traits as drivers of wild bee pollination in intensive agroecosystems -a metabarcoding approach

Wild bees are known to be efficient pollinators of wild plants and cultivated crops and they are essential ecosystem service providers. However, wild bee populations have been suffering from significant declines in the last decades mainly due to the use of agrochemicals. Within this framework, we aimed to characterize wild bees pollination spectrum (i.e. the community of pollinated flowering plants) in intensive agroecosystems, and describe the environmental variables and wild bee species traits influencing the pollination. To do this, we conducted metabarcoding analyses of pollen loads from wild bees collected in sunflower crops in the French region of Nouvelle-Aquitaine. Our study revealed that wild bees visited flowering plants corresponding to 231 different Operational Taxonomic Units, classified in 38 families of which Asteraceae, Brassicaceae and Apiaceae were the most visited and more than 90% of the visited taxa turned out to be wild flowers. We also analysed the potential effect of environmental variables and wild bee species traits in governing their choice of pollinated plants. The community composition of pollinated plants varied depending on the flowering stages of the sunflower and the farming system. Our results also show that pollination niche breadth (alpha diversity) varied depending on the flowering stages of the sunflower but was not different between organic and conventional farming systems. Regarding wild bee species traits, the community composition of pollinated plants varied in relation to wild bees body sizes and, sociality levels. Our results are consistent with previous studies, suggesting that solitary bees are more specialists when it comes to flower selection than social bees, which are more generalist. The metabarcoding of pollen loads enabled us to draw a global picture of plant-wild bee interactions in an intensive agroecosystem. Our findings support the hypothesis that a higher diversity of weeds may increase wild bee diversity in intensive agroecosystems.

ecology↗

bioRxiv2023

A comparison of live versus kill pitfall traps to assess the diet of carabids through a metabarcoding approach

Metabarcoding approaches are powerful tools to unravel trophic relationships between predators and prey. To apply metabarcoding analyses on invertebrate gut contents, specimens must be well preserved from DNA degradation, thus the trapping method should be selected accordingly. Dry pitfall traps are commonly assumed to provide a better DNA preservation than traps that use a killing agent. However, this assumption has never been specifically tested for gut content analyses. In our study, we compared how two types of pitfall trapping, dry vs. with brine, affect the conservation of prey DNA contained in the digestive tract of predators and subsequent metabarcoding analyses. We placed dry and "classic" pitfall traps in oilseed rape fields within an intensive agricultural area in the French Nouvelle-Aquitaine region. Traps were set up in autumn and compared for carabid trapping efficiency as well as our capacity to retrieve dietary information from the digestive tract of the main carabid species, Nebria salina and Calathus fuscipes. PCR success rate was higher in dry pitfall traps compared to classic ones for N. salina. We hypothesise that this was due to the presence of PCR inhibitors in the gut of this species. The ability to sequence prey DNA did not differ between specimens caught in both trap types. The list of predated species was similar between both trap types. However, sequencing yielded more prey OTUs from specimens caught in dry pitfall traps, leading to difference in prey community composition and a greater ability to reconstruct prey community Our analyses also shed light on the prey spectrum of Calathus fuscipes and Nebria salina in oilseed rape in autumn.

ecology↗

bioRxiv2020

Habitat fragmentation and food security in crop pollination systems

Ensuring stable food supplies is recognized as a major challenge for the 21st century, and one of the UN Sustainable Development Goals. Biodiversity-based approaches to food security are increasingly being supported based on the fact that biodiversity can increase and stabilize crop yields. But agricultural systems are often highly fragmented and it is unclear how such fragmentation affects biodiversity and food production, limiting our capacity to manage agricultural landscapes for food security. Here, we develop a model of crop yield dynamics to investigate how fragmentation of natural habitats for agricultural conversion impacts food production, with a focus on crop pollination. Our results show that fragmentation produces spatial and biodiversity-mediated effects that affect the mean and stability of pollination-dependent crops, with strong consequences for food security. The net effects of fragmentation depend on the strength of the spillover of pollinators to crop land and the degree to which crops depend on animal pollination. Our study sheds new light in the food security debate by showing that high and stable yields depend on biodiversity and the spatial structure of agricultural landscapes, and by revealing the ecological mechanisms of food security in crop pollination systems.

ecology↗

bioRxiv2019

A Nature-based solution in practice: ecological and economic modelling shows pollinators outperform agrochemicals in oilseed crop production

AO_SCPLOWBSTRATC_SCPLOWNature-based agriculture, reducing dependency on chemical inputs, requires using ecological principles for sustainable agro-ecosystems, balancing ecology, economics and social justice. There is growing evidence that pollinator-dependent crops with high insect pollination service can give higher yields. However, the interacting effects between insect pollination and agricultural inputs on crop yields and farm economics remain to be established to reconcile food production with biodiversity conservation. We investigated the effects of insect pollination and agricultural inputs on oilseed rape (Brassica napus L.). We show that not only yield but also gross margins are 16-40% higher in fields with higher pollinator abundance than in fields with reduced pollinator abundance. This effect is however strongly reduced by pesticides use. Higher yields may be achieved by either increasing agrochemicals (reducing pests) or increasing bee abundance, but crop economic returns was only increased by the latter, because pesticides did not increase yields while their costs reduced gross margins.

ecology↗

bioRxiv2018

Reconciling biodiversity conservation, food production and farmers’ demand

Agricultural management should consider multiple services and stakeholders. Yet, it remains unclear how to guarantee the provision of ecosystem services that reaches stakeholders demands, especially considering the observed biodiversity decline and the current global change predictions that may affect food security. Here, we use a model to examine how landscape composition - fraction of semi-natural habitat (SNH) - affects biodiversity and crop production services in intensively-managed agricultural systems. We analyse three groups of stakeholders assumed to value different ecosystem services most - individual farmers (crop yield per area), agricultural unions (landscape production) and conservationists (biodiversity). We find that trade-offs among stakeholders demands strongly depend on the degree of pollination dependence of crops, the strength of environmental and demographic stochasticity, and the relative amount of an ecosystem service demanded by each stakeholder, i.e. function thresholds. Intermediate amounts of SNH can allow for the delivery of relatively high levels of the three ecosystem services. Our analysis further suggests that the current levels of SNH protection lie below these intermediate amounts of SNH in intensively-managed agricultural landscapes. Given the worldwide trends in agriculture and global change, these results suggest ways of managing landscapes to reconcile the demands of several actors and ensure for biodiversity conservation and food production.

ecology↗

bioRxiv2018

Trade-offs in provisioning and stability of multiple ecosystem services in agroecosystems

Changes in land use generate trade-offs in the delivery of ecosystem services in agricultural landscapes. However, we know little about how the stability of ecosystem services responds to landscape composition, and what ecological mechanisms underlie these trade-offs. Here, we develop a model to investigate the dynamics of three ecosystem services in intensively-managed agroecosystems, i.e. pollination-independent crop yield, crop pollination, and biodiversity. Our model reveals trade-offs and synergies imposed by landscape composition that affect not only the magnitude but also the stability of ecosystem service delivery. Trade-offs involving crop pollination are strongly affected by the degree to which crops depend on pollination and by their relative requirement for pollinator densities. We show conditions for crop production to increase with biodiversity and decreasing crop area, reconciling farmers profitability and biodiversity conservation. Our results further suggest that, for pollination-dependent crops, management strategies that focus on maximising yield will often overlook its stability. Given that agriculture has become more pollination-dependent over time, it is essential to understand the mechanisms driving these trade-offs to ensure food security.

ecology↗