The service of regulation by predation

Project title and acronym: Study of potential crop pests in peri-urban agricultural context -Pests
Project leader: Elsa Bonnaud (ESE laboratory)      Type and date of project: innovation (2017-2019)
Non-academic partners: Hauts de Seine departmental council and the association Terre et Cité, as part of the LEADER program

The Saclay plateau is currently undergoing a strong ecological transition, with current and future developments having a lasting influence on human activities, biotic interactions in this ecosystem, and also having an influence on existing farms. At present, the Saclay plateau is a typical example of an agro-ecosystem adjacent to moderate to dense peri-urban residential areas. Trophic interactions are strongly structuring ecosystems and the Saclay Plateau is no exception with the presence of top predators, prey species including crop consumers, and abundant anthropogenic resources represented here by cultivated fields (Figure 1).

Figure 1: General diagram of trophic links between different animal organisms in relation to agricultural practices and possible changes in land use.

The issues at stake in this project were mainly focused on maintaining or even improving the functioning of ecosystems in transition following the present and future development of the Saclay plateau. The main objective of this project was to study the animal organisms that are potential or proven consumers of crops currently present on the Saclay plateau. We focused on small mammals, lagomorphs and birds (corvids, pigeons) by studying their presence, their distribution within the ecosystems and their relationship with other components of the ecosystem such as (i) predators, potential regulators of these pests, and (ii) agricultural crops constituting abundant and easily accessible resources leading to an important influx of these pests.

The main beneficiaries of the project were the farmers with the consideration of their problems directly related to their agricultural productions (monitoring of potential or proven animals consuming the crops), and the EPAPS by the integration in the development plans of the preservation of biodiversity and ecosystem services rendered for a better management of the "natural" spaces within the territory.

The results and spin-offs of this project have also affected all the users of the plateau (inhabitants, scientists, employers/employees, vacationers) due to the sustainability of agricultural crops, associated practices, the improvement of the landscape structure, studies related to the perception of biodiversity and the consideration of the role of top predators in the potential regulation of crop consumers.

Due to current developments on the Saclay plateau (increased artificialization, growing urbanization, habitat fragmentation and increased human frequentation), certain biotic interactions will be further modified, in particular a possibly higher mortality for top predators, which may further accentuate this phenomenon of predation release on crop-consuming species. It is thus essential to be able to quantify and better understand these biotic interactions that directly or indirectly impact the functioning of these peri-urban agricultural environments in order to be able to reconcile sustainable agriculture, the promotion of biodiversity, the maintenance of ecosystem services and the reconnection of users of the Saclay plateau with "nature" and its associated benefits.

Results

The monitoring of predator and prey populations on the plateau allowed us to deduce that the low number of predators results in a predation pressure that is too low to be able to regulate prey densities. The analyses also show that birds and small mammals are more frequently found in "non-crop" environments, reflecting the need to conserve or create natural habitats in order to promote biodiversity on the plateau and increase predator diversification. Finally, the return of certain raptor species (e.g. Falcons sp., Owls sp.) through actions facilitating their arrival and establishment (e.g. nest boxes and perches), would enhance the biodiversity of predators and reinforce the regulation of crop-eating species.

==> The project leader explains the project and its RESULTS in VIDEO (LabEx scientific days, Dec. 2020)

Leverage effects

This study emphasizes the need for further studies on the functioning of prey-predator relationships within agrosystems, further discussions with farmers and local stakeholders to discuss and inform about the role of natural predation, and also on the possibility of diversifying predators and habitats to enhance natural predation.
Thanks to the results of this study, an ANR JCJC project has been submitted and accepted (project start 04/2021).

Perspectives

To quantify the main trophic links and the predation regulation service, the consequences of the perception and actions of the stakeholders on the predator dynamics, and the possible cascade effects, we will work on three axes. The first is aimed at determining diet, habitat use by predators and prey densities. In the second axis, we will build predictive mathematical models of these food webs and test population trajectories as a function of environmental constraints and stakeholders actions. The third axis will study the perceptions and actions of stakeholders influencing the dynamics of predators. This project will simultaneously study different scales of study (individual, population, species and community), and will combine basic ecology, applied ecology, and social sciences in a multidisciplinary approach (biology, mathematics and social sciences) in order to provide new knowledge, predictive models and collaborative guidelines to improve biodiversity, agroecosystem functioning and their services.

Publications

> Castañeda I., Zarzoso-Lacoste D., Bonnaud E.. Feeding behaviour of red fox and domestic cat populations in suburban areas in 1 the south of Paris 2. Urban Ecosystems, Springer Verlag, 2020, 23 (4), pp.731-743. doi 10.1007/s11252-020-00948-w. ⟨hal-02985985