Léo Ledru

38530, Pontcharra, France ledru.leo@hotmail.fr

I hold a Ph.D. in Biodiversity, Ecology, and the Environment from the Alpine Ecology Laboratory (LECA). My research covers a wide range of topics, from studying the spatial dynamics of ecological models to analyzing food webs and exploring eco-evolutionary models. However, all these areas share a common feature: they fall within the realm of theoretical ecology, whether from the perspective of numerical modeling or contemplation of conceptual questions.
For instance, the framework of my thesis "Modelling part-whole interactions in ecology and evolution, spatial structure and multilevel selection" lies in materialist dialectics, a subject specific to conceptual thinking but also guiding the formalization of models in ecology, evolution and biology (and others !). Thus, I can assert that I am interested in both conceptual issues and the technical challenges associated with modeling.
I'm now interested in a job as a modeling/data engineer. This reflects my preference for discovering new themes rather than specializing in a particular field.

Professionally, I've also decided to develop a science popularisation activity through videos (youtube channel) based on modelling to explain what theoretical ecology is. This allows me to combine my taste for exploring new subjects with the technical challenges of modelling.

Download my CV

Skills

Programming Languages & Tools
  • Matlab
  • Python
  • R
  • LaTeX
  • Blender
  • Git / Github
Mathematical modelling
  • Dynamical Systems Analysis (ODE, PDE)
  • Spatialy Explicit Individual Based Models
Data science
  • Descriptive statistics
  • Multivariate analysis
Communication
  • Writing of scientific articles / Scientific and technical toolbox
  • Scientific conference

Publications

Trophic Cascade Paradigm’s Complex Reality: The Role of Large-Order Indirect Interactions (In Prep.)

Léo Ledru , Jean-François Arnoldi, Arnaud Sentis, Victor Frossard
The trophic cascade, a fundamental ecological concept, posits that a predator exerts a positive indirect effect on a resource via its negative impact on a consumer. This concept has received empirical recognition, with observations frequently aligning with its predictions. However, there exist numerous instances where biological systems deviate from the expected trophic cascade dynamics. Explanations for these deviations are often attributed to idiosyncratic factors, such as complex trait-based interactions. From the analysis of food webs either generated by niche models or empirical, we strive to provide a more comprehensive explanation for trophic cascade failures by investigating large-order indirect effects. We present evidence that in systems where these indirect effects are non-negligible, they can disrupt the trophic cascade, leading to its failure. This disruption may result in the attenuation of the cascade within isolated trophic chains or even its inversion when considering broader trophic food webs. We show that the trophic cascade concept is more robust in its community-cascade form than in its species-cascade form. Yet, it becomes intricate to view food webs solely as linear trophic chains, as this oversimplification obscures potential deviations from the cascade concept at the species level. Furthermore, our study challenges the conventional definition of a trophic cascade by demonstrating that its failure can stem from interference with indirect effects originating from the cascade itself. This research not only enhances our understanding of trophic cascades but also underscores the importance of considering large-order interactions in ecological studies.
Ongoing

Comparative metabolomics reveals how the severity of predation by the invasive insect Cydalima perspectalis modulates the metabolism re-orchestration of native Buxus sempervirens Plant Biology

A. E. Hay, C. Deborde, T. Dussarrat, A. Moing, A. Millery, T. P. T. Hoang, D. Touboul, M. Rey, L. Ledru, S. Ibanez, P. Pétriacq, C. Vanhaverbeke, C. Gallet
The recent biological invasion of box tree moth Cydalima perspectalis on Buxus trees has a major impact on European boxwood stands through severe defoliation. This can hinder further regrowth and threaten survival of populations. In a mesocosm approach and controlled larval density over a 2-month period, responses of B. sempervirens essential and specialized metabolites were characterized using metabolomics, combining 1H–NMR and LC–MS/MS approaches. This is the first metabolome depiction of major Buxus responses to boxwood moth invasion. Under severe predation, remaining green leaves accumulate free amino acids (with the noticeable exception of proline). The leaf trans-4-hydroxystachydrine and stachydrine reached 10–13% and 2–3% (DW), while root content was lower but also modulated by predation level. Larval predation promoted triterpenoid and (steroidal) alkaloid synthesis and diversification, while flavonoids did not seem to have a relevant role in Buxus resistance. Our results reveal the concomitant responses of central and specialized metabolism, in relation to severity of predation. They also confirm the potential of metabolic profiling using 1H–NMR and LC–MS to detect re-orchestration of metabolism of native boxwood after severe herbivorous predation by the invasive box-tree moth, and thus their relevance for plant–insect relationships and ecometabolomics.
July 2024

The evolutionary dynamics of plastic foraging and its ecological consequences: a resource-consumer model Peer Community Journal

Léo Ledru , Jimmy Garnier, Océane Guillot, Erwan Faou, Camille Noûs, Sébastien Ibanez
Phenotypic plasticity has important ecological and evolutionary consequences. In particular, behavioural phenotypic plasticity such as plastic foraging (PF) by consumers, may enhance community stability. Yet little is known about the ecological conditions that favor the evolution of PF, and how the evolutionary dynamics of PF may modulate its effects on community stability. In order to address these questions, we constructed an eco-evolutionary model in which resource and consumer niche traits underwent evolutionary diversification. Consumers could either forage randomly, only as a function of resources abundance, or plastically, as a function of resource abundance, suitability and consumption by competitors. PF evolved when the niche breadth of consumers with respect to resource use was large enough and when the ecological conditions allowed substantial functional diversification. In turn, PF promoted further diversification of the niche traits in both guilds. This suggests that phenotypic plasticity can influence the evolutionary dynamics at the community-level. Faced with a sudden environmental change, PF promoted community stability directly and also indirectly through its effects on functional diversity. However, other disturbances such as persistent environmental change and increases in mortality, caused the evolutionary regression of the PF behaviour, due to its costs. The causal relationships between PF, community stability and diversity are therefore intricate, and their outcome depends on the nature of the environmental disturbance, in contrast to simpler models claiming a direct positive relationship between PF and stability.
October 2023

Mutualists construct the ecological conditions that trigger the transition from parasitism Peer Community Journal

Léo Ledru , Jimmy Garnier, Matthias Rohr, Camille Noûs, Sébastien Ibanez
The evolution of mutualism between hosts and initially parasitic symbionts represents a major transition in evolution. Although vertical transmission of symbionts during host reproduction and partner control both favour the stability of mutualism, these mechanisms require specifically evolved features that may be absent in the first place. Therefore, the first steps of the transition from parasitism to mutualism may suffer from the cost of mutualism at the organismic level. We hypothesize that spatial structure can lead to the formation of higher selection levels favouring mutualism. This resembles the evolution of altruism, with the additional requirement that the offspring of mutualistic hosts and symbionts must co-occur often enough. Using a spatially explicit agent-based model we demonstrate that, starting from a parasitic system with global dispersal, the joint evolution of mutualistic effort and local dispersal of hosts and symbionts leads to a stable coexistence between parasites and mutualists. The evolution of local dispersal mimics vertical transmission and triggers the formation of mutualistic clusters, counteracting the organismic selection level of parasites that maintain global dispersal. The transition occurs when mutualistic symbionts increase the density of hosts, which strengthens competition between hosts and disfavours hosts inhabiting areas dominated by parasitic symbionts: mutualists construct the ecological conditions that allow their own spread. Therefore, the transition to mutualism may come from an eco-evolutionary feedback loop involving spatially structured population dynamics.
July 2022

Spatial structure of natural boxwood and the invasive box tree moth can promote coexistence Ecological Modelling

Léo Ledru , Jimmy Garnier, Christiane Gallet, Camille Noûs, Sébastien Ibanez
In the absence of top-down and bottom-up controls, herbivores eventually drive themselves to extinction by exhausting their host plants. Poorly mobile herbivores may experiment only local disappearance, because they can recolonize intact plant patches elsewhere, leaving time to previously over-exploited patches to regrow. However most herbivores such as winged insects are highly mobile, which may prevent the formation of spatial heterogeneity. We test if long-distance dispersal can preclude coexistence using the invasion of box tree moth (Cydalima perspectalis) in Europe as a model system. We build a lattice model and estimate the parameters with a combination of field measurements, experimental data and literature sources. Space corresponds either to a realistic boxwood landscape in the Alps, or to theoretical landscapes of various sizes. We find that both species persist under a large range of realistic parameter values, despite a severe reduction in boxwood biomass, with an alternation of outbreaks and near-to-extinction moth densities. Large landscapes are necessary for coexistence, allowing the formation of spatial structure. Slow plant regrowth combined with long-distance dispersal could drive moths to extinction, because of resources depletion at the global scale even without a complete synchronization of the local dynamics. The spatial dynamics leads to formation of small plant patches evenly distributed in the landscape, because of a combination of local plant dispersal and global indirect competition between plants through their positive effect on moth population size. Coexistence is favoured by such heterogeneous landscapes, because empty patches increase moth mortality during dispersal: the system thus creates its own stability conditions.
March 2022

Talks

Talk at the Pole-ECLA seminar "Trophic cascades in complex ecological networks."

University Savoie Mont Blanc, Le Bourget-du-Lac, France

A 45-minutes presentation in which I discuss our findings on food webs analysis. I redefine the trophic cascade concept and demonstrate that for food webs with sufficient community structure, it is arbitrary not to consider indirect effects that extend beyond those specific to the trophic cascade. Furthermore, I show that taking into account these larger-order indirect effects can lead to interferences with the trophic cascade. Thus, we suggest that significant larger-order indirect effects may be a general cause for cases where the trophic cascade does not manifest as expected in food webs.

October 2023

Talk at the LECA-CARRTEL inter-laboratory seminar "Re-exploration of the trophic cascade concept: collectivity & indirect interactions."

University Savoie Mont Blanc, Le Bourget-du-Lac, France

A 45-minutes presentation in which I discuss our preliminary findings on food webs analysis. I redefine the trophic cascade concept and demonstrate that for food webs with sufficient community structure, it is arbitrary not to consider indirect effects that extend beyond those specific to the trophic cascade. Furthermore, I show that taking into account these larger-order indirect effects can lead to interferences with the trophic cascade. Thus, we suggest that significant larger-order indirect effects may be a general cause for cases where the trophic cascade does not manifest as expected in food webs.

June 2024

Talk at the LECA-CARRTEL inter-laboratory seminar "The evolution of cooperation in an ecological context: an agent-based model"

University Savoie Mont Blanc, Le Bourget-du-Lac, France

A 45-minutes talk in which I replicate the findings of Pepper & Smuts (2000) using a didactic approach supported by engaging visuals (3D animations using Blender and Manim). I also extend the results by incorporating a genuine evolutionary process into the initial model, along with an emerging spatial dynamic rather than one fixed by the experimenter.

October 2020

Talk at the Gdr TheoMoDive Annual Meeting: "How adaptive is adaptive foraging"

SETE Cnrs, Moulis, France

A 20-minutes talk about the evolutionary consequences of plastic foraging.

October 2019

Poster session at the GfÖ Annual Meeting: "Spatial structure of natural boxwood and box tree moth in Europe can promote long-term coexistence"

University of Münster, Germany
9-13 September 2019

Talk at the GfÖ Annual Meeting: "How adaptive is adaptive foraging"

University of Münster, Germany

A 20-minutes talk about the evolutionary consequences of plastic foraging in the session "Traits, networks, and ecosystem functioning". I explained how my model shows that the foraging behavior is not always adaptive in the sense of favoured by natural selection. I also showed that the evolution of foraging behavior can have consequence at the community scale, especially on diversification and stability.

9-13 September 2019

Talk at the National Symposium "Boxwood, issues, garden renewal and rebirth"

Orléans, France

A 20-minutes talk about my work on the box tree moth invasion. . The symposium is about ecology of conservation so I presented the results about the persistence of the box tree moth and the impact on the natural boxwoods.

14 March 2019

Education

University Savoie Mont Blanc

Phd's degree in Biodiversity, Ecology, Environment: Modelling part-whole interactions in ecology and evolution, spatial structure and multilevel selection
Section population biology and ecology
2018

University Aix-Marseille

Master's degree in Oceanography
Specialising in Marine Biology and Ecology
2018

University Savoie Mont Blanc

Bachelor's degree in Life Science
Specialising in Population Biology Ecology
2016

High school Ambroise Croizat Moûtiers

National Certificate of Search and Rescue Ski Patroller, Alpine Skiing Option, 1st Degree National PSE2 Certificate of competence as a first-aid crew member level 2
2013

High school Ambroise Croizat Moûtiers

High school diploma in scientific series
Specialising in mathematics
2013

Other Interests

Popularization of science

I plan to do science popularization based on youtube videos. The objective is to propose theoretical ecology topics, with mathematical and numerical analysis, but with a playful visual. It also allows me to develop my skills in programming and 3D animation, a field I really enjoy learning.

Assiduous consumer of scientific content and critical thinking

I follow several scientific videographers (Mr Phi, Science Étonnante, Primer, Veritassium), and critical thinkers (R. Monvoisin, Hygiène Mentale). I enjoy the multitude of subjects, although lately I've been particularly interested in LLMs.

DALL.E

Mountain sports

I am passionate about the mountains and most of the possible ways to travel them: skiing, snowboarding, mountaineering, climbing, trail running, paragliding, cycling. I particularly appreciate the brain shutdown in very long efforts.

I like to share achievements in skiing, mainly because I find this discipline very aesthetic, while trying to stay on the edge of the powerful attractor of social networks.