Université Paris Dauphine-PSL

We study the long-time behavior of solutions to a kinetic equation inspired by a model of sexual populations structured in phenotypes. The model features a nonlinear integral reproduction operator derived from the Fisher infinitesimal operator and a trait-dependent selection term. The reproduction operator describes here the inheritance of the mean parental traits to the offspring without variability. We show that, under assumptions on the growth of the selection rate, Dirac masses are stable around phenotypes for which the difference between the selection rate and its minimum value is less than $\frac{1}{2}$. Moreover, we prove the convergence in some Fourier-based distance of the centered and rescaled solution to a stationary profile under some conditions on the initial moments of the solution.

We study a generalization of the multi-marginal optimal transport problem, which has no fixed number of marginals N and is inspired of statistical mechanics. It consists in optimizing a linear combination of the costs for all the possible N’s, while fixing a certain linear combination of the corresponding marginals.

Marine protected areas (MPAs) are widely implemented tools for long‐term ocean conservation and resource management. Assessments of MPA performance have largely focused on specific ecosystems individually and have rarely evaluated performance across multiple ecosystems either in an individual MPA or across an MPA network. We evaluated the conservation performance of 59 MPAs in California's large MPA network, which encompasses 4 primary ecosystems (surf zone, kelp forest, shallow reef, deep reef) and 4 bioregions, and identified MPA attributes that best explain performance. Using a meta‐analytic framework, we evaluated the ability of MPAs to conserve fish biomass, richness, and diversity. At the scale of the network and for 3 of 4 regions, the biomass of species targeted by fishing was positively associated with the level of regulatory protection and was greater inside no‐take MPAs, whereas species not targeted by fishing had similar biomass in MPAs and areas open to fishing. In contrast, species richness and diversity were not as strongly enhanced by MPA protection. The key features of conservation effectiveness included MPA age, preimplementation fisheries pressure, and habitat diversity. Important drivers of MPA effectiveness for single MPAs were consistent across MPAs in the network, spanning regions and ecosystems. With international targets aimed at protecting 30% of the world's oceans by 2030, MPA design and assessment frameworks should consider conservation performance at multiple ecologically relevant scales, from individual MPAs to MPA networks.

Over the past decades, human impacts have changed the structure of tropical benthic reef communities towards coral depletion and macroalgal proliferation. However, how these changes have modified chemical and microbial waterscapes is poorly known. Here, we assessed how the experimental removal of macroalgal assemblages influences the chemical and microbial composition of two reef boundary layers, the benthic and the momentum. Chemical and microbial waterscapes were spatially structured, both horizontally and vertically, according to macroalgal dominance and boundary layers. Microbes associated with reef degradation were enriched in the boundary layers surrounding macroalgal-dominated substrata. Dominant macroalgae were surrounded by a distinct chemical pool of diverse lipid classes (e.g., diterpenoids and glycerolipids) and labile organic matter (e.g., organooxygen compounds), which diffused from algal tissues to boundary layers according to their polarity. Finally, our results highlighted strong co-variations between specific algal-derived metabolites and planktonic microbes, giving insight into their roles in coral reef functioning and resilience.

Mesophotic coral ecosystems (MCEs) have gained considerable attention this last decade but the paucity of knowledge on these ecosystems is pronounced, particularly in the Southwestern Indian Ocean region. We explore the spatial variation in macro-benthic and scleractinian communities along a wide depth gradient (15–95 m) and among contrasted sites around Reunion Island. Values for percent cover of macro-benthic and scleractinian communities varied significantly along depth, resulting in a vertical zonation of communities. We recorded a transition of light-dependent communities towards heterotrophic organisms between shallow and upper mesophotic zones at 30–45 m, and a community shift in the lower mesophotic zone at 75 m. Despite overlaps in scleractinian genera distribution along the depth gradient, predominant genera of shallow depths were in low abundance in MCEs (> 30 m). Our findings highlight the importance of MCEs as distinct ecosystems sheltering diverse, unique habitats and harboring abundant cnidarian-habitat forming organisms. Supporting the ‘Deep Reef Refuge Hypothesis’, 56% of scleractinian genera spanned shallow to mesophotic depths, while one-third were depth specialists, either shallow or mesophotic. This highlights the limited refuge potential of mesophotic reefs for Southwestern Indian Ocean coral communities. Our findings establish baseline data for monitoring and conserving Reunion Island’s MCEs.

We study social reactions on Twitter to job destructions. We use information on large‐scale restructuring events announced in the United Kingdom from 2013 to 2018. We match it with data on the number and sentiments of the tweets involving the company name posted around the time of the announcement. We show that job destruction announcements elicit numerous, strongly negative reactions, four times larger than the positive reactions to job creation announcements. We also show that these negative reactions are associated with significant losses in the market value of the downsizing firms, pointing to costs that add to standard dismissal costs.

Nowadays, pricing is one of the most challenging tasks for marketers. Despite its importance for both academics and practitioners, consumers’ reactions to prices remain not clear, especially with the emergence of new forms of prices, among which we can highlight the use of complex prices, which is becoming increasingly popular. Complex prices’ perception is highly dependent on the way they are communicated; consequently, complex prices communication plays a crucial role in shaping perception. This study is a continuity of previous researches that have validated the perceptual effects of complex prices communication. It attempts to show the effects complex prices communication has on its perceived fairness. In addition, the effects of the moderating variables; Seller Credibility and Responsibility Attribution (i.e., inferred motive) are studied. One hundred thirty-five undergraduate students participated in the study. They were randomly assigned to 2 (sequential communication of complex price vs non sequential communication of complex price) x2 (credible seller vs less credible seller) conditions. Manipulation consisted of presenting a scenario of buying an online air ticket. The results of our research highlight that sequential complex price communication has a significant effect on its perceived fairness. In particular, the results show that the perceived fairness of price is more negatively affected when the seller lacks credibility according to consumers. Also, it has been proved that the delayed communication of some of the complex price components could be perceived as a way to get a higher profit, which deepens the negative perceived fairness.

This paper provides evidence of merger timing induced by investors’ overoptimism. We distinguish between hot and cold merger markets and examine the movements of bidding firms’ stock prices, around, before and after mergers announcements. Our results provide strong evidence that mergers are driven by stock market valuation and that these events occur during periods when investors are highly overoptimistic and react irrationally to a merger announcement. We find evidence that bidders’ managers are aware of the overvaluation of their firms and act rationally by timing their mergers and paying with stock. The market can however, correct itself when merger results start to appear.

Growing numbers of people are commodifying their leisure activities on the internet. This article’s mixed-method study of French food bloggers and Etsy handicrafters focuses on the overflow of digital market work into amateurs’ domestic lives. Building on the sociology of ‘serious leisure’, the study examines the novelty of such social phenomena. We show that traditional serious leisure activities have already revealed comparable forms of overflow and similar motives for consent to such spillover effects. However, the study also brings to light three specific effects of online commodification on leisure activities: the new forms of extra work in which amateurs are involved, the transformation of the leisure activity, and the shortening of amateurs’ careers.

Ecotourism is branded as transforming wildlife biodiversity conservation; yet, its positive and negative effects are not always assessed in wild populations. Wildlife viewing with feeding is a popular form of ecotourism, but its potential health impacts on wildlife are becoming increasingly evident. Shark feeding is a global phenomenon; however, impact studies on species' persistence (i.e. survival and reproduction) are lacking. In this study, we expand upon previous work on shark tourism and use physiological indicators to assess the sub‐lethal health and fitness consequences of shark feeding. Blood cellular, biochemical and endocrinological parameters were sampled from 117 adult wild blacktip reef sharks, Carcharhinus melanopterus, at feeding and non‐feeding sites around Mo'orea, French Polynesia, to compare general condition, nutritional status, a metabolism proxy and reproductive investment on the respective sites. In addition to sex‐ and season‐specific differences observed in multiple physiological parameters, we found lower haematocrit levels (condition) at feeding sites for both sexes, as well as lower insulin levels (metabolism proxy) in male sharks at feeding sites. Further impacts of feeding on physiology were found in interaction with the breeding season: adult females using feeding sites had lower glucose levels (nutritional status), as well as lower 17β‐oestradiol levels during the breeding season (reproductive investment) compared to non‐feeding sites. Male sharks using feeding sites during the breeding season exhibited higher levels of testosterone compared to non‐feeding sites. Our results suggest that tourism feeding activity in Mo'orea provides poor nutrition and/or unpredictable food, especially for site‐attached females during the energy‐intensive breeding season. We highlight how physiological indicators reveal negative health and fitness impacts of shark feeding, with the reproductive impacts potentially having longer‐lasting consequences for population dynamics, making feeding an ecological trap. Animal sex and season should be considered when evaluating feeding impacts, and stricter regulations for the nutritional content of the food given to sharks are needed in ecotourism management.

Rather than leading to the emergence of a problem, some processes contribute to limiting their scope and impeding agenda-setting. These “nonproblems” are situations that could have led to social mobilizations or public intervention but end up neither being publicized nor subject to strong policy. We use occupational health in France to illustrate these mechanisms. The social invisibility of work-related ill-health is linked to the joint contribution of two processes. Firstly, from the perspective of research on ignorance and undone science, scientific knowledge is under-developed compared to other public health issues. And even available knowledge is rarely used by policy-makers. Secondly, policies use underestimated numbers from the occupational diseases compensation system. This specific configuration of knowledge/ignorance and official counting plays a central role in the production of occupational health issues as a nonproblem. Their invisibility contributes to the production of inertia and public inaction that characterize public policy in this field.

Artificial light at night (ALAN) is an anthropogenic pollutant that is intensifying and expanding in marine environments, but experimental studies of community-level effects are generally lacking. The inshore, shallow, and clear-water locations of coral reefs and their diverse photosensitive inhabitants make these ecosystems highly susceptible to biological disturbances; at the same time, their biodiversity and accessibility make them model systems for wider insight. Here, we experimentally manipulated ALAN using underwater LED lights on a Polynesian reef system to investigate the influence on localised nighttime fish communities compared to control sites without ALAN. We collected infrared video censuses of baseline communities prior to manipulation, which we repeated following short-term (mean of three nights) and prolonged (mean of 25 nights) exposures to ALAN. Short-term ALAN exposure did not induce any significant alterations to the nighttime fish community, but prolonged ALAN exposure increased nighttime species richness. Species compositions exposed to prolonged ALAN were more dissimilar from their baseline compared to control sites. The difference between community compositions at prolonged ALAN exposure and control sites was not apparent at the family level; instead, it was observed from the composition of trait guilds. Following pro-longed ALAN exposure, more diurnal and nocturnal predatory species (piscivores, invertivores, and planktivores)—particularly those that are site-attached or mobile within reefs—were present in nighttime assemblages. Our experimental findings show that coastal ALAN could cause trophic imbalances and circadian disturbances in localised nighttime reef fish communities. Given that community-wide consequences were only apparent after prolonged ALAN exposure suggests that management of the duration of artificial lighting could potentially be used to reduce impacts on marine ecosystems.

To promote the circular economy and change unsustainable business practices, policymakers are increasingly implementing novel policy instruments. Fostering repair is increasingly seen as a concrete strategy towards strong circularity, involving disruptive business model (BM) transformations. This study explores the impact of the recently implemented mandatory repairability index in France on BMs, utilizing a case study methodology with an embedded design. Our findings reveal 19 emerging company practices that affect all main BM dimensions. We identify three ways retailers and manufacturers adopt the index to shift towards repair‐oriented BMs. While the literature on the interplay between public policies and circular BMs has mainly focused on command‐and‐control policies for circular economy strategies other than repair, we show how an informative policy instrument transcends its role as mere consumer information. Instead, it emerges as a versatile management tool, facilitating the adoption or up scaling of diverse repair activities. However, informative instruments do not ensure widespread diffusion of repair‐based BMs. Instead, we emphasize the imperative of promoting repair through a comprehensive and evolving policy mix.

We present a game-theoretic model of a polymorphic cancer cell population where the treatment-induced resistance is a quantitative evolving trait. When stabilization of the tumor burden is possible, we expand the model into a Stackelberg evolutionary game, where the physician is the leader and the cancer cells are followers. The physician chooses a treatment dose to maximize an objective function that is a proxy of the patient’s quality of life. In response, the cancer cells evolve a resistance level that maximizes their proliferation and survival. Assuming that cancer is in its ecological equilibrium, we compare the outcomes of three different treatment strategies: giving the maximum tolerable dose throughout, corresponding to the standard of care for most metastatic cancers, an ecologically enlightened therapy, where the physician anticipates the short-run, ecological response of cancer cells to their treatment, but not the evolution of resistance to treatment, and an evolutionarily enlightened therapy, where the physician anticipates both ecological and evolutionary consequences of the treatment. Of the three therapeutic strategies, the evolutionarily enlightened therapy leads to the highest values of the objective function, the lowest treatment dose, and the lowest treatment-induced resistance. Conversely, in our model, the maximum tolerable dose leads to the worst values of the objective function, the highest treatment dose, and the highest treatment-induced resistance.