Michel WIEVIORKA, L'impératif numérique

Compte rendu.Compte rendu de Michel WIEVIORKA, L'impératif numérique, Paris : CNRS éditions, 2013, 64 p. publié dans le Bulletin des bibliothèques de France, n°1, mars 2014, p. 189-191

Extraordinary Sex Ratios: Cultural Effects on Ecological Consequences

We model sex-structured population dynamics to analyze pairwise competition between groups differing both genetically and culturally. A sex-ratio allele is expressed in the heterogametic sex only, so that assumptions of Fisher's analysis do not apply. Sex-ratio evolution drives cultural evolution of a group-associated trait governing mortality in the homogametic sex. The two-sex dynamics under resource limitation induces a strong Allee effect that depends on both sex ratio and cultural trait values. We describe the resulting threshold, separating extinction from positive growth, as a function of female and male densities. When initial conditions avoid extinction due to the Allee effect, different sex ratios cannot coexist; in our model, greater female allocation always invades and excludes a lesser allocation. But the culturally transmitted trait interacts with the sex ratio to determine the ecological consequences of successful invasion. The invading female allocation may permit population persistence at self-regulated equilibrium. For this case, the resident culture may be excluded, or may coexist with the invader culture. That is, a single sex-ratio allele in females and a cultural dimorphism in male mortality can persist; a low-mortality resident trait is maintained by father-to-son cultural transmission. Otherwise, the successfully invading female allocation excludes the resident allele and culture, and then drives the population to extinction via a shortage of males. Finally, we show that the results obtained under homogeneous mixing hold, with caveats, in a spatially explicit model with local mating and diffusive dispersal in both sexes.Comment: final version, reflecting changes in response to referees' comment

Roberto CASATI, Contre le colonialisme numérique. Manifeste pour continuer à lire

Compte rendu.Compte rendu de Roberto CASATI, Contre le colonialisme numérique. Manifeste pour continuer à lire, coll. "Bibliothèque Idées", Albin Michel, 2013, 208 p. publié dans le Bulletin des bibliothèques de France, n°1, mars 2014, p. 187-189

Olivier ERTZSCHEID, Qu'est-ce que l'identité numérique ? Enjeux, outils, méthodologies

Compte rendu.Compte rendu de Olivier Ertzscheid, Qu'est-ce que l'identité numérique ? Enjeux, outils, méthodologies [en ligne], coll. " Encyclopédie numérique ", OpenEdition Press, 2013, 72 p., URL : http://books.openedition.org/oep/332 publié dans le Bulletin des bibliothèques de France, n°2, juin 2014, p. 192-193

Restoration Ecology: Two-Sex Dynamics and Cost Minimization

We model a spatially detailed, two-sex population dynamics, to study the cost of ecological restoration. We assume that cost is proportional to the number of individuals introduced into a large habitat. We treat dispersal as homogeneous diffusion. The local population dynamics depends on sex ratio at birth, and allows mortality rates to differ between sexes. Furthermore, local density dependence induces a strong Allee effect, implying that the initial population must be sufficiently large to avert rapid extinction. We address three different initial spatial distributions for the introduced individuals; for each we minimize the associated cost, constrained by the requirement that the species must be restored throughout the habitat. First, we consider spatially inhomogeneous, unstable stationary solutions of the model's equations as plausible candidates for small restoration cost. Second, we use numerical simulations to find the smallest cluster size, enclosing a spatially homogeneous population density, that minimizes the cost of assured restoration. Finally, by employing simulated annealing, we minimize restoration cost among all possible initial spatial distributions of females and males. For biased sex ratios, or for a significant between-sex difference in mortality, we find that sex-specific spatial distributions minimize the cost. But as long as the sex ratio maximizes the local equilibrium density for given mortality rates, a common homogeneous distribution for both sexes that spans a critical distance yields a similarly low cost