Jean-François Gerard | National Institute of Agricultural Research (INRA) (original) (raw)

Papers by Jean-François Gerard

Ethology Ecology & Evolution, 1992

The aims of this paper are to recall and to illustrate one of the validity range boundaries of be... more The aims of this paper are to recall and to illustrate one of the validity range boundaries of behavioural ecology and the evolutionary theory of games, within the field of neo-darwinian theory. The principles underlying these two disciplines can apply at the minimum condition that the pure or mixed strategy, which must remain at selective equilibrium, reproduces its kind. This important restriction has been explicitly stated by evolutionary games theorists, but not so clearly in the case of frequencyindependent selection which is also considered by behavioural ecologists. In sexual populations, this precludes in particular all the cases where the expected optimal or evolutionarily stable strategy is achieved in hétérozygotes, as hétérozygotes produce homozygotes at each generation.

Comptes Rendus Biologies, 2006

In gregarious ruminants, females and males tend to live in separate groups outside the rutting se... more In gregarious ruminants, females and males tend to live in separate groups outside the rutting season. According to the 'activity budget' hypothesis, this is due to an activity asynchrony between the two sexes reducing the lifetime of mixed-sex groups. We tested this hypothesis in a fallow deer population. Activity asynchrony was more frequent in mixed-sex than in single-sex groups. In addition, mixed-sex groups had a higher probability of splitting-up than all-female groups, and they mainly split up into singlesex groups. However, activity asynchrony did not appear as a major cause of splitting-up.

HAL (Le Centre pour la Communication Scientifique Directe), Nov 13, 2014

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HAL (Le Centre pour la Communication Scientifique Directe), May 15, 2017

Journal of Theoretical Biology, 1992

In evolutionary biology, the axiom that natural selection tends ideally to maximize inclusive fit... more In evolutionary biology, the axiom that natural selection tends ideally to maximize inclusive fitness of the individual or some other suitable quantity is often advanced (Cody, 1974; Maynard Smith, 1978; Krebs & McCleery, 1984; Houston et al., 1988). Moreover, the evolutionists generally distinguish two situations (Dawkins, 1980; Maynard Smith, 1982): one in which fitness is independent of the frequency of the phenotypes present in the population (frequency-independent selection), and one in which it does depend on this frequency (frequency-dependent selection). This led some authors such as Parker (1984), and more recently Parker & Maynard Smith (1990), to consider "a 2-speed optimization": frequency-independent selection should lead to a "simple optimum" at the end of the selective process, since all the individuals should have the same strategy and the mean fitness of the population should be maximized; frequency-dependent selection, formulated in terms of the theory of games, should lead to a "competitive optimum" even though the "evolutionary stable strategy" (or "ESS"; Maynard Smith & Price, 1973) characterizing the equilibrium "is not the strategy that maximizes fitness in a population sense" (Parker & Maynard Smith, 1990: 30). Our aim in this short communication is to criticize the concept of "competitive optimum" by Parker & Maynard Smith, as well as the general ability of natural selection to "maximize fitness", even in "phenotypic models" (Lloyd, 1977). These models, devoid of genetic constraints since each strategist is assumed to reproduce its own kind, are especially suitable for examining the ideal effect of natural selection.

HAL (Le Centre pour la Communication Scientifique Directe), 1995

Canadian Journal of Zoology, 2008

Woodland fragmentation through land consolidation practices (the merging of small fields by the r... more Woodland fragmentation through land consolidation practices (the merging of small fields by the removal of separating structures like hedgerows) is recognised as a major threat to biodiversity in Europe. While its impact on the occurrence of species has frequently been the object of focus, its impact on the movements of individuals has rarely been studied. We used paths of radio-tracked European pine martens ( Martes martes (L., 1758)), a forest-dwelling species, with fixes taken at 3 min intervals to determine their habitat use in fragmented landscape. Our results differ from those generally reported in the literature. Monitored individuals were not confined to large forests, and made additional use of small wood plots and hedgerows. Indeed, individuals moved faster in forests than in all other habitat types, which suggests that martens preferentially foraged in small woods, edges, and hedgerows. Roads and buildings were not avoided; fields, however, were avoided, although they did...

The Biological Bulletin, 2002

In large mammalian herbivores, the increase of group size with habitat openness was first assumed... more In large mammalian herbivores, the increase of group size with habitat openness was first assumed to be an adaptive response, encoded in the individual. However, it could, alternatively, be an emergent property: if groups were nonpermanent units, often fusing and splitting up, then any increase of the distance at which animals perceive one another could increase the rate of group fusion and thus mean group size. Dynamical models and empirical data support this second hypothesis. This is not to say that adaptive modifications of mean herd size cannot occur. However, this changes the way in which we can envisage the history of gregariousness in large herbivores during the Tertiary.

Revue d'Écologie (La Terre et La Vie)

Chez les Artiodactyles, un accroissement de la taille des groupes avec l’ouverture du milieu et l... more Chez les Artiodactyles, un accroissement de la taille des groupes avec l’ouverture du milieu et le fait que les jeunes soient rarement à la périphérie des groupes, sont généralement considérés comme des « stratégies » anti-prédatrices. Le fait que les groupes soient régulièrement menés par des individus âgés permettrait par ailleurs aux jeunes de profiter de l’expérience de ces derniers. En termes de causalité immédiate, ces trois phénomènes découlent vraisemblablement de mécanismes particulièrement simples. En premier lieu, les animaux doivent se percevoir pour former des groupes, si bien que la taille des groupes doit dépendre des possibilités qu’ont les individus de se percevoir. Les positions centrales des jeunes découlent sans doute de ce qu’ils interagissent entre eux de façon privilégiée et forment ainsi des sous-groupes compacts au sein des groupes auxquels ils participent. Enfin, les individus âgés deviennent probablement « meneurs » du simple fait qu’ils se déplacent en te...

Diurnal space and habitat use by field roe deer, Capreolus capreolus, was investigated in mid-win... more Diurnal space and habitat use by field roe deer, Capreolus capreolus, was investigated in mid-winter (January-February) and mid-growing season (June-mid-July) by radio-tracking eleven individuals in an agricultural plain in Northern France. Home ranges, as determined by the minimum convex polygon method, were smaller and more dispersed in mid-growing season than in mid-winter. In mid-winter, home ranges included more stubble and cereal fields than the remaining study area. Furthermore, stubble fields were overused with respect to the proportion of the home ranges they covered. In mid-growing season, the habitat composition of the home ranges and of the remaining study area differed little. Moreover, in contrast with mid-winter, woods and hedges were overused with respect to their availability in the home ranges. The management implications of these results are discussed.

La taille et la composition des groupes d'isards, Rupicapra pyrenaica, ont été étudiées tout ... more La taille et la composition des groupes d'isards, Rupicapra pyrenaica, ont été étudiées tout au long de l'année sur trois sites pyrénéens, par observation sur itinéraires et sur postes fixes (nombre de groupes observés : N = 1 886 à Orlu, Ariège, en 1990 ; N = 301 au "Carlit" et N = 255 au Soula de Carol, Pyrénées-Orientales, en 1981 et 1982). Les structures sociales ainsi que les structures en sexe et âge sont significativement différentes sur les trois sites. La réserve d'Orlu est caractérisée par des possibilités importantes pour les animaux de se percevoir à grande distance (paysage ouvert et peu accidenté), par une forte densité d'isards (30 individus pour 100 ha) et par une forte proportion de femelles adultes et de chevreaux. Les groupes de grande taille et ceux incorporant toutes les classes d'âge et de sexe y sont plus fréquents que sur les autres sites ; les groupes composés d'unités mère-jeune y sont abondants. Le Soula de Carol est carac...

Zoo Biology, 2008

We studied over 1 year the spatial organization and the spatial distribution of activities in a c... more We studied over 1 year the spatial organization and the spatial distribution of activities in a captive springbok (Antidorcas marsupialis) population living in an 18-ha enclosure located in southern France. Throughout the study period, the two adult males occupied fairly exclusive home ranges, in the overlapping part of which the three subadult males were restricted. The spatial and temporal distribution of aggressive, marking, and avoidance behavior of males showed that the two adults were territorial, except during summer. They accounted for 71% of all marking behaviors recorded, for 77% of the aggressive behavior, and for 91% of the sexual interactions, whereas subadult males accounted for 94% of the avoidance behavior observed. The adult females used the whole enclosure, moving through the males' home ranges. They fed everywhere, but they all had the same preferred resting area, located in the center of the territory of one of the two adult males. They gave birth, accounted for maternal behavior and were engaged in sexual interactions in sectors differing from one individual to the other, but mainly outside the sector where all males' home ranges overlapped. Our results are compared to those reported in natural conditions and lead us to discuss both the functional interpretations of marking behavior, and the signification of a home range for an ungulate.

Oikos, 1992

ABSTRACT The reasoning and conclusions of the evolutionary theory of games are based on the hypot... more ABSTRACT The reasoning and conclusions of the evolutionary theory of games are based on the hypothesis that each strategist reproduces its own kind. Using digenic variants of the Hawk-Dove-Bourgeois game, we illustrate the fact that the transposition of this type of approach to sexual diploid populations, for which the evolutionary theory of games also initially attempted to explain, is not quite straightforward. It is clear that a pure ESS cannot be reached if it is solely dependent on heterozygotes. However, more unexpectedly, the fact that an ESS can be reached does not guarantee the absence of alternative attractors, not fulfilling ESS conditions, thereby involving a genetic load for the populations.

Behavioural Processes, 1995

Different theoretical models and methods exist which help to tackle the question of perception an... more Different theoretical models and methods exist which help to tackle the question of perception and learning in evolution. Waddington's genetic assimilation and its counterpart, the 'Wright Effect', provide a good methodological framework for experiments and simulations. Comparative analysis, in which phylogenetic as well as ecological aspects are considered, is another useful tool. These approaches consider cognitive processes with their simultaneous involvement in selective processes; they say very little about their emergence.

Animal Behaviour, 2008

Several models have recently confirmed the hypothesis that mean group size should increase with p... more Several models have recently confirmed the hypothesis that mean group size should increase with population density in animal species in which groups are unstable. Based upon different assumptions with respect to the mechanisms of groups merging and splitting up, these models, however, predict quantitatively different relations between mean group size and population density. Taking advantage of a quasiexperimental situation, we studied the diurnal group dynamics of the Pyrenean chamois within a 58-ha open pasture in a protected area during winter. Mean group size scaled with local population density raised to the power of 2/3 within the pasture, which implies that the mean number of groups was related to the cube root of local population density. On the basis of the fate of groups that included tagged individuals, we found that: (1) the rate at which groups joined increased as the number of groups within the pasture increased; (2) the rate at which groups split up increased with their size; and (3) the rate at which groups were involved in both fusion and fission events increased as the local population density increased. We discuss the possible role of population spatial structure and motherekid association in both the dynamics of group formation and the relations between mean group size and population density.

En vue de l'obtention du D DO OC CT TO OR RA AT T D DE E L L' 'U UN NI IV VE ER RS SI IT TÉ É D D... more En vue de l'obtention du D DO OC CT TO OR RA AT T D DE E L L' 'U UN NI IV VE ER RS SI IT TÉ É D DE E T d'attente, des déceptions… pour finalement partager la vie secrète des beiras. Ils ont été mes professeurs de Somali, de brousse, et tellement plus... Je remercie Nabil Mohamed du CERD pour sa disponibilité et son encadrement à Djibouti. Un grand merci également à Alain Laurent, grâce à qui je suis partie à la rencontre de cette petite antilope violette méconnue, pour son implication et sa pratique du 'keep on fighting' et à Nicolas Prévôt, djiboutien d'adoption, qui m'a fait découvrir ce pays d'une richesse insoupçonnée, mais également les gens qui l'habitent, leurs us et leurs coutumes. Merci aussi à Bertrand Lafrance et sa famille pour leur soutien, leur présence et leur beau projet : DECAN. J'adresse toute ma reconnaissance à M. (et Mme) Jean-Pierre Galland du MAE, qui a cru en ce projet au point de le rendre possible et m'a offert la chance de réaliser cette expérience unique, mais également aux autres personnes et structures qui m'ont permis de financer la suite de ce travail : Cathy Pelsy et Jean-Marc Lernould de la CEPA, Eric Bairrão Ruivo et Rodolphe Delord de l'ABCR, Jens-Ove Heckel du zoo de Landau et du ZGAP. Je remercie Catrin Hammer pour nos échanges constructifs et ses informations précieuses sur cette petite antilope dont nous partageons la passion. Et pour finir de façon traditionnelle, je remercie de tout mon coeur ceux dont le soutien m'a donné la force nécessaire pour tenir dans les moments difficiles, car il y en a eu aussi… Boris, qui m'a accompagnée et encouragée toutes ces années, et notre petite Sasha, qui, même si elle a un peu compliqué la donne, rayonne comme le soleil de Djibouti. Sans oublier ma famille, mes parents et mon frère, avec qui j'ai notamment acquis le goût du voyage et de la différence, et enfin mes proches, mes copines, mes amis, mes belles familles, et mon chat même… bien que lui n'y soit vraiment pour rien !