Search results for "INTRAS"
showing 10 items of 183 documents
Date de semis du mil et variabilité intrasaisonnière des précipitations au Niger
2012
Le rôle du déterminisme pluviométrique, et plus spécifiquement du démarrage de la saison des pluies, sur les pratiques agricoles a été évalué à partir de l'exemple de la culture du mil dans la région de Niamey parce que celle-ci y occupe une place prépondérante. Cette analyse, à l'interface du climat et des sociétés, a été réalisée à partir d'enquêtes agronomiques conduites en milieu paysan sur l'observatoire AMMA-CATCH Niger sur un carré de100 km x 100 km au NE de Niamey entre 2004 et 2007. Par ailleurs, le démarrage de la saison des pluies repose sur des considérations subjectives qui dépendent fortement de l'utilisateur. Ainsi, ce dernier est de nature équivoque dans ces régions semi-ari…
The impact of variable hatching rates on parasite control: a model of an aquatic ectoparasite in a Finnish fish farm
2006
Summary 1 Many parasites of medical and veterinary importance infect via free-living stages that undergo a period of development in the environment before seeking a host. Frequently, considerable variation is observed in the development rates of these stages, such that some individuals may be considered to occupy distinct subpopulations, similar to a plant's seed bank. Under certain conditions, these subpopulations may act as a reservoir for the parasite, buffering it from the impact of management strategies and reducing control success. 2 We assessed the impact of intraspecific variation in development rates on parasite control by developing a population dynamic model of the ectoparasite A…
Inclusive fitness and sexual conflict: How population structure can modulate the battle of the sexes
2014
Competition over reproductive opportunities among members of one sex often harms the opposite sex, creating a conflict of interest between individual males and females. Recently, this battle of the sexes has become a paradigm in the study of intersexual coevolution. Here, we review recent theoretical and empirical advances suggesting that – as in any scenario of intraspecific competition – selfishness (competitiveness) can be influenced by the genetic relatedness of competitors. When competitors are positively related (e.g. siblings), an individual may refrain from harming its competitor(s) and their mate(s) because this can improve the focal individual's inclusive fitness. These findings r…
Variability for mixis initiation in Brachionus plicatilis
2001
Deductions from both evolutionary models and inductive argumentation from empirical data support the notion of intraspecific variability for the initiation of sexual reproduction (mixis) within rotifer populations. In this study, we focus on the time and density at which mixis is initiated in a growing population. Cyclical parthenogenetic clones of Brachionus plicatilis established by hatching of resting eggs, isolated from a natural habitat, have been tested at the start of their sexual phase. Clones exhibited great variation for this trait, their time of switching to sexual reproduction being correlated with population density. Most of the variation for mixis initiation has either low or …
Competition for breeding sites and site-dependent population regulation in a highly colonial seabird, the common guillemot Uria aalge
2004
Summary 1. The hypothesis of site-dependent population regulation predicts that birds utilize available nesting sites in a pre-emptive (ideal despotic) manner, leading to density dependence in heterogeneous habitats as poorer sites are used at higher population densities. At small population sizes adaptive site choice protects populations against fluctuations (the buffer effect). 2. Common guillemots Uria aalge (Pontoppidan) breed at high density on sea-cliffs. The population breeding on the Isle of May, Scotland increased by 60% between 1981 and 2000. A good nest-site is a prerequisite for successful breeding and there is much competition for the best sites. Throughout this period, site us…
On the evolutionary stability of female infanticide
1997
Territoriality among female rodents may have evolved as an adaptation to intraspecific competition for resources or, alternatively, to defend pups against infanticide. In order to evaluate the latter, we analyse the conditions that allow an infanticidal strategy to invade a population of non-infanticidal females, and the circumstances under which infanticide may become an evolutionarily stable strategy (ESS). Our game theoretical analyses indicate that infanticide has to be associated with some direct (cannibalism) or indirect (reduced competition) resource benefits in order to invade a non-infanticidal population. We also expect that females will primarily kill litters of nearby neighbors,…
WHO BEARS THE COSTS OF INTERSPECIFIC COMPETITION IN AN AGE-STRUCTURED POPULATION?
2003
Social and density-dependent life history processes may differ according to age and the reproductive history of individuals. Arvicoline rodents have a typical, season-dependent, bimodal, age distribution of breeding individuals within a population. This distribution may influence population fluctuations. In this study, we measured effects of interspecific competition from field voles (Microtus agrestis) on various fitness components of female bank voles (Clethrionomys glareolus) in an age-structured breeding population in large (0.25 ha) outdoor enclosures. We monitored survival, reproduction, and space use of experimental bank vole populations with females from two different age groups. Wi…
Larval Arrest in Development of Tribolium castaneum (Coleoptera: Tenebrionidae)
1986
Arrested larval development (in the last larval instar) of part of the total larval population has been detected in moderately crowded situations (40 larvae in 2 g food) in Tribolium castaneum (Herbst) cultures This phenomenon is the same found previously in highly crowded cultures of Drosophila melanogaster (Meigen) and other related species. The arrest may be viewed as a mechanism of physiological adaptation of organisms to competitive situations.
Foraging site fidelity shapes the spatial organisation of a population of female western barbastelle bats
2009
Abstract Information about the spatial distribution of individual foraging habitats, which determines the space required by a population to be viable, is vitally important for the conservation of bats. Detailed knowledge of this kind is crucial for the design of nature reserves and management plans. Recent field studies that examined habitat use and home range distribution of bats largely ignored factors like traditional range use vs. intra- and interspecific competition, which may be responsible for the spatial organisation of a population home range. We investigated the home range sizes and distribution of a maternity colony of the western barbastelle bat via radio telemetry in four conse…
Tetraploid European Salicornia species are best interpreted as ecotypes of multiple origin
2011
Abstract Salicornia procumbens and S. stricta are two tetraploid European salt marsh species of locally adjacent but ecologically differentiated distribution. Whereas S. procumbens grows in the lowest part of the salt marsh, it is replaced by S. stricta in the middle part (and diploid Salicornias in the upper part). Using AFLPs and a reciprocal transplantation experiment, we investigated whether the two species represent distinct evolutionary lineages. The analysis of AFLP variation clearly showed that both species are not monophyletic. Also, accessions do not cluster according to geographical origin. The transplantation experiment revealed that S. procumbens shows significantly reduced fit…