Search results for "Population Density"
showing 10 items of 194 documents
THE COST OF REPRODUCTION INDUCED BY BODY SIZE AT BIRTH AND BREEDING DENSITY
2007
Body size at birth has implications for the quality of individuals throughout their life. Although large body size is generally considered an advantage, the relationship between body size at birth and long-term fitness is often complicated. Under spatial or temporal variation in environmental conditions, such as the seasonally changing densities of Fennoscandian vole populations, selection should favor variation in offspring phenotypes, as different qualities may be beneficial in different conditions. We performed an experiment in which a novel hormonal manipulation method was used to increase phenotypic variance in body size at birth in the bank vole (Myodes glareolus). The effects of body…
Stability of Corynosoma populations with fluctuating population densities of the seal definitive host.
2004
In theory there should be a strong coupling between host and parasite population sizes. Here, we investigated population size and structure in 3 species of acanthocephalans,Corynosoma semerme,C. strumosumandC. magdaleni, in ringed seals (Phoca hispida) from the Bothnian Bay over a period of more than 20 years. During this period, seal numbers first decreased markedly and then increased steadily; at the same time, a paratenic fish host particularly important forC. strumosumhas gradually disappeared from the bay due to decreasing salinity. We found no evidence that the mean abundance of any of the 3 acanthocephalan species changed significantly over time, nor was there any relationship betwee…
A nationwide school fruit and vegetable policy and childhood and adolescent overweight: A quasi-natural experimental study
2022
Background School free fruit and vegetable (FFV) policies are used to promote healthy dietary habits and tackle obesity; however, our understanding of their effects on weight outcomes is limited. We assess the effect of a nationwide FFV policy on childhood and adolescent weight status and explore heterogeneity by sex and socioeconomic position. Methods and findings This study used a quasi-natural experimental design. Between 2007 and 2014, Norwegian combined schools (grades 1–10, age 6 to 16 years) were obligated to provide FFVs while elementary schools (grades 1–7) were not. We used 4 nationwide studies (n = 11,215 children) from the Norwegian Growth Cohort with longitudinal or cross-secti…
Predominance of outcrossing in Lymnaea stagnalis despite low apparent fitness costs of self-fertilization.
2007
We have quantified the natural mating system in eight populations of the simultaneously hermaphroditic aquatic snail Lymnaea stagnalis, and studied the ecological and genetic forces that may be directing mating system evolution in this species. We investigated whether the natural mating system can be explained by the availability of mates, by the differential survival of self- and cross-fertilized snails in nature, and by the effects of mating system on parental fecundity and early survival. The natural mating system of L. stagnalis was found to be predominantly cross-fertilizing. Density of snails in the populations had no relationship with the mating system, suggesting that outcrossing ra…
Helminth communities of two green frogs (Rana perezi and Rana saharica) from both shores of the Alboran Sea.
2006
Les communautes d'helminthes de deux populations de grenouilles vertes des rivages de la mer d'Alboran (mediterraneen occidental) ont ete etudiees. Des 79 grenouilles examinees pour etudier les helminthes, 39 exemplaires de Rana saharica ont ete captures a Bab-Taza (Maroc), et 40 de l'espece Rana perezi dans le Parc Naturel Sierra de Grazalema (Espagne). Bien que la richesse des especes d'helminthes soient identique dans les deux secteurs d'echantillonnage, les differences observees dans la structure des infracommunautes d'helminthes sont assez importantes. Statistiquement, des differences significatives ont ete trouvees entre la richesse en especes et la diversite des infracommunautes chez…
The benefits of interpopulation hybridization diminish with increasing divergence of small populations.
2012
Interpopulation hybridization can increase the viability of small populations suffering from inbreeding and genetic drift, but it can also result in outbreeding depression. The outcome of hybridization can depend on various factors, including the level of genetic divergence between the populations, and the number of source populations. Furthermore, the effects of hybridization can change between generations following the hybridization. We studied the effects of population divergence (low vs. high level of divergence) and the number of source populations (two vs. four source populations) on the viability of hybrid populations using experimental Drosophila littoralis populations. Population v…
Overweight, obesity, and thinness among a nationally representative sample of Norwegian adolescents and changes from childhood: Associations with sex…
2021
Objective To estimate the prevalence of overweight, obesity, and thinness among Norwegian 13-year-olds and the changes from childhood (age 8 years) to adolescence (age 13 years); and to explore associations with sex, region, and population density from childhood to adolescence. Design We used longitudinal, anthropometric data collected by school health nurses conducted in Norway. Weight status was classified according to the International Obesity Task Force cut-offs for overweight, obesity, and thinness, and according to mean body mass index (kg/m2). Participants The Norwegian Youth Growth Study, consisting of a nationally representative sample of Norwegian 13-year-olds (n = 1852; 50.7% gi…
Larval competition in Drosophila melanogaster: effects on development time
1990
The effects on development time of larval competition that is interrupted at different times are analyzed in an experiment with constant larval density and varying proportions of two competing strains. Interruption of competition is carried out by means of the overfeeding technique, which allows for the study of individuals that, after several days under competition stress, either complete their development in crowded conditions or migrate to a vial with fresh food where the rest of their development takes place. Results of mean development time and within-vial variance of development time show that individuals under strong competition stress can arrest their development retaining the capab…
Environment-mediated morph-linked immune and life-history responses in the aposematic wood tiger moth
2012
1. Warning signals are expected to evolve towards conspicuousness and monomorphism, and thereby hamper the evolution of multiple colour morphs. Here, we test fitness responses to different rearing densities to explain colour polymorphism in aposematic wood tiger moth (Parasemia plantaginis) males. 2. We used larval lines sired by white or yellow adult males selected for small or large melanization patterns of coloration. We reared these selected lines either solitarily (favourable conditions) or in aggregations (challenged conditions), and followed their performance to adult stage. We tested whether differences in larval density affected life-history traits, adult melanin expression, adult …
Is metal accumulation in Pomphorhynchus laevis dependent on parasite sex or infrapopulation size?
2010
SUMMARYConcentrations of the elements As, Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, Sn, V, Zn were analysed by inductively coupled plasma mass spectrometry (ICP-MS) in the acanthocephalan Pomphorhynchus laevis and its fish host Barbus barbus. A total of 27 barbels were collected from the Danube River in autumn 2006 close to the town Kozloduy (685 river kilometer) on the Bulgarian river bank. Fish were divided into 3 groups. According to their P. laevis infrapopulation size hosts were considered as heavily infected (>100 worms per fish) and lightly infected (<20 worms per fish). The third group was used to compare heavy metal concentrations between male and female P. laevis. The 5 elements As, C…