Search results for " Systematics."
showing 10 items of 4820 documents
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,…
Resident and transient dynamics, site fidelity and survival in wintering Blackcaps Sylvia atricapilla: evidence from capture-recapture analyses
2007
In their winter quarters, migrant birds may either remain within a small area (resident strategy) or move frequently over a large area looking for locally abundant food (transient strategy). It has been suggested that both strategies could simultaneously occur in the same population. We used time-since-marking capture‐recapture models to infer the coexistence of these two behavioural strategies (transient and resident) among wintering Blackcaps Sylvia atricapilla using weekly recapture data over a 7-year period. A related question is whether Blackcaps, if surviving to the next winter, always return to the same wintering area, so we also used this approach to analyse winter site fidelity and…
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…
Optimal rates of bisexual reproduction in cyclical parthenogens with density‐dependent growth
1999
This work explores theoretical patterns of reproduction that maximize the production of resting eggs and the long-term fitness of genotypes in cyclical parthenogens. Our focus is on density-dependent reproduction as it influences the consequences of a trade-off between producing amictic daughters – which reproduce parthenogenetically and subitaneously – and producing mictic daughters – which undergo meiosis and bisexual reproduction. Amictic females increase competitive ability and allow the population to achieve a larger size; mictic females directly contribute to population survival through harsh periods by producing resting eggs. Although morphologically indistinguishable, the two types …
The role of local adaptation in the relationship between an endangered root hemiparasite Euphrasia rostkoviana, and its host, Agrostis capillaris
1999
We experimentally studied the role of local adaptation and the co-evolutionary relationship between an annual, endangered root hemiparasite Euphrasia rostkoviana and its main host Agrostis capillaris. According to our hypothesis, the existence of local adaptation in hemiparasites should be observable in better hemiparasite performance when attached to A. capillaris hosts originating from Euphrasia populations. After one month of growth, the height and the number of leaves of hemiparasites were not affected by the origin of their hosts. The differences in growth were due to between population effects. The situation remained constant after three months. Hemiparasite biomass was not affected b…
Can adaptation lead to extinction?
2005
Ever since J.B.S. Haldane proposed the idea, evolutionary biologists are aware that individual level adaptations do not necessarily lead to optimal population performance. A few deeply mathematical models, drawing from a diverse range of systems, even predict that individual selection can lead to the extinction of the whole population, a phenomenon which has become known as evolutionary suicide. Due to the complexity of both following adaptation and determining the exact cause of an extinction, evolutionary suicide has remained untested empirically. However, three recent empirical studies suggest that it may occur, and that suicide should be taken seriously as a potentially important evolut…
Spatial analysis of lanner falcon habitat preferences: Implications for agro-ecosystems management at landscape scale and raptor conservation
2014
Abstract Sicily hosts the largest European population of the endangered lanner falcon, a poorly known species which needs conservation planning based on habitat preferences. A distribution model on 10 × 10 km cells of Sicily was described using Generalized Linear Models and variation partitioning methods. This modelling approach extracted explanatory factors, pure and joint effects of greatest influence from subsets of variables controlled for multi-collinearity and spatial autocorrelation. Analytical cartography used the environmental favourability function to assess habitat preferences, and the insecurity index estimated the degree to which lanner falcon occupancy is represented in the Na…
Physiological and reproductive differences between hermaphrodites and males in the androdioecious plant Fraxinus ornus
2004
8 páginas, 4 figuras, 1 tabla.
Sex and population variation in ultraviolet reflectance of colour patches in Gallotia galloti (Fam. Lacertidae) from Tenerife (Canary Islands)
2005
Sex and population differences in the ultraviolet (UV) reflectance patterns of two phenotypically divergent lacertids from Tenerife, Gallotia galloti eisentrauti and G. g. galloti, are described. Adults in both populations have rows of lateral and ventro-lateral blue patches on either side of the trunk that show a single peak of reflectance in the near UV. The lateral patches of males are more intensely reflective than those of females, but females have more chromatic and UV-shifted lateral patches than males. Most G. g. eisentrauti and some G. g. galloti also have blue cheek patches on either side of the gular area. Male cheek patches have reflectance peaks in the near UV, whereas those of…