Search results for "evolution"
showing 10 items of 11096 documents
Population processes under the influence of disasters occurring independently of population size
1989
Markov branching processes and in particular birth-and-death processes are considered under the influence of disasters that arrive independently of the present population size. For these processes we derive an integral equation involving a shifted and rescaled argument. The main emphasis, however, is on the (random) probability of extinction. Its distribution density satisfies an equation which can be solved numerically at least up to a multiplicative constant. In an example it is also found by simulation.
The use of Markovian metapopulation models: Reducing the dimensionality of transition matrices by self-organizing Kohonen networks
2006
Abstract Markovian population models are used in conservation biology to find an accurate estimate of a population's extinction probability. Such models require handling of large transition matrices and calculations are thus extremely time-consuming when large populations have to be studied. To accomplish these problems, some authors have suggested to group together several states/sizes of the population. Unfortunately, this so-called binning frequently results in errors in estimates obtained. The main problem with binning is that it assumes that grouped states behave nearly identical with respect to the underlying stochastic population process and that so far binning methods implicitly vio…
Noise in ecosystems: a short review
2004
Noise, through its interaction with the nonlinearity of the living systems, can give rise to counter-intuitive phenomena such as stochastic resonance, noise-delayed extinction, temporal oscillations, and spatial patterns. In this paper we briefly review the noise-induced effects in three different ecosystems: (i) two competing species; (ii) three interacting species, one predator and two preys, and (iii) N-interacting species. The transient dynamics of these ecosystems are analyzed through generalized Lotka-Volterra equations in the presence of multiplicative noise, which models the interaction between the species and the environment. The interaction parameter between the species is random …
Landscape and anti-predation determinants of nest-site selection, nest distribution and productivity in a Mediterranean population of Long-eared Owls…
2006
Nest predation is an important determinant of owl breeding success. We studied Long-eared Owl Asio otus productivity and attributes of nest-sites at the microhabitat and landscape scales in a Mediterranean locality over an 8-year period. We examined the effect on nest location and productivity of protective cover in concealing the nest from aerial and terrestrial predators. A dense cover of ivy and tree-foliage at canopy level favoured nest location but not productivity. By contrast, high shrub cover beneath the nest was selected by Owls and was positively related to both the site reoccupancy rate and the overall number of young fledged. Pre-fledging Owls use the ground, where they are expo…
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.
Monitoring fungal biodiversity – towards an integrated approach
2012
Biodiversity information databases and platforms have seen considerable progress in recent years. They have a high potential in conservation science in general, but may be even more revolutionary in relation to poorly known species groups such as fungi, whose practical conservation work has been jeopardised by scattered and poorly controlled information. We review the tradition of collecting information on species occurrences in mycology and discuss the characteristics of the present fungal biodiversity information databases. With a special focus on population trend monitoring of fruit body producing macrofungi, we emphasise several unrealised opportunities of these databases and point out …
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…
An existence and uniqueness principle for a nonlinear version of the Lebowitz-Rubinow model with infinite maximum cycle length
2017
The present article deals with existence and uniqueness results for a nonlinear evolution initial-boundary value problem, which originates in an age-structured cell population model introduced by Lebowitz and Rubinow (1974) describing the growth of a cell population. Cells of this population are distinguished by age a and cycle length l. In our framework, daughter and mother cells are related by a general reproduction rule that covers all known biological ones. In this paper, the cycle length l is allowed to be infinite. This hypothesis introduces some mathematical difficulties. We consider both local and nonlocal boundary conditions.
Genetic database development for the characterisation of Sicilian sheep population
2019
The most representative sheep in Sicily are Belicina, Comisana, Pinzirita, Barbarescaand the crossbred derived sheep from all this species. In this study, the allelic frequencies of the Sicilian sheep population were investigated. It currently represents the best way to determine the genetic identity and/or family even with limited amounts of sample or when the DNA is degraded. The aim of the study was to provide a reference data bank and to evaluate a microsatellite panel for pedigree analysis as suggested by the International Society for Animal Genetics (ISAG). There are various studies on European sheep, but few datasets were developed on the population of Sicilian sheep. The reference d…