Search results for "Population"

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 …

Using probability of extinction to evaluate the ecological significance of toxicant effects

2000

A large component of uncertainty in ecological risk assessment (ERA) arises from the disparity between the time scale of toxicity measurements and the time scale of predictions of ERA models. It is difficult to make predictions about the persistence of populations from data from short-term toxicity tests. Reproductive toxicity tests provide data about how population growth rate (r) is reduced with toxicant exposure. Although reduction in r is believed to be one of the most important effects of toxicant exposure, its ecological significance has been difficult to quantify. For rotifers, r is typically reduced by 10 to 15% at no-observed-effect concentrations (NOEC). We investigated r reductio…

2021

The COVID-19 pandemic and social distancing measures targeting the transmission of the virus impacted everyday life in 2020. This study investigated pre- to in-pandemic changes in health behaviors and depressive symptoms during the COVID-19 pandemic and the role of personality traits in these changes in Finland. Data from a larger population-based cohort study of 51–59-year-old Finnish women were used (n = 358). Self-reported questionnaires gathered information about depressive symptoms, eating behavior, physical activity, and alcohol consumption before the pandemic time, at the onset, and at the end of the COVID-19 emergency conditions. Information about personality traits (extraversion an…

Menores inmigrantes no acompañados, las orillas de la vulnerabilidad, estatus de irregulares y su tratamiento al llegar a España

2018

Different migration processes have been carried out in history, which usually travel in conditions of vulnerability and undermine the dignity of people. Therefore, currently, the migration of unaccompanied minors shakes the receiving society; it is a defenseless population group that is exposed to situations of vulnerability. Unaccompanied immigrant minors and in an irregular situation, whether adolescents, girls or boys, are faced with a dream to improve their lives and those of their families that they left in their country; this is a very dangerous journey where, during the crossing, they are condemned to risk situations and adventures, without the support and safety of their families. T…

Loneliness and its relation to mental health in the general population: Validation and norm values of a brief measure

2021

Abstract Background Loneliness has been increasingly recognized as an important determinant of mental health. The purposes of this study were to (1) determine the degree of loneliness of women and men across different age groups, (2) explore its association with distress, (3) psychometrically evaluate the Three-Item Loneliness Scale, (4) provide norm values. Methods The Three-Item Loneliness Scale was applied in a representative survey of the German population (N=2527; 14–95 years). Standardized scales were used measuring distress (depression and anxiety symptoms, perceived stress, hopelessness, suicidal ideation, fatigue, life satisfaction). Factor structure and measurement invariance acro…

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…

Age, lithology and structural evolution of the c. 3.53 Ga Theespruit Formation in the Tjakastad area, southwestern Barberton Greenstone Belt, South A…

2009

Abstract A field and petrographic re-assessment of rocks from the Theespruit Formation near Tjakastad, southwestern Barberton Greenstone Belt, is combined with new zircon U–Pb ages and whole-rock Sm–Nd isotopic results to reveal several important inconsistencies with a previous thrust-accretion model for this area. It was found that faults previously interpreted as ‘thrusts’ are extensional, ‘thrust slices of basement orthogneiss’ are little deformed quartz-feldspar porphyries or sheared felsic volcaniclastic sedimentary rocks, and ‘sedimentary diamictites’ are felsic agglomerates. These observations, combined with consistent facing directions of bedding, the recognition of distinct stratig…