Search results for "Population"
showing 10 items of 9945 documents
Consequences of correlations between habitat modifications and negative impact of climate change for regional species survival
2011
Abstract While several empirical and theoretical studies have clearly shown the negative effects of climate or landscape changes on population and species survival only few of them addressed combined and correlated consequences of these key environmental drivers. This also includes positive landscape changes such as active habitat management and restoration to buffer the negative effects of deteriorating climatic conditions. In this study, we apply a conceptual spatial modelling approach based on functional types to explore the effects of both positive and negative correlations between changes in habitat and climate conditions on the survival of spatially structured populations. We test the…
Analysis of gene flow and habitat patch network for Chazara briseis (Lepidoptera: Satyridae) in an agricultural landscape
1997
Abstract A fine geographic-scale population genetic structure analysis was performed for the endangered butterfly species Chazara briseis in the region of Halle an der Saale, Germany, for the investigation of gene flow and possible effects of habitat fragmentation on genetic variability. Patterns of genetic variance were estimated by allozyme electrophoresis and quantified with F -statistics. Levels of genetic variation were high, expected heterozygosity H e = 0.20, and mean number of alleles per locus, A = 1.93, indicating large population sizes. Butterflies inhabiting the study area probably constituted just one population and the fragmented nature of the habitat patches did not substanti…
Effects of fragmented breeding habitat and resource distribution on behavior and survival of the bank vole ( Myodes glareolus )
2010
Habitat fragmentation causes negative population trends or even local extinction in many species. Understanding the role of fragmentation on behavior and space use of animals is an essential part of revealing the mechanism behind observed population declines. We studied experimentally the effects of small-scale habitat fragmentation on the distribution and movement of bank voles (Myodes glareolus) in seminatural enclosures. We predicted that besides habitat structure, availability of two resources, food for both sexes, and receptive females for males, determine individual distribution. We manipulated female density (either 0, 4, or 12 per enclosure) and followed movements of radio-collared …
Changing female spacing behaviour and demography in an enclosed breeding population of Clethrionomys glareolus
1988
The social organization of Clethrionomys glareolus Schreber was studied by live trapping in an enclosure of 0.8 ha in Central Finland between the years 1982–1986. The enclosure consisted of three habitats: abandoned field, brushwood, and moist spruce heath forest. The population density increased from 50 voles ha−1 in 1982 and 1983 to 150 ha−1 in 1984 and 1985. In the summer of 1986 the population crashed to almost zero. In the summer of 1984 after winter breeding the number of breeding females grew to 22 compared with 6–7 in previous years. In 1984 the mature females changed from territorial to group behaviour. During the high population density in 1984 and 1985 breeding stopped already in…
Mixis strategies and resting eeg production of rotifers living in temporally-varying habitats
1993
A dynamic model based on six differential equations has been developed to explore the control of mixis of rotifers living in temporally-varying habitats. The equations give variation rates of amictic females, three stages of mictic females, males and resting eggs. The model takes into account some constraints on mixis (e.g., male-female encounter probability and effort involved in resting egg production) and its predictions have been generated by computer simulation using parameter values from the literature. For simulation, a time-dependent birth rate function was assumed to account for changes in the environment, and several mixis patterns (i.e., moment of mixis induction and mictic rate …
Experimental assessment of the fecundity of Eucypris virens (Ostracoda, Crustacea) under natural sex ratios
2007
Summary 1. The adaptive significance of the observed variations in sex ratios in non-marine ostracods is unclear. This study quantified the fecundity of females taken from a presumed fully sexual Eucypris virens population that were experimentally combined with different proportions of males (male : female sex ratios: 1 : 1, 1 : 2, 1 : 4, 1 : 8 and 0 : 1). 2. The results yielded no indications that female fecundity is altered by short-term variations in the proportion of males, at least not within the range of sex ratios that are common in natural ostracod populations. Complete removal of males, however, did strongly reduce hatching success of dried eggs. This suggests the need for multiple…
Running against time: conservation of the remaining hawksbill turtle (Eretmochelys imbricata) nesting population in the Dominican Republic
2012
Saona Island hosts the last hawksbill turtle (Eretmochelys imbricata) nesting population in the Dominican Republic, which has experienced a severe decline in the last decades, mostly due to illegal egg take. Here we present the results of an artificial incubation programme started in 2007 to protect the clutches from human predation. A preliminary survey in 2006 showed that about 60% of clutches laid were taken by humans. Over the study period (2007–2010) we recorded 400 clutches, of which 38.2% were predated by humans, 40.7% were artificially incubated and 21% were incubated in situ. Overall, the artificial incubation programme allowed the release of 12,340 hatchlings. No differences were …
Mental States of Addiction
2015
An increasing number of studies have examined lay meanings of addiction. The purpose of this study was to explore whether a generalized conception of an addiction mind-set was evident in the beliefs of a sample of 1,062 Norwegian adults responding to an online survey. The respondents were given a rating task in the following form: “Addiction to [substance/behavior] is/represents [descriptive term].” For each of the nine different addictive behaviors (cocaine, cannabis, alcohol, gambling, smoking, amphetamine, sedatives, snus, and heroin), the respondents rated their endorsement of 11 descriptive terms (mental states): reduced self-determination, obsession, strong urge, strong appetite, stro…
Diferencias entre empleabilidad, inseguridad laboral y salud en trabajadores y desempleados
2018
ResumenEl desempleo y la inseguridad laboral tienen efectos negativos sobre la salud, aunque la empleabilidad podría mediar dichos efectos. El presente artículo tiene como objetivo analizar las posibles diferencias entre trabajadores y desempleados en empleabilidad y variables de salud psicosocial, así como explorar el papel de la empleabilidad y la inseguridad laboral en la salud psicosocial. Para esto, se utilizó metodología cuasiexperimental, donde se administraron una serie de cuestionarios que evaluaban empleabilidad e inseguridad laboral a 97 trabajadores (35 desempleados y 62 en activo), junto a otras variables psicosociales y de salud. Los resultados muestran que la empleabilidad es…
Parasites as indicators of social structure and stock identity of marine mammals
1995
Abstract Introduction: the use of parasites as biological indicators of marine mammals has not yet received all the necessary attention. The aim of this review is to show the value of parasite data in studies of stock identity and social structure. Methods: the application of the technique to marine mammals is hampered by the lack of control over sampling conditions and the paucity of information about the biology of their parasites. Relevant criteria for, suitable parasite tags are discussed. Case studies: previous work on marine mammals is presented to illustrate the usefulness and limitations of parasite data. A study of pilot whales revealed that differences in helminth infections betwe…