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PubMed2005

Reproduction, foraging and the negative density-area relationship of a generalist rodent.

While many species show positive relationships between population density and habitat patch area, some species consistently show higher densities in smaller patches. Few studies have examined mechanisms that may cause species to have negative density-area relationships. We tested the hypothesis that greater reproduction in edge versus interior habitats and small versus large fragments contributes to higher densities of white-footed mice (Peromyscus leucopus) in small versus large forest fragments. We also examined vegetation structure and foraging tray utilization to evaluate if greater reproduction was a result of higher food availability. There were greater number of litters and proportion of females producing litters in the edge versus interior of forest fragments, which may have contributed to greater population growth rates and higher densities in edge versus interior and small versus large fragments. Data on vegetation structure and giving-up densities of seeds in artificial patches suggest that food availability may be higher in edge versus interior habitats and small versus large fragments. These results, in an area with few or no long-tailed weasels, provide a distinct contrast to the findings of Morris and Davidson (Ecology 81:2061, 2000) who observed lower reproduction in forest edge habitat as a result of high weasel predation, suggesting that specialist predators may be important in affecting the quality of edge habitat. While we cannot exclude the potential contributions of immigration, emigration, and mortality, our data suggest that greater reproduction in edge versus interior habitat is an important factor contributing to higher densities of P. leucopus in small fragments.

Analysis of Variance↗
PubMed2003

Metapopulation-level adaptation of insect host plant preference and extinction-colonization dynamics in heterogeneous landscapes.

Species living in highly fragmented landscapes typically occur as metapopulations with frequent turnover of local populations. The turnover rate depends on population sizes and connectivities, but it may also depend on the phenotypic and genotypic composition of populations. The Glanville fritillary butterfly (Melitaea cinxia) in Finland uses two host plant species, which show variation in their relative abundances at two spatial scales: locally among individual habitat patches and regionally among networks of patches. Female butterflies in turn exhibit spatial variation in genetically determined host plant preference within and among patch networks. Emigration, immigration and establishment of new populations have all been shown to be strongly influenced by the match between the host plant composition of otherwise suitable habitat patches and the host plant preference of migrating butterflies. The evolutionary consequences of such biased migration and colonization with respect to butterfly phenotypes might differ depending on spatial configuration and plant species composition of the patches in heterogeneous patch networks. Using a spatially realistic individual-based model we show that the model-predicted evolution of host plant preference due to biased migration explains a significant amount of the observed variation in host plant use among metapopulations living in dissimilar networks. This example illustrates how the ecological extinction-colonization dynamics may be linked with the evolutionary dynamics of life history traits in metapopulations.

Adaptation, Physiological↗
PubMed2000

Do herbivore-induced plant volatiles influence predator migration and local dynamics of herbivorous and predatory mites?

If predators lack information on the prey's position, prey have more chance to escape predation and will therefore reach higher population densities. One of the many possible cues that predators may use to find their prey are herbivore-induced plant volatiles. Although their effects on the behaviour of foraging predators have been well studied, little is known about how these prey-related odours affect predator-prey dynamics on a plant. We hypothesise that herbivore-induced plant volatiles provide the major cue eliciting predator arrestment on prey-infested leaves and that the response to these volatiles ultimately leads to lower prey densities. To test this hypothesis experimentally, we created two types of odour-saturated environments: one with herbivore-induced plant volatiles (treatment), and one with green-leaf volatiles (control). An odour-free environment could not be tested because herbivores require plants for population growth. We measured the rate at which predatory mites (Phytoseiulus persimilis) immigrate, emigrate and exploit a single leaf infested by two-spotted spider mites (Tetranychus urticae). The experiments did not show a significant difference between treatment and control. At best, there was a somewhat higher rate of predator (and possibly also prey) emigration in the treatment. The lack of a pronounced difference between treatment and control indicates that at the spatial scale of the experiments random searching for prey was as effective as directional searching. Alternatively, predators were arrested in the prey patch by responding not merely to herbivore-induced plant volatiles, but also to other prey-related cues, such as web and faeces. Based on our current experience we advocate to increase the spatial scale of the experiment (> 1 m2) and we provide other suggestions for improving the set-up.

Animals↗
PubMed2003

Influence of spatial structure on genetic isolation in Plebejus argus populations (Lepidoptera: Lycaenidae).

Populations of Plebejus argus were sampled in southwest Finland, both on the mainland and on islands, and in and around the Doñana National Park in southwest Spain. A total of 453 individuals coming from 14 locations were investigated using allozyme electrophoresis on a total of 10 polymorphic allozyme loci. Contrary to earlier studies, all conducted in Britain, our samples showed little differentiation between sampled locations. In Spain, the populations of the Donaña area showed no differentiation despite being up to 36 km apart; only the population to the south of the Guadalquivir river showed a significant difference to the others. In Finland the population on one island showed marked genetic differentiation from all the others, which showed little or no difference from each other. No isolation-by-distance effect could be detected in either system. We hypothesise that emigration-immigration events are more frequent in the Spanish and Finnish populations than in the British ones. We did, however, find two isolated populations, one in Spain and one in Finland; both were small and geographically isolated and shared evident drift.

Animals↗
PubMed1990

[Accuracy of forecasts of annual numbers based on monthly numbers].

"Since 1985 monthly forecasts have been made of yearly numbers of births, deaths, immigration, emigration and marriages [in the Netherlands] on the basis of monthly figures. The forecasts are equal to the arithmetic average of an ARIMA projection and a naive forecast.... This article compares the forecasts for the years 1985-1989 with forecasts obtained from a simple alternative method." (SUMMARY IN ENG)

Developed Countries↗
PubMed2002

Long-term persistence of species and the SLOSS problem.

The single large or several small (SLOSS) problem has been addressed in a large number of empirical and theoretical studies, but no coherent conclusion has yet been reached. Here I study the SLOSS problem in the context of metapopulation dynamics. I assume that there is a fixed total amount A(0) of habitat available, and I derive formulas for the optimal number n and area A of habitat patches, where n=A(0)/A. I consider optimality in two ways. First, I attempt to maximize the time to metapopulation extinction, which is a relevant measure for metapopulation viability for rare and threatened species. Second, I attempt to maximize the metapopulation capacity of the habitat patch network, which corresponds both with maximizing the distance to the deterministic extinction threshold and with maximizing the fraction of occupied patches. I show that in the typical case, a small number of large patches maximizes the metapopulation capacity, while an intermediate number of habitat patches maximizes the time to extinction. The main conclusion stemming from the analysis is that the optimal number of patches is largely affected by the relationship between habitat patch area and rates of immigration, emigration and local extinction. Here this relationship is summarized by a single factor zeta, termed the patch area scaling factor.

Animals↗
PubMed1993

[The diagnosis of malaria by the thick film and the QBC: a comparative study of both technics].

BACKGROUND: The diagnosis of paludism is important because of the severity of the clinical picture caused by Plasmodium falciparum, the increasing number of travellers to endemic zones and the emigration from these zones. A comparative study of the QBC techniques (staining with acridin orange and observation with ultraviolet light) and the thick film with Giemsa staining was carried out. METHODS: The QBC and thick film were performed parallelly for 17 months in a total of 623 samples pertaining to subjects from endemic zones of paludism (emigrants, immigrants and travellers). RESULTS: Of the 623 samples studied 49 were positive for paludism by both techniques. Ten were positive with only the thick film and six were positive only with QBC. The sensitivity of QBC versus thick film was 83% and specificity 98.9%. The time used to determine diagnosis with the QBC technique ranged from 6 to 12 minutes from withdrawal of the sample, while with the thick film the time spent was more than 2 hours. The cases positive by thick film and negative with QBC corresponded to patients with very low parasitation. The intensity of parasitation was difficult to determine quantitatively by QBC. CONCLUSIONS: Although the QBC technique has the advantage of speed it is inexact with respect to the quantification of parasitemia. Moreover, it is less sensitive than the thick film in patient with very low parasitations and cannot thus substitute the thick film.

Africa↗
PubMed1992

[Experiences in family therapy with immigrants].

By emigrating, the foreigner has to meet with various expectations and therefore stands under pressure. On one hand, his decision is closely linked to his wish for new achievements and prosperity--his relatives and friends attentively watch over him to make sure that he succeeds. On the other hand, the new environment requires him to adapt to new ways of thinking and behaving. His own values are neither followed anymore nor considered as general guideline through everyday life. In a relatively short time, therefore, the emigrant has to make the strenuous effort to change his views, even if it involves neglecting old family traditions. For the emigrant these demands are often too excessive, so that he becomes insecure and sceptical, finally desperately but subconsciously clinging to his traditional values. Furthermore, he might feel to be surrounded by enemies. All that makes the integration become sluggish if not impossible. Mechanisms of thought and behaviour such as these, are the starting point in family therapy with emigrants. The goal is to make the foreigner more aware of his life in emigration. The experience acquired in family therapy is certainly useful in the rehabilitation of foreign workers who have fallen victim to an accident or an illness.

Acculturation↗
PubMed2005

The "emigration, migration, and immigration"of prostate cancer.

In the vast majority of cases, cancer continues to be an incurable disease when it has spread beyond the primary organ. Most cancer research and therapy design to date has focused on chemotherapy directed at killing the replicating tumor cells. Little attention has been placed on targeting the microenvironments of the primary tumor site, the circulating tumor cells, or the metastatic or secondary (target) tumor site and how cancer cells move among them. To develop these targets, a better understanding of metastasis and the mechanisms underlying the spread of tumors is required. This review describes the steps of metastasis using a paradigm of emigration to migration to immigration, with prostate cancer as a model system.

Cell Movement↗
PubMed1965

MEDICAL ASPECTS OF THE WESTWARD MIGRATIONS, 1830-60.

The exodus to the West which occurred in 1830-60, partly due to the discovery of gold in California in 1849, is examined from a medicohistorical viewpoint. The motivations of the emigrants, their medical emergencies, problems, and practices, and the state of the medical arts in the Western settlements are discussed in terms of the prevailing systems of therapeutics, the availability of supplies and equipment, and the presence or absence of professional doctors.

California↗
PubMed1995

[Mexico and Japanese emigrants].

"Japanese immigration to Mexico began in the last decade of the 19th century with a coffee growing project, and proved a failure. Subsequent attempts [at] sending contract labor migrants by emigration agencies, which involved 10,000 Japanese emigrants in 1901-1908, were also unsuccessful, and Mexico turned for Japanese emigrants into a short step on their way to the United States. The evolution of those who remained in Mexico and the different developments of the Japanese communities in Mexico [are] analyzed here until the period after World War II." (SUMMARY IN ENG)

Americas↗