Impact of climatic change on the northern latitude limit and population density of the disease-transmitting European tick Ixodes ricinus.
(25/3450)
We examined whether a reported northward expansion of the geographic distribution limit of the disease-transmitting tick Ixodes ricinus and an increased tick density between the early 1980s and mid-1990s in Sweden was related to climatic changes. The annual number of days with minimum temperatures above vital bioclimatic thresholds for the tick's life-cycle dynamics were related to tick density in both the early 1980s and the mid-1990s in 20 districts in central and northern Sweden. The winters were markedly milder in all of the study areas in the 1990s as compared to the 1980s. Our results indicate that the reported northern shift in the distribution limit of ticks is related to fewer days during the winter seasons with low minimum temperatures, i.e., below -12 degrees C. At high latitudes, low winter temperatures had the clearest impact on tick distribution. Further south, a combination of mild winters (fewer days with minimum temperatures below -7 degrees C) and extended spring and autumn seasons (more days with minimum temperatures from 5 to 8 degrees C) was related to increases in tick density. We conclude that the relatively mild climate of the 1990s in Sweden is probably one of the primary reasons for the observed increase of density and geographic range of I. ricinus ticks. (+info)
Population dynamical consequences of climate change for a small temperate songbird.
(26/3450)
Predicting the effects of an expected climatic change requires estimates and modeling of stochastic factors as well as density-dependent effects in the population dynamics. In a population of a small songbird, the dipper (Cinclus cinclus), environmental stochasticity and density dependence both influenced the population growth rate. About half of the environmental variance was explained by variation in mean winter temperature. Including these results in a stochastic model shows that an expected change in climate will strongly affect the dynamics of the population, leading to a nonlinear increase in the carrying capacity and in the expected mean population size. (+info)
Unanswered questions in ecology.
(27/3450)
This is very much a personal view of what I think are some of the most important unanswered questions in ecology. That is, these are the questions that I expect will be high on the research agenda over the coming century. The list is organized hierarchically, beginning with questions at the level of individual populations, and progressing through interacting populations to entire communities or ecosystems. I will try to guess both at possible advances in basic knowledge and at potential applications. The only thing that is certain about this view of the future is that much of it will surely turn out to be wrong, and many of the most interesting future developments will be quite unforeseen. (+info)
Density-dependent aposematism in the desert locust.
(28/3450)
The ecological processes underlying locust swarm formation are poorly understood. Locust species exhibit phenotypic plasticity in numerous morphological, physiological and behavioural traits as their population density increases. These density-dependent changes are commonly assumed to be adaptations for migration under heterogeneous environmental conditions. Here we demonstrate that density-dependent nymphal colour change in the desert locust Schistocerca gregaria (Orthoptera: Acrididae) results in warning coloration (aposematism) when the population density increases and locusts consume native, toxic host plants. Fringe-toed lizards (Acanthodactylus dumerili (Lacertidae)) developed aversions to high-density-reared (gregarious-phase) locusts fed Hyoscyamus muticus (Solanaceae). Lizards associated both olfactory and visual cues with locust unpalatability, but only gregarious-phase coloration was an effective visual warning signal. The lizards did not associate low rearing density coloration (solitarious phase) with locust toxicity. Predator learning of density-dependent warning coloration results in a marked decrease in predation on locusts and may directly contribute to outbreaks of this notorious pest. (+info)
Malaria prevalence and a brief entomological survey in a village surrounded by rice fields in Khammouan province, Lao PDR.
(29/3450)
We surveyed Nongceng, a village in a south-eastern province of Lao PDR, for malaria and its vectors. Nongceng is situated in a basin and surrounded by rice fields. In February 1998 (dry season), 28.6% of 126 villagers were infected with malaria, and in September 1998 (rainy season), 16.3% of 147 villagers. The prevalence of malaria infection was consistently high in children under 10, and the predominant malaria species was Plasmodium falciparum. In brief surveys of the mosquitoes performed on the same day as the malaria surveys, 2007 Anopheles females from 12 species were collected by means of human bait, animal bait and resting collections. Of the vector species known to be important in transmitting malaria in neighbouring Thailand - An. minimus, An. dirus, and An. maculatus groups - only An. minimus was found. Its density was, however, very low in both seasons and it was therefore unlikely to be the vector. In fact, An. nivipes accounted for more than 65% of all mosquitoes collected and was the most common species collected from human baits. The results of this study show that endemic areas of malaria in Lao PDR are not necessarily related to forest. Rather, An. nivipes is suspected to be the most important vector. (+info)
Environmental injustice in North Carolina's hog industry.
(30/3450)
Rapid growth and the concentration of hog production in North Carolina have raised concerns of a disproportionate impact of pollution and offensive odors on poor and nonwhite communities. We analyzed the location and characteristics of 2,514 intensive hog operations in relation to racial, economic, and water source characteristics of census block groups, neighborhoods with an average of approximately 500 households each. We used Poisson regression to evaluate the extent to which relationships between environmental justice variables and the number of hog operations persisted after consideration of population density. There are 18.9 times as many hog operations in the highest quintile of poverty as compared to the lowest; however, adjustment for population density reduces the excess to 7.2. Hog operations are approximately 5 times as common in the highest three quintiles of the percentage nonwhite population as compared to the lowest, adjusted for population density. The excess of hog operations is greatest in areas with both high poverty and high percentage nonwhites. Operations run by corporate integrators are more concentrated in poor and nonwhite areas than are operations run by independent growers. Most hog operations, which use waste pits that can contaminate groundwater, are located in areas with high dependence on well water for drinking. Disproportionate impacts of intensive hog production on people of color and on the poor may impede improvements in economic and environmental conditions that are needed to address public health in areas which have high disease rates and low access to medical care as compared to other areas of the state. (+info)
A dynamical model of communities and a new species-abundance distribution.
(31/3450)
It is known to many field biologists that biosurveys of natural communities tend to produce a J-shaped curve when the numbers of species are plotted against abundance. In other words, when the number of species of abundance k is plotted against k (running from 1 to some large number), the resulting distribution peaks at the lowest abundance, then forms a concave ramp as it approaches zero at the far end of the abundance axis. Does this distribution represent a single formula operating behind the scenes, or does it represent several formulas, appropriate for different types of community? Or does it represent no particular formula at all? The research reported here has three components: (1) The analysis of a new dynamical system that simulates multispecies communities (producing J-curves in the process) and the derivation of the "logistic-J" distribution, as the underlying community equilibrium curve; (2) the summary of a general theory of sampling as a bridge between natural communities and samples of them; (3) the evaluation of extant proposals for species-abundance distributions by application of a general theory of sampling or by cross-comparison via 100 biosurveys randomly selected from the literature. (+info)
Historical analysis of the development of health care facilities in Kerala State, India.
(32/3450)
Kerala's development experience has been distinguished by the primacy of the social sectors. Traditionally, education and health accounted for the greatest shares of the state government's expenditure. Health sector spending continued to grow even after 1980 when generally the fiscal deficit in the state budget was growing and government was looking for ways to control expenditure. But growth in the number of beds and institutions in the public sector had slowed down by the mid-1980s. From 1986-1996, growth in the private sector surpassed that in the public sector by a wide margin. Public sector spending reveals that in recent years, expansion has been limited to revenue expenditure rather than capital, and salaries at the cost of supplies. Many developments outside health, such as growing literacy, increasing household incomes and population ageing (leading to increased numbers of people with chronic afflictions), probably fueled the demand for health care already created by the increased access to health facilities. Since the government institutions could not grow in number and quality at a rate that would have satisfied this demand, health sector development in Kerala after the mid-1980s has been dominated by the private sector. Expansion in private facilities in health has been closely linked to developments in the government health sector. Public institutions play by far the dominant role in training personnel. They have also sensitized people to the need for timely health interventions and thus helped to create demand. At this point in time, the government must take the lead in quality maintenance and setting of standards. Current legislation, which has brought government health institutions under local government control, can perhaps facilitate this change by helping to improve standards in public institutions. (+info)