Dynamics of climate and ecosystem coupling: abrupt changes and multiple equilibria. (57/740)

Interactions between subunits of the global climate-biosphere system (e.g. atmosphere, ocean, biosphere and cryosphere) often lead to behaviour that is not evident when each subunit is viewed in isolation. This newly evident behaviour is an emergent property of the coupled subsystems. Interactions between thermohaline circulation and climate illustrate one emergent property of coupling ocean and atmospheric circulation. The multiple thermohaline circulation equilibria that result caused abrupt climate changes in the past and may cause abrupt climate changes in the future. Similarly, coupling between the climate system and ecosystem structure and function produces complex behaviour in certain regions. For example, atmosphere-biosphere interactions in the Sahel region of West Africa lead to multiple stable equilibria. Either wet or dry climate equilibria can occur under otherwise identical forcing conditions. The equilibrium reached is dependent on past history (i.e. initial conditions), and relatively small perturbations to either climate or vegetation can cause switching between the two equilibria. Both thermohaline circulation and the climate-vegetation system in the Sahel are prone to abrupt changes that may be irreversible. This complicates the relatively linear view of global changes held in many scientific and policy communities. Emergent properties of coupled socio-natural systems add yet another layer of complexity to the policy debate. As a result, the social and economic consequences of possible global changes are likely to be underestimated in most conventional analyses because these nonlinear, abrupt and irreversible responses are insufficiently considered.  (+info)

Spleen volume varies with colony size and parasite load in a colonial bird. (58/740)

Comparisons across bird species have indicated that those more exposed to parasites and pathogens invest more in immunological defence, as measured by spleen size. We investigated how spleen volume varied with colony size, parasite load and an individual's colony-size history in the cliff swallow, Petrochelidon pyrrhonota, a colonial passerine bird of North America. We used a sample of over 1700 birds that had all died during a period of inclement weather in 1996. We experimentally manipulated ectoparasitism by fumigating nests in some colonies prior to the bad weather. Birds from parasite-free colonies had significantly smaller spleens than those from naturally infested sites; spleen volume did not differ between the sexes and did not vary with age. Mean spleen volume increased significantly with the colony size at a site prior to the bad weather in 1996 and at the site in 1995, both measures of colony size being indices of ectoparasitism at a site. An individual's history of breeding-colony size (defined as the average colony size it had occupied in years prior to 1996) had no association with its spleen size. The results are consistent with parasite-induced splenomegaly whenever birds are exposed to large numbers of ectoparasites. The results do not support spleen size as being a signal of differential life-history investment in immunological defence among individuals and thus run counter to interpretations from recent cross-species comparisons.  (+info)

Betula and Populus pollen counts and meteorological conditions in Szczecin, Poland. (59/740)

The aim of the study was to analyse a relationship between the meteorological conditions and the pollen counts of selected allergenic taxa (Betula spp., Populus spp.) in the air of Szczecin city (north western Poland) in 2001. Apart from the individual rhythm of plant pollination, weather conditions are considered the most important factors determining the dispersion and content of pollen in the air. The meteorological parameters analysed were the minimum, maximum and average values of air temperature, relative humidity, solar radiation and wind speed. The beginning and end of a season were established by the 98 % method. The concentration of birch pollen in the air in 2001 was very high, the pollen season started in the third decade of April and lasted till the 10 May. The highest airborne concentration of 3,712 grains in 1 m(3) per 24 h was noted at the beginning of May on a sunny day with strong wind, and air temperature above 20 degrees C. The concentration of poplar pollen in 2001 was low. The pollen season started from the beginning of April and lasted till the beginning of May. The maximum concentration of airborne poplar pollen of 222 grains in 1 m(3) per 24 h was observed in the third decade of April and was preceded by several days with low temperature (1- 2 degrees C), rain, snowfalls and strong wind. A positive and statistically significant correlation was found between the air temperature and the birch pollen concentration, while a similar but negative correlation was found for poplar pollen.  (+info)

Virtual migration in tethered flying monarch butterflies reveals their orientation mechanisms. (60/740)

A newly developed flight simulator allows monarch butterflies to fly actively for up to several hours in any horizontal direction while their fall migratory flight direction can be continuously recorded. From these data, long segments of virtual flight paths of tethered, flying, migratory monarch butterflies were reconstructed, and by advancing or retarding the butterflies' circadian clocks, we have shown that they possess a time-compensated sun compass. Control monarchs on local time fly approximately southwest, those 6-h time-advanced fly southeast, and 6-h time-delayed butterflies fly in northwesterly directions. Moreover, butterflies flown in the same apparatus under simulated overcast in natural magnetic fields were randomly oriented and did not change direction when magnetic fields were rotated. Therefore, these experiments do not provide any evidence that monarch butterflies use a magnetic compass during migration.  (+info)

Associations of cold temperatures with GP consultations for respiratory and cardiovascular disease amongst the elderly in London. (61/740)

BACKGROUND: The relationships between cold temperatures and cardio-respiratory mortality in the elderly are well documented. We wished to determine whether similar relationships exist with consultations in the primary care setting and to assess the lag time at which the effects were observed. METHODS: Generalized additive models were used to regress time-series of daily numbers of general practitioner (GP) consultations by the elderly against temperature, after control for possible confounders and adjustment for overdispersion and serial correlation. Consultation data were available from between 38 452 and 42 772 registered patients aged >or=65 years from 45-47 London practices contributing to the General Practice Research Database between January 1992 and September 1995. RESULTS: There was little relationship between consultations for respiratory disease and mean temperature on the same day as the day of consultation. However, a strong association was apparent with temperature levels up to 15 days previously, with an increase in consultations being observed particularly as temperatures drop below 5 degrees C. Every 1 degrees C decrease in mean temperatures below 5 degrees C was associated with a 10.5% (95% CI: 7.6%, 13.4%) increase in all respiratory consultations. No relationship was observed between cold temperatures and GP consultations for cardiovascular disease. CONCLUSIONS: Our study suggests a delayed effect of a drop in temperature on consultations for respiratory disease in the primary care setting. Information such as this could be used to help prepare practices to anticipate increases in respiratory consultation rates associated with low temperatures.  (+info)

The role of sea spray in cleansing air pollution over ocean via cloud processes. (62/740)

Particulate air pollution has been shown to strongly suppress precipitation from convective clouds over land. New observations show that precipitation from similar polluted clouds over oceans is much less affected, because large sea salt nuclei override the precipitation suppression effect of the large number of small pollution nuclei. Raindrops initiated by the sea salt grow by collecting small cloud droplets that form on the pollution particles, thereby cleansing the air. Therefore, sea salt helps cleanse the atmosphere of the air pollution via cloud processes. This implies that over oceans, the climatic aerosol indirect effects are significantly smaller than current estimates.  (+info)

The role of parasites in the dynamics of a reindeer population. (63/740)

Even though theoretical models show that parasites may regulate host population densities, few empirical studies have given support to this hypothesis. We present experimental and observational evidence for a host-parasite interaction where the parasite has sufficient impact on host population dynamics for regulation to occur. During a six year study of the Svalbard reindeer and its parasitic gastrointestinal nematode Ostertagia gruehneri we found that anthelminthic treatment in April-May increased the probability of a reindeer having a calf in the next year, compared with untreated controls. However, treatment did not influence the over-winter survival of the reindeer. The annual variation in the degree to which parasites depressed fecundity was positively related to the abundance of O. gruehneri infection the previous October, which in turn was related to host density two years earlier. In addition to the treatment effect, there was a strong negative effect of winter precipitation on the probability of female reindeer having a calf. A simple matrix model was parameterized using estimates from our experimental and observational data. This model shows that the parasite-mediated effect on fecundity was sufficient to regulate reindeer densities around observed host densities.  (+info)

Impact of the El Nino/Southern Oscillation on visceral leishmaniasis, Brazil. (64/740)

We used time-series analysis and linear regression to investigate the relationship between the annual Nino-3 index from 1980 to 1998 and the annual incidence of visceral leishmaniasis (VL) in the State of Bahia, Brazil, during 1985-1999. An increase in VL incidence was observed in the post-El Nino years 1989 (+38.7%) and 1995 (+33.5%). The regression model demonstrates that the previous year's mean Nino-3 index and the temporal trend account for approximately 50% of the variance in the annual incidence of VL in Bahia. The model shows a robust agreement with the real data, as only the influence of El Nino on the cycle of VL was analyzed. The results suggest that this relationship could be used to predict high-risk years for VL and thus help reduce health impact in susceptible regions in Brazil.  (+info)