High Immigration Rates Research Articles

Source–sink dynamics sustain central stonerollers (Campostoma anomalum) in a heavily urbanized catchment

Summary1. The influence of spatial structure on population dynamics within river–stream networks is poorly understood. Utilizing spatially explicit analyses of temporal genetic variance, we tested whether persistence of central stonerollers (Campostoma anomalum) reflects differences in habitat quality and location within a highly modified urban catchment in southwestern Ohio, U.S.A.2. Estimates of genetic diversity did not vary with habitat quality. Nevertheless, evidence of weak but temporally stable genetic structure, location‐dependent effective population sizes and rates of immigration among sites, together suggest that persistence of central stonerollers within the catchment may be attributable to source–sink dynamics driven by habitat heterogeneity.3. Under this scenario, migrant‐pool colonization from areas of relatively high habitat quality in the upper catchment sustains the presence of central stonerollers at degraded sites in the main stem and dampens population subdivision within the catchment. However, because intact habitat is restricted to the upper portion of the catchment, it is not possible to preclude net downstream dispersal as a mechanism contributing to source–sink dynamics. The slight genetic structure that persists appears to reflect weak isolation by distance diminished by high rates of immigration.4. This study suggests that without a systems perspective of the conditions that sustain populations in degraded waterways, environmental assessments may underestimate levels of impairment. Conservation and management of stream fishes could be improved by maintaining habitat in areas that are net exporters of migrants or by remediation of impaired habitat.

Dermatovenereology in the Post-Communist Era: Syphilis in Prague During 1999 to 2005

This article presents a retrospective case-note review of patients diagnosed and hospitalized with acquired syphilis between January 1999 and December 2005 performed at the two Departments of Dermatovenereology in Prague. The syphilis epidemic in the Czech Republic between 1994 and 2001 now seems to be declining. The high rates of immigration from Eastern Europe, unprotected sex, and prostitution provide the basis for an epidemic of sexually transmitted infections. Early identification of infected individuals and high-risk population groups, adequate treatment, partner notification, and treatment of infected partners therefore is essential.

Assessing the importance of seed immigration on coexistence of plant functional types in a species-rich ecosystem

Modelling and empirical studies have shown that input from the regional seed pool is essential to maintain local species diversity. However, most of these studies have concentrated on simplified, if not neutral, model systems, and focus on a limited subset of species or on aggregated measures of diversity only (e.g., species richness or Shannon diversity). Thus they ignore more complex species interactions and important differences between species. To gain a better understanding of how seed immigration affects community structure at the local scale in real communities we conducted computer simulation experiments based on plant functional types (PFTs) for a species-rich, fire-prone Mediterranean-type shrubland in Western Australia. We developed a spatially explicit simulation model to explore the community dynamics of 38 PFTs, defined by seven traits – regeneration mode, seed production, seed size, maximum crown diameter, drought tolerance, dispersal mode and seed bank type – representing 78 woody species. Model parameterisation is based on published and unpublished data on the population dynamics of shrub species collected over 18 years. Simulation experiments are based on two contrasting seed immigration scenarios: (1) the ‘equal seed input number’ scenario, where the number of immigrant seeds is the same for all PFTs, and (2) the ‘equal seed input mass’ scenario, where the cumulative mass of migrating seeds is the same for all PFTs. Both scenarios were systematically tested and compared for different overall seed input values. Without immigration the local community drifts towards a state with only 13 coexisting PFTs. With increasing immigration rates in terms of overall mass of seeds the simulated number of coexisting PFTs and Shannon diversity quickly approaches values observed in the field. The equal seed mass scenario resulted in a more diverse community than did the seed number scenario. The model successfully approximates the frequency distributions (relative densities) of all individual plant traits except seed size for scenarios associated with equal seed input mass and high immigration rate. However, no scenario satisfactorily approximated the frequency distribution for all traits in combination. Our results show that regional seed input can explain the more aggregated measures of local community structure, and some, but not all, aspects of community composition. This points to the possible importance of other (untested) processes and traits (e.g., dispersal vectors) operating at the local scale. Our modelling framework can readily allow new factors to be systematically investigated, which is a major advantage compared to previous simulation studies, as it allows us to find structurally realistic models, which can address questions pertinent to ecological theory and to conservation management.

The importance of matrix quality in fragmented landscapes: Understanding ecosystem collapse through a combination of deterministic and stochastic forces

Increasing fragmentation of natural landscapes due to anthropogenic forces are changing the ecological structure of many systems. The corpus of literature has addressed the fact that there are many complex mechanisms that may lead to population and ecosystem collapse. Here, we propose an additional mechanism that combines the deterministic framework of complex oscillatory phenomena with the stochastic framework based on the spatial phenomena of island biogeography and metapopulation theory. Combining these two frameworks, which we believe exist in disturbed natural systems, we construct a situation in which collections of competitors are controlled by specialist natural enemies. Species are isolated in fragmented habitats separated by a matrix of decreasing ecological quality, which will determine immigration potential. In this system, species are exposed to stochastic extinction of spatial immigration potential and deterministic extinction of standard oscillatory frameworks. Through the combination of these extinction events, we see that many natural systems may become increasingly unstable and subject to unexpected consequences with changes to the matrix environment. The combined effect of these two extinctions pathways highlights the need to maintain high immigration rates in order to offset possible ecosystem collapse in fragmented systems. The results highlight the importance of landscape conservation efforts, especially towards maintaining matrix environments with greater ecological integrity.

The Impact of Ecology and Biogeography on Legume Diversity, Endemism, and Phylogeny in the Caribbean Region: A New Direction in Historical Biogeography

The legume family is so well represented in the Caribbean that if a preserve was needed somewhere on earth to harbor all of the primary lineages in this family, the flora of just Cuba would suffice. Molecular phylogenetic, biogeographic, and evolutionary rates analysis all suggest that legume diversity and endemism in the Caribbean are mostly of recent origin and are likely a function of the abundance of seasonally dry tropical forests (SDTFs) throughout the neotropics. Legumes have a strong ecological affinity for SDTFs, and the Caribbean basin is well covered by this forest type. Rate-variable molecular clock analysis suggests that the majority of worldwide island lineages of legumes have ages of much less than 30 Ma. Singular historical events invoking land bridges or mobile continental plates are thus not needed to explain Caribbean legume diversity and endemism. The Greater Antilles are large islands located close to the American continent. They are therefore expected to fairly represent the diverse continental lineages of legumes. Yet, they are distant enough to be dispersal limited. As such, island lineages can speciate and diversify over evolutionary time unimpeded by high rates of immigration from the mainland. Vicariance and other standard phylogenetic methods of historical biogeography are likely to be replaced by those of ecological and island biogeography. This is because model selection approaches derived from the neutral concept of isolation by distance will be able to quantify patterns of alpha and beta diversity and detect niche assembly and phylogenetic niche conservatism within and among metacommunities that are hypothesized to constrain phylogeny.

Ivermectina como alternativa terapéutica en neurocisticercosis resistente al tratamiento farmacológico convencional

Neurocysticercosis is a public health problem that can be found in many parts of the world, especially in developing countries, and today's high rates of immigration are making it increasingly more common in developed countries. Cysticidal treatment of neurocysticercosis is a controversial issue because it is only partially effective against vesicular and colloidal-shaped cysts when the parasite persists after a course of albendazole or praziquantel, the only two therapeutic options that are currently available. Ivermectin is a very effective, safe veterinary and human antiparasitic drug, with occasional very mild side effects. It has been used for over 25 years in cases of endoparasitosis that do not respond well to treatment, such as filariasis, oncocerciasis, strongyloidiasis, etc. and also in ectoparasitoses, such as pediculolsis capitis and myasis. It acts in the myoneural junction on the receptors in the chloride channel by increasing their permeability and causing paralysis in adult worms or by a mediated immune mechanism when it acts on immature forms. We report the cases of four patients who were previously treated with albendazole reiteratively with radiological evidence, which shows the persistence of viable vesicular or colloidal-shaped cysts. These patients were given 10 mg/day of ivermectin for 15 consecutive days or 10 mg/day as an average for 30 days, with excellent clinical and radiological progress. Ivermectin was effective and did not give rise to any side effects when used to treat these four patients, who were resistant to conventional treatment with albendazole and/or praziquantel.

The Long and Short of Housing: The Home Ownership Boom and the Subprime Foreclosure Bust

The increasing risks that subprime lenders have been willing to take have culminated in a debacle of rising foreclosures. So far, however, subprime defaults and foreclosures are lower than they were about five years ago, and the problem is likely to be confined to the subprime market, rather than the conventional mortgage market or the US economy. Extensive public and private efforts are being made to mitigate the problem. In addition, despite popular consensus to the contrary, house prices in general have not fallen over the past year, and few markets are experiencing a substantial decline. Lenders and regulators are both taking action to reform subprime lending, and the foreclosure problem is likely to be limited to the 2004-2006 books of business. Meanwhile, there has been a long-term homeownership boom, extending broadly across American society and including minority groups with high immigration rates. This boom has been facilitated by the revolution in information technology, making it possible for lenders to measure risk more accurately, and by the growth of financial literacy initiatives and counseling. For these reasons, the subprime foreclosure problem is likely to be short-term. Looking at individual markets, many areas in Indiana, Michigan and Ohio are having serious problems, though there are some grounds for hope that they will not experience the worst of the subprime debacle.

Genetic reconstruction of the population dynamics of a carnivorous marsupial (Antechinus flavipes) in response to floods

Human activities such as regulating river flows, logging and removing fallen timber adversely affect floodplain ecosystems around the world. Studies of the dynamics of floodplain-dwelling populations will help to understand the effects of altered flood regimes and to manage and restore floodplains. The yellow-footed antechinus (Antechinus flavipes) is the only small, native, carnivorous mammal (Marsupialia) on many degraded floodplains in south-eastern Australia, where its abundance appears to increase with proximity to floods, which is partly due to enhanced survival (as inferred from increased abundance of second-year females). We analysed population genetic patterns and maternity among samples collected following the period of postnatal dispersal, in the years preceding and following planned floods, at different distances from flood locations along the Murray River. Our genic and genotypic analyses of mitochondrial DNA (mtDNA) control region haplotypes and 11 microsatellite loci demonstrated high immigration rates into sites in close proximity to floods. All sampled males emigrated from their natal sites to points of capture, while some females were philopatric. There were high rates of dispersal of males among all sites within a partially flooded forest, while females dispersed more to locations closest to inundations rather than to distant places. These results suggest that environmental flows are beneficial to antechinus both by enhancing adult survival and promoting dispersal of females.

Genetic variation in a network of natural and reintroduced populations of Griffon vulture (Gyps fulvus) in Europe

It is generally considered that limiting the loss of genetic diversity in reintroduced populations is essential to optimize the chances of success of population restoration. Indeed, to counter founder effect in a reintroduced population we should maximize the genetic variability within the founding group but also take into account networks of natural populations in the choice of the reintroduction area. However, assessment of relevant reintroduction strategies requires long-term post-release genetic monitoring. In this study, we analyzed genetic data from a network of native and reintroduced Griffon vulture (Gyps fulvus) populations successfully restored in Southern Europe. Using microsatellite markers, we characterized the level of genetic diversity and degree of genetic structure within and among three native colonies, four captive founding groups and one long-term monitored reintroduced population. We also used Bayesian assignment analysis to examine recent genetic connections between the reintroduced population and the other populations. We aimed to assess the level of fragmentation among native populations, the effectiveness of random choice of founders to retain genetic variability of the species, the loss of genetic diversity in the reintroduced population and the effect of gene flow on this founder effect. Our results indicate that genetic diversity was similar in all populations but we detected signs of recent isolation for one native population. The reintroduced population showed a high immigration rate that limited loss of genetic diversity. Genetic investigations performed in native populations and post-released genetic monitoring have direct implications for founder choice and release design.

Education, race/ethnicity and out-migration from a border city

Through a combination of high immigration rates and differential fertility, communities along the U.S.-Mexico border have become overwhelmingly Hispanic. El Paso, Texas, located across the border from Ciudad Juarez, forms part of the world’s largest urban center on a land border. El Paso ranks among the bottom 10 large U.S. metropolitan areas with the smallest proportion of college-educated adults, causing concerns among policy makers regarding its prospects for economic development. Local discourse suggests that low educational levels result from the out-migration of educated groups that find higher wages or better jobs elsewhere. Two sources of data are used to explore the association between education, race/ethnicity, and out-migration: the five percent 2000 PUMS and a survey conducted among students at the University of Texas at El Paso. We find that between 1995 and 2000 a large net outflow of non-Hispanic whites and blacks of all educational levels took place. Among Mexicans and Mexican Americans, college graduates were more likely to leave compared to high school graduates, but place of birth and language preference influenced these odds. Student data confirmed that non-Hispanics are significantly more likely to plan to leave compared to students of Mexican origin or descent. Among Mexicans and Mexican Americans, those who prefer English and mentioned jobs and lifestyle as the most important factors in choosing a place to live and work were more likely to have plans to leave upon graduation. Policy implications are discussed regarding the future of border communities.

The Political Color Line in America: Many “Peoples of Color” or Black Exceptionalism?

Despite the successes of the civil rights movement, a largely impermeable color line continues to restrict African Americans from assimilation into the broader American society. In the meantime high rates of immigration have produced an increasingly culturally diverse population. A “people of color” hypothesis suggests that the color line the new immigrants face resembles that imposed on African Americans. A “black exceptionalism” hypothesis suggests instead that the color line will be more porous for them, allowing for greater assimilation over successive generations, including a gradual weakening of politicized racial and ethnic group consciousness. Using data from Los Angeles County Social Surveys, we find that the largest new immigrant group, Latinos, like blacks, show strongly group‐interested policy preferences and strong group consciousness. However, both effects are stronger for recent Latino immigrants than for the U.S.‐born. We conclude that the new immigrant groups are increasingly likely to assimilate politically into the broader society in future generations, whereas a rather strict color line will continue to restrict blacks and maintain their distinctiveness.

Acculturation strategies and attitudes according to the Relative Acculturation Extended Model (RAEM): The perspectives of natives versus immigrants

The purpose of this work was to study acculturation of the African immigrant and host populations in an area in the southeast of Spain (Almería), characterized by a high rate of immigration. A new acculturation model, the Relative Acculturation Extended Model, RAEM [Navas, M., Pumares, P., Sánchez, J., García, M. C., Rojas, A. J., Cuadrado, I., & Asensio, M. (2004). Estrategias y actitudes de aculturación: la perspectiva de los inmigrantes y de los autóctonos en Almería. Sevilla: Dirección General de Coordinación de Políticas Migratorias. Consejería de Gobernación. Junta de Andalucía; Navas, M., García, M. C., Sánchez, J., Rojas, A. J., Pumares, P., & Fernández, J. S. (2005). Relative Acculturation Extended Model: New contributions with regard to the study of acculturation. International Journal of Intercultural Relations, 29, 21–37], is used for this. This model differentiates between the real and ideal planes of acculturation, that is, between the strategies that are actually put into practice and attitudes that are preferred. Moreover, the model distinguishes seven spheres, or domains, of acculturation (political, work, economic, social, family, religious and ways of thinking), in which persons (immigrants and natives) adopt and prefer different acculturation options (strategies and attitudes). About 1523 persons (397 Maghrebis, 434 Sub-Saharans, 398 Spaniards who evaluated the Maghreb exogroup and 385 Spaniards who evaluated the Sub-Saharan exogroup), answered a questionnaire made expressly for the study. According to our predictions, immigrants and natives coincide in their choices for acculturation (“assimilation”) in the peripheral domains of the RAEM (work, economic); they also coincide in their acculturation attitudes in the social domain (“integration”); however, they differ enormously in the options preferred for the central spheres, or hard core, of the culture (e.g., family, religious, ways of thinking): While immigrants prefer “separation”, natives continue to prefer “assimilation”. Advantages of the RAEM division into domains of acculturation are discussed with regard to previous models, as well as the implications for predicting inter-group conflict.

IMMIGRATION, ECONOMIC RESTRUCTURING, AND LABOR RUPTURES: FROM THE AMALGAMATED TO CHANGE TO WIN

The 2005 and 1936 “labor ruptures” from the House of Labor occurred under parallel conditions that expressed and reaffirmed the model of universalistic industrial unionism in the U.S. This essay extracts from these parallels a sociological analysis of the recurring configuration of organizational, social, demographic, and economic conditions that have generated the fractious rebirthing of universalistic industrial unionism in the modern U.S. labor movement. The origins of the Amalgamated Clothing Workers of America, Congress of Industrial Organizations, and Change to Win illustrate this rebirthing. The recurring configuration of rebirthing conditions includes high rates of immigration, seismic restructuring of the national economy, the creation of a vulnerable and marginalized segment of the national labor force, heightened identity politics, sharpening income inequality, and a bureaucratized and stalled labor movement struggling to revitalize itself. Under these conditions, both labor ruptures expressed universalistic industrial unionism as a strategy for organizing the most marginalized groups of workers.

Genetic Characterization of Diverse HIV-1 Strains in an Immigrant Population Living in New York City

New York City (NYC) is one of the original foci of the HIV-1 epidemic and has a greater number of AIDS cases than any other city in the United States. NYC also hosts the highest number of immigrants among the nation's cities: more than 2 million among a total population of 8 million. Such a high rate of immigration could act as a potential source for introducing and disseminating novel HIV-1 strains into the United States. Our current study focuses on the genetic characterization of HIV-1 strains circulating in an immigrant population in NYC. Of the 505 HIV-1-positive specimens obtained, 196 were available for viral sequencing from the C2 to V3 region of env. Phylogenetic analysis using maximum-likelihood and neighbor-joining methods demonstrated that non-B subtypes and circulating recombinant forms (CRFs) accounted for 43.4% (85 of 196 cases), whereas the remaining 56.6% (111 of 196) cases had viral variants similar to the typical North American subtype B virus. Of those non-B subtypes and CRFs, subtype A and CRF02 dominated (63.5% combined); other subtypes, including C, D, F1, G, CRF01_AE, and CRF06_cpx, were also detected. Two HIV-1 sequences do not cluster with any known subtypes or CRFs. Furthermore, the distribution of non-B subtypes and CRFs was consistent with the countries of origin, suggesting that many of the study subjects were likely infected in their home country before they entered the United States. Subtype B viruses identified in the immigrant population showed no significant differences from the typical North American B subtype, however, indicating that a significant proportion of the immigrants must have been infected after they came to the United States. Public health officials and physicians should be aware of the growing genetic diversity of HIV-1 in this country, particularly in areas with sizable immigrant populations.

Cost-Effective Strategies for the Sustained Control of Bait-Shy Vertebrate Pests in New Zealand

The brushtail possum is a significant conservation pest and major vector of bovine tuberculosis in New Zealand. Previous control simulation studies have suggested that aerial control with bait containing sodium monofluoroacetate (1080) is the most cost-effective large-scale possum control strategy. However, there is a growing awareness that the survivors of 1080 control can develop ‘bait shyness’, and this can markedly alter the efficacy of ongoing 1080 control operations. Several alternative toxicants are registered for possum control but all are ground based, differ in their mode of action, and are more expensive than aerial 1080 control. A new possum control simulation model was developed to assist in identifying the most cost-effective control strategy that would achieve a sustained 80% population reduction, given bait-shy behaviour and immigration from adjacent non-controlled areas. The simulation results indicated that it is possible to achieve a sustained 80% population reduction (over a 10-year period) using a 1080-based control strategy, provided at least 90% of all ‘susceptible’ possums are killed in each control operation. In the event of an unsuccessful 1080 control operation (i.e., only a 60% kill), cyanide bait plus trapping, or brodifacoum bait provided the most cost-effective strategy of ‘mopping up’ 1080 bait-shy survivors. However, sufficient numbers of traps must accompany the cyanide bait to ensure that the majority of 1080 bait-shy possums are targeted. Sensitivity analysis indicated that the most important variable influencing the overall success of any control strategies was the rate of re-colonization following control. With the high rates of immigration that are sometimes observed in small forest reserves (i.e., <100 ha), it was not possible to sustain an 80% population reduction using any combination of toxicants. However, higher rates of immigration are probably exceptional and the rate used in these simulations is considered more typical, particularly for moderate-to-large forest stands where most possum control is conducted.

Inbreeding from isonymy and repeated pairs of surnames in the Ebro Delta region (Tarragona, Spain)

The aim of the study was to evaluate the levels of inbreeding calculated from isonymy with its random (Fr) and nonrandom (Fn) components, and repeated pairs of surnames (RP2) and their random component (RP2r) in the Ebro River Delta region (Tarragona, Spain). This region is made up of four parishes, and data correspond to the period 1939-1995. The global results are on the same levels as observed in other studies, but the values obtained in 3 of 4 parishes are relatively high. The Fn global value is higher than Fr, as opposed to what happens in each parish, so there is a clear Wahlund effect of subdivision of the region into parishes. Among the parishes there is a clear differentiation for Amposta, with values much lower than for the rest, due to the behavior of this population, i.e., a high immigration rate.

Assortative mating and differential male mating success in an ash hybrid zone population

BackgroundThe structure and evolution of hybrid zones depend mainly on the relative importance of dispersal and local adaptation, and on the strength of assortative mating. Here, we study the influence of dispersal, temporal isolation, variability in phenotypic traits and parasite attacks on the male mating success of two parental species and hybrids by real-time pollen flow analysis. We focus on a hybrid zone population between the two closely related ash species Fraxinus excelsior L. (common ash) and F. angustifolia Vahl (narrow-leaved ash), which is composed of individuals of the two species and several hybrid types. This population is structured by flowering time: the F. excelsior individuals flower later than the F. angustifolia individuals, and the hybrid types flower in-between. Hybrids are scattered throughout the population, suggesting favorable conditions for their local adaptation. We estimate jointly the best-fitting dispersal kernel, the differences in male fecundity due to variation in phenotypic traits and level of parasite attack, and the strength of assortative mating due to differences in flowering phenology. In addition, we assess the effect of accounting for genotyping error on these estimations.ResultsWe detected a very high pollen immigration rate and a fat-tailed dispersal kernel, counter-balanced by slight phenological assortative mating and short-distance pollen dispersal. Early intermediate flowering hybrids, which had the highest male mating success, showed optimal sex allocation and increased selfing rates. We detected asymmetry of gene flow, with early flowering trees participating more as pollen donors than late flowering trees.ConclusionThis study provides striking evidence that long-distance gene flow alone is not sufficient to counter-act the effects of assortative mating and selfing. Phenological assortative mating and short-distance dispersal can create temporal and spatial structuring that appears to maintain this hybrid population. The asymmetry of gene flow, with higher fertility and increased selfing, can potentially confer a selective advantage to early flowering hybrids in the zone. In the event of climate change, hybridization may provide a means for F. angustifolia to further extend its range at the expense of F. excelsior.

A Church-Based Sampling Design for Research with Latina Immigrant Women

The U.S. is experiencing its highest immigration rate since the 1930s. The largest proportion of immigrants comes from Latin America, and women constitute a large and growing fraction of this group. Although our knowledge of the relationship between migration and women’s health is increasing, research in this area is still needed, particularly in areas experiencing rapid changes in their Latino populations. Yet research is impeded by the absence of an adequate sampling frame: Latina immigrants remain a largely hidden population. This study tests in four North Carolina counties a church-based sampling frame for Latina immigrant women in their reproductive years. In the study area, on an average week, 20% of the Spanish-speaking population attends church (two-thirds are Catholic). Compared against Census data for the study area, the study sample (n = 706) provided a comparable representation of different national origins. New entrants to the U.S. and married women were overrepresented in the church-based sample. The young (under age 30), and women at the lowest and highest extremes of educational attainment were underrepresented in churches. While a church-based sample is not entirely comparable to the Census, churches can provide timely and cost-effective access to a rapidly changing population of new immigrants. Church-based research should be complemented with research in other settings, adjusting sampling weights for overlap between sampling frames.

Interactions between environmental variability and immigration rate control patterns of species diversity

Theories focussing on local competition processes predict that species diversity is maximised with high-frequency environmental variability or alternatively with intermediate frequencies. The models coupling regional processes to local explanations of diversity patterns predict that the immigration rate from a regional species pool can strongly increase diversity. However, the interaction between local and regional processes in temporally fluctuating environment has received little attention. We explored in a simulation study how the patterns of species diversity are affected by the frequency spectrum of stochastic environmental variations and density independent immigration rate in a competition model. Environmental variations were assumed to affect the growth rate of competing species. The growth rate of a species had a unimodal response to a continuous environmental variable, such as salinity and temperature. The location of optimum and breadth of the growth response in the environmental niche axis is treated as a species-dependent trait. Consequently, environmental variations can affect competitive ranking of the species. Decreasing the frequency of environmental variations produced monotonically decreasing or unimodal “intermediate disturbance type” diversity patterns in the competition model. The level of diversity and type of the pattern was determined by immigration rate, and the number and traits of the species initially placed along the environmental niche axis. Immigration generally increased diversity, but the amount of increase in intermediate immigration rates was strongly modified by the frequency spectrum of the environmental variation. Decreasing the frequency of the environmental variation always produced a monotonically decreasing diversity pattern in a two-species system where the growth optima are positioned symmetrically around the mode of the environmental noise. However, increasing the species number and asymmetry of optima makes the diversity pattern sensitive to immigration rate: diversity can be very low and unaffected by the frequency of environmental variation in the absence of immigration, peak in low-frequency environment with small immigration rate (i.e. produce the IDH type pattern), or decrease monotonically with high immigration rate. Diversity is most sensitive to small changes in the initial species number and position of the species growth optima when environmental fluctuations have high frequency. That immigration can change the impact of the frequency of the environmental variation on diversity from monotonically decreasing to unimodal (IDH type) pattern emphasizes that the regional process can be important for explanations of the diversity patterns, especially when the immigration rates are uncorrelated to the local conditions. The strong interactions between community properties, immigration rate, and the spectrum of environmental variation suggest that small changes in community properties or in dispersal rates can have a large impact on species diversity.

Neurocysticercosis

Neurocysticercosis is the most common helminthic disease of the nervous system and currently represents a major public health problem in developing countries of Latin America, Asia, and Africa, as well as in industrialized nations with a high immigration rate of people from endemic areas. The disease occurs when humans become the intermediate host in the life cycle of Taenia solium by ingesting its eggs from contaminated food. Neurocysticercosis is pleomorphic in its presentation due to individual differences in the number, size, and location of the parasites, as well as differences in the severity of the host's immune reaction to the parasite. Epilepsy, focal neurological signs, and intracranial hypertension are the most common clinical manifestations of the disease. The diagnosis of neurocysticercosis is based on clinical data, neuroimaging abnormalities, and the results of immunological tests. Two drugs, albendazole and praziquantel, are cysticidal and destroy most intracranial parasites; however, surgery may be necessary in the management of some forms of the disease, particularly hydrocephalus and intraventricular cysts. Although the development of modern diagnostic tests and the introduction of potent cestocidal drugs have increased our ability to make the diagnosis of neurocysticercosis and improved prognosis, some patients still have a torpid clinical course despite prompt diagnosis and proper therapy.