Invading parasites cause a structural shift in red fox dynamics.
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The influence of parasites on host life histories and populations is pronounced. Among several diseases affecting animal populations throughout the world, sarcoptic mange has influenced many carnivore populations dramatically and during the latest epizootic in Fennoscandia reduced the abundance of red fox by over 70%. While the numerical responses of red fox populations, their prey and their competitors as well as clinical implications are well known, knowledge of how sarcoptic mange affects the structure of the dynamics of red fox populations is lacking. Integrating ecological theory and statistical modelling, we analysed the long-term dynamics (1955-1996) of 14 Danish red fox populations. As suggested by the model, invading sarcoptic mange significantly affected direct and delayed density dependence in red fox dynamics and concomitant shifts in fluctuation patterns were observed. Our statistical analyses also revealed that the spatial progressive spread of mange mites was mirrored in the autocovariate structures of red fox populations progressively exposed to sarcoptic mange. (+info)
Habitat loss and raptor predation: disentangling long- and short-term causes of red grouse declines.
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The number of red grouse (Lagopus lagopus scoticus) shot in the UK has declined by 50% during the 20th century This decline has coincided with reductions in the area of suitable habitat and recoveries in the populations of some avian predators. Here we use long-term records of shooting bags and a large-scale manipulation of raptor density to disentangle the effects of habitat loss and raptor predation on grouse populations. The numbers of grouse harvested on the Eskdale half of Langholm Moor in southern Scotland declined significantly during 1913-1990 and grouse bags from the whole moor from 1950 to 1990 exhibited an almost identical but non-significant trend. Hen harriers (Circus cyaneus) and peregrine falcons (Falco peregrinus) were absent or bred at low densities on this moor throughout this period but heather-dominant vegetation declined by 48% between 1948 and 1988. Harrier and peregrine breeding numbers on Langholm Moor increased to high levels following protection in 1990 whilst grouse density and grouse bags declined year after year until shooting was abandoned in 1998. The prediction of a peak in grouse bags on Langholm Moor in 1996 based on the patterns of bags during 1950-1990 was supported by the observed peaks in 1997 on two nearby moors with few raptors which formerly cycled in synchrony with Langholm Moor. This study demonstrates that, whilst long-term declines in grouse bags were most probably due to habitat loss, high levels of raptor predation subsequently limited the grouse population and suppressed a cycle. This study thus offers support to theoretical models which predict that generalist predators may suppress cycles in prey populations. (+info)
Population structure and population history of Anopheles dirus mosquitoes in Southeast Asia.
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Separating the confounding effects of long-term population history from gene flow can be difficult. Here, we address the question of what inferences about gene flow can be made from mitochondrial sequence data in three closely related species of mosquitoes, Anopheles dirus species A, C, and D, from southeast Asia. A total of 84 sequences of 923 bp of the mitochondrial cytochrome oxidase I gene were obtained from 14 populations in Thailand, Myanmar, and Bangladesh. The genealogy of sequences obtained from two populations of AN: dirus C indicates no contemporary gene flow between them. The F(ST) value of 0.421 therefore probably represents a recent common history, perhaps involving colonization events. Anopheles dirus A and D are parapatric, yet no differentiation was seen either within or between species. The starlike genealogy of their haplotypes, smooth unimodal mismatch distributions, and excess of low frequency mutations indicate population expansion in An. dirus A and D. This, rather than widespread gene flow, explains their low within-species F(ST) values (0.018 and 0.022). The greater genetic diversity of An. dirus D suggests that expansion occurred first in species D and subsequently in species A. The current geographical separation and low hybrid fitness of these species also argue against ongoing interspecific gene flow. They suggest instead either historical introgression of mtDNA from An. dirus D into species A followed by independent range expansions, or a selective sweep of mtDNA that originated in An. dirus D. While not excluding contemporary gene flow, historical population processes are sufficient to explain the data in An. dirus A and D. The genealogical relationships between haplotypes could not be used to make inferences of gene flow because of extensive homoplasy due to hypervariable sites and possibly also recombination. However, it is concluded that this approach, rather than the use of fixation indices, is required in the future to understand contemporary gene flow in these mosquitoes. The implications of these results for understanding gene flow in another important and comparable group of malaria vector mosquitoes in Africa, the An. gambiae complex, are also discussed. (+info)
The biology, behaviour, and ecology of Mastomys natalensis in southern Africa.
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The multimammate mouse, Mastomys natalensis, is the most widespread and common rodent in Africa south of the Sahara. It is an ideal carrier of normally non-human diseases to the domestic environment, not only because of its semi-commensal habit but also because of a combination of other behavioural and ecological factors. Of these, the most important is an exceptionally high propagation rate. (+info)
Evaluation of demographic parameters of native rodent populations and implications for control.
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The ecology of the multimammate mouse ,Mastomys natalensis, is reviewed and approximations are derived for the parameters governing population growth. By means of computer simulation, the relative importance of the timing of reproduction, the age class distribution or age structure of the population, the competition between Mastomys and Rattus, and the interaction with a predator are evaluated. Although each of these demographic or ecological factors modifies the fate of the Mastomys population, the greatest single impact results from a reproductive season that is divided into two parts rather than a single continuous reproductive season. Division into two parts, correlated with a similar distribution of rainfall, allows time for maturing of the young born early in the season and for production of young by them, thus adding to the momentum of population increase. The interaction of density-dependent factors controlling population growth, competition with another rodent, or predation by a Viverrid predator, may increase the growth rate of the Mastomys population or may depress population growth rate, even to the point of extinction. These simulation studies demonstrate the necessity for critical evaluation of the demographic parameters and ecological characteristics of a particular Mastomys population before an effective control programme can be designed. They also demonstrate, however, that if the programme is based upon sound ecological theory control can be effected. (+info)
Impacts of a global climate cycle on population dynamics of a migratory songbird.
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Progress toward understanding factors that limit abundances of migratory birds, including climate change, has been difficult because these species move between diverse locations, often on different continents. For black-throated blue warblers (Dendroica caerulescens), demographic rates in both tropical winter quarters and north temperate breeding grounds varied with fluctuations in the El Nino Southern Oscillation. Adult survival and fecundity were lower in El Nino years and higher in La Nina years. Fecundity, in turn, was positively correlated with subsequent recruitment of new individuals into winter and breeding populations. These findings demonstrate that migratory birds can be affected by shifts in global climate patterns and emphasize the need to know how events throughout the annual cycle interact to determine population size. (+info)
Myxobolus cerebralis infection in rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) exposed under natural stream conditions.
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From early April into mid-June 1977, sequential groups of juvenile rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) were each exposed for 10 days to the parasite Myxobolus cerebralis by immersion in a stream inhabited by infected wild trout. Following incubation in a M. cerebralis-free facility, trout were subsequently killed, and heads and gill arches were examined by routine histologic methods. A grading scale to quantify lesion severity was developed and applied. Percentage infected, lesion severity scores, effects of water temperature and flow rates on percentage infected and lesion severity scores, and resulting pathology were determined for each species at each exposure period. The percentage of rainbow trout infected with M. cerebralis was significantly higher than the percentage of brown trout infected for each exposure period. The percentages of rainbow trout infected in exposure periods later in the calendar year were significantly higher than those in earlier periods. The percentages of brown trout infected were not significantly different among exposure periods. Overall average lesion severity scores were significantly higher in rainbow than in brown trout. Lesion severity scores in rainbow trout increased over time (a positive correlation with exposure period). Lesion severity scores were not significantly different for brown trout among exposure periods. A significant correlation existed between water temperature and percentage of rainbow trout infected; a significant correlation also existed between water temperature and lesion severity scores in rainbow trout. Similar correlations did not exist for percentage of brown trout infected or accompanying lesion severity scores. In rainbow trout, ventral calvarium was the most common site of M. cerebralis replication, followed by gill arches. In brown trout, lesions were virtually confined to gill arches. Early lesions consisted of foci of cartilage necrosis with small numbers of M. cerebralis developmental stages. More advanced lesions consisted of multifocal areas of cartilage necrosis with numerous M. cerebralis developmental stages and/or mature myxospores bordered and/or infiltrated by mono- and multinuclear leukocytes. Lesions in brown trout were smaller and had fewer associated leukocytes and M. cerebralis developmental stages and/or mature myxospores. Higher infection rates, lesion severity scores, and differences in lesion location in rainbow versus brown trout explain in part why numbers of rainbow but not brown trout have fallen in western rivers inhabited with M. cerebralis-infected trout. (+info)
Early experience with 'new federalism' in health insurance regulation.
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The authors monitored the implementation of the Health Insurance Portability and Accountability Act (HIPAA) from 1997 to 1999. Regulators in all states and relevant federal agencies were interviewed and applicable laws and regulations studied. The authors found that HIPAA changed legal protections for consumers' health coverage in several ways. They examine how the process of regulating such coverage was affected at the state and federal levels and under an emerging partnership of the two. Despite some early implementation challenges, HIPAA's successes have been significant, although limited by the law's incremental nature. (+info)