ABSTRACT
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Auseinandersetzungen daruber, welche wissenschaftliche Disziplin und welcher Gegenstand der Forschung zu den bedeutendsten gehoren, sind letzten Endes alle unproduktiv. Es kann jedoch niemand die aktuelle und grundsatzliche Bedeutung der... more
Auseinandersetzungen daruber, welche wissenschaftliche Disziplin und welcher Gegenstand der Forschung zu den bedeutendsten gehoren, sind letzten Endes alle unproduktiv. Es kann jedoch niemand die aktuelle und grundsatzliche Bedeutung der vielen, von Okologen behandelten angewandten Probleme bezweifeln, von denen wir drei in diesem Kapitel betrachten werden. Das erste, die Schadlingsbekampfung, betrifft die Reduzierung der Haufigkeit unerwunschter Arten, der Schadlinge, die oft drastisch reduziert werden mussen, um die Hungernden zu ernahren oder die verheerenden Auswirkungen von Seuchen zu verhindern. Das zweite Problem, die Nutzung naturlicher Populationen durch Fang oder Ernte, verlangt eine kontrollierte Verringerung der Haufigkeit, die sicher stellt, das die aktuellen Bedurfnisse befriedigt werden, aber die Populationen fur eine zukunftige Nutzung erhalten bleiben. Das dritte Problem, die Erhaltung gefahrdeter Arten, verlangt einen Anstieg ihrer Haufigkeit — oder doch wenigstens die Verhinderung weiterer Haufigkeitsabnahmen.
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In diesem und den folgenden Kapiteln werden wir Faktoren betrachten, welche die Lebensgemeinschaften gestalten und strukturieren. Insbesondere sollten Kapitel 20 und 21 zusammen gelesen werden. Die Ideen, welche sie enthalten, sind eng... more
In diesem und den folgenden Kapiteln werden wir Faktoren betrachten, welche die Lebensgemeinschaften gestalten und strukturieren. Insbesondere sollten Kapitel 20 und 21 zusammen gelesen werden. Die Ideen, welche sie enthalten, sind eng miteinander verbunden und reflektieren einen Disput, der in den siebziger und achtziger Jahren eine zentrale Rolle in der Okologie gespielt hat. Wie wir weiter unten erklaren, gibt es gute theoretische Grunde, das interspezifische Konkurrenz bei der Gestaltung von Gesellschaften eine wichtige Rolle spielt, indem sie bestimmt, wie viele Arten koexistieren konnen. In der Tat war in den Siebzigern die vorherrschende Ansicht unter Okologen, das Konkurrenz von uberragender Bedeutung ist (MacArthur 1972; Cody 1975). In letzter Zeit ist die traditionelle Lehrmeinung in der Okologie von dieser festgefugten Ansicht abgeruckt. Man legt mehr Gewicht auf Ungleichgewichte und stochastische Faktoren, wie physikalische Storungen und wechselnde Umweltbedingungen (Diamond & Case 1986; Gee & Giller 1987). In diesem Kapitel wird die Rolle interspezifischer Konkurrenz in Theorie und Praxis sorgfaltig analysiert. Im folgenden Kapitel betrachten wir die Faktoren, welche die Konkurrenz in einigen Lebensgemeinschaften und fur einige Organismen weit weniger einflusreich machen.
Research Interests: Philosophy and Ökologie
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Okologen haben aus zwei Grunden Interesse an der Stabilitat von Lebensgemeinschaften gezeigt. Der erste ist ein praktischer und wirklich dringlicher. Da der moderne Mensch naturliche und landwirtschaftliche Lebensgemeinschaften... more
Okologen haben aus zwei Grunden Interesse an der Stabilitat von Lebensgemeinschaften gezeigt. Der erste ist ein praktischer und wirklich dringlicher. Da der moderne Mensch naturliche und landwirtschaftliche Lebensgemeinschaften fortwahrend in steigendem Mase stort, ist es wichtig zu wissen, wie die Lebensgemeinschaften auf solche Storungen reagieren und wie sie wahrscheinlich zukunftig reagieren werden. Die Stabilitat einer Lebensgemeinschaft mist ihre Empfindlichkeit gegenuber Storungen.
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Lebende Organismen entnehmen ihrer Umwelt chemische Stoffe, binden sie wahrend einer gewissen Periode und verlieren sie dann wieder. Physiologen richten ihre Aufmerksamkeit auf die Art und Weise, wie individuelle Organismen die von ihnen... more
Lebende Organismen entnehmen ihrer Umwelt chemische Stoffe, binden sie wahrend einer gewissen Periode und verlieren sie dann wieder. Physiologen richten ihre Aufmerksamkeit auf die Art und Weise, wie individuelle Organismen die von ihnen benotigten chemischen Stoffe erwerben und nutzen (Townsend & Calow 1980, Chapin 1987, und Kapitel 3). In diesem wie auch im vorangegangenen Kapitel richten wir unsere Aufmerksamkeit auf die Art und Weise, wie Biota einer Landflache oder eines Wasservolumens Materie akkumulieren, transformieren und bewegen (Evans 1956). Die Flache, welche wir betrachten, kann der ganze Planet Erde sein, ein Kontinent, ein Landwirtschaftsbetrieb, das Einzugsgebiet eines Flusses oder einfach ein Quadratmeter.
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Als Okologen versuchen wir, die Verbreitung und Abundanz von Organismen zu beschreiben und zu verstehen. Grunde dafur konnen beispielsweise sein, eine Schadlingsart unter Kontrolle zu bekommen, eine gefahrdete Art erhalten zu wollen oder... more
Als Okologen versuchen wir, die Verbreitung und Abundanz von Organismen zu beschreiben und zu verstehen. Grunde dafur konnen beispielsweise sein, eine Schadlingsart unter Kontrolle zu bekommen, eine gefahrdete Art erhalten zu wollen oder einfach auch nur unsere Faszination von der Welt um uns herum.
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The Workshop on Tropical Zoonoses inWest Africa was held at the NoguchiMemorial Institute for Medical Research inLegon, Ghana, 3–5 February 1999. The suc-cess of this meeting was attributable to theenthusiasm and expertise of the... more
The Workshop on Tropical Zoonoses inWest Africa was held at the NoguchiMemorial Institute for Medical Research inLegon, Ghana, 3–5 February 1999. The suc-cess of this meeting was attributable to theenthusiasm and expertise of the regionalcontributors from Ghana, Nigeria, Togo,Burkina Faso, Tanzania and Zambia. We areparticularly grateful for the full support givento the meeting by the Honorary Minister ofHealth for Ghana, whose presence did muchto highlight the serious consideration thegovernment of Ghana has placed on thisissue. Financial and logistical support wasprovided by the British Council, Accra
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Theoretical studies have established clearly that age- dependence in the association between parasitoids and hosts (and predators and prey generally), including age- dependence in the susceptibility of hosts to attack, is of potentially... more
Theoretical studies have established clearly that age- dependence in the association between parasitoids and hosts (and predators and prey generally), including age- dependence in the susceptibility of hosts to attack, is of potentially great importance as an influence on the dynamics of their populations (Godfray
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Many parasitoids can develop successfully in different stages of the same host but the costs of parasitism may vary between the stages. The stage of host attacked has generally been determined when there is no choice, giving a misleading... more
Many parasitoids can develop successfully in different stages of the same host but the costs of parasitism may vary between the stages. The stage of host attacked has generally been determined when there is no choice, giving a misleading impression of host selection or preference. 2. The rate of parasitism by a solitary endoparasitoid, Venturia canescens, of each larval stage of the Indian meal moth, Plodia interpunctella, was examined with and without a host refuge from parasitism. In addition, when given a choice of host stages, with and without a refuge, the influence of parasitoid age on host selection was examined. 3. Wasps were able to parasitize all except the first instar, but second instars experienced significantly reduced parasitism, in both refuge treatments, compared with third to fifth instars. Whilst parasitoid emergence was always significantly less when all host stages had a refuge, the reduction was only marginally significant when second instars were attacked. 4. When given a choice of second- and fifth-instar larvae, wasps consistently parasitized more fifth instars, both with and without a refuge. Moreover, significantly fewer second-instar larvae were parasitized in the presence of fifth instars than when presented alone to the wasps. This pattern of parasitism was unaffected by the increasing age of the parasitoids. 5. Host selection by V. canescens is discussed in terms of host-parasitoid population dynamics and structure.
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Research Interests: Biochemistry, Bioinformatics, Evolutionary Biology, Environmental Science, Developmental Biology, and 15 moreClimate Change, Computational Biology, Biotechnology, Cancer, Biology, Cell Cycle, Ecology, Drug Discovery, Evolution, Astrophysics, Astronomy, DNA, Cell Signalling, Earth Science, and Chaotic
The importance of wild rodents as reservoirs of zoonotic tick-borne pathogens is considered low in the United Kingdom because, in studies to date, those parasitized by exophilic Ixodes ricinus ticks carry almost exclusively larvae and... more
The importance of wild rodents as reservoirs of zoonotic tick-borne pathogens is considered low in the United Kingdom because, in studies to date, those parasitized by exophilic Ixodes ricinus ticks carry almost exclusively larvae and thus have a minor role in transmission cycles. In a cross-sectional study, 11 (6.7%) of 163 field voles (Microtus agrestis) captured at field sites in Northern England were PCR-positive for Anaplasma phagocytophilum. The voles were found to act as hosts for both larval and nymphal I. ricinus and all stages of the nidicolous tick I. trianguliceps, and eight individuals were infested with ticks of both species at the same time. Two of 158 larval and one of 13 nymphal I. ricinus, as well as one of 14 larval and one of 15 nymphal I. trianguliceps collected from the rodents were PCR-positive. These findings suggest that habitats where field voles are abundant in the United Kingdom may pose a risk of A. phagocytophilum infection because (i) field voles, the most abundant terrestrial mammal in the United Kingdom, may be a competent reservoir; (ii) the field voles are hosts for both nymphal and larval ixodid ticks so they could support endemic cycles of A. phagocytophilum; and (iii) they are hosts for nidicolous I. trianguliceps, which may alone maintain endemic cycles, and exophilic I. ricinus ticks, which could act as a bridge vector and transmit infections to humans and domesticated animals.
Research Interests: Zoology, Biology, Medicine, United Kingdom, Humans, and 15 moreAnimals, Polymerase Chain Reaction, Microtus, Great Britain, Ixodes ricinus, Public health systems and services research, Tick Infestations, Ehrlichiosis, Arvicolinae, Seasons, Vector Borne Disease, Cross Sectional Studies, Anaplasma Phagocytophilum, Tick, and Ixodes
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Pathogens may be important for host population dynamics, as they can be a proximate cause of morbidity and mortality. Infection dynamics, in turn, may be dependent on the underlying condition of hosts. There is a clear potential for... more
Pathogens may be important for host population dynamics, as they can be a proximate cause of morbidity and mortality. Infection dynamics, in turn, may be dependent on the underlying condition of hosts. There is a clear potential for synergy between infection and condition: poor condition predisposes to host infections, which further reduce condition and so on. To provide empirical data that support this notion, we measured haematological indicators of infection (neutrophils and monocytes) and condition (red blood cells (RBCs) and lymphocytes) in field voles from three populations sampled monthly for 2 years. Mixed-effect models were developed to evaluate two hypotheses, (i) that individuals with low lymphocyte and/or RBC levels are more prone to show elevated haematological indicators of infection when re-sampled four weeks later, and (ii) that a decline in indicators of condition is likely to follow the development of monocytosis or neutrophilia. We found that individuals with low ...
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Research Interests: Biology, Population Dynamics, Medicine, Linear models, England, and 15 moreBiological Sciences, Population, Mycobacterium, Animals, Density dependence, Microtus, Fluorescent Antibody Technique, Population Cycles, North East, Cowpox virus, Arvicolinae, Clinical Signs, cowpox, disease transmission, and Medical and Health Sciences
To investigate the prevalence of a flea-borne protozoan (Trypanosoma (Herpetosoma) microti) in its field vole (Microtus agrestis) host, we monitored over a 2-year period a range of intrinsic and extrinsic parameters pertaining to host... more
To investigate the prevalence of a flea-borne protozoan (Trypanosoma (Herpetosoma) microti) in its field vole (Microtus agrestis) host, we monitored over a 2-year period a range of intrinsic and extrinsic parameters pertaining to host demographics, infection status and vector (flea) prevalence. Generalized Linear Mixed Modelling was used to analyse patterns of both flea and trypanosome occurrence. Overall, males of all sizes and ages were more likely to be infested with fleas than their female counterparts. Flea prevalence also showed direct density dependence during the winter, but patterns of density dependence varied amongst body mass (age) classes during the summer. Trypanosome prevalence did not vary between the sexes but was positively related to past flea prevalence with a lag of 3 months, with the highest levels occurring during the autumn season. A convex age-prevalence distribution was observed, suggesting that individuals develop a degree of immunity to trypanosome infect...
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SUMMARYVole tuberculosis (TB;Mycobacterium microti) is an understudied endemic infection. Despite progressing slowly, it causes severe clinical pathology and overt symptoms in its rodent host. TB was monitored for 2 years in wild field... more
SUMMARYVole tuberculosis (TB;Mycobacterium microti) is an understudied endemic infection. Despite progressing slowly, it causes severe clinical pathology and overt symptoms in its rodent host. TB was monitored for 2 years in wild field voles in Kielder Forest, UK. The prevalence of characteristic cutaneous TB lesions was monitored longitudinally at 4 sites, with individuals live-trapped and repeatedly monitored. A prevalence of 5·2% of individuals with lesions was recorded (n=2791). In a cross-sectional study, 27 sites were monitored bi-annually, with TB assessed by post-mortem examination for macroscopic lesions, and by culture and histopathology. Seventy-nine voles (10·78%;n=733) were positive for mycobacteria, with the highest prevalence in spring (13·15%;n=327). TB prevalence varied, with between 0% and 50% of voles infected per site. Prevalence increased with age (mass), and apparent seasonality was due to a higher proportion of older animals in spring. Survival analysis suppor...
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SUMMARYResearch on the interactions between the field voles (Microtus agrestis) of Kielder Forest and their natural parasites dates back to the 1930s. These early studies were primarily concerned with understanding how parasites shape the... more
SUMMARYResearch on the interactions between the field voles (Microtus agrestis) of Kielder Forest and their natural parasites dates back to the 1930s. These early studies were primarily concerned with understanding how parasites shape the characteristic cyclic population dynamics of their hosts. However, since the early 2000s, research on the Kielder field voles has expanded considerably and the system has now been utilized for the study of host–parasite biology across many levels, including genetics, evolutionary ecology, immunology and epidemiology. The Kielder field voles therefore represent one of the most intensely and broadly studied natural host–parasite systems, bridging theoretical and empirical approaches to better understand the biology of infectious disease in the real world. This article synthesizes the body of work published on this system and summarizes some important insights and general messages provided by the integrated and multidisciplinary study of host–parasite...
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SUMMARYThe physiological and immunological state of an animal can be influenced by current infections and infection history. Consequently, both ongoing and previous infections can affect host susceptibility to another parasite, the... more
SUMMARYThe physiological and immunological state of an animal can be influenced by current infections and infection history. Consequently, both ongoing and previous infections can affect host susceptibility to another parasite, the biology of the subsequent infection (e.g. infection length) and the impact of infection on host morbidity (pathology). In natural populations, most animals will be infected by a succession of different parasites throughout the course of their lives, with probably frequent concomitant infections. The relative timing of different infections experienced by a host (i.e. the sequence of infection events), and the effects on factors such as host susceptibility and host survival, can only be derived from longitudinal data on individual hosts. Here we review some of the evidence for the impact of co-infection on host susceptibility, infection biology and pathology focusing on insights obtained from both longitudinal studies in humans and experiments that explicit...
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ABSTRACT
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The seasonality of recurrent epidemics has been largely neglected, especially where patterns are not driven by forces external to the population. Here, we use data on cowpox virus in field voles to explore the seasonal patterns in... more
The seasonality of recurrent epidemics has been largely neglected, especially where patterns are not driven by forces external to the population. Here, we use data on cowpox virus in field voles to explore the seasonal patterns in wildlife (variable abundance) populations and compare these with patterns previously found in humans. Timing in our system was associated with both the number and the rate of recruitment of susceptible hosts. A plentiful and sustained supply of susceptible hosts throughout the summer gave rise to a steady rise in infected hosts and a late peak. A meagre supply more limited in time was often insufficient to sustain an increase in infected hosts, leading to an early peak followed by a decline. These seasonal patterns differed from those found in humans, but the underlying association found between the timing and the supply of susceptible hosts was similar to that in humans. We also combine our data with a model to explore these differences between humans and...
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Blood samples were repeatedly collected from 12 sympatric woodland rodents over a 12-month period and DNA extracts from each were incorporated into a bartonella-specific PCR targeting a fragment of the 16S/23S rRNA intergenic spacer... more
Blood samples were repeatedly collected from 12 sympatric woodland rodents over a 12-month period and DNA extracts from each were incorporated into a bartonella-specific PCR targeting a fragment of the 16S/23S rRNA intergenic spacer region (ISR). The composition of each amplicon was analysed using restriction enzyme analysis (REA) and base sequence comparison. Bartonella DNA was detected in 70 of 109 samples. Eleven samples contained DNA derived from more than one strain. Sequence analysis of 62 samples found 12 sequence variants (ISR genotypes) that were provisionally assigned to 5 different species, 2 of which were newly recognized. Up to five different species were detected in each animal. On about two-thirds of occasions, a species detected 1 month was not there the next, but never was a genotype superseded by another of the same species. However, a genotype could be re-encountered months later in the same animal, even if interim samples contained other genotypes. Our results su...
Research Interests: Epidemiology, Biology, Medicine, DNA, Extracts, and 15 moreAnimals, Bacteria, Polymerase Chain Reaction, Research article, Fragmentation, Great Britain, Longitudinal Studies, Genotype, Public health systems and services research, Genotyping, Bartonella, Arvicolinae, Muridae, Amplicon, and intergenic region
Phylogenetic analyses of bartonella have suggested divergence between bartonellae that infect mammals native to the Old and New Worlds. We characterized bartonella isolated from Eastern grey squirrels (Sciurus carolinensis) in the United... more
Phylogenetic analyses of bartonella have suggested divergence between bartonellae that infect mammals native to the Old and New Worlds. We characterized bartonella isolated from Eastern grey squirrels (Sciurus carolinensis) in the United States and from grey and red squirrels (Sciurus vulgaris) in the United Kingdom by nucleotide sequence comparison (gltA and groEL). Isolates from grey squirrels in the United States and the United Kingdom were identical, and most similar to Bartonella vinsonii, a species associated with New World rodents. A single and novel bartonella genotype was obtained from all 12 red squirrel isolates. Although grey squirrels were first introduced into the United Kingdom over 125 years ago, they continue to be infected solely by the bartonella associated with grey squirrels native to the United States. These results illustrate that exotic species may be accompanied by the introduction and maintenance, over many generations, of their microparasites.
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SUMMARYRecent studies have provided evidence that endemic pathogens may affect dynamics in animals. However, such studies have not typically considered that infected individuals might have a preceding underlying poor condition. We... more
SUMMARYRecent studies have provided evidence that endemic pathogens may affect dynamics in animals. However, such studies have not typically considered that infected individuals might have a preceding underlying poor condition. We examined whether individuals in poor condition are more likely to become infected by an endemic pathogen, using as a system the dynamics of cowpox virus in field voles. With data from monthly sampled vole populations, a nested case-control study evaluated whether susceptible individuals with poorer condition had higher probabilities of contracting cowpox. The influence of condition was found to be considerable, especially for males. At times when a susceptible male with good body condition had a relatively low probability of becoming infected, a susceptible male with poor body condition was twice as likely to contract cowpox; if this male was also anaemic, the chances were almost quadrupled. We discuss the care needed when interpreting the findings of wild...
Research Interests: Epidemiology, Disease ecology, Biology, Population Dynamics, Medicine, and 15 moreFemale, Animals, Male, Ciencias veterinarias, Anemia, Endemic Diseases, Susceptibility, Great Britain, Sex Factors, Cowpox virus, Arvicolinae, Ciencias Agrícolas, Case Control Studies, cowpox, and Population surveillance
Cowpox is an orthopoxvirus infection endemic in European wild rodents, but with a wide host range including human beings. In this longitudinal study we examined cowpox in two wild rodent species, bank voles Clethrionomys glareolus and... more
Cowpox is an orthopoxvirus infection endemic in European wild rodents, but with a wide host range including human beings. In this longitudinal study we examined cowpox in two wild rodent species, bank voles Clethrionomys glareolus and wood mice Apodemus sylvaticus, to investigate the dynamics of a virus in its wild reservoir host. Trapping was carried out at 4-weekly intervals over 3 years and each animal caught was uniquely identified, blood sampled and tested for antibodies to cowpox. Antibody prevalence was higher in bank voles than in wood mice and seroconversion varied seasonally, with peaks in autumn. Infection was most common in males of both species but no clear association with age was demonstrated. This study provides a model for studying other zoonotic infections that derive from wild mammals since other approaches, such as one-off samples, will fail to detect the variation in infection and thus, risk to human health, demonstrated here.
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It is generally accepted that the reservoir hosts of cowpox virus are wild rodents, although direct evidence for this is lacking for much of the virus's geographic range. Here, through a combination of serology and PCR, we demonstrate... more
It is generally accepted that the reservoir hosts of cowpox virus are wild rodents, although direct evidence for this is lacking for much of the virus's geographic range. Here, through a combination of serology and PCR, we demonstrate conclusively that the main hosts in Great Britain are bank voles, wood mice and short-tailed field voles. However, we also suggest that wood mice may not be able to maintain infection alone, explaining the absence of cowpox from Ireland where voles are generally not found. Infection in wild rodents varies seasonally, and this variation probably underlies the marked seasonal incidence of infection in accidental hosts such as humans and domestic cats.
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Transmission is the driving force in the dynamics of any infectious disease. A crucial element in understanding disease dynamics, therefore, is the ‘transmission term’ describing the rate at which susceptible hosts are ‘converted’ into... more
Transmission is the driving force in the dynamics of any infectious disease. A crucial element in understanding disease dynamics, therefore, is the ‘transmission term’ describing the rate at which susceptible hosts are ‘converted’ into infected hosts by their contact with infectious material. Recently, the conventional form of this term has been increasingly questioned, and new terminologies and conventions have been proposed. Here, therefore, we review the derivation of transmission terms, explain the basis of confusion, and provide clarification. The root of the problem has been a failure to include explicit consideration of the area occupied by a host population, alongside both the number of infectious hosts and their density within the population. We argue that the terms ‘density-dependent transmission’ and ‘frequency-dependent transmission’ remain valid and useful (though a ‘fuller’ transmission term for the former is identified), but that the terms ‘mass action’, ‘true mass ac...
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1. The population dynamics of bank voles and wood mice, and of cowpox virus infection in these two species, was studied over a 2-year period in a mainland population and in 14 nearby island populations of varying sizes. 2. For both... more
1. The population dynamics of bank voles and wood mice, and of cowpox virus infection in these two species, was studied over a 2-year period in a mainland population and in 14 nearby island populations of varying sizes. 2. For both species, there was no intrinsic variation in the ...
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Research Interests: Risk, Multidisciplinary, Disease susceptibility, Community Detection, Parasite, and 15 moreFemale, Animals, Male, Microbial Interactions, Babesiosis, Bartonella, Ehrlichiosis, Captive Wild Animals, Arvicolinae, Risk Factors, Host Pathogen Interactions, Babesia Microti, Anaplasma Phagocytophilum, cowpox, and Environmental factor
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A key aim in epidemiology is to understand how pathogens spread within their host populations. Central to this is an elucidation of a pathogen's transmission dynamics. Mathematical models have generally assumed that either contact... more
A key aim in epidemiology is to understand how pathogens spread within their host populations. Central to this is an elucidation of a pathogen's transmission dynamics. Mathematical models have generally assumed that either contact rate between hosts is linearly related to host density (density-dependent) or that contact rate is independent of density (frequency-dependent), but attempts to confirm either these or alternative transmission functions have been rare. Here, we fit infection equations to 6 years of data on cowpox virus infection (a zoonotic pathogen) for 4 natural populations to investigate which of these transmission functions is best supported by the data. We utilize a simple reformulation of the traditional transmission equations that greatly aids the estimation of the relationship between density and host contact rate. Our results provide support for an infection rate that is a saturating function of host density. Moreover, we find strong support for seasonality i...