bluuebunny/crossref_metadata_2025 huggingface dataset:
Strategy and constraint in the winter fattening response to temperature in the great tit Parus major
Authors: Gosler Andrew G.
Published: March 2003

For many small birds at temperate latitudes, the low temperatures and long nights of winter are associated with an increased risk of starvation. Birds such as the great tit Parus major L. face this by increasing their fat reserves. Theoretical, correlative and experimental evidence indicates that the amount of fat carried is not maximized for a given set of circumstances, but optimized, at least partly because of a need to trade off starvation risk against predation risk, part of which may be mass‐dependent, and therefore increased by carrying increased reserves. Evidence for such a trade‐off strategy includes the observed negative correlation between fat reserves and ambient winter temperature operating as a proximate factor.

However, the relationship between fat and temperature requires further investigation for two reasons. First, field evidence that temperature acts as a proximate factor is equivocal. Secondly, measures of temperature used (e.g. mean temperature over the previous 24 h) have given little resolution as to the time over which temperature effects operate, and whether low temperatures might constrain the bird's ability to fatten, in addition to signalling the need to fatten further.

This paper uses observations of fat from a wild great tit population, studied over 17 years, to address these two areas. First, it demonstrates that temperature acts as a proximate factor influencing fat reserve levels. Secondly, by relating the time of observation more precisely than previously to temperatures prevailing at particular times during the previous 24 h, it is shown that while past temperature (e.g. 5 + h previously) is used to optimize fat reserves (strategic fattening), more immediate temperature may constrain the bird's ability to achieve the optimum.

This constraint is demonstrated by a positive correlation between fat reserves and current temperature; probably the first demonstration of such a relationship. However, this constraining effect of temperature has diminished over the last 17 years, presumably because of climate amelioration.
Parasite transmission: reconciling theory and reality
Authors: Fenton A. , Fairbairn J. P. , Norman R. , Hudson P. J.
Published: March 2003

Arguably the most important and elusive component of host–parasite models is the transmission function. Considerable empirical and theoretical work has focused on determining the correct formulation of this function although, to date, there has been little attempt to combine these studies to develop general insights into how observed transmission rates affect host–parasite dynamics.

Here, estimates of transmission rates from a range of host–parasite systems in the literature are described using a phenomenological function which takes into account how transmission varies with host and parasite densities. This function is placed in the appropriate model framework to determine the consequences of the observed transmission rates for each system.

All of the parasites had decreasing per capita transmission rates with increasing parasite densities suggesting that parasites tend to saturate at high densities, either as hosts become limiting or due to heterogeneities amongst the host population. In terms of the responses to host density, the parasites fell into two groups: those with increasing or decreasing transmission rates. This dichotomy was due to the biology of the organisms; the former group infect through cannibalism, which increased at high densities as the individuals became stressed, whereas the latter group infected through free‐living stages, resulting in a form of spatial structuring reducing the number of hosts available for infection.

A metapopulation model was developed where hosts and parasites interacted in discrete patches according to the appropriate transmission function, with neighbouring patches linked by dispersal. The model suggested that small‐scale, localized transmission events can drive large‐scale epizootics at the metapopulation level. This emphasizes the importance of correctly describing and quantifying the transmission function at the individual level.

Traditionally, the formulation of the transmission function has depended on the scale of observation. This work shows that transmission should be considered from the viewpoint of the organisms concerned. Observed transmission rates are a consequence of the biology of the individuals meaning it should be possible to develop a priori hypotheses concerning the nature of the transmission function from a basic understanding of the life history of the organisms concerned.
Group living and investment in immune defence: an interspecific analysis
Authors: Wilson Kenneth , Knell Robert , Boots Michael , Koch‐Osborne Jane
Published: March 2003

Since parasite transmission is often density‐dependent, group living is normally thought to lead to an increased exposure to parasitism. As a consequence, it is predicted that animals living in groups will invest more resources (energy, time, risk, etc.) in parasite defence than those living solitarily.

We tested this prediction by measuring basal immune parameters in the larvae of 12 species of Lepidoptera, grouped into six phylogenetically matched species‐pairs, each comprising one solitary feeding and one gregariously feeding species.

Contrary to expectation, the solitary species in all six species‐pairs had higher total haemocyte counts than the gregarious species, and in five out of six species‐pairs the solitary species also exhibited higher phenoloxidase activity. Both measurements were positively correlated with each other and with the magnitude of the cellular encapsulation response.

The relationship between infection risk and group living was investigated with a dynamic, spatially explicit, host–pathogen model. This shows that when individuals aggregate in groups, theper capitarisk of infection can be reduced if the lower between‐group transmission more than compensates for the higher within‐group transmission.

We conclude that the expectation that group living always leads to increased exposure to pathogens and parasites is overly simplistic, and that the specific details of the social system in question will determine if there is increased or decreased exposure to infection.
Size‐ and density‐dependent habitat use in predators: consequences for habitat shifts in young fish
Authors: Byström Pär , Persson Lennart , Wahlström Eva , Westman Erika
Published: March 2003

When different size classes of predators use different habitats, the habitat‐specific predation risk for prey may change as prey increase in size due to the size‐dependency in predator–prey interactions.

To study the effects of predation risk on habitat shifts in growing prey, we used a combination of whole‐lake manipulations and field data, covering 5 years from three lakes on (1) body sizes at habitat shifts in young‐of‐the‐year perch (YOY) perch (Perca fluviatilis) and (2) habitat use and densities of two size classes of cannibals (1 year old and ≥ 2 years old).

YOY perch shifted habitat to the pelagic immediately after hatching and exhibited a second shift back to the littoral zone at a size range of 11–30 mm. Cannibalism from 1‐year‐old perch decreased over time, whereas cannibalism from perch ≥ 2 years old increased over time but did not include early larval stages. The habitat use of 1‐year‐old perch was restricted to the littoral habitat, whereas perch ≥ 2 years old used both the pelagic and the littoral habitats.

Habitat shifts in YOY perch were unrelated to differences in resource levels between the two habitats as YOY perch were either yolk sac feeding (first habitat shift) or had similar foraging gains in both habitats (second habitat shift).

The size when YOY perch shifted back to the littoral zone was related positively to the densities of 1‐year‐old perch, whereas no clear relationship was found between shift size and the density of perch 2 ≥ years old. The latter was suggested to be due to the higher density and the larger variation in densities of 1‐year‐old perch and that the predation risk from perch ≥ 2 years old was less habitat‐specific.

Our results suggest that size‐dependent habitat use and size specific predation risk evoked by cannibals affect the size when YOY perch shift back to the littoral zone.
Effects of phosphate on the reproductive symbiosis between bitterling and freshwater mussels: implications for conservation
Authors: REYNOLDS JOHN D. , GUILLAUME HENRI P.
Published: March 2003

We examined the effects of phosphorus, an important pollutant in fresh waters, on musselsAnodonta anatinaand embryos of European bitterlingRhodeus sericeus amarus. These species are involved in an unusual symbiosis, with the fish depositing eggs inside the mussels' gills, where the embryos develop for 3–6 weeks until the larvae leave the mussel.

High concentrations of phosphate (500 μg L−1and higher) caused a significant increase in the rate of premature expulsion and emergence of bitterling embryos from the mussels, with a concomitant increase in fish mortality.

At concentrations of 750 μg L−1and higher, mussels reduced their frequency of ventilation and movements through the substratum.

These results have implications for understanding the nature of the symbiosis between the fish and their mussel hosts, showing that mussels have control over bitterling developing in their gills. The premature expulsion of bitterling embryos at high phosphate levels is detrimental to the fish that they harbour.

Recommendations for the conservation of bitterling and species of mussels, which are threatened or endangered over parts of their ranges, include reductions in levels of phosphorus in natural habitats and the need for low levels in reintroduction sites for the fish and their mussel hosts.
The effect of predation by wintering cormorants Phalacrocorax carbo on grayling Thymallus thymallus and trout (Salmonidae) populations: two case studies from Swiss rivers. Reply
Authors: SUTER WERNER
Published: March 2003

Data relating to possible predatory effects of cormorants Phalacrocorax carbo (L.) on grayling Thymallus thymallus (L.) in the river Rhine did not support hypotheses of overfishing, but were consistent with changes in the fish population resulting from variable recruitment and density‐dependent effects (Suter 1995). In a government report, fisheries managers using the same data claimed to have found a causal relationship between cormorant predation and grayling decline (Staub et al. 1992). In their comment, these authors argue that certain data transformations and statistical procedures in my paper were responsible for the different outcome (Staub et al. 1998). However, the authors are unable to quantify any effects of procedures they question, and resort to vague reasoning. Their technical objections are either irrelevant or misleading, since they repeatedly make wrong assumptions or misinterpret parts of my analysis. Different interpretations of predation effects are rather a consequence of the shortcomings of the original report: Staub et al. (1992) had not applied any statistical treatment to the data not tested any hypotheses, but had arrived at their ‘conclusions’ simply by looking at a number of raw graphs depicting grayling catches grouped by fish‐length classes. Moreover, their approach (both in the original report and in the present comment) suffers from a lack of biological understanding, particularly of dynamic processes in fish populations and density‐related effects.
Attempts to control tuberculosis in cattle by removing infected badgers: constraints imposed by live test sensitivity
Authors: Woodroffe Rosie , Frost Simon D.W. , Clifton‐Hadley Richard S.
Published: March 2003

1. Bovine tuberculosis is a serious disease of cattle caused by the bacillus Mycobacterium bovis. In south‐west England, badgers Meles meles sustain endemic M. bovis infection and almost certainly transmit the disease to cattle. When tuberculosis outbreaks have occurred in cattle, the Ministry of Agriculture, Fisheries and Food (MAFF) therefore culled badgers to try to avert further outbreaks.

2. To limit the number of badgers killed, MAFF has assessed a possible new strategy (the ‘live test strategy’) that used a serological test to identify and remove infected badgers. However, because the test correctly identified only 41% of truly infected badgers, individuals were pooled according to the setts at which they were sampled. All badgers were culled at setts where one or more seropositive animals were caught.

3. On average, 1·9 ± 1·4 (SD) badgers were sampled at each sett. Using a simple model, we show that this level of sampling still gives a low (24–37%) probability of detecting infection at a given sett.

4. Badger social groups typically occupy more than one sett. We allocated setts to social groups by using Dirichlet tessellations and field signs to predict territory borders. On average, 3·3 ± 2·8 badgers were sampled in each group. Our model shows that this increase in sample size gives probabilities of detecting M. bovis in truly infected groups of 43–62%, which is still likely to be unacceptably low.

5. Culling badgers according to the setts where they were trapped led to incomplete removal of social groups; some seronegative badgers were released in 61% of groups containing seropositive animals. As infection is clustered within groups, it is likely that some infected animals were released even though they tested seronegative. Incomplete removal might also cause social disruption that could accelerate the transmission of M. bovis between social groups.

6. We conclude that the live test strategy, as implemented, would be unlikely to reduce the overall prevalence of M. bovis infection in badgers, and thus the risk to cattle. Furthermore, the poor sensitivity of the serological test makes it unlikely that modifications to the live test protocol could increase its cost‐effectiveness.
Variation in standing stock of the mackerel icefish Champsocephalus gunnari at South Georgia
Authors: Everson Inigo , Parkes Graeme , Kock Karl‐Hermann , Boyd Ian L.
Published: March 2003

1. Bottom trawl surveys on the South Georgia shelf indicate episodic declines in the abundance of the mackerel icefish Champsocephalus gunnari that, since 1990, are not directly attributable to commercial fishing.

2. The greatest effect has been observed in years when krill are known to have been scarce on the South Georgia shelf.

3. It is thought that C. gunnari survivorship is closely related to, but indirectly influenced by, krill availability.

4. Examination of food chain relationships indicates that predation by fur seals is likely to play a major role in the observed changes in C. gunnari abundance.

5. Periodic shifts in food chain relationships, involving krill, C. gunnari and fur seals, are postulated that could explain the episodic declines in the abundance of C. gunnari in the absence of fishing.

6. The study demonstrates how a key predator can have an over‐riding impact on a commercial fish species, highlighting the importance of the ecosystem approach to fisheries management.
The impact of American mink Mustela vison on water birds in the upper Thames
Authors: Ferreras P. , Macdonald D.W.
Published: March 2003

1. The effect of mink predation on water birds during the breeding season was studied between March and September 1996 in a 33‐km long stretch of the upper Thames river, England.

2. Mink presence significantly affected the density of breeding coots and the number of chicks hatched per pair of coots, as well as the average number of nests per pair of moorhens and the percentage of moorhen clutches hatched.

3. Mink diet during the birds’ breeding season (March–September) was studied through scat analysis. Ralliformes (coots or moorhens) represented 10% of the ingested biomass and were the fourth prey in importance after rabbits (45%), fish (25%) and small mammals (14%). Mink obtained 11% of their energy requirements from coots and moorhens.

4. Impact of predation by mink during the bird breeding season was moderate to high for moorhens (16–27% of adults and 46–79% of broods) and high for coots (30–51% of adults and 50–86% of broods).

5. Although moorhens seem well adapted to withstand predation by mink, nesting behaviour by coots make them very vulnerable to mink predation. We hypothesize that the persistence of coot populations in areas with high mink density requires immigration from surrounding populations with lower mink impact.
Alate production by aphids on sugar beet: how likely is the evolution of sugar beet‐specific biotypes?
Authors: Williams I.S. , Dewar A.M. , Dixon A.F.G. , Thornhill W.A.
Published: March 2003

1. Aphid clones that feed on the same plant species for many generations often develop biotypes specifically adapted to the particular host‐plant. Such biotypes can be particularly damaging to crops. In the case of sugar beet Beta vulgaris, which is not available for colonization for parts of the year, aphids must migrate into and out of the crop each year if host‐specific biotypes are to evolve. The likelihood of biotypes evolving to be specifically adapted to sugar beet was examined and the results are discussed in relation to the control of aphids on this crop.

2. The frequency and causes of alate production by aphids on sugar beet were investigated by examining natural field populations, manipulated field populations and laboratory populations. Data from these studies were used in a model that estimated the probability of an aphid clone on sugar beet successfully migrating from the crop, surviving the winter and migrating back on to the crop the following year.

3. In 2 years out of 4, no alatoid nymphs of the aphids Myzus persicae and Macrosiphum euphorbiae were produced on naturally infested crops of sugar beet, and negligible numbers were produced in the other 2 years.

4. In spring, a much greater proportion of the My. persicae population was alatoid on oilseed rape Brassica napus than on sugar beet. Similarly in laboratory studies, a greater proportion of My. persicae was alatoid on Chinese cabbage Brassica pekinensis than on sugar beet at the same levels of crowding. The colour of the alatoid nymphs reared on Chinese cabbage indicated that it was a more suitable host than sugar beet and this might account for the greater alate production. Infection of sugar beet with beet yellows virus did not increase alate production by My. persicae.

5. A deterministic model showed that the probability of an alate My. persicae migrating from sugar beet and recolonizing sugar beet the following year would, at best, be only 1 in 40 000.

6. As there is negligible transfer of genetic material from year to year, we suggest that biotypes of My. persicae specifically adapted to sugar beet are unlikely to evolve. As a result, if particular aphicides were only used on sugar beet, resistance to those aphicides would be unlikely to evolve because any new resistance would not be transmitted from year to year.
Spatial synchrony in field vole Microtus agrestis abundance in a coniferous forest in northern England: the role of vole‐eating raptors
Authors: Petty S.J. , Lambin X. , Sherratt T.N. , Thomas C.J. , Mackinnon J.L. , Coles C.F. , Davison M. , Little B.
Published: March 2003

1. The regional synchrony hypothesis (RSH) states that synchrony in microtine abundance over large geographical areas is caused by nomadic avian predators that specialize on small mammals for food. This has proved a difficult hypothesis to test because experiments at an appropriate scale are almost impossible.

2. We used the decline of the most abundant, nomadic vole‐eating raptors in an extensive conifer forest in northern England (Kielder Forest) as a natural experiment to evaluate their influence on synchronizing voles at different spatial scales. Field vole populations fluctuated on a 3–4‐year cycle of abundance, similar to the periodicity in central Fennoscandia.

3. Over a 23‐year period, the combined numbers and density of kestrels and short‐eared owls significantly declined. If these raptors were responsible for synchronizing vole abundance, the decline should have been associated with a decrease in synchrony. We could find no change in synchrony during the period of the greatest decline in kestrel and short‐eared owl numbers (1980–97).

4. In Kielder, vole abundance has been shown to change in a wave‐like manner, with synchrony in the direction of the wave being 5–10‐fold smaller than that reported in Fennoscandia. Tawny owls are sedentary and the most abundant vole‐eating raptor in our study area, and might have an equalizing influence on vole abundance over smaller areas if they foraged in a density‐dependent manner and responded functionally to increasing vole density. If this was the case, spatial variability in vole density should have been less in occupied than unoccupied owl territories, especially in years of low vole density when owls could take a larger proportion of the standing crop of voles. Even though tawny owls caught a significant proportion of the vole population, we could find no difference in variation in vole density between owl territories that were unoccupied, occupied with no breeding attempt, or occupied with a successful breeding attempt.

5. We conclude that the small‐scale synchrony in field vole abundance is unlikely to be caused by avian predators. Instead, it is more likely to be related to the pattern of clear‐cutting that has developed in Kielder, which restricts vole dispersal. If this assumption is correct, we would predict more widespread synchrony in vole abundance in first‐generation forests when extensive areas are planted over short periods of time, and this is supported by anecdotal evidence. These conclusions indicate that foresters may be able to manipulate the spatial dynamics of voles and vole predators by varying patch sizes within forests.
Testing genetically engineered potato, producing the lectins GNA and Con A, on non‐target soil organisms and processes
Authors: Griffiths B.S. , Geoghegan I.E. , Robertson W.M.
Published: March 2003

1. Two lectins, concanavalin A (Con A) andGalanthus nivalisagglutinin (GNA), have anti‐feedant properties that suggest a potential for the control of invertebrate pests of plants. We tested potato plants genetically engineered to produce each of these lectins constitutively, as well as the purified lectins, for possible non‐target effects.

2. Laboratory studies with soil bacterial communities and a ciliate protozoan could detect no direct effect of either lectin over a range of concentrations. There was a significant inhibition in the host‐finding response of a bacterial‐feeding nematode when Con A or GNA was present in the medium at 0·5–50 µg ml−1.

3. A number of GNA‐ and Con A‐producing potato lines had no detectable effects on the rhizosphere microbial and microfaunal populations when examined in pot trials. The incorporation of leaves from transgenic plants into soil reduced protozoan populations significantly, but there was no subsequent effect on the decomposition of added cotton strips.

4. Controlled field‐release experiments demonstrated that, although GNA‐producing potato lines consistently altered the physiological profile of the rhizosphere microbial community at harvest, the effect did not persist from one season to the next over a trial period of two field seasons. There was no significant effect of the best performing GNA line on the development of a subsequent barley crop.

5. A single Con A‐producing line was tested in a controlled field‐release. The only significant effects were transient reductions ofc. 40% in soil protozoan populations and ofc. 10% in potential microbial activity.
Modelling the effects of mink and habitat fragmentation on the water vole
Authors: Rushton S.P. , Barreto G.W. , Cormack R.M. , Macdonald D.W. , Fuller R.
Published: March 2003

1. The decline of the water voleArvicola terrestrisin the UK has been attributed to the spread of the introduced American minkMustela vison. Understanding the causes and dynamics of this decline is vital to water vole conservation. We investigated the dynamics of water voles in relation to habitat fragmentation and mink predation using an individual‐based spatially explicit model of population dynamics on the River Windrush, Oxfordshire, UK.

2. A sensitivity analysis was undertaken using values for life‐history parameters drawn from known ranges using Latin hypercube sampling. Partial correlation coefficients were used to estimate how the predicted size of water vole population and extinction were determined by the life‐history parameters. The model was then validated by comparing model predictions with observed distributions of water voles.

3. The effects of mink predation and habitat fragmentation on the future viability of water vole populations on the River Windrush were analysed after artificially manipulating habitat fragmentation on the river and running the model in the presence and absence of mink predation.

4. The match between predicted and observed distributions was significantly related to home range requirement and high reproductive success. At low fragmentation, home range requirement was the most important influence on the number of populations. Reproductive output, and adult and juvenile mortality, became increasingly important with increased fragmentation. At high levels of fragmentation demographic stochasticity had a large influence on population size.

5. We deduce that the importance of demography in determining population persistence will depend on the level of fragmentation. Additionally, life‐history parameters that are crucial to the viability of water vole populations can only be identified in the context of the landscape in which populations are found.

6. The extinction of water vole on the River Windrush became more likely as habitat fragmentation and mink predation increased. Mink predation effectively doubled the probability of extinction over that arising from fragmentation alone.

7. These simulations indicate that extant populations on the Windrush are now so fragmented that populations may not be viable even in the absence of mink predation. We assessed the extent of habitat restoration necessary to ensure population persistence on the River Windrush and considered developments of the model for use in water vole conservation.
Effects of grazing by free‐ranging cattle on vegetation dynamics in a continental north‐west European heathland
Authors: Bokdam Jan , Gleichman J. Maurits
Published: March 2003

1. Abandonment and eutrophication are major threats to traditional pastoral landscapes and their wildlife in Europe. Social and economical developments have rendered traditional pastoralism impracticable. More knowledge is needed about the effects of grazing with free‐ranging herbivores, which is increasingly used as a substitute for the traditional herding system.

2. We studied the effects of free‐ranging cattle on the recovery of Calluna heather, tree encroachment and plant species richness in six habitats in a grass‐rich Dutch heathland during a 10‐year period. The habitats differed in soil fertility, initial heather–grass ratio and developmental stage of Calluna.

3. Despite preferential grass defoliation, cattle grazing neither reduced grass cover in grass heath nor prevented grass invasion in heather. Grass invasion failed only in a nitrogen‐poor turf‐stripped Calluna heath. Grazing induced a substantial Calluna recovery in grass heaths on podzolic soils, but its recovery failed in grass heath on a phosphorus‐rich medieval arable field. As a consequence, the grass–heather mosaics generated by free‐ranging cattle were restricted to habitats of intermediate soil fertility.

4. Grazing did not prevent encroachment by pine and birch. Removal by the site manager prevented conversion of 10–20% of the open heathland to forest.

5. During the first 5 years, grazing induced a significant increase in species richness in all habitats. During the second 5 years, species richness stabilized in grass heath and heather–grass mosaics and it declined in the pioneer Calluna heaths.

6. We found indications of various nutrient‐mediated grazing effects on the competitive balance between grass and woody pioneers. These suggest that nutrient‐mediated feedback might be an important explanatory mechanism for the described vegetation mosaic cycling in heathlands.

7. Free‐ranging grazing did not remove the high atmospheric nutrient inputs of the whole area. Substantial amounts of nutrients were redistributed from the grass lawns to the forest.

8. Free‐ranging grazing combined with tree cutting appeared to be a suitable management regime for the maintenance of species‐rich open heathlands with dynamic grass–heather mosaics.

9. Without tree cutting, free‐ranging grazing would have created dynamic tree–grass–heather mosaics in open heathland. Wood–pasture landscapes are fundamentally different from the open heather‐dominated heathlands produced by the traditional sedentary farming system. Integrated grazing of heathland, nutrient‐rich farmland and forests accelerates this change. Alternative grazing regimes are discussed.
Effects of vegetation structure, food and shelter on the home range and habitat use of an endangered wallaby
Authors: Fisher D.O.
Published: March 2003

1. Bridled nailtail wallabies Onychogalea fraenata are medium‐sized, nocturnal, solitary macropods that persist in only one conservation reserve in central Queensland, Australia. They use shrubs, grass and logs as diurnal shelters. Factors affecting shelter choice, habitat use and home range size were interpreted in terms of habitat management, and shelter provision was assessed as a potential management tool.

2. Shelter selection, food and variation in cover were assessed at two sites that differed in vegetation density and population density. In order to determine how habitat quality and potential visibility to predators affect ranging behaviour, the relationships among home range size, grass biomass, sex, site, habitat edge availability and moon phase were determined for 37 radio‐collared wallabies during and after a severe drought.

3. Open habitats contained more food, whereas wooded habitat contained more preferred shelter. Shelter but not food availability differed between the sites. Wallabies used a higher proportion of wooded habitat, and increasingly avoided open areas, as food biomass in wooded areas increased after the drought.

4. Home range size differed between the sexes but not between the sites. It tended to be inversely related to availability of food and habitat edge. Diurnal home range size was correlated with grass biomass and was larger at the site with the lowest population density and lowest availability of cover, but it did not differ between sexes.

5. A preference for habitat edges may reflect shelter quality. Animals chose shelter sites with the densest cover at wallaby height; cover was densest at this height at the forest edge.

6. Wallabies used individual shelters repeatedly, were faithful to diurnal range areas, but did not appear to share shelter sites. They used experimentally provided shelter extensively, and more frequently than other medium‐sized mammals at the sites.

7. Increasing natural grass cover was associated with diurnal home range shifts and expansion, but experimental shelter provision had no effect on diurnal range size or location. Shelter did not explain differences in diurnal range size between the sites, which may instead be related to population density.

8. Neither vegetation type was obviously better habitat. Ongoing large‐scale manipulation of forest regrowth may be needed to increase habitat edges and maintain vegetation at the optimum height to provide shelter and food. Patchy clearing is therefore a potential strategy for habitat management for this species and other medium‐sized forest‐dwelling mammals.
Simulating the spread and management of alien riparian weeds: are they out of control?
Authors: Wadsworth R.A. , Collingham Y.C. , Willis S.G. , Huntley B. , Hulme P.E.
Published: March 2003

1. This paper examines the circumstances under which control programmes may reduce the range of two widespread invasive weeds of riparian habitats: Impatiens glandulifera (Himalayan balsam) and Heracleum mantegazzianum (giant hogweed).

2. The spread of both species was modelled using MIGRATE, a spatially explicit model that incorporates realistic demographic parameters and multiple dispersal mechanisms. Simulations of a range of control scenarios were run within a geographical information system (GIS) using authentic landscapes based on topographic, hydrological and land cover maps of County Durham, UK. Results were interpreted at both a catchment and a regional scale.

3. Six representative strategies were explored that prioritized control as follows: at random, in relation to human population density, or by the size, age (new and old) or spatial distribution of weed populations. These strategies were assessed at different intensities of management (area treated per year) and for varying efficiencies (proportion of plants destroyed) as well as the timeliness (how long since the species became established) of implementations.

4. Strategies that prioritized control based on weed population and spatial characteristics were most effective, with plant population size and spatial distribution being the key parameters. The reduction in geographical range within a catchment or region following control was always greater for H. mantegazzianum than I. glandulifera due to its slower rate of spread.

5. Successful control of both species at a regional scale is only possible for strategies based on species distribution data, undertaken at relatively high intensities and efficiencies. The importance of understanding the spatial structure of the population and potential habitat available, as well as being able to monitor the progress of the eradication programme, is highlighted. Tentative conclusions are offered as to the feasibility of eradicating these species at a regional scale.
The responses of floodplain primary production to flood frequency and timing
Authors: Robertson A.I. , Bacon P. , Heagney G.
Published: March 2003

River regulation and abstraction have dramatically altered the natural flow regime of many rivers world‐wide, but experimental investigations of the biological effects are infrequent. In the mid‐region of the Murray River, Australia, river regulation has reduced the frequency and duration of spring floods and increased the frequency of summer floods. We used controlled floods (treatments: no floods, spring floods, summer floods and spring + summer floods) to determine how the growth of river red gum Eucalyptus camaldulensis trees, aquatic macrophytes and biofilms varied with the seasonal timing and frequency of flooding.

 After 6 years of controlled flooding, above‐ground net production of wood by river red gum trees was equal and greatest in plots receiving spring + summer floods and summer floods (mean 496 g m−2 year−1). Production was significantly lower in plots receiving spring floods or no controlled floods, which had similar rates of production (mean 330 g m−2 year−1).

 During 2 years of measurement in wetlands created by flooding, production and species richness of aquatic macrophyte were both greater in spring than in summer floods. The history of flood frequency at any experimental site did not affect macrophyte production or species richness. The aquatic macrophyte community in shallow regions of wetlands differed significantly with the seasonal timing of floods, but not flood frequency.

 The accumulation of chlorophyll a and total mass of biofilm on wood surfaces in wetlands created by flooding were greater in spring (mean chlorophyll a, 0·88 µg cm−2; mean mass, 0·066 mg cm−2) than in summer floods (mean chlorophyll a, 0·09 µg cm−2; mean mass, 0·034 mg cm−2). The history of flood frequency at any experimental site did not affect accumulation of either the autotrophic or heterotrophic components of biofilms.

 Spring flooding, while not as beneficial for tree growth, is critical for the growth of wetland macrophytes, the maintenance of macrophyte species richness, and favours better development of autotrophic biofilms. Maintenance of both the timber harvest and wetland conservation values of these floodplains will require the return of more natural flood flows in the spring period. Restoration of floodplain rivers requires a thorough understanding of the relationships between ecological functions and the natural flow regime.
Interactions between the rust fungus Puccinia punctiformis and ectophagous and endophagous insects on creeping thistle
Authors: Stephanie Kluth , Andreas Kruess , Teja Tscharntke
Published: March 2003

Plant–pathogen–insect interactions may have various outcomes that are of great interest when considering the combined use of insects and pathogens in the biological control of weeds. Here effects of rust infection on herbivore attack and of herbivory on rust infection were analysed to ensure that these possible control agents do not impede each other.

 The system studied was the weed creeping thistle Cirsium arvense, the specialized rust fungus Puccinia punctiformis, and ectophagous and endophagous insect herbivores. On 20 sites around Göttingen, Germany, the abundance of ectophagous and endophagous insects on systemically rust‐infected and uninfected plants was quantified by suction samples and the dissection of shoots.

 Abundance of ectophagous insects was not reduced by rust infection, and aphids as well as several beetle species were more abundant on systemically infected plants. Preference of endophagous insects differed between species: larvae of Apion weevils were more abundant in infected shoots, whereas Melanagromyza aeneoventris, Urophora cardui, all of them oligophagous, and some leaf miners preferred uninfected plants. In dual‐choice feeding tests, larvae of the oligophagous chrysomelid beetle Cassida rubiginosa were more likely to feed on leaf segments of uninfected thistles.

 Enhancement of rust infection rate by simulated herbivory was analysed. Thistle leaves were perforated and infection rate was recorded after 2 weeks under natural Puccinia punctiformis spore concentrations. Numbers of uredosori were significantly higher in perforated leaves. Artificial inoculation resulted in an even greater increase in uredosori, both in perforated and unperforated thistles.

 As the majority of ectophagous and endophagous insects did not discriminate between systemically infected and uninfected thistles, herbivore damage together with infection with Puccinia punctiformis can be expected to increase stress on creeping thistle when used in biological control of the weed. Insects may not only affect plant growth by herbivory but may also increase the susceptibility of healthy thistles to local rust infection by wounding of leaves.
Using stochastic dynamic programming to determine optimal fire management for Banksia ornata
Authors: McCarthy M.A. , Possingham H.P. , Gill A.M.
Published: March 2003

A model of the population dynamics of Banksia ornata was developed, using stochastic dynamic programming (a state‐dependent decision‐making tool), to determine optimal fire management strategies that incorporate trade‐offs between biodiversity conservation and fuel reduction.

 The modelled population of B. ornata was described by its age and density, and was exposed to the risk of unplanned fires and stochastic variation in germination success.

 For a given population in each year, three management strategies were considered: (i) lighting a prescribed fire; (ii) controlling the incidence of unplanned fire; (iii) doing nothing.

 The optimal management strategy depended on the state of the B. ornata population, with the time since the last fire (age of the population) being the most important variable. Lighting a prescribed fire at an age of less than 30 years was only optimal when the density of seedlings after a fire was low (< 100 plants ha−1) or when there were benefits of maintaining a low fuel load by using more frequent fire.

 Because the cost of management was assumed to be negligible (relative to the value of the persistence of the population), the do‐nothing option was never the optimal strategy, although lighting prescribed fires had only marginal benefits when the mean interval between unplanned fires was less than 20–30 years.
Does host genotype diversity affect the distribution of insect and disease damage in willow cropping systems?
Authors: Peacock L. , Hunter T. , Turner H. , Brain P.
Published: March 2003

Planting of willow genotype mixtures for biomass production has been suggested as a non‐chemical strategy for pest management. Basic information on spatial dynamics of important insects and pathogens is necessary for the effective deployment of host genotypes in a plantation. In 1998 and 1999 the degree and spatial distribution of damage by Melampsora spp. and Phratora vulgatissima were studied concurrently in a field trial containing monocultures of willow Salix genotypes with different willow rust and beetle susceptibilities, and two design mixtures (random or regular) of three or five genotypes.

For both years, there was more rust and beetle damage on plants in monocultures than in mixtures. There were significant differences in the vertical distribution of beetle damage along stems between plantation designs for the 2 years, yet only in 1999 for rust. Rust severity along stems was significantly correlated between leaves, indicating localized spread of disease. In contrast, beetle damage severity along stems was weakly correlated between alternate leaves and leaves farther apart, suggesting beetle movement from tree to tree.

In 1998, spatial distribution of rust was aggregated in 67% of plots studied and in 40% for beetles. There was no significant difference in the distribution of beetle damage between planting design, but rust was aggregated in 75% of mixtures and 33% of monocultures. While beetle damage distribution was similar between years, rust was aggregated in all monoculture plots but in only 8% of mixtures in 1999. The difference between years and design for rust was probably because of the later stage of rust development in 1999 and the delaying effect of mixtures on this development.

In 1998, there were significant negative correlations between the extent of rust and beetle damage on individual trees. However, only 20% of plots showed a significant spatial dissociation between these two types of damage. There were fewer discernible interactions in 1999.

Plantation design provides the basis for integrated control of rust and beetle damage within willow cropping systems by delaying the spread and development of both organisms. Both pest and disease can be assessed successfully simultaneously under field conditions, a major saving in human resources. Initial selection of willow mixture configuration should primarily take into account the effects of spatial design on rust development.
The role of Varroa and viral pathogens in the collapse of honeybee colonies: a modelling approach
Authors: Martin Stephen J.
Published: March 2003

The ecto‐parasitic mite Varroa destructor is a serious world‐wide pest of the honeybee Apis mellifera and has being linked with the death of millions of colonies, although its role in colony death has remained elusive.

A simulation model was developed to explain the link between the mite and collapse of the host bee colony, given that colony death does not always occur. We investigated the effects of two pathogens, deformed wing virus (DWV) and acute paralysis virus (APV), vectored by the mite, on the host colony.

Two previously published simulation models, a bee and a mite, were combined and adapted for use in temperate climates with a variety of bee diseases. The model was constructed using Modelmaker® software, which allows the progression of a disease in the host colony to be followed daily.

The population dynamics generated by the model were similar to those observed in a natural honeybee colony. When DWV‐ or APV‐transmitting mites were introduced into the colony, its adult worker bee population collapsed either during winter or spring for DWV, or autumn to spring for APV. This corresponds well with field observations of colony death in Europe.

The model revealed that DWV initially had little effect on the colony but during late summer, as the population of DWV‐transmitting mites increased, the virus caused a reduction in the number of healthy young bees entering the overwintering population. This imbalance in the age structure of the overwintering bees resulted in the eventual death of the colony during the winter or spring. As few as 2000–3600 mites in autumn could kill a colony.

In contrast, APV transmitted by Varroa was only able to kill the honeybee colony if a large (10 000+) mite population was already present when an overt APV infection occurred. It was difficult for APV to become established within the bee population due to it causing rapid host death.

The model predicts that the less virulent DWV will become more widely established than the highly virulent APV, and that mite control measures need to be taken prior to the production of overwintering bees.
Effect of forskolin on endothelin‐induced phosphoinositide hydrolysis and calcium mobilization in cultured canine tracheal smooth muscle cells
Authors: Yang C. ‐M. , Pan S. ‐L. , Chiu C. ‐T. , Lin C. ‐C. , Hsu Y. ‐M.
Published: March 2003

1 The effects of increase in intracellular adenosine 3′:5′‐cyclic monophosphate (cAMP) on endothelin‐1 (ET‐1)‐induced generation of inositol phosphates (IPs) and increase in intracellular Ca2+ ([Ca2+]i) were investigated in canine cultured tracheal smooth muscle cells (TSMCs).

2 Pretreatment of TSMCs with either cholera toxin (CTX; 10 μg ml−−1, 4 h), forskolin (10 μm, 30 min), or dibutyryl cAMP (1 mm, 30 min) inhibited ET‐1‐stimulated Ca2+ mobilization (by 23 ± 5%, n = 8) and IPs accumulation (by 32 ± 6%, n = 4). While after treatment with forskolin for 24 h, the cells retained the ability to respond to ET‐1‐induced Ca2+ mobilization to the same extent as the control group.

3 Forskolin (1–100 μm) inhibited the ET‐1‐induced increase in [Ca2+]i, but the lower concentrations had little effect on this response. The inhibitory effects of these agents produced both depression of the maximal response and a shift to the right of the concentration–response curve of ET‐1 without changing the –logEC50 values.

4 The water‐soluble forskolin analogue L‐858051, 7‐deacetyl‐7β‐(γ‐N‐methylpiperazino)‐butyryl forskolin, significantly inhibited ET‐1‐stimulated IPs accumulation. In contrast, the addition of 1,9‐dideoxy forskolin, an inactive analogue of forskolin, had little effect on stimulated responses. Moreover, SQ‐22536, 9‐(tetrahydro‐2‐furanyl)‐9H‐purin‐6‐amine, an inhibitor of adenylate cyclase, and both H‐89, N‐(2‐aminoethyl)‐5‐isoquinolinesulfonamide, and HA‐1004, N‐(2‐guanidinoethyl)‐5‐isoquinolinesulfonamide, inhibitors of cAMP‐dependent protein kinase (PKA), attenuated the ability of forskolin to inhibit ET‐1‐induced IPs accumulation. These results suggest that activation of cAMP/PKA was involved in these inhibitory effects of forskolin.

5 The locus of this inhibition of forskolin treatment on AlF4−−‐stimulated IPs accumulation was investigated in canine TSMCs. The AlF4−−‐induced IPs accumulation was inhibited by forskolin, supporting that G protein(s) are directly activated by AlF4−− and uncoupled to phospholipase C by forskolin treatment.

6 We conclude that cAMP elevating agents inhibit ET‐1‐stimulated generation of IPs and Ca2+ mobilization in canine cultured TSMCs. Since generation of IPs and increases in [Ca2+]i are very early events in the activation of ET‐1 receptors, attenuation of these events by cAMP elevating agents might well contribute to the inhibitory effect of cAMP on tracheal smooth muscle function.