bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of dieldrin on population growth rates of sparrowhawks 1963–1986
Authors: Sibly R.M. , Newton I. , Walker C.H.
Published: March 2003

1. A recent reappraisal of the evidence of the effects of cyclodiene insecticides on sparrowhawks Accipiter nisus and kestrels Falco tinnunculus in Britain suggested that during 1963–75 at least 29% of sparrowhawks found in an eastern area of high cyclodiene use died directly from dieldrin poisoning, compared with only 6% in a more western area of low cyclodiene use. Here, these data are used in a life‐history analysis of the quantitative effects of dieldrin on some British sparrowhawk populations. Where necessary, life‐history parameters were taken from two British study populations, one stable and one increasing.

2. Four scenarios were analysed. In scenario 1, reflecting high cyclodiene use, the effect of dieldrin poisoning was to increase the instantaneous mortality rate by 0·20 year−1. Life‐history modelling revealed that this would have produced a population decline of 20% year−1 (λ = 0·82 year−1). Adding in possible sublethal effects of dieldrin produced an even more serious decline of 60% year−1 (scenario 2).

3. Data suggested that population growth rate increased linearly as population density decreased. A simple analysis omitting age structure suggested that density‐dependence would not save the scenario 2 population from extinction, but would hold the scenario 1 population at 64% of its former value (scenario 3). The available data suggest the former is correct, i.e. sublethal effects were important during the population decline.

4. During 1976–82, when use of cyclodienes was reduced, the effect of dieldrin poisoning on sparrowhawks in eastern Britain was estimated as an increased instantaneous mortality rate of 0·05 year−1. This is low enough to allow population recovery from low density, at a rate of 13% year−1 (scenario 4).

5. Another way to analyse the effects of dieldrin (or any other additional density‐independent mortality agent) is to ask what reductions in fecundity or survival could be sustained long‐term by an otherwise increasing population. The data suggested that the population could withstand a halving of fecundity (from 2·07 to 1·035) or a reduction of adult survival from 0·74 to 0·55.

6. The analyses presented are based on field data, and are thought to be reasonably realistic of the true impacts of dieldrin and other cyclodienes on British sparrowhawks.
The spatio‐temporal distribution of a rodent reservoir host of cutaneous leishmaniasis
Authors: Fichet‐Calvet E. , Jomâa I. , Zaafouri B. , Ashford R.W. , Ben‐Ismail R. , Delattre P.
Published: March 2003

1. The rodent Psammomys obesus is the main reservoir host for Leishmania major, the causative agent of cutaneous leishmaniasis in Tunisia, much of North Africa and mid‐western Asia. An understanding of the population dynamics of this rodent is essential to establish a preventive control strategy based on the early prediction of rodent outbreaks.

2. The study of P. obesus dynamics at a regional scale requires index‐based sampling. Rodent numbers were monitored twice per year at the beginning and end of the breeding season, using transects around the Sidi Bouzid region in central Tunisia.

3. Two different types of dynamics occurred in two drainage basins. Rodents living in the northern basin were at low density and those living in the southern basin were at high density.

4. At the scale of a plot, occupied burrows were generally associated with the presence of three Chenopodiaceae: Arthrocnemum glaucum, Salsola tetrandra and Suæda fruticosa, rarely in monospecific formations. However, in dry periods, occupied burrows drifted to A. glaucum formation linked with high moisture and salinity of the soil (χ2 MacNemar = 6·26).

5. The risk of a P. obesus outbreak can be assessed by a simultaneous knowledge of flooding regimes in the drainage basins, the distribution of halophytic plant formations, and the progressive movements of the rodents as drying out proceeds. The transect indices of rodents are easily repeatable, economical and would be applicable in other developing countries where cutaneous leishmaniasis occurs.

6. This work illustrates that simple ecological methods can assist the assessment of spatial and temporal components of epidemiological risk such as the proximity between rodent colonies and human habitats at the time of outbreaks.
Winter habitat ecology of mountain caribou in relation to forest management
Authors: Terry Eliot L. , McLellan Bruce N. , Watts Glen S.
Published: March 2003

1. During winter, mountain caribou Rangifer tarandus caribou live in late successional and old‐growth coniferous forests, where they feed almost exclusively on arboreal lichens. Because some of these forests are also valuable to the forest industry, caribou ecology and forest management remains a central conservation issue in British Columbia. To improve our understanding of caribou habitat use in relation to forest management, we investigated the winter habitat selection patterns of mountain caribou at a range of spatial scales between 1988 and 1993 in the northern Cariboo Mountains, British Columbia.

2. Within winter ranges, caribou selected forest stands dominated by subalpine fir (> 80% Abies lasiocarpa) and with moderate slopes (16–30%) during early winter (November–December). Although stands with moderately high timber volumes (201–300 m3 ha−1) were used the most during early winter, caribou used these stands in proportion to their availability. Caribou primarily used open‐canopy subalpine fir stands (i.e. parkland) later in the winter (January–March), where low stocking and inoperable timber volumes (< 100 m3 ha−1) reduced direct conflicts with forest harvesting.

3. Characteristics of subalpine forests at early winter caribou foraging areas did not differ significantly from random sites for most variables measured. However, a multivariate analysis indicated that sites used by caribou had slightly less total basal area, more moderate slopes and slightly heavier lichen loads than unused sites.

4. Within early winter foraging areas, caribou chose foraging paths with more trees and greater accessible lichen biomass per standing tree compared with random paths. Although windthrown trees and lichen litterfall were encountered infrequently, caribou rarely rejected these sources of lichen when encountered.

5. The relatively low basal area (27 m2 ha−1) and minor component of economically valuable Engelmann spruce Picea engelmannii (< 20%) at early winter caribou foraging areas suggests less conflicts with forestry compared with other caribou populations in southern British Columbia and Idaho.

6. Selection silvicultural systems may provide solutions to caribou–forestry conflicts, particularly in mid‐elevation subalpine fir stands (1325–1525 m) that may have both operable timber volumes and high caribou numbers.
Effects of water regime and competition on the establishment of a native sedge in restored wetlands
Authors: Budelsky Rachel A. , Galatowitsch Susan M.
Published: March 2003

1.
 Restoration of depressional wetlands in mid‐continental North America typically involves reflooding formerly drained basins. There have been several thousand restorations in this manner over the past 10 years. Deliberate revegetation is rarely attempted as it is assumed that native vegetation will eventually establish naturally. Carex (sedges), which occur commonly on the periphery of native wetlands and in adjacent saturated meadows, do not readily re‐establish in reflooded basins. It is unlikely that Carex will reappear without deliberate reintroduction. Criteria for introduction and establishment of native sedges do not currently exist because environmental constraints are not well understood.

2.
 In this study we investigated the environmental constraints that might limit the establishment of the native wetland sedge, Carex lacustris, in reflooded wetland basins. Immature sedges were planted in three experimental wetlands with different water‐level fluctuation regimes (i.e. falling, rising, static) along an elevational gradient, to determine the effects on survival and stand development of changing water level, water depth, competition from naturally recruited vegetation, and planting density.

3.  The response of immature sedges to water‐level fluctuation in the first growing season did not indicate the outcome of mature stand development by the end of three growing seasons. Whereas initial survival and growth were lowest in the falling water basin, stem density, height and biomass were greatest under this type of water‐level fluctuation by the third growing season.

4.  Interspecific competition was most intense at the upper elevations, particularly in the rising water basin. Although sedge growth was limited by increasing water depth in the absence of competition, growth was uniformly low across all elevations in the presence of competition. Competition reduced sedge growth to differing degrees in the rising vs. falling and static water basins.

5.
 Results suggest that C. lacustris can produce dense stands under a primarily annual weed community within two to three growing seasons, but that Phalaris arundinacea (reed canary grass) can preclude successful establishment of C. lacustris.

6.  Control of water‐level conditions and competition is most crucial during the first growing season to ensure appropriate conditions for successful stand establishment. The potential for growth as well as mortality is greatest during this first year.

7.
 Competition can be a significant constraint on the successful establishment of C. lacustris and should be considered explicitly when developing a restoration plan.
The interactive effects of management on the productivity and plant community structure of an upland meadow: an 8‐year field trial
Authors: Smith R.S. , Shiel R.S. , Millward D. , Corkhill P.
Published: March 2003

1.
 Agricultural policy in the Pennine Dales Environmentally Sensitive Area in northern England aims to enhance plant species diversity in agriculturally improved meadows and return them to a ‘traditional’ species composition. The interacting effects of management on vegetation and productivity were tested in a split‐split‐split plot experiment. Three grazing treatments (autumn grazing with cattle and sheep, spring grazing with sheep, both regimes) were applied between 1990 and 98. Two fertilizer treatments (25 kg ha−1 N plus 12·5 kg ha−1 P2O5 and K2O, no fertilizer); three hay cut date treatments (14 June, 21 July, 1 September) and two seed addition treatments (no seed, seed of many species) were used within the grazing treatments.

2.  By 1998, all the main treatments had produced small but significant changes to plant species diversity. A particularly large increase in diversity occurred with the combination of autumn and spring grazing, 21 July hay cut date and seed addition treatments. This change was achieved by an episodic rather than a regular increase in species over time.

3.
 
Rhinanthus minor spread to most plots after its introduction as a constituent of the seed treatment. By 1996 it was particularly abundant in all treatment combinations that included autumn grazing, no mineral fertilizer and a July haycut. Populations of > 40 plants m−2 were associated with the lowest yields of hay.

4.
 
‘Unimproved‐traditional’ plant communities, mainly Festuca ovina–Agrostis capillaris–Galium saxatile grassland, occupied more than 66% of the trial area. Anthoxanthum odoratum–Geranium sylvaticum grasslands were most abundant in 1996, being primarily associated with the combination of autumn and spring grazing, 21 July and 1 September hay cut dates and seed addition treatments, over both fertilizer treatments.

5.  Yields of herbage biomass initially declined over time in all treatment combinations. Lowest yields in most years were associated with the autumn and spring grazing, 14 June cutting date and no fertilizer treatments.

6.  Management to increase the number of plant species in agriculturally improved mesotrophic grassland requires the joint implementation of appropriate cut date and grazing regimes, probably to provide regeneration niches, and the application of seed to provide species to fill these niches. The small amount of mineral fertilizer used in this experiment had a measurable effect, but was of lesser importance.
Living where the food is: web location by linyphiid spiders in relation to prey availability in winter wheat
Authors: Harwood J.D. , Sunderland K.D. , Symondson W.O.C.
Published: March 2003

Spiders form a major component of the generalist predator fauna, potentially able to restrict pest population growth, but their populations may be food‐limited under current farming regimes. This study aimed to quantify food availability to spiders in winter wheat and to determine whether spider web locations are positively associated with available food resources.

 Mini‐sticky traps (availability rate per 24 h, including prey falling from the crop) and mini‐quadrats (instantaneous density on the ground by day) were used, in combination, to monitor the availability of potential prey to web‐building species of money spider (Linyphiidae) in fields of winter wheat in Warwickshire, UK, 1997–98.

 These methods were applied to web sites of individual spiders and to non‐web sites located randomly up to 30 cm away from each web. A total of 18 546 invertebrates were captured using these methods.

 Overall, significantly more potential prey were available in web sites than in non‐web sites (both on sticky traps and in quadrats).

 Prey availability in May and July was about a third of that in June (both on sticky traps and in quadrats) and may have been below that known to be necessary for spiders to realize their maximum population growth rate.

 The peak rate of capture of linyphiid spiders on mini‐sticky traps was 0·6 trap−1 day−1 at web sites, and approximately half this value at non‐web sites. Numbers of spiders captured by mini‐sticky traps and mini‐quadrats increased exponentially as the season progressed. The high capture frequency in relation to population density, and the differential between web and non‐web sites, points to a dynamic and aggregated distribution of spiders in winter wheat, which is consistent with what is known about mate‐searching and web site abandonment rates by the Linyphiidae.

 The combination of techniques described here is recommended for monitoring prey availability in prey‐enhancement programmes and may prove useful in quantitative studies of both intra‐ and interspecific interactions between spiders.
A model of bovine tuberculosis in the badger Melesmeles: the inclusion of cattle and the use of a live test
Authors: Smith G.C. , Cheeseman C.L. , Wilkinson D. , Clifton‐Hadley R.S.
Published: March 2003

An individual‐based stochastic simulation model was used to investigate the control of bovine tuberculosis (TB) in the European badger Meles meles by using a live test to determine the presence of infection. The model was an extension of earlier models, and nearly all population and epidemiological parameters were derived from one study site.

 This is the first TB model to examine sex differences in disease epidemiology, and the transmission of TB from badgers to cattle. The latter is an essential step if reactive badger control strategies are to be modelled.

 Heterogeneity was introduced to the simulation model by the use of a carrying capacity, which defined the maximum number of breeding females per social group.

 The prevalence of TB, and the number of simulated cattle herd breakdowns, was reduced for all control strategies using a live test, namely localised culling, ring culling and proactive culling. However, only proactive culling resulted in a marked reduction in these values within a few years.

 If trapping efficacy was increased above its current value (80%), this did not improve the effectiveness of these culling strategies.

 If the number of individual badgers caught and tested per social group was doubled from two to four animals per group, then the overall level of effectiveness of these strategies could be doubled.

 The effectiveness could be improved if the sensitivity of the live test was increased, but did not continue to show an improvement above a sensitivity of about 70%.

 Given the constraints of the current live test sensitivity (41%) and a trapping efficacy of 80%, proactive culling, following the testing of four individuals per group, led to an average of three cattle herd breakdowns per year in the simulation, compared with an average of 31 per year when simulating the live test trial as used between 1994 and 1996.
Measuring the range to animals at sea from boats using photographic and video images
Authors: Gordon Jonathan
Published: March 2003

Estimating range to objects at sea by eye is notoriously difficult yet there are many occasions in management and research when accurate measures of range are required.

A new method is described in which range is calculated from the angle subtended between the horizon and the waterline of the object measured from single video or photographic images taken at a known elevation. Possible errors are explored and practical analysis methods outlined. Images can be collected and analysis performed using relatively inexpensive standard equipment.

In offshore waters, uncertainty in the height of the camera and target object due to the effects of waves and swell are likely to be the most significant sources of error. The effects of errors in camera height on ranges calculated using this method are approximately proportional to the ratio of the height error to camera height. Simulations indicate that wave‐ and swell‐induced errors in the height of both object and camera will lead to range estimates with a standard deviation (SD) of 0·5 × (error due to wave height)/(camera height).

Three trials were conducted in which ranges (out to 2000 m) measured using this method were compared with those determined using alternative methods (laser range‐finding binoculars or non‐differential global positioning system). Mean percentage discrepancies in range measurements between the two methods varied from 6·4% to 2·6%, while the SD of discrepancies in trials varied between 6·5% and 4·3%. The independent range measuring methods used here were not without error, however, and it is suggested that a mean absolute error of > 2% is an appropriate figure for the video method.

Field tests indicated that the necessary photos or video sequences could be collected from most types of cetaceans in the field. A variety of applications for the method during activities such as line transect surveys, mitigation monitoring and behavioural studies are suggested and discussed.
The effect of provenance on the performance of Crataegus monogyna in hedges
Authors: Jones A.T. , Hayes M.J. , Sackville Hamilton N.R.
Published: March 2003

Grants for wildlife enhancement in the British Isles have supported the widespread planting of new hedges along field margins. However, much of the planted material, particularly of hawthorn Crataegus monogyna, has been obtained from the continental mainland of Europe. There is a need to assess the implications of this practice for hedgerow performance and for the conservation of indigenous genetic variation.

One local ecotype and eight commercial provenances (four British and four continental European) of hawthorn were planted in an experimental hedge at both an exposed upland site and a sheltered lowland site. Sections of hedge were planted with or without fencing and with or without mulching in all combinations. Growth and thorniness were assessed over 3 years, and phenology and disease over 2 years.

At both sites, the most locally obtained provenance had the latest bud‐burst, exhibited the least severe symptoms of mildew and was the most thorny. It also showed the greatest height increment at the upland site, but was relatively slow‐growing at the lowland site.

An imported Hungarian provenance had early bud‐burst, showed a high growth rate and suffered the most severe mildew. A commercially obtained British native provenance was aberrant in its extremely early bud‐burst and other attributes comparable with the Hungarian provenance, indicating the possibility of misidentification at some stage of production or supply.

In the absence of fencing, at the upland site hawthorn mortality was 100% compared with only 3% at the lowland site. In fenced plots there was c. 320% greater growth when mulching was used.

The results suggest that for greater establishment success and hence cost benefits in hedge planting, as well as for greater environmental benefits, there should be closer matching of hawthorn provenance to the planting site. The use of commercial material has demonstrated that locally provenanced material can be superior to any commercially available material, and that the current state of the commercial sector is insufficient to enforce the necessary controls over provenance of material used for hedge renovation.
Comparing strategies for controlling an African pest rodent: an empirically based theoretical study
Authors: Stenseth Nils Chr. , Leirs Herwig , Mercelis Saskia , Mwanjabe Patrick
Published: March 2003

Small rodents in general and the multimammate rat Mastomys natalensis in particular cause major economic losses in Africa through damage to crops. Attempts to develop dynamic population models for this and other pest rodents are ongoing.

Demographic estimates from a capture–mark–recapture (CMR) study in Tanzania were used to parameterize a population model for this species. This model incorporated three functional age categories (juveniles, subadults and adults) of both sexes and used density‐dependent and density‐independent factors, the latter represented by rainfall.

The model was used to analyse the effect of rodent control on the population dynamics and resulting number of rats. Control measures affecting survival as well as reproduction were considered.

The model showed that control measures reducing survival will only have long‐term effects on population size if they are also applied when rodent densities are low. Control measures applied only when rodent densities are high will not have persistent effects, even at high mortality rates.

The model demonstrated that control measures reducing reproduction are likely to prevent Mastomys outbreaks, but will keep densities low over a long period only when the contraceptive effect is strong (> 75% reduction).

Provided that CMR data are available, we recommend developing Leslie‐type population models for rodent pests on the basis of CMR‐estimated demographic schedules. Such models have great potential in rodent management and allow the evaluation of different strategies.

Besides improving the ecological basis of the population modelling, economic considerations need to be incorporated into decisions about rodent control. We suggest that appropriate population models will provide important input into such decision making.
Brown locust outbreaks and climate variability in southern Africa
Authors: Todd Martin C. , Washington Richard , Cheke Robert A. , Kniveton Dominic
Published: March 2003

The brown locust Locustana pardalina is a major agricultural pest in southern Africa, with populations periodically reaching plague proportions. Management and control would benefit from a predictive capacity at seasonal time scales, as yet unavailable.

The results of a study into the dynamics and potential predictability of locust populations in southern Africa are presented here. The number of districts reporting locust control measures was used as a proxy for swarming brown locust populations.

Spectral analysis of the annual number of brown locust infestations over southern Africa revealed dominant periodicity at 17·3 years. The data were low‐pass filtered and the low‐frequency and high‐frequency components were retained. The low‐frequency component led the observed 18‐year cycle in southern African rainfall by about 3 years, and was therefore likely to reflect endogenous controls on populations.

Variability in the interannual high‐frequency component of brown locust infestations was strongly related to rainfall over the Karoo and Eastern Cape regions of South Africa. The highest correlations were with rainfall over the 12 months prior to the locust season (r = 0·64) and in particular with rainfall during December (r = 0·55).

Evidence is presented that the high‐frequency component is related to the Pacific El Niño/Southern Oscillation (ENSO) and that high‐frequency locust activity is abnormally high (low) during La Niña (El Niño) events.

The high‐frequency component of locust activity correlates positively and negatively, respectively, with sea‐surface temperatures over the tropical western and eastern Pacific Ocean many months in advance of the locust season. Activity also correlates positively (negatively) with sea‐surface temperatures over the south‐west Indian Ocean and the Southern Ocean (west and north‐west Indian Ocean). These relationships occur later than those in the Pacific, developing in the austral winter and peaking in early summer. This pattern of correlations and the associated atmospheric circulation anomalies is consistent with ENSO‐related and non‐ENSO related patterns of climate variability.

The results suggest that there may be considerable scope for future development of models for the seasonal prediction of brown locust activity in which high‐frequency variability is related to climatic indices.
Effects of Phalaris arundinacea and nitrate‐N addition on the establishment of wetland plant communities
Authors: Green Emily K. , Galatowitsch Susan M.
Published: March 2003

Nutrient enrichment may adversely impact plant species richness in wetlands and enhance their susceptibility to colonization and dominance by invasive species. For North American prairie wetlands, enrichment by nitrate‐N (NO3‐N) from agricultural runoff is thought to contribute to the increasing colonization and dominance of Phalaris arundinacea (reed canary grass), especially during restoration. If true, P. arundinacea might compromise the re‐establishment of sedge meadow vegetation on sites reflooded with agricultural drainage water.

We tested this hypothesis using a fertilization experiment in wetlands with controlled hydrology. A community mixture comprising 11 species from native sedge meadow was seeded in mesocosms and grown under one of three NO3‐N levels (0 g m−2 year−1, 12 g m−2 year−1, 48 g m−2 year−1) with or without P. arundinacea. Above‐ and below‐ground biomass were measured after two growing seasons to assess the response of vegetation to NO3‐N and P. arundinacea treatments.

The total shoot biomass of the native community was suppressed in the presence of P. arundinacea at all NO3‐N levels, but shoot suppression was significantly greater at the highest NO3‐N dose level (48 g m−2). Shoot growth of the native community was reduced by nearly one‐half under these conditions.

The total root biomass of the community was also suppressed by P. arundinacea when no NO3‐N was added.

As NO3‐N increased, the relative abundance (shoot biomass) of native graminoids declined while native forbs increased in communities with and without Phalaris. The most common graminoid, Glyceria grandis, was suppressed by P. arundinacea at all levels, with suppression enhanced at the 48 g m−2 NO3‐N level. Three other species were suppressed at the highest NO3‐N level, in the presence of Phalaris. The two most common forbs, Asclepias incarnata and Sium suave, exhibited a continual increase in growth with NO3‐N additions along with overall suppression by P. arundinacea.

Community diversity and evenness declined with increasing NO3‐N levels, whether or not P. arundinacea was present.

Our results demonstrate that if P. arundinacea is present, the restored sedge meadow community will not achieve levels of abundance that are possible when this species is absent, regardless of NO3‐N enrichment conditions.

At the same time, the increased suppression by P. arundinacea at the 48 g m−2 NO3‐N dose level supports the hypothesis that the dominance of this species over the native sedge meadow community is enhanced by NO3‐N inputs at levels that are common in agricultural landscapes.

Our results carry two implications for achieving biodiversity conservation in agricultural landscapes. First, reducing nitrate loads to wetland reserves is essential for minimizing declines in community diversity. Secondly, the use of P. arundinacea for soil conservation and other agri‐environmental purposes should be curtailed because of the likelihood of off‐site impacts to wetland biodiversity.
Using ants as bioindicators in land management: simplifying assessment of ant community responses
Authors: Andersen Alan N. , Hoffmann Benjamin D. , Müller Warren J. , Griffiths Anthony D.
Published: March 2003

The indicator qualities of terrestrial invertebrates are widely recognized in the context of detecting ecological change associated with human land‐use. However, the use of terrestrial invertebrates as bioindicators remains more a topic of scientific discourse than a part of land‐management practice, largely because their inordinate numbers, taxonomic challenges and general unfamiliarity make invertebrates too intimidating for most land‐management agencies. Terrestrial invertebrates will not be widely adopted as bioindicators in land management until simple and efficient protocols have been developed that meet the needs of land managers.

In Australia, ants are one group of terrestrial insects that has been commonly adopted as bioindicators in land management, and this study examined the reliability of a simplified ant assessment protocol designed to be within the capacity of a wide range of land managers.

Ants had previously been surveyed intensively as part of a comprehensive assessment of biodiversity responses to SO2 emissions from a large copper and lead smelter at Mt Isa in the Australian semi‐arid tropics. This intensive ant survey yielded 174 species from 24 genera, and revealed seven key patterns of ant community structure and composition in relation to habitat and SO2 levels.

We tested the extent to which a greatly simplified ant assessment was able to reproduce these results. Our simplified assessment was based on ant ‘bycatch’ from bucket‐sized (20‐litre) pitfall traps used to sample vertebrates as part of the broader biodiversity survey. We also greatly simplified the sorting of ant morphospecies by considering only large (using a threshold of 4 mm) species, and we reduced sorting time by considering only the presence or absence of species at each site. In this manner, the inclusion of ants in the assessment process required less than 10% of the effort demanded by the intensive ant survey.

Our simplified protocol reproduced virtually all the key findings of the intensive survey. This puts effective ant monitoring within the capacity of a wide range of land managers.
Population dynamics of the sheep blowfly Lucilia sericata: seasonal patterns and implications for control
Authors: Cruickshank Isla , Wall Richard
Published: March 2003

The infestation of sheep with blowfly larvae (sheep strike) is a significant animal welfare and economic problem in many regions of the world. Improved control requires greater knowledge of the population dynamics of the primary agent of strike in temperate areas, the blowfly Lucilia sericata (Diptera: Calliphoridae).

 The abundance of L. sericata was recorded on two farms in south‐west England between 1990 and 2000, and the time‐series analysed to describe and explain the nature of population change within and between years.

 To examine the catch time‐series for periodicity, the data were detrended, demeaned and tapered, and plotted against a day‐degree time base. Spectral analysis of periodograms showed that the clearest signal present was the low‐frequency seasonal cycle. The only other significant signal in both series had a periodicity corresponding to the day‐degree requirements for the entire life cycle of this insect species. This suggests that, within each season, the abundance pattern is composed of a series of semi‐discrete generation peaks.

 Significant density‐dependence was detected in the seasonal change in fly abundance and this was shown to be approximately compensatory in action.

 The results suggest that populations of L. sericata show relatively stable and predictable dynamics, with populations passing through three or four relatively discrete generations each year prior to diapause and limited by strong, apparently compensatory, density‐dependence each season.

 The results have important implications for the control of this insect parasite. In general, earlier and more intense farmer intervention, to reduce sheep susceptibility and treat struck animals during the blowfly season, would result in a lower L. sericata population and reduced strike incidence. However, at the start of the season, when fly abundance may be lower than the number of susceptible hosts, direct fly control, in addition to treatment, may be a more effective strategy.
The ecology and growth patterns of Cleistogenes species in degraded grasslands of eastern Inner Mongolia, China
Authors: Liang Chen , Michalk D. L. , Millar G. D.
Published: March 2003

Cleistogenes is an important perennial grass genus found in the pastoral steppes of eastern Inner Mongolia. Despite its dominance in many grassland types, the value of Cleistogenes as a key genus for sustainable grassland development has only recently been recognized. To understand better how to manage Cleistogenes‐dominant grasslands, an experiment was conducted in China, to characterize the growth patterns of two Cleistogenes species (C. polyphylla and C. squarrosa) in relation to environmental parameters.

Sampling exclosures were established on uniform grasslands at Mangha and Liuhe gachas. Over two growing seasons (1999–2000) vegetation cover, green and dry biomass by species, species height and tiller density of Cleistogenes were measured at about monthly intervals starting in mid‐May and ending in mid‐October. Cleistogenes polyphylla at Mangha and C. squarrosa at Liuhe accounted for > 50% of green biomass. Neither species made any significant growth before late June, even though soil moisture was available and a large number of tillers were present that had survived the subzero winter intact. In contrast, other species (Prunus sibirica, Potentilla spp. Aneurolepidium chinense) produced up to 500 kg ha−1 biomass in early spring.

A relationship between temperature and green weight (wt) tiller−1 indicated that Cleistogenes required an average air temperature > 20 °C to initiate growth, most probably due to its C4 photosynthetic pathway. In this region, temperatures above 20 °C also coincide with periods of most reliable rainfall, which may explain the success of Cleistogenes in grassland degraded by overgrazing. In contrast, competing C3 species (e.g. Stipa spp. and Aneurolepidium chinense) initiate growth earlier in spring when rainfall is highly variable and when small plants are most exposed to severe grazing pressure by livestock emerging from winter in poor condition.

Where Cleistogenes spp. completely dominated the grassland, the length of the growing season was shorter and feed shortages in early spring became more acute than for grasslands dominated by C3 species. Livestock producers can minimize this effect by adopting management tactics such as resting pastures in spring to maintain a balance between C3 and C4 perennial grasses. Further research is needed to establish when grazing and strategic rest have most impact on the stability of Cleistogenes‐dominant grasslands.
Evidence of pesticide resistance in medium‐sized mammalian pests: a case study with 1080 poison and Australian rabbits
Authors: Twigg Laurie E. , Martin Gary R. , Lowe Tim J.
Published: March 2003

Toxicant‐resistance is a potential, or very real, problem with many pest‐control programmes world‐wide. However, apart from rodents, pesticide‐resistance has not been well documented in vertebrates. We assessed the potential impact of developing resistance to 1080 in rabbit populations with differing levels of historical exposure to 1080‐baiting programmes in south‐western Australia.

The sensitivity to 1080 of three out of the four populations of rabbits Oryctolagus cuniculus examined had decreased significantly since Australian rabbits were last tested over 25 years ago. The lethal dose50 (LD50) values for these populations, as determined from formal toxicity trials, ranged from 0·744 to 1·019 mg pure 1080 kg−1, and were significantly greater (P < 0·05) than the previously reported values for Australian rabbits (LD50 range 0·34–0·46 mg pure 1080 kg−1). The LD50 value for the fourth population (0·584 mg pure 1080 kg−1), which has had the least exposure to 1080, did not differ from that reported previously (P > 0·05).

The lethal dose99 (LD99) values for the four rabbit populations tested ranged from 1·181 to 1·666 mg pure 1080 kg−1, and suggested that, theoretically, all rabbits should be killed during routine baiting campaigns provided that there is no loss of active ingredient from the bait. In reality, the efficacy of 1080 poison bait laid in trails for controlling free‐ranging rabbits was reduced in those populations where rabbits had decreased sensitivity to 1080. Mean reductions in rabbit numbers 7–9 days after trail baiting of resistant and sensitive populations ranged from 51·2% to 65·2%, and from 76·4% to 76·5%, respectively.

These findings suggest that genetic resistance to 1080 is developing in at least some populations of Australian rabbits. This has world‐wide implications for agricultural protection and wildlife conservation programmes that rely on a 1080‐baiting strategy for reducing the impact of vertebrate pests.
Is habitat linearity important for small mammal communities on farmland?
Authors: Tattersall F. H. , Macdonald D. W. , Hart B. J. , Johnson P. , Manley W. , Feber R.
Published: March 2003

Farmland is readily divisible into linear habitats such as hedges, and non‐linear habitats such as fields and woodlots. In agricultural landscapes, conservationists have generally focused on enhancing linear habitats, but there are few data from which to judge whether or not this is a good strategy for biodiversity.

We investigated whether the linear or non‐linear character of habitat patches, mediated by edge effects, has an impact on the abundance, diversity and richness of the small mammal communities that live within and between them.

In particular, we hypothesized, first, that edge effects cause narrow linear habitats to be avoided by specialists such as the bank vole Clethrionomys glareolus, but not by generalists such as the wood mouse Apodemus sylvaticus; secondly, that edge effects lead to specialists being present in atypical habitat, through excursions at the interface between two habitats.

We tested these hypotheses by live‐trapping small mammals in grids in the centres of three non‐linear farmland habitats (woodlots, set‐aside and crop fields) and in field boundaries consisting of a series of adjoining linear habitats. We compared mammal communities in the non‐linear habitats with the field boundary as a whole, and with the individual linear habitat elements within the boundary.

There was no evidence that specialists avoided linear habitats. Indeed, the field boundary was the most species‐rich habitat surveyed, and bank voles were more abundant in linear hedgerow than in non‐linear woodland. Bank voles were present in linear set‐aside and in the crop edge, but never in non‐linear blocks of set‐aside or crop, implying that they diffused out of the hedgerow into the adjacent habitats. There was no evidence of an effect of habitat linearity on field voles Microtus agrestis, wood mice or common shrews Sorex araneus.

Our results suggest that on uncropped land such as set‐aside, the linear or non‐linear character of habitats will make little difference to small mammal abundance and diversity. We advocate similar assessments for other taxa so that the effects of farm management and habitat configuration on biodiversity can be understood more fully.
The prevalence and number of Salmonella in sausages and their destruction by frying, grilling or barbecuing
Authors: Mattick K.L. , Bailey R.A. , Jørgensen F. , Humphrey T.J.
Published: March 2003

Aims: To determine the prevalence and number of Salmonella and Campylobacter in sausages and to evaluate their destruction during cooking. Methods and Results: One hundred and sixty-two packs of uncooked economy or catering sausages, comprising 53 packs of frozen and 109 of chilled sausages, were purchased in Devon between March and July 2000. All were tested for the presence of Salmonella and 51 packs of chilled sausages were also examined for the presence of Campylobacter spp. To investigate the heat tolerance of Salmonella enterica serovar Typhimurium DT104 in sausage-meat, chilled, handmade and frozen sausages were inoculated with approx. 1·5 × 104 bacterial cells per sausage (∼300 cfu g−1) and then cooked by frying, grilling or barbecuing. The levels of creatinine kinase, lactate dehydrogenase and alkaline phosphatase in uncooked and cooked sausages were measured to evaluate their potential as indicators of adequate cooking and, therefore, pathogen elimination. Salmonella were detected in 7·5% of frozen and 9·1% of the chilled sausages (8·6% overall) but Campylobacter spp. were not isolated. After cooking, a visual assessment suggested that all of the sausages were thoroughly cooked. Despite this, barbecuing and frying sometimes allowed Salmonella cells to survive and the temperature profiles during cooking indicated that the lethal range was sometimes not reached. The enzyme levels tested were not reliable indicators of the inactivation of bacterial pathogens because Salmonella were sometimes isolated from sausages with low values of all three enzymes. Conclusions:Salmonella spp. are present in a significant proportion of sausages and are not always killed during the cooking process. Significance and Impact of the Study: These findings have clear implications for public health.
Mechanisms of 5‐hydroxytryptamine‐induced inhibition in the porcine myometrium
Authors:   Kitazawa, Takaoka K. , Taneike T.
Published: March 2003

1 The present experiments were designed to clarify the mechanisms of the inhibitory response of 5‐hydroxytryptamine (5‐HT) in the porcine uterine circular muscle.

2 Inhibitory responses induced by 5‐HT (1 n
m–1 μm) were not affected by apamin (1 μm), charybdotoxin (100 n
m) or glibenclamide (20 μm) but were significantly attenuated by 4‐aminopyridine (3 m
m) and tetraethylammonium (3 m
m).

3 Imidazole (100 μm) decreased but 3‐isobutyl‐1‐methylxanthine (30 μm), milrinone (30 μm) and Ro 20–1724 (10 and 30 μm) potentiated the 5‐HT‐induced inhibition. On the other hand, zaprinast (3–30 μm) had no significant effect on the inhibitory response of 5‐HT.

4 5‐HT caused a time (0–5 min)‐and concentration (1 n
m–1 μm)‐dependent increase in the tissue cyclic AMP level, but had no effect on the tissue cyclic GMP level. A significant correlation (P < 0.05) was observed between the inhibition of contraction and tissue cyclic AMP level.

5 The effect of 5‐HT on contractile force and cytosolic Ca2+ level ([Ca2+]i) was investigated using fura‐PE3‐loaded myometrial strips. A low concentration of 5‐HT (≤ 10 n
m) inhibited the spontaneous contraction without changing the amplitude of the spontaneous [Ca2+]i increase, but a higher concentration of 5‐HT (≥ 100 n
m) decreased the resting [Ca2+]i and inhibited both the spontaneous [Ca2+]i increase and spontaneous contraction.

6 High‐K+ (50 m
m) caused increases in muscle contractile force and [Ca2+]i. 5‐HT concentration‐dependently inhibited the high‐K+‐induced contraction (EC50, 45 n
m) with only a small decrease in [Ca2+]i increase.

7 Carbachol also caused increases in muscle contractile force and [Ca2+]i. 5‐HT significantly decreased both the carbachol‐induced contraction and [Ca2+]i increase, but was more potent at inhibition of contractile force than [Ca2+]i.

8 In Ca2+ ‐loaded myometrial strips, carbachol, but not caffeine, caused a transient increase in [Ca2+]i and contraction in the absence of external Ca2+ (EGTA, 1 m
m). 5‐HT inhibited both the carbachol‐induced increases in [Ca2+]i release and contractile force.

9 In the β‐escin permeabilized myometrium, 5‐HT significantly inhibited the Ca2+‐induced contraction.

10 The present results indicate that 5‐HT stimulates tissue cyclic AMP production, and inhibits the porcine uterine muscle contractility by a reduction in [Ca2+]i and in Ca2+ sensitivity of the contractile elements. Activation of K+ channels might be partially involved in 5‐HT‐induced inhibition of the myometrial contractility.
Characterization of mechanisms involved in presynaptic inhibition of sympathetic pressor effects induced by some 5‐HT1 receptor antagonists
Authors: Fernández M. M. , Calama E. , Morán A. , Martín M. L. , San Román L.
Published: March 2003

1 In a previous study, we showed that the presynaptic inhibitory action of 5‐hydroxytryptamine receptor agonists on sympathetic pressor effects obtained in the pithed rats were mainly mediated by activation of 5‐HT1A and 5‐HT1D receptor subtypes. At the time, we observed that some 5‐HT1 receptors antagonists – WAY 100,635 and NAN‐190 (both 5‐HT1A receptor antagonists), methiothepin (a 5‐HT1,2,5,6,7 receptor antagonist) and spiperone (a 5‐HT1,2 receptor antagonist) – reduced per se the pressor effects obtained by electrical stimulation. The aim of the present work was to investigate the mechanism participating in this inhibitory effect.

2 The inhibition induced by WAY 100,635 (1000 μg kg−1, i.v.) was blocked after i.v. treatment with idazoxan, an α2‐adrenoceptor antagonist (300 and 1000 μg kg−1) and was not modified after i.v. treatment with propranolol, a β‐adrenoceptor antagonist (1000 μg kg−1) and sulpiride, a D2 receptor antagonist (1000 μg kg−1). The inhibition induced by spiperone (500 μg kg−1 i.v.) was significantly blocked by sulpiride (1000 μg kg−1) and was not modified by idazoxan or propranolol.

3 Sulpiride (1000 μg kg−1) partially blocked the inhibition induced by methiothepin (50 μg kg−1 i.v.). Only pretreatment with idazoxan (300 μg kg−1) modified the inhibition induced by NAN‐190 (100 μg kg−1 i.v.), such inhibition increasing after intravenous administration of idazoxan.

4 All the antagonists used in our experiments failed to inhibit the pressor responses elicited by i.v. noradrenaline administration.

5 The above results suggest that the inhibitory effects of these 5‐HT1 receptor antagonists are presynaptic in nature, but not related to the blockade of 5‐HT1 receptors subtypes. The simultaneous activation or inhibition of other receptor systems could explain the inhibition produced by each 5‐HT1 receptor antagonist studied.
The effect of isolation and history on colonization patterns of plant species in secondary woodland
Authors: Grashof‐Bokdam C. , Geertsema W.
Published: March 2003

Colonization success of woodland originating after 1850 was determined for seventeen forest plant species having different dispersal strategies. Colonization rate of the studied endo‐and exozoochorous species apparently was considerable higher than that of species having short distance dispersal like myrmecochores and species lacking dispersal mechanisms. The occurrence of eight species in this young forest habitat was related to the distance to the nearest source patch (DNS), as well as to the age of the young patches and to their former land use. DNS calculated to old, existent and occupied source patches affected most analysed species. Only Ilex aquifolium L. had a significant higher occurrence in woodland originating before 1916 than in those originating after 1916. Former land use showed significant effects for three species. Although colonization rate and effects of studied parameters on occurrence were different for the studied species, no clear differences were found between different dispersal groups. The consequences of these results for the understanding of colonization processes of the species studied is discussed.