bluuebunny/crossref_metadata_2025 huggingface dataset:
Polyandry and competition for territories in bronze‐winged jacanas
Authors: Butchart Stuart H. M. , Seddon Nathalie , Ekstrom Jonathan M. M.
Published: March 2003

1. We tested the hypothesis that in territorial, sex‐role reversed birds the distribution of resources may determine the dispersion of males, which may, in turn, determine the dispersion of females (i.e. the converse of the classical view of breeding systems in most species).

2. Bronze‐winged jacana (Metopidius indicus) territories were exclusive within the sexes, and female territories encompassed 1–4 male territories. The breeding density was limited by both habitat availability (floaters settled when new habitat flooded) and competition for territories (floaters filled natural and experimental vacancies).

3. Territory vacancies created by removal experiments were filled quickly either by floaters, neighbours, or male co‐mates that expanded their territories. Changes in male territories had a significantly greater impact on female territories than vice versa, in terms of size and overlap before and after the experiment. Female dispersion was therefore influenced by the dispersion of males. However, males also played an active part in mate changes through occasional territory adjustments, and sexual interactions with females.

4. There was no evidence for a relationship between dispersion of resources and male territory size, but heavier males defended larger territories. Both neighbouring males and co‐mates constrained the size of male territories. There was no evidence that polyandry arose through males settling on and subdividing female territories, but rather males competed for space, and female territories were superimposed on the mosaic of male territories.

5. Female territory size was positively correlated with harem size, but seemed to be unrelated to habitat quality. Females may have attempted to maximize territory size to encompass as many males as possible. Males in larger harems defended smaller territories. The degree of polyandry therefore depended on both male and female territory sizes.
Demographic estimates from radio‐tagging: models of age‐specific survival and breeding in the goshawk
Authors: Kenward R. E. , Marcström V. , Karlbom M.
Published: March 2003

1. Age‐specific survival and breeding (ASSAB) models were developed with data from 318 goshawks (Accipiter gentilis L.) fitted during 1980–7 on the Baltic island of Gotland with tail‐mounted radio‐tags.

2. Comparisons with recaptures and recoveries of 238 ringed juveniles without radio‐tags detected no marking bias among hawks radio‐tagged at nests, nor survival bias from tag impacts or signal‐loss effects, but disproportionate adult deaths within a month of trapping.

3. Among 63 dead hawks found by radio‐tagging, 35% were killed by humans and 65% died from natural causes, mainly starvation. Ring recoveries over‐represented killing by humans.

4. Radio‐tagging estimated first‐year male survival rates of 0·49–0·54 to the next spring, lower than estimates of 0·69–0·71 for females; combined survival was higher than in contemporary ringing records. Excluding first‐month data from trapped adults, second‐year survival was 0·59 for males, 0·71 for females, and 0·79–0·83 for both sexes thereafter.

5. No hawks were observed to build nests or lay eggs in their first year. Only 8% of radio‐tagged females laid eggs in their second year, but 47% of older females. Second‐year males were as often as older males in egg‐laying pairs (70%), but were less likely to rear young.

6. Mark‐recapture of 351 goshawks ringed in nests estimated that 262 fledged on Gotland annually, from 151 nests with eggs. Emigration was 3% (SE ± 2%), with 1 ringed immigrant.

7. An ASSAB model with staggered‐entry survival estimates predicted no population change when based on males, with breeding success of 75% from laying to fledging, and a brood size of 2·27; independently recorded values for 165 nests were 75% (± 3%) and 2·24 (± 0·08).

8. The model required a 0·5% increase in female survival rate for equal numbers of hawks to pair, and an increase in fledging success from 73% to 75% for a balanced population with a brood size matching the 2·27 of males. The model estimated a male : female ratio of 1·0 : 1·78 in the adult population, with 71% of males breeding annually but only 40% of females.
Direct and indirect competitive effects of foliage feeding guilds on the performance of the birch leaf‐miner Eriocrania
Authors: Fisher A. E. I. , Hartley S. E. , Young M.
Published: March 2003

1. Competitive interactions between Eriocrania spp. Zeller (Lepidoptera: Eriocraniidae) leaf‐miners and other folivorous guilds (free‐living Lepidoptera and phloem feeding aphids) of silver birch (Betula pendula Roth) were examined experimentally.

2. Measurements of the foliage quality were taken from the experimental trees in order to discover whether variation in nitrogen and secondary compounds (specifically total phenolics), had an effect on the strength of any competitive interactions between the guilds.

3. There was evidence for indirect interactions within the leaf‐mining guild mediated by the host plant: miners in aggregations had double the mortality of single miners. Interactions with leaf‐chewing Lepidoptera were limited to interference and resource removal since only damage to the leaf being mined had an effect on the miner performance. There were no interactions between Eriocrania and aphids, despite the presence of aphids reducing the quantity of foliage available by 33%.

4. The strength of the competitive interactions, either within or between guilds, was not modified by the quality of the host trees. However, biomass of emerging larvae was negatively related to increased phenolic content of host trees and positively related to increased nitrogen content. Furthermore, larvae emerged later from trees where foliage had higher phenolic content.

5. The longevity of feeding events by competitive folivore guilds and the proximity of the feeding to the miners were identified as the key factors influencing the effects of foliage damage on the performance of Eriocrania.
On the misuse of residuals in ecology: testing regression residuals vs. the analysis of covariance
Authors: García‐Berthou Emili
Published: March 2003

An analysis of variance (anova) or other linear models of the residuals of a simple linear regression is being increasingly used in ecology to compare two or more groups. Such a procedure (hereafter, ‘residual index’) was used in 8% and 2% of the papers published during 1999 in the Journal of Animal Ecology and in Ecology, respectively, and has been recently recommended for studying condition.

Although the residual index is similar to an analysis of covariance (ancova), it is not identical and is incorrect for at least four reasons:

 the regression coefficient used by the residual index differs from the one used in ancova and is not the least‐squares estimator of the model.

in contrast to the ancova, the error d.f. in the residual index are overestimated because of the estimation of the regression coefficient.

the residual index also assumes the homogeneity of regression coefficients (parallelism assumption), which should be tested with a special ancova design.

even if the assumptions of the linear model hold for the original variables, they will not hold for the residuals.

More importantly, the residual index is an ad hoc sequential procedure with no statistical justification, unlike the well‐known ancova. For these reasons, I suggest that a t‐test or an anova of the residuals should never be used in place of an ancova to study condition or any other variable.
Statistical modelling of the population dynamics of a raptor community in a semi‐desert environment
Authors: Krüger Oliver , Liversidge Richard , Lindström Jan
Published: March 2003

We performed an extensive statistical modelling study on the population fluctuations and population growth rates of 15 raptor species in the Kalahari desert in South Africa.

The correlation pattern between rainfall and population abundance changed systematically with raptor body weight and diet type. The abundance of heavier raptors feeding on larger prey‐items had lower correlations with rainfall than lighter raptors feeding on small prey‐items. Whereas raptor species feeding on small prey‐items were more affected by immediate rainfall, species feeding on large prey‐items were more affected by rainfall in the previous year.

Population abundances were explained most parsimoniously by direct and delayed density dependence and rainfall during the current and previous breeding season. Interspecific competition was never a predictor variable. Population abundances of species best described by rainfall fed on larger prey‐items than population abundances of species best described by density dependence.

Population growth rates were always best described by direct density dependence. The strength of density dependence was positively correlated with reproduction rate, due mainly to Falconiform species having higher reproduction rates than Accipitrid species.

Shifting from the species to the guild level, we found that abundance and biomass shares of feeding guilds did not vary significantly over time, supporting the hypothesis of guild constancy.
Resource availability and goshawk offspring sex ratio variation: a large‐scale ecological phenomenon
Authors: Byholm Patrik , Ranta Esa , Kaitala Veijo , Lindén Harto , Saurola Pertti , Wikman Marcus
Published: March 2003

Local population studies have shown that sex allocation among many birds and mammals seems to be partly non‐random and in connection to surrounding factors, such as environmental or parental quality. In this scenario, if environmental quality varies in space and time, it is feasible that environmental quality also comes to influence offspring sex ratio on larger geographical scales.

Investigating this idea – using nation‐wide data sets on size‐dimorphic Finnish northern goshawks Accipiter gentilis from 1989 to 1998 – we found that offspring sex ratio is related to spatial and temporal variation in availability of their main prey, woodland grouse species.

In a majority of locations (n = 73), broods are large and male‐biased when grouse density is high, while small and female‐biased broods are found in areas and times with low grouse density. When adjusted for grouse density, the correlation between brood size and sex ratio disappears, but the correlation between grouse density and sex ratio remains.

We also found evidence indicating a mechanism balancing local offspring sex ratios towards the previously rarer sex with a time lag of 1 year. That is, local sex ratios in subsequent years are negatively correlated.

Our study highlights the importance of inclusion of both time and space in sex ratio studies. Ignorance of these dimensions could explain a great deal of the inconsistency in many earlier local sex ratio studies.

Irrespective of whether the observed pattern is the result of facultative manipulation, sex biased mortality, or both, it is suggested that the male‐biased sex ratio during periods of high grouse availability maximizes goshawk reproductive success.
Seasonal patterns of growth, expenditure and assimilation in juvenile Atlantic salmon
Authors: Jones Wayne , Gurney William S. C. , Speirs Douglas C. , Bacon Philip J. , Youngson Alan F.
Published: March 2003

We report a modelling study of a data‐set describing the growth of individual Atlantic salmon (Salmo salar L.) parr in the Girnock Burn (Scotland). A development of the compensatory growth model due to Broekhusien et al. (1994) was fitted to these data by numerical optimization.

The model uses carbon mass as a surrogate for an energy currency. This mass is divided into structure and reserve components, so as to describe decoupled changes in length and wet‐weight.

Using the same parameters for all fish, our model explained 83% of the variability in length and weight at age. Adding a single additional parameter for each individual enabled the model to explain over 96% of length and weight variability.

Weak negative correlation between size at first capture and within‐study growth argues against genetic causality of observed growth variability.

The energetic basis of our model enables us to infer time‐series of net assimilation and basal maintenance rates for the observed individuals. Maximal growth occurs early in the season when high assimilation is accompanied by low temperatures and maintenance rates. In late season, continuing high assimilation is balanced by high maintenance rates consequent on summer temperatures.
Winter management of Californian rice fields for waterbirds
Authors: Elphick Chris S. , Oring Lewis W.
Published: March 2003

1.  Recent legislation designed to reduce air pollution has restricted Californian rice‐farmers from burning rice stubble after harvest. Intentional flooding of fields during winter to speed straw decomposition is becoming increasingly common as growers seek alternatives to burning residual straw. The potential for flooded fields to act as a surrogate for destroyed wetland habitat may be an additional benefit in a region that hosts a large proportion of North America’s wintering waterbirds. We investigated the degree to which waterbirds use flooded fields and whether the method of flooding affects their use. Specifically, we tested whether waterbird use (a) was greater in intentionally flooded fields than in unflooded fields, (b) differed among flooded fields receiving different straw manipulations and (c) varied with water depth.

2.  Intentionally flooded rice fields received significantly greater use by 24 of 31 species studied. Only great blue herons Ardea herodias and sandhill cranes Grus canadensis were significantly more common in unflooded fields. Geese densities did not differ between flooded and unflooded fields.

3.  We found no differences in the densities of most species in flooded fields that received different straw manipulations to improve decomposition rates. Exceptions included several small shorebirds which occurred at highest densities in fields where straw was incorporated into the soil.

4.  Species differed in their use of different water depths. For 14 species we tested whether preferred depths, suggested in the literature, received disproportionately higher use. Most of these species were more likely to be encountered within the suggested depth ranges. Depth, however, was a poor predictor of bird density. Depths of 15–20 cm resulted in frequent use by the greatest number of species.

5.  We conclude that flooding rice fields increased suitable habitat for most, but not all, species studied. Different straw manipulation methods had little effect on most species. Water depth, however, was important in determining species occurrence. During the first half of the winter, water depths were greater than the median depths used by most species.
Modelling Chlamydia–koala interactions: coexistence, population dynamics and conservation implications
Authors: Augustine David J.
Published: March 2003

1.  Considerable research has been conducted on koala Phascolarctos cinereus population dynamics and the epidemiology of Chlamydia psittaci infection in koalas, but the impact of Chlamydia on koala populations has been difficult to assess.

2.  I developed a model of koala and Chlamydia population dynamics to examine interactions between Chlamydia transmission and pathogenicity, koala mating behaviour and demography, and koala population persistence.

3.  Simulations based on sexual and parent–offspring parasite transmission demonstrate that stable Chlamydia–koala coexistence is possible in a small population for a broad range of demographic, behavioural, pathogenicity and transmission parameter estimations. Koala population persistence was most sensitive to reduced annual survivorship of adults (4–10‐year‐old males and 2–12‐year‐old females), highlighting the need for accurate field estimates of adult survivorship in order to assess Chlamydia’s impact on specific populations.

4.  If koalas become less resistant to disease in fragmented, high‐stress habitats (i.e. experience increased Chlamydia‐induced mortality and sterility rates), Chlamydia is not predicted to cause koala extinctions under most conditions. Extinctions are only predicted if Chlamydia transmission rates also increase (e.g. due to new transmission pathways or increased mating frequency), or other non‐disease factors change birth and mortality rates to reduce the koala population’s intrinsic rate of increase below 0·1.

5.  The most important predicted effect of habitat fragmentation and other forms of human disturbance on this unique host–parasite relationship is the extinction of Chlamydia in populations where koala resistance to disease decreases.
Soil seed bank of an upland calcareous grassland after 6 years of climate and mangement manipulations
Authors: AKINOLA M. OLATUNDE , THOMPSON KEN , BUCKLAND SARAH M.
Published: March 2003

The soil seed bank of limestone grassland plots was investigated after 6 years of manipulation of temperature, rainfall, fertility and disturbance. An inoculum of seeds of species alien to the site was also added to the experiment.

The seed bank was largely made up of species that were native to the site and had small, persistent seeds. Large‐seeded species, whether native or introduced, were rare or absent in the seed bank. Small‐seeded species were generally more deeply buried than large‐seeded species. Total seed density was comparable with that of other limestone grasslands.

Significant climate effects were few, although the seed bank of the winter annual Arabidopsis thaliana was increased by summer drought and that of Cerastium fontanum was increased by winter heating.

The density of seeds of native species declined in response to disturbance and increased fertility treatments, while that of introduced species increased. Changes in the seed bank lagged behind changes in the vegetation, with introduced species making up a higher proportion of the vegetation than of the seed bank after 6 years of manipulation.
Root vole movement patterns: do ditches function as habitat corridors?
Authors: Mauritzen Mette , Bergers Piet. J. M. , Andreassen Harry P. , Bussink Harry , Barendse Rutger
Published: March 2003

1. Ditches are often connected to root vole habitat patches (i.e. moist reed patches) in the Netherlands. Due to the linear structure of ditches and because ditch habitat is qualitatively similar to root vole habitat patches, we hypothesized that ditches could function as habitat corridors facilitating dispersal movement of root voles. In order to test this hypothesis, we radiotracked root voles released in a landscape novel to them, consisting of ditches and agricultural meadows.

2. Agricultural meadows often surround the marsh patches inhabited by root voles. As the meadows are mowed regularly, we included the length of the meadow vegetation as an experimental factor in the study.

3. Assuming that ditches function as habitat corridors, we expected root voles in the ditches to move faster and more unidirectionally than root voles in the meadows, and to prefer the ditches to meadows.

4. We found that the ditches did not facilitate faster movements than the meadows. Although the root voles moved back and forth within the ditches, they showed a more directional movement pattern than the root voles in the meadows. Furthermore, the root voles preferred the ditch habitat irrespective of the vegetative cover in the meadow.

5. We conclude that ditches could function as habitat corridors for root voles, as they preferred to move in ditches when in unfamiliar areas.
Between‐observer variation in the application of a standard method of habitat mapping by environmental consultants in the UK
Authors: Cherrill Andrew , McClean Colin
Published: March 2003

1. In the UK, Phase 1 survey is a standard method of habitat mapping that has been used widely for environmental assessment and management planning. In this paper we make the first rigorous test of the precision with which environmental consultants apply the technique.

2. Six ecologists surveyed independently the same upland site in northern England. In pairwise comparisons between maps, spatial agreement was found to average 25·6% (with a range of 17·3–38·8%) of the area of the study site. The numbers of land cover types that were identified ranged from 13 to 21. Four or more surveyors agreed on the classification of 19% of the study site, while the area of land upon which all six agreed was only 7·9% of the study site. Spatial errors in the positioning of habitat boundaries occurred, but were a relatively minor source of the differences between maps. The majority of differences between maps were due to classification errors. Land cover types with similar species compositions were most frequently confused.

3. Spatially referenced field ‘target notes’ giving additional information on the vegetation mapped in each survey varied in number between 18 and 56. The contents of target notes were inadequate to allow a retrospective assessment of mapping decisions. The total numbers of species listed in target notes varied between surveys from 25 to 145. Sorenson's similarity for species lists derived from pairs of surveys ranged from 18·8% to 63·7%, and was not related to spatial agreement between surveys.

4. Time spent at the field site was not a correlate of any aspect of the results or cost of the survey. Three surveys conducted by members of a professional institute for ecologists were the most expensive, and also recorded larger numbers of target notes and species than the other surveys. However, their maps were no more similar than other pairs of maps.

5. Analysis of the survey results and comparisons with other methods of vegetation mapping suggest that mapping precision could be increased by (i) placing a greater emphasis on use of aerial photographs and other extant map data prior to (and during) field work; (ii) making greater provision for mapping of mosaics and increasing the level of floristic information in habitat definitions; (iii) recording a greater number of more detailed target notes in the field; and (iv) providing office‐based support to assist in the interpretation of aerial photographs, and the cross‐checking of field surveyors’ preliminary classifications against the contents of target notes and habitat definitions. The current application of the Phase 1 approach by environmental consultants places too great a reliance on decision‐making by the (frequently) unsupported lone surveyor whilst in the field.
Releasing genetically modified organisms: will any harm outweigh any advantage?*
Authors: Beringer John E.
Published: March 2003

1.  The public debate about genetically modified organisms has concentrated largely on concerns about food safety and potential risks to the environment. In both cases there appears to be an assumption that existing crops and animals are safe. I discuss the experience we have to date from traditional methods and conclude that most concerns about environmental harm are more relevant to existing crops.

2.  The flow of genes among species, and even within different genera, is discussed with due attention being paid to the need for inherited genes to confer a selective advantage on hosts.

3.  A reason why so many people are critical of intensive agriculture and biotechnology is that virtually all changes in agricultural practice have an adverse impact on wildlife, particularly when such change leads to increased intensification. The problem of deciding how to manage agriculture to ensure that we maintain or enhance species diversity of wild plants and animals is discussed against the background that most of the UK environment is the result of human intervention.

4.  Nature and dense human populations cannot coexist without the former suffering. Our objective should be to develop and exploit our understanding of ecology to provide the information required to enable us to develop a far more enlightened future for agriculture and wildlife.
The impacts of non‐native species on UK biodiversity and the effectiveness of control
Authors: Manchester Sarah J. , Bullock James M.
Published: March 2003

1. The introduction of non‐native species continues to cause ecological concern globally, but there have been no published reviews of their effects in the UK. Impacts in the UK are therefore reviewed, along with current legislation and guidelines relating to the introduction and control of such species.

2. A large number of non‐native species have been introduced to the UK, both deliberately and accidentally, but only a small number of introduced non‐native species have established and caused detrimental ecological impacts. However, general declines in UK biodiversity, and the potential effects of future climate change, may increase the susceptibility of ecosystems to invasions.

3. Detrimental impacts of non‐native species on native biota have occurred through competition, predation, herbivory, habitat alteration, disease and genetic effects (i.e. hybridization). There are potential effects on genetic biodiversity as well as species biodiversity.

4. Several high profile examples highlight the technical difficulties, and financial implications, of removing an introduced species once it is established. Few UK control or eradication programmes have been successful.

5. Control might be more feasible if ‘problem’ species could be identified at an earlier stage of establishment. However, the poor success of attempts to characterize invasive species and predict which will have negative impacts highlight the individual and unpredictable nature of invasions. The difficulties of making general predictions suggest that every proposed species introduction should be subject to rigorous ecological characterization and risk assessment prior to introduction.

6. The plethora of UK legislation and guidelines developed to reduce impacts of non‐native species only go part of the way towards ameliorating impact. Many species already established in the wild might cause future problems. Illegal releases and escapes of non‐native species may augment feral populations or establish new colonies. While regulation of imports and releases is important, further enforcement of existing legislation and action against unlicensed releases is necessary.
On the measure of sampling effort used in species accumulation curves
Authors: Moreno Claudia E. , Halffter Gonzalo
Published: March 2003

We agree with Willott (2001) that number of individuals would be an appropriate measure of sampling effort to compare species accumulation curves among sites, but the reason is not sampling bias. It has been shown theoretically that number of individuals is an unbiased effort unit when density varies among sites, although our results with bats do not prove this.

We compared our results using nights and individuals as measures of effort in bat species accumulation curves, but did not detect changes in the estimated richness using the two measures.

We maintain our position about the utility of species accumulation curves as practical tools for inventory assessment, even for very diverse groups. To compare curves from different sites, we agree that number of individuals may be an unbiased measure of effort. But to give practical recommendations for sampling, we suggest that effort also be expressed in standard sampling units.
Long‐term indirect effects of mechanical cockle‐dredging on intertidal bivalve stocks in the Wadden Sea
Authors: Piersma Theunis , Koolhaas Anita , Dekinga Anne , Beukema Jan J. , Dekker Rob , Essink Karel
Published: March 2003

There is world‐wide concern about the effects of bottom‐dredging on benthic communities in soft sediments. In autumn 1988, almost a third of the 50‐km2 intertidal system around the island of Griend in the western Dutch Wadden Sea was suction‐dredged for edible cockles Cerastoderma edule and this study assessed subsequent effects. An adjacent area not directly touched by this fishery and an area from which the mussel Mytilus edulis beds were removed, served as reference areas.

Sediment characteristics, together with the total stock size and settlement densities of Cerastoderma, Baltic tellin Macoma balthica and soft‐shelled clam Mya arenaria, were documented during 11 successive autumns before (August–September 1988) and after (August–September 1989–98) the suction‐dredging event in fished and unfished areas. Four other areas in the Dutch Wadden Sea, where changes in densities of juvenile bivalves from 1992 to 1998 were measured, served as additional reference locations.

Between 1988 and 1994, median sediment grain size increased while silt was lost from sediments near Griend that were dredged for cockles. The initial sediment characteristics were re‐attained by 1996.

After the removal of all Mytilus and most Cerastoderma, the abundance of Macoma declined for 8 years. From 1989 to 1998, stocks of Cerastoderma, Macoma and Mytilus did not recover to the 1988 levels, with the loss of Cerastoderma and Macoma being most pronounced in the area dredged for cockles. Declines of bivalve stocks were caused by particularly low rates of settlement in fished areas until 1996, i.e. 8 years after the dredging.

A comparison of settlement in the short (1992–94) and medium term (1996–98) after cockle‐dredging in several fished and unfished areas spread over the entire Dutch Wadden Sea, showed a significant negative effect of dredging on subsequent settlement of Cerastoderma. Macoma also declined, but not significantly.

We conclude that suction‐dredging of Cerastoderma had long‐lasting negative effects on recruitment of bivalves, particularly the target species, in sandy parts of the Wadden Sea basin. Initially, sediment reworking by suction‐dredging (especially during autumn storms) probably caused losses of fine silts. Negative feedback processes appeared to follow that prevented the accumulation of fine‐grained sediments conducive to bivalve settlement.
The importance of arable habitat for farmland birds in grassland landscapes
Authors: Robinson Robert A. , Wilson Jeremy D. , Crick Humphrey Q.P.
Published: March 2003

Over the last 25 years, populations of seed‐eating birds have declined severely over most of western Europe. Local extinctions have occurred in grassland‐dominated areas in western Britain, which may be influenced by loss in habitat diversity and a decline in the amount of arable cultivation.

We used the large‐scale British Breeding Bird Survey of 1998 to investigate the importance of arable habitat within grassland landscapes for 11 common seed‐eating birds and four similar sized insectivores. Generalized linear models were used to model the number of birds recorded in agricultural habitat within survey squares as a function of the amount of arable habitat present.

Numbers of grey partridge Perdix perdix, skylark Alauda arvensis, tree sparrow Passer montanus, corn Miliaria calandra and reed buntings Emberiza schoeniclus, yellowhammer Emberiza citrinella and whitethroat Sylvia communis increased with the amount of arable habitat present in a survey square; the numbers of house sparrow Passer domesticus, four finch species, dunnock Prunella modularis, robin Erithacus rubecula and blackcap Sylvia atricapilla did not.

The positive association between numbers of some species and arable habitat within 1‐km squares was strongest where arable habitat was rare in the surrounding area, and weakest or even reversed when arable habitat was common. These results demonstrate the scale‐dependence of bird–habitat associations in agricultural landscapes, only demonstrable where data are available at fine grain over large geographical areas.

These results support the hypothesis that range contractions (i.e. local extinctions) of some granivorous species have occurred because of contraction in arable cultivation. The loss of arable habitat where it is scarce may be causing declines in some areas, even though intensification of arable management is thought to be the main cause of declines elsewhere. Agri‐environment schemes may need to vary between regions, for example to encourage arable cultivation in pastoral areas.
Optimal application strategies for entomopathogenic nematodes: integrating theoretical and empirical approaches
Authors: Fenton A. , Gwynn R. L. , Gupta A. , Norman R. , Fairbairn J. P. , Hudson P. J.
Published: March 2003

The nematode Steinernema feltiae has been developed commercially as a biocontrol agent and is successful in controlling sciarid flies in mushroom houses. We used a simple model developed in parallel with a series of field trials, to optimize the application strategy of the nematode.

 The first field trial provided life‐history parameter estimates for both the sciarid flies and the nematodes and showed there to be substantial levels of nematode recycling, leading to high levels of control. Crucially, the field trial showed that by splitting the application into two, and applying half the nematodes at day 0 and half at day 7, the overall number of nematodes (dose) could be substantially reduced from currently recommended levels without sacrificing control success.

 The model confirmed that there should be a benefit in splitting the dose, if the second application is timed to coincide with the peak in numbers of highly susceptible sciarid larvae. Importantly, the model provided insight into the dynamics of the sciarid larvae, even though the original data set only recorded adult fly numbers.

 Using a split dose, optimally timed, the model suggested that total doses could be reduced by up to 75% and still achieve control comparable to that found with currently recommended dosages. The timing of the second application of nematodes was crucial in determining the level of control.

 The model predictions were validated against a second independent field trial with considerably lower fly densities. Even under these different conditions, the predictions were accurate, indicating the robustness of the modelling approach.

 To date models have rarely provided genuine practical advice to applied agriculturists and biocontrol practitioners. This study shows how a simple model developed in parallel with replicated field trials leads to a better understanding of the biological processes underlying successful control, resulting in improvements in recommended application strategies.
Impact of the rosette crown weevil Trichosirocalus briesei on the growth and reproduction of Onopordum thistles
Authors: Briese D. T. , Thomann T. , Vitou J.
Published: March 2003

Several European thistle species of the genus Onopordum have become naturalized in Australia and are considered serious pasture weeds, leading to a project aimed at their biological control.

The population structure of a potential control agent, the crown weevil Trichosirocalus briesei, a newly described member of the Trichosirocalus horridus species group, was studied under natural conditions on its Onopordum spp. host‐plants in northern Spain.

Trichosirocalus briesei was found to be the most abundant of three species of crown‐feeding insect utilizing these plants. Adults of this univoltine weevil began to lay eggs in mid‐autumn and larval population sizes increased over winter until pupation in early spring.

The spatial distribution of the immobile larvae was not random, indicating that females were selective in their oviposition behaviour. Field data suggested that plants in dense patches were attacked less frequently, and larger rosettes were preferred for egg‐laying.

A preliminary cage experiment indicated that feeding by T. briesei could damage Onopordum spp. thistles. A second experiment using plants in individual cages showed a clear relationship between the density of the weevils and the reduction in several growth parameters and seed production. At the highest densities, larval feeding could kill Onopordum rosettes before they produced flowering stems.

These results indicated that T. briesei has the potential to contribute to the biological control of Onopordum spp. thistles in Australia. Following host‐specificity testing, the weevil was released in 1997.
Effect of PCP and sigma ligands on both noradrenaline‐ and electrically‐induced contractions and on [3H]‐noradrenaline uptake in rat vas deferens
Authors: Pubill D. , Canudas A. M. , Sureda F. X. , Camins A. , Pallas M. , Escubedo E. , Camarasa J.
Published: March 2003

1 Electrically induced contractions of the epididymal portion of rat vas deferens were potentiated in concentration‐dependent manner (0.1–30 μm) by different sigma and PCP receptor ligands (PCP, TCP, (+)‐MK‐801, dextromethorphan and (+)‐3‐PPP); dextrorphan did it in a minor extent.

2 Sigma and PCP receptor ligands also potentiated the effect of noradrenaline, inducing a reduction of the noradrenaline EC50 value in the rat vas deferens. The rank order of potencies was: PCP > TCP > (+)‐3‐PPP > (+)‐MK‐801 > dextrorphan > > > dextrometorphan.

3 In contrast, haloperidol (1 μm), a sigma receptor ligand, inhibited both the neurogenic and noradrenaline‐induced responses in this tissue.

4 The effect of PCP and sigma receptor ligands on noradrenaline uptake was evaluated. All compounds tested, including haloperidol, inhibited the tritiated noradrenaline incorporation to the tissue. IC50 values were in the micromolar range, between 1.09 μm for dextrophan and 18 μm for dextrometorphan.

5 It is concluded that a direct interaction with the noradrenaline uptake system is involved in the potentiating effect of some sigma and PCP receptor ligands in the epididymal portion of rat vas deferens.
Cholinergic influence on the sensitivity of cough reflex in awake guinea‐pigs
Authors: Jia Y. X. , Sekizawa K. , Sasaki H.
Published: March 2003

1 We studied the effects of an intraperitoneal (i.p.) administration of atropine on bronchomotor tone induced by carbachol aerosols in anaesthetized and ventilated guinea‐pigs and on the sensitivity of cough reflex to capsaicin aerosols in awake guinea‐pigs.

2 The intraperitoneal administration of atropine (10−−8–10−−6 m kg−−1) reduced carbachol (8 mgml−−1; 1 min)‐induced increases in pulmonary insufflation pressure and a complete inhibition was achieved at a dose of 10−−6 m kg−−1 in anaesthetized guinea‐pigs.

3 In awake guinea pigs, capsaicin aerosols (10−−5–10−−3 m) caused dose‐dependent increases in the number of coughs. Atropine (10−−7–10−−6 m kg−−1 i.p.) shifted the dose–response curves to capsaicin to the right in a dose‐dependent fashion. Carbachol aerosols, at the maximal concentration (2 mg ml−−1) that did not cause bronchoconstriction, shifted them to the left compared with the control.

4 Atropine (10−−6 m kg−−1 i.p.) significantly increased the provocative concentration of capsaicin that caused five coughs (P < 0.01) and carbachol aerosols (2 mg ml−−1) significantly decreased it (P < 0.01).

5 We conclude that cholinergically mediated airway tone regulates cough sensitivity in awake guinea pigs.
The offset of β‐adrenoceptor antagonism of the responses of the rat right ventricle to isoprenaline
Authors: Doggrell S. A. , Henderson C. J.
Published: March 2003

1 The aim of the study was to test the hypothesis that the offset of action of β‐adrenoceptor antagonists on the heart is related to their lipophilicity, with low and highly lipophilic drugs having a rapid and slow offset, respectively. The effects of β‐blockers with low (atenolol), moderate (celiprolol), high (propranolol) and very high (bopindolol) lipophilicity on the contractile responses of the rat right ventricle to isoprenaline were determined.

2 Atenolol at 10−−6 and 10−−5 m, celiprolol at 10−−7, 10−−6 and 10−−5 m, propranolol at 10−−8, 10−−7 and 10−−6 m and bopindolol at 2 × 10−−9 and 10−−8 m caused parallel rightward shifts of the isoprenaline response curves with no effect on maximum responses. The Schild plots for atenolol, celiprolol and propranolol had slopes that were not significantly different from 1, which is indicative of competitive reversible antagonism. The pKB values were 7.33, 7.78, and 8.79 for atenolol, celiprolol, and propranolol, respectively. The Schild plot for bopindolol had a slope that was significantly greater than 1.

3 Our hypothesis is supported as the effects of propranolol and bopindolol were more slowly offset than those of atenolol and celiprolol. Thus, the concentration‐ratio of 141 in the presence of atenolol at 10−−5 m was reduced to 4 after the first wash, whereas the ratio of 100 in the presence of propranolol at 10−−7 m was only reduced to 45 after a similar wash. The ratio of 54 with celiprolol at 10−−6 m was reduced to 5, whereas the ratio of 70 with bopindolol at 10−−8 m was only reduced to 28 by the first wash.

4 The effects of bopindolol were very slowly or not reversible over two washes in the absence or presence of atenolol at 10−−6 m. It is suggested that bopindolol is a very slowly reversible β‐blocker, and that this contributes to its slow offset of action.
Blood pressure control in kidney transplant recipients: influence of immunosuppression
Authors: Gerhardt U. , Riedasch M. , Hohage H.
Published: March 2003

1 Disturbances of the blood pressure regulation, probably due to dysfunction of the autonomic nervous system, are well known complications in chronic renal failure. Haemodialysis and transplantation have been reported to ameliorate nerve dysfunction.

2 In this study, the function of the blood pressure control was investigated in kidney transplant recipients after longtime haemodialysis treated with ciclosporine A and tacrolimus and compared to healthy individuals. To investigate the influence of immunosuppression, the measurements were performed twice, at low and high whole blood concentrations of ciclosporine and tacrolimus. Besides ciclosporine, tacrolimus, azathioprine and prednisolone no other drugs were used in the group of kidney transplant recipients.

3 Kidney transplant recipients (KTR) treated with ciclosporine showed reduced blood pressure and heart rate responses to the cardiovascular stress tests (head‐up tilt and cold pressure test) under basal conditions. Two hours after ciclosporine application, the differences in the responses to cardiovascular stress tests between KTR and controls were significantly more pronounced.

4 Patients with tacrolimus immunosuppression showed a similar blood pressure and heart rate response under basal conditions. Two hours after drug application, the blood pressure response following orthostatism and heart rate response to the cold pressure test were significantly higher in tacrolimus treated patients.

5 Our results indicate, that kidney transplant recipients still express an altered function of the blood pressure control. Furthermore, ciclosporine A and tacrolimus seem to contribute to dysfunction of the blood pressure regulation by their own. Tacrolimus immunosuppression does not seem to offer advantages concerning the function of the blood pressure control as compared to ciclosporine A.
P‐glycoprotein phosphorylation/dephosphorylation and cellular accumulation of L‐DOPA in LLC‐GA5 Col300 cells
Authors: Sampaio‐Maia B. , Gomes R. , Soares‐da‐Silva P.
Published: March 2003

1 The present work was aimed to study the effect of PKC activation and protein‐serine/threonine phosphatase (PP1/PP2 A) inhibition on P‐glycoprotein (P‐gp) mediated transport of L‐DOPA in LLC‐GA5 Col300 cells, a renal cell line expressing the human P‐glycoprotein in the apical membrane.

2 L‐DOPA accumulation was a time‐and concentration‐dependent process with the following kinetic characteristics: kin, 57.3 ± 1.2 pmol mg protein−1 min−1; kout, 3.3 ± 0.1 pmol mg−1 protein min−1; Amax, 10.6 ± 0.8; Km, 198 ± 64 μm; Vmax, 5.2 ± 0.7 nmol mg protein−1.

3 Verapamil (25 μm), a P‐glycoprotein inhibitor, markedly increased (≈ 40% increase) the accumulation of a non‐saturating concentration of L‐DOPA (2.5 μm) at both initial rate of uptake (IRU, 6 min incubation) and at steady‐state (SS, 30 min incubation).

4 PKC activation with phorbol 12,13‐dibutyrate (PDBu, 1, 3 and 10 n
m) produced a concentration‐dependent decrease in L‐DOPA accumulation at SS, but not at IRU. The inactive phorbol ester, 4α‐phorbol 12,13‐didecanoate (100 n
m), produced no change in L‐DOPA accumulation. The effect of PDBu was completely reverted by staurosporine (100 n
m). The phosphatase inhibitor okadaic acid (100 n
m) reduced by 20% the accumulation of L‐DOPA at IRU, but not at SS.

5 It is suggested that P‐glycoprotein plays a role in regulation of intracellular availability of L‐DOPA in renal epithelial cells, and phosphorylation/dephosphorylation of P‐glycoprotein may be involved in the regulation of the transporter.
Vascular actions of 17β‐oestradiol in rat aorta and mesenteric artery
Authors: Browne M. , Connolly C. , Docherty J. R.
Published: March 2003

1 It has been proposed that the cardiovascular protective actions of 17β‐oestradiol may involve calcium antagonistic actions. We have examined the effects of 17β‐oestradiol on contractions to noradrenaline and KCl in male rat small mesenteric artery and aorta.

2 In rat mesenteric artery, 17β‐oestradiol (10 μm) significantly reduced the maximum contraction to noradrenaline (67.7 ± 5.8% of control) and KCl (38.8 ± 3.1% of control) without affecting potency.

3 In rat aorta, 17β‐oestradiol (10 μm) also significantly reduced contractions to noradrenaline (77.5 ± 4.8% of control), and the effects were mimicked by droloxifene (10 μm). The effect of oestrogen was not prevented by the protein synthesis inhibitor cycloheximide (10 μm). In experiments carried out in calcium‐free solution in which calcium stores were depleted, 17β‐oestradiol (10 μm) significantly reduced the contraction to calcium restoration in rat aorta.

4 In aorta from female rats, 17β‐oestradiol (10 μm) significantly reduced contractions to noradrenaline (73.6 ± 10.8% of control), but this effect of oestrogen was not prevented by cycloheximide (10 μm).

5 In summary, 17β‐oestradiol diminishes the maximum contractile response to noradrenaline in both rat small mesenteric artery and aorta, an effect which at least in the aorta is mimicked by the oestrogen receptor antagonist/partial agonist droloxifene, and may be due to restriction of calcium entry by a nongenomic action.
Potassium channels in gastrointestinal smooth muscle
Authors: Vogalis F.
Published: March 2003

1 Electromechanical coupling in smooth muscle serves to coordinate the contractile activity of the syncytium. Electrical activity of smooth muscle of the gut is generated by ionic conductances that regulate and in turn are regulated by the membrane potential of smooth muscle cells. This activity determines the extent of Ca2+ entry into smooth muscle cells, and thus, the timing and intensity of contractions.  2 Potassium channels play an important role in regulating the excitability of the syncytium. The different types of K+ channel are characterized by different sensitivities to membrane potential, to intracellular Ca2+ levels and to modulation by agonists.  3 This review highlights the different types of K+ channels found in gut smooth muscle and describes their possible roles in regulating the electrical activity of the muscle.