bluuebunny/crossref_metadata_2025 huggingface dataset:
Does Holling’s disc equation explain the functional response of a kleptoparasite?
Authors: Caldow R. W. G. , Furness R. W.
Published: March 2003

Type II functional responses, which can be described by Holling’s disc equation, have been found in many studies of predator/prey and host/parasite interactions. However, an increasing number of studies have shown that the assumptions on which the disc equation is based do not necessarily hold. We examine the functional response of kleptoparasitically feeding Arctic skuas (Stercorarius parasiticus L.) to the abundance of fish‐carrying auks and, by examination of the assumptions of the disc equation, test whether it can explain the function.

The rate at which individual skuas make successful chases is a decelerating function of the abundance of auks. However, it would appear that this is not determined by factors that influence their probability of success, but by the rate at which they initiate chases. This too is a decelerating function of the abundance of auks. Arctic skuas have a Type II functional response.

Although Arctic skuas exhibited a direct numerical response there was no evidence that components of predation connected to the density of predators (direct prey stealing, or increased host avoidance) had any effect on the rate at which individual skuas made chases or were successful in their chases. We conclude that the observed functional response is free from any effects of interference.

We suggest that abnormally high levels of foraging effort expended by breeding skuas and their poor breeding success in the years of observation argue against the limit to the observed functional response being determined by skuas’ energetic requirements.

Several of the assumptions underlying the disc equation do not hold. The duration of chases (handling time) was not a constant; it decreased with increasing host abundance. Moreover, the chase duration predicted by the disc equation, if handling time limited the functional response, was far in excess of that observed. Furthermore, the observed rate of decline in the searching time per victim with increasing host abundance suggested that skuas’ instantaneous rate of discovery was also not constant. Possible reasons for these observations are discussed. The basic disc equation may describe Arctic skuas’ functional response, but it cannot explain it.
Condition‐dependent dispersal and ontogeny of the dispersal behaviour: an experimental approach
Authors: Massot M. , Clobert J. , Lorenzon P. , Rossi J.‐M.
Published: March 2003

Although little investigated, developmental processes that generate dispersal condition evolution of this behaviour. We have shown previously prenatal and postnatal influences on dispersal in the common lizard (Lacerta vivipara). The observation of these developmental processes was based on independent experiments; our primary goal in this paper is to test their interactions. Interactions could indeed be a source of inconsistencies in studies because they can mask, or even reverse, effects of factors treated additively.

We studied dispersal of juveniles releasedin naturafrom 416 pregnant females captured in the field. We used a factorial design to test interactions among the maternal habitat (dry vs. humid), prenatal conditions (temperature, humidity), and postnatal environments (dry vs. humid).

We found that juvenile dispersal was dependent on the humidity level at different developmental stages, but with varying and sometimes opposite effects. Dispersal was also influenced by the temperature during gestation and by populational differences not related to humidity (differences between replicated populations for the maternal and postnatal habitats).

These results confirm our previous findings that dispersal of the common lizard is condition‐dependent and has multiple causation. In addition, most of the effects exhibited interactions, and the ontogeny of dispersal appeared as a sequential process where the maternal habitat conditioned prenatal influences, and the prenatal environment modulated postnatal influences.

The robustness of our results is supported by the finding of the same interactions in independent tests on both juvenile males and females. This militates in favour of future studies on the multiple causation of dispersal because the same dispersal status might originate from different causes, and different dispersal outcomes might be due to the same factor.
Density‐dependent populations require density‐dependent elasticity analysis: an illustration using the LPA model of Tribolium
Authors: Grant Alastair , Benton Tim G.
Published: March 2003

Elasticity and sensitivity analyses are used widely in evolutionary biology, ecology and population management. However, almost all applications ignore density dependence, despite the widespread assumption that density dependence is ubiquitous. We assess whether this matters by comparing density‐dependent and density‐independent elasticity analyses for the LPA model of Tribolium.

Density‐independent elasticities of λ are a poor indicator of the effects of changes in demographic parameters on population size, even for populations at stable equilibrium. With non‐equilibrium dynamics, the divergence can be particularly large. In the extreme, a change in a demographic parameter with a positive effect on individual fitness can reduce mean population size, so even the sign of a density‐independent elasticity may be wrong. Elasticities of larval, pupal and adult numbers are not proportional to each other, neither are they proportional to elasticities of total population size.

A full density‐dependent analysis is therefore vital when concerned with effects on population numbers, as in population management, pest control and prediction of population effects of toxins.

When examining the consequences for individual fitness of changes in demographic parameters, density‐independent elasticities provide a more useful approximation to the density‐dependent values. However, they fail to detect cases where non‐equilibrium dynamics means that particular life histories gain an advantage by exploiting predictable periods when density dependence is relaxed.

This phenomenon can produce a marked change in the pattern of elasticities as a bifurcation is crossed. The corresponding changes in selection pressures may act to stabilize dynamics in some circumstances and destabilize them in others. There is no single answer to the question of whether selection should favour equilibrium or non‐equilibrium dynamics.
Demography of the vegetable ivory palm Phytelephas seemannii in Colombia, and the impact of seed harvesting
Authors: Bernal Rodrigo
Published: March 2003

1.  The demography of the vegetable ivory palm Phytelephas seemannii was studied on the Pacific coast of Colombia and a female‐based matrix model was used to determine the proportion of seed that can be sustainably harvested from the population.

2.  The density of the palm stands ranged from 240 to 420 adult palms ha−1. The sex ratio was 1:1 and palms of both sexes produced leaves at the same rate. Seedlings produced 1·2 leaves per year on average, juveniles 1·8, and adults 6·1–7·4.

3.  Adult females had fewer leaves than males (18·5 vs. 21·3 on average). Leaves of females lasted about 2·7 years in the crown, those of males about 3·2 years.

4.  Stems creep on the ground, growing at the apex and often dying behind, the extant portion not always reflecting the palm’s total age. The longest stem of a female palm in the study plots was 2·5 m, corresponding to an ‘extant’ age of 85 years; the longest stem recorded was that of a male (outside the plots) 10·5 m long, corresponding to an ‘extant’ age of 184 years. These figures reflect differences in growth habit, not in longevity.

5.  Reproduction began at about 24 years, when the palm still lacked an above‐ground stem.

6.  The population growth rate λ was 1·059, and was most sensitive to changes in survival of juveniles and adults, and relatively insensitive to changes in fecundity and growth.

7.  River channel migration is the most important cause of adult mortality. Phytelephas seemannii is apparently an efficient colonizer of the understorey in the late phases of riverine forest succession.

8.  The population can tolerate a harvest intensity of 86% of all seeds before λ decreases to the equilibrium level of 1·00. Monitoring of the populations under intensive harvesting is required.
The effect of predation by wintering cormorants Phalacrocorax carbo on grayling Thymallus thymallus and trout (Salmonidae) populations: two case studies from Swiss rivers. Comment
Authors: STAUB E. , EGLOFF K. , KRÄMER A. , WALTER J.
Published: March 2003

Using the same data on the predation effect of cormorants Phalacrocorax carbo on the grayling Thymallus thymallus population located in the river Rhine below Lake Constance, Staub et al. (1992) and Suter (1995) reached contradictory conclusions (additional and compensatory mortality, respectively). This comment clarifies the reasons for the differences.

The biomass of older fish (age classes 4 and 5–7) was not judged to be decreasing by Suter because of the use of inappropriate (parametric) inferential statistics and no use of power analysis. More powerful (non‐parametric) inferential tests show a significant decrease in biomass.

Staub et al. compared fish numbers per length class in the angling catch (autumn) and in the spawning catch (spring). Differences were thought to be the effect of cormorant predation during winter. Suter converted fish numbers per length class into biomass per age class for the same comparisons. However, this conversion considered neither the length increases of grayling during winter (c. 1 cm) nor the dominance of faster growing males (> 1.5 cm longer than females of the same age) in the spawning catch. Thus, changes of the age pyramid during winter have been masked.
Do host‐plant requirements and mortality from soil cultivation determine the distribution of graminivorous sawflies on farmland?
Authors: Barker A. M. , Brown N. J. , Reynolds C. J. M.
Published: March 2003

1.There are many arthropod species on farmland that are not economic pests but which have an important role in the wider ecology of agricultural ecosystems. Few of these have been studied in detail. This study investigated the factors underlying the distribution of one such group, graminivorous sawflies (Hymenoptera: Tenthredinidae).

2.In a farm survey, sawfly larvae of the generaDolerusandPachynematuswere over six times more abundant in fields of sown perennial rye‐grassLolium perenneL. than in fields of spring barley, winter wheat or long‐established grazing pastures.

3.In rearing trials the growth rates and survival of larvae of the two genera were high onL. perenne andlow on two cereals, spring barley and winter wheat. Differences were sufficiently marked to have had a strong influence on the distribution of larvae between crops in the field.

4.In an experimental study, nearly twice as many adults emerged from uncultivated as from cultivated ground, suggesting that disturbance of the overwintering prepupae and pupae in the soil caused about 50% extra mortality. This mortality will have reinforced the effects of host‐plant requirements, suppressing sawfly numbers in annually cultivated cereal fields whilst numbers built up in less‐frequently cultivated grass fields.

5.Sawfly abundance is known to have declined on farmland. Our results suggest that changes in patterns of crop rotation have been the main cause of this decline. Farming practice in Britain has moved away from mixed rotations alternating cereals with undersown grass fields. Modern intensive farms grow monocultures of cereal crops or of heavily grazed grass, both poor habitats for sawflies.

6.Increasing insecticide use in cereals has probably been only a minor influence on population abundance of sawflies as wheat and barley fields are not high‐quality habitats.

7.Provision of undisturbed grassy habitats would promote the conservation of graminivorous sawflies on farmland.
Extinction risk assessment and optimal harvesting of anchovy and sprat in the Azov Sea
Authors: Senina Inna , Tyutyunov Yuri , Arditi Roger
Published: March 2003

1. We explored harvested fish populations in which an extinction risk exists as a consequence of a notable drop in abundance. An adequate formulation of the optimal harvesting problem must account for several criteria. Economic maximization should be balanced against minimization of extinction risk. In addition, environmental stochasticity should be taken into consideration to obtain a realistic description of the population dynamics.

2. The approach to multicriteria optimization of the harvesting policy is illustrated by models of two commercially harvested planktophagous fish found in the Azov Sea in Russia. A stochastic simulation model for the community of competing anchovy Engraulis encrasicholus and sprat Clupeonella delicatula was developed and investigated. The parameters of the model were estimated on the basis of time series of population abundance and environmental factors that influence reproduction.

3. The model was used to assess numerically the extinction risk of this exploited community. A Pareto approach was used to treat the optimization problem with two criteria: maximizing the total catch and minimizing the extinction probability. No single solution exists but a set of Pareto‐optimal fishing strategies was defined, i.e. a set of trade‐off solutions. These various solutions can easily be compared by fishery managers and experts before making final decisions.

4. It was found that the harvesting strategy that is currently applied is quite efficient since it is very close to the Pareto‐optimal set of solutions. Our recommendation is that these two populations should be considered as a community. Specifically, by increasing the harvest of endemic sprat and decreasing the harvest of the less productive migratory anchovy, fishermen will obtain a higher total harvest with only a slightly higher extinction risk.
Breeding success of the hen harrier Circus cyaneus in relation to the distribution of grouse moors and the red fox Vulpes vulpes
Authors: Green R.E. , Etheridge B.
Published: March 2003

1. A recent analysis showed that the survival and breeding success of female hen harriers were much lower on grouse moors than on other upland land management classes in Scotland, excluding the Orkney islands: a difference attributed to persecution of hen harriers by humans on grouse moors. However, this study did not look for possible beneficial effects on hen harrier breeding success of the control by moorland gamekeepers of other predators, particularly red foxes.

2. These and other recently published data were re‐examined to see whether there was regional variation in hen harrier nest success associated with the presence or absence of foxes and the control of foxes and other predators by moorland gamekeepers.

3. The main finding of the previous analysis, that nest success was much lower on grouse moors than on moorland that was not managed for grouse or in young conifer forests, was even more striking when comparisons were made among land management classes within the same region.

4. The mean number of broods fledged per female hen harrier per year on two grouse moors at which gamekeepers prevented human interference with harrier nests and continued to control other predators was compared with the average for moorland in Scotland. Harrier productivity on these moors was much higher than the average for grouse moors, but similar to the average for moorland not managed for grouse shooting.

5. Nest success of hen harriers breeding on moorland not managed for grouse averaged 19% higher in regions where there were, on average, more grouse moors in the vicinity, but in young conifer forests success was 34% lower in regions with more grouse moors nearby. Neither of these differences was statistically significant.

6. Nest success within a particular land management class was not significantly different inside and outside the range of the red fox.

7. Even a generous assessment of the magnitude of a supposed beneficial effect of the control of foxes and other predators by moorland gamekeepers on hen harrier nest success indicated that its effect on the population trend of hen harriers would be small relative to the large negative effect of persecution of harriers on grouse moors.
Does culling predatory gulls enhance the productivity of breeding common terns?
Authors: Magella Guillemette , Brousseau Pierre
Published: March 2003

Large gulls Larus spp. are voracious predators of eggs and chicks of other colonial birds and may threaten rare or endangered species. In this study we tested the effectiveness of removing individual predatory gulls as a management technique for enhancing the productivity of common terns Sterna hirundo nesting in Carleton, Québec, Canada.

 The productivity and fate of common tern chicks were assessed by following ringed individuals from hatching to fledging during three breeding seasons (1993–95). Concurrently, predation and consumption rates of all predatory gulls were measured before and after the culling started. The culling programme was conducted serially in 1994 by removing the most important predator first until all predators were removed.

 The rate of chick disappearance was lower and the life span of tern broods was higher in 1994 when the culling was conducted, compared with 1993 and 1995. As a result, the productivity of the tern colony was zero in 1993 and 1995, but positive in 1994 (0·33 chicks pair−1). Measurements of chick mass in 1993 and 1994 showed that growth was normal, indicating that poor feeding conditions or disease were not the cause of chick disappearance.

 Average predation rates for 1993 (23·3 chicks day−1) and 1995 (14·8 chicks day−1) equated to 61% and 66% of available chicks being taken by gulls, respectively. The predation rate before the culling started in 1994 was similar to 1993 and 1995, with 15·9 chicks day−1, but dropped to 5·1 chicks day−1 after the first gull was shot, and decreased to zero once all predatory gulls were removed. Only five individual predatory gulls were identified during the cull.

 Predation rates differed markedly amongst specialist predatory gulls, with one individual accounting for 85% of all successful attempts made during the baseline period. Once that gull was removed, the remaining predators increased their predation rate in a manner suggestive of a despotic system. Observations conducted in 1995 showed that the predation rate was almost zero at the beginning of the season but increased dramatically later in the summer, with two gulls together making about 60% of the captures.

 It is concluded that culling predatory gulls can be an effective management tool to enhance productivity in sensitive or endangered species. However, our data suggest that such culling would need to be repeated each year in order to protect a sensitive species over consecutive years.
Species accumulation curves and the measure of sampling effort
Authors: Willott S.J.
Published: March 2003

Moreno & Halffter (2000) described the problems associated with comparing species richness among communities that have inventories compiled using different methods or with different sampling effort. They used species accumulation curves to standardize samples among sites, to predict the species richness of sites and to estimate the minimum effort required for adequate completeness of inventories.

I argue that their measure of sampling effort, number of nights, is inappropriate because it does not distinguish between genuine differences in species richness among sites and differences in trap efficiency. The number of individuals is the best measure of sampling effort to avoid this problem, as illustrated by data on moths collected from a Bornean rainforest. Furthermore, the approach of Moreno & Halffter requires the species accumulation curves to be approaching an asymptote for accurate estimation, and so for practical reasons is probably limited to less diverse taxa.
Grasslands, grazing and biodiversity: editors’ introduction
Authors: A.R. Watkinson , S.J. Ormerod
Published: March 2003

Natural, semi‐natural and artificial grasslands occur extensively around the globe, but successful management for production and biodiversity poses several dilemmas for conservationists and farmland managers. Deriving from three continents (Africa, Australia and Europe), papers in this Special Profile interface three specific issues: plant responses to grazing, plant invasions and the responses to management of valued grassland biota.

Although pivotal in grassland management, plant responses to grazing are sometimes difficult to predict. Two alternative approaches are presented here. The first uses natural variations in sheep grazing around a water hole to model the dynamic population response of a chenopod shrub. The second analyses a long‐term grazing experiment to investigate the links between plant traits and grazing response.

Linked often crucially with grazing, but also driven sometimes by extrinsic factors, invasions are often cause for concern in grassland management. The invasions of grasslands by woody plants threatens grassland habitats while the invasions of pastures by alien weeds reduces pasture productivity. The papers in this section highlight how a complementary range of management activities can reduce the abundance of invaders. A final paper highlights how global environmental change is presenting new circumstances in which grassland invasion can occur.

The impact of grassland management on biodiversity is explored in this Special Profile with specific reference to invertebrates, increasingly recognized both for the intrinsic conservation value of many groups and for their role in ecosystem processes. The potential for manipulating flooding in wet grasslands to increase the soil invertebrate prey of wading birds is illustrated, together with the roles of management and landscape structure in enhancing insect diversity.

In the face of climate change and growing demands for agricultural productivity, future pressures on grassland ecosystems will intensify. In this system in which productivity and conservation are so closely bound, there is a need both to raise the profile of the issues involved, and to improve our understanding of the applied ecology required for successful management.
Experimental removal of introduced hedgehogs improves wader nest success in the Western Isles, Scotland
Authors: Jackson Digger B.
Published: March 2003

Introduced predators are a major threat to island avifaunas world‐wide. In the Western Isles of Scotland, recently introduced hedgehogs Erinaceus europaeus have become a serious predator of bird eggs and are an important cause of declines of some waders (Charadrii).

 Experiments at two sites in 1998 measured the effect on wader nest success resulting from hedgehog removal from fenced exclosures. The nest success of waders inside the plots (where hedgehog densities were zero or low) was approximately 2·4 times that of birds nesting in the adjacent control areas (where hedgehog densities were high). There was no evidence of a compensatory increase in egg loss to native avian predators.

 The experiment was an integral part of a research programme to support wader conservation efforts. On the basis of the experiment it can be predicted that the removal of hedgehogs on a larger scale would result in a large increase in nest success.

 The study also tested the practicalities of using relatively cheap fences against hedgehogs. Fences were generally effective, but on dry sandy ground rabbits Oryctolagus cuniculus burrowed under fences, enabling some hedgehogs to re‐enter plots. Well‐designed fences could be used as a conservation tool, both as a barrier to protect key sites, and to aid the trapping and removal of hedgehogs. However, fences cannot be seen as a long‐term solution to the problem.

 Radio‐tagged hedgehogs removed from the plots and released nearby all attempted to re‐enter the plots. Two tracking methods revealed that displaced hedgehogs followed fences for distances up to 500 m looking for an entry point. There was no evidence that hedgehogs were able, or even attempted, to climb over or dig under fences.

 The establishment of hedgehogs in the Western Isles provides an example of a threat to biodiversity following human‐mediated redistribution of a species native to the UK to parts of the UK (Scottish islands) outside the species’ natural range, an activity not currently prohibited by law. Policy action to deter or control species introduction should consider ecological range even within national boundaries.
PCR detection of potentially pathogenic aeromonads in raw and cold-smoked freshwater fish
Authors: González-Rodríguez M.N. , Santos J.A. , Otero A. , García-López M.L.
Published: March 2003

Aims: Development of a PCR assay for detection of aeromonads carrying the hlyA and/or aerA genes in fish. Methods and Results: The protocol involves an overnight selective enrichment step in tryptic soy broth yeast extract containing 10 µg ml-1 of ampicillin followed by extraction of DNA and PCR amplification of two haemolysin genes that contribute to the virulence of Aer. hydrophila. This procedure can detect initial populations of 1–10 cfu g−1 within 24 h in artificially contaminated samples. In naturally contaminated fish, both genes were detected in 13 out of 14 fresh fish lots (aeromonads levels between < 1 and 5·42 log cfu g−1) and in 4 out of 16 lots of vacuum-packed cold-smoked fish (aeromonads levels between < 1 and 3·37 log cfu g−1). Before enrichment, dominant species were Aer. hydrophila HG1 (aerA+hlyA+), Aer. bestiarum HG2 (aerA+hlyA+) and Aer. caviae HG4 (aerA–hlyA–). After enrichment, Aer. hydrophila HG1 (aerA+hlyA+) was dominant. Conclusions: Fresh fish and even smoked fish carry hlyA+ and/or aerA+ aeromonads that can be detected by PCR within 24 h. Significance and Impact of the Study: The PCR assay described offers considerable potential as a rapid method with specificity, sensitivity and simplicity.
Survival of Escherichia coli O157:H7 in farm water: its role as a vector in the transmission of the organism within herds
Authors: McGee P. , Bolton D.J. , Sheridan J.J. , Earley B. , Kelly G. , Leonard N.
Published: March 2003

Aims: The study aimed to investigate the survival characteristics of Escherichia coli O157:H7 in farm water (FW), and in sterile distilled municipal water (SDW), stored outdoors under field conditions, with or without the addition of faeces (1% w/v), in a farmyard shed and the laboratory at 15°C. Methods and Results: Water samples were inoculated with E. coli O157:H7 at 103 and 106 ml−1, and sampled over a 31-day period. In FW stored outdoors in a field, E. coli O157:H7 survived for 14 days at temperatures <15°C, at both inoculation levels, while in the laboratory at 15°C, the organism was still detectable at low levels (<1 log10 cfu ml−1) after 31 days. The addition of bovine faeces to water outdoors (1% w/v) resulted in survival for 24 days. In SDW inoculated at 106 ml−1 and stored in the laboratory (15°C), only a 2·5 log reduction was observed after 31 days, while the organism could not be detected after 17 days in the field. Preliminary screening of water samples stored outdoors isolated a bacterium which exhibited antimicrobial activity towards E. coli O157:H7. Conclusions: The survival of E. coli O157:H7 observed in this study illustrates the potential of farm water to act as a vehicle in the transfer of the organism across a herd. Significance and Impact of the Study: The difficulty in extrapolating results from controlled laboratory situations to on-farm conditions is also highlighted in this study.
Influence of pH, temperature and culture media on the growth and bacteriocin production by vaginalLactobacillus salivariusCRL 1328
Authors: Juarez Tomás M.S. , Bru E. , Wiese B. , De Ruiz Holgado A.A.P. , Nader-Macías M.E.
Published: March 2003

Aims: To study the influence of pH, temperature and culture medium on the growth and bacteriocin production by vaginal Lactobacillus salivarius subsp. salivarius CRL 1328. Methods and Results: The study was performed using a complete factorial experimental design. Lactobacillus salivarius was cultivated in LAPTg and MRS broths, adjusted to specific initial pH, and at different temperatures of incubation. The growth, which was evaluated by the Gompertz model, was higher in MRS broth than in LAPTg broth. The initial pH of the culture medium and the temperature had a dramatic effect on the production of bacteriocin. The optimal conditions for bacteriocin production were different to those for optimal growth. The decrease in the pH of the culture medium was parallel to the growth; pH had similar final values in both the MRS and the LAPTg broths. Conclusions: The optimal growth conditions were recorded in MRS broth, with an initial pH of 6·5 and a temperature of 37°C. The maximum bacteriocin activity was obtained in LAPTg after 6 h at 37°C, and at an initial pH of 6·5 or 8·0. Significance and Impact of the Study: The application of a complete factorial design, and the evaluation of the growth parameters through the Gompertz model, enabled a rapid and simultaneous exploration of the influence of pH, temperature and growth medium on both growth and bacteriocin production by vaginal Lact. salivarius CRL 1328.
Evidence for the presence of muscarinic M2 and M4 receptors in guinea‐pig gallbladder smooth muscle
Authors: Oktay Ş. , Cabadak H. , İskender E. , Gören Z. , Çallşkan E. , Orun O. , Aslan N. , Karaalp A. , Tolun A. , Ulusoy N. B. , Levey A. I. , El‐Fakahany E. E. , Kan B.
Published: March 2003

1 The affinities of 10 selective muscarinic receptor antagonists against [3H]‐quinuclidinyl benzilate (QNB) binding were determined to characterize the muscarinic receptors present in guinea‐pig gallbladder smooth muscle. The highest correlation was obtained for the comparison between the pKi values for the gallbladder smooth muscle and M2 sites. Pirenzepine revealed two binding sites with affinities indicating the presence of muscarinic M2 receptors in abundance and a minor population of an additional site(s).

2 Carbachol produced gallbladder contractions, stimulated phosphoinositide (PI) hydrolysis and inhibited cAMP formation concentration‐dependently with pD2 values of 6.12 ± 0.11, 5.18 ± 0.33 and 7.19 ± 0.15, respectively.

3 Pirenzepine, 4‐DAMP, HHSiD, pF‐HHSiD, AF‐DX 116, methoctramine, AQ‐RA 741, guanylpirenzepine and AF‐DX 384 showed competitive antagonism against carbachol‐induced gallbladder contractions. There was no correlation between the pA2 values for the gallbladder and pKi values for the M2 sites, whereas significant correlations were found for the M1, M3 and M4 sites, the best correlation being between the pA2 values for the gallbladder and M4 subtypes.

4 Finally, the presence of both m2 and m4 receptor proteins were demonstrated by Western blot analysis. It is concluded that guinea‐pig gallbladder smooth muscle has both muscarinic M2 and M4 receptors, which are coupled to adenylate cyclase inhibition and PI hydrolysis.

5 Although it seems likely that M2 receptors do not play a primary role in carbachol‐induced guinea‐pig gallbladder contraction, the characterization of the muscarinic subtypes which mediate these contractile responses needs further evidence.
Peripheral blood lymphocyte muscarinic cholinergic receptors in airway hyperresponsiveness: a marker of cholinergic dysfunction?
Authors: Ricci A. , Mannino F. , Bronzetti E. , Felici L. , Adani O. , Gemma D. , Amenta F.
Published: March 2003

1 Muscarinic cholinergic receptors were assayed in human peripheral blood lymphocytes of healthy control and airway hyperresponsive subjects using a radioligand binding assay technique and the muscarinic cholinergic receptor antagonist [3H]‐quinuclidinyl benzilate (QNB) as a radioligand. Subjects investigated were divided in four different groups based on threshold responses to methacholine inhaled as challenge test.

2 [3H]‐QNB was bound to human peripheral blood lymphocytes in a manner consistent with the labelling of muscarinic cholinergic receptors. Dissociation constant (Kd) values of [3H]‐QNB binding were similar in the different groups examined, whereas maximum density of binding sites (Bmax) was increased in airway hyperresponsive subjects in comparison with healthy controls.

3 The above findings indicate that the density of muscarinic cholinergic receptors is increased in peripheral blood lymphocytes of airway hyperresponsive subjects.

4 This suggests that airway hyperresponsiveness is associated with cholinergic hyperreactivity and is probably a systemic cholinergic dysfunction since it is accompanied by changes in the density of muscarinic cholinergic receptors expressed by peripheral blood lymphocytes.
Involvement of nitric oxide in the mediation of NANC inhibitory neurotransmission of guinea‐ pig trachea
Authors: Venugopalan C. S. , Krautmann M. J. , Holmes E. P. , Maher T. J.
Published: March 2003

1 The involvement of nitric oxide (NO) in the non‐adrenergic non‐cholinergic inhibitory (NANC‐i) neurotransmission was evaluated in guinea‐pigs anaesthetized with chloralose–urethane, using a tracheal pouch preparation.

2 The tracheal pouch, a surgically isolated segment of trachea with intact nerve and blood supply, is an in situ method to demonstrate NANC‐i response after complete cholinergic and adrenergic blockade using atropine (5 mg kg−−1) and propranolol (1 mg kg−−1), respectively. Cervical vagi and sympathetic trunks were isolated and cut cranially. The distal ends of the vagi were positioned on bipolar electrodes for subsequent stimulation with 5 V pulses for 2 ms duration at 15 Hz for a total of 90 s. The relaxation response was measured as a pressure drop (cm of H2O) in the pouch. Each experimental group was composed of six animals.

3 NANC‐i responses to two consecutive nerve stimulations at 25 min apart were reproducible.

4 Pouch relaxation responses to electrical nerve stimulations were determined before and after incubation of the pouch with Nω‐nitro‐l‐arginine methyl ester (l‐NAME; 10−−5 m), a NO synthase (NOS) inhibitor, for 30 min. l‐NAME significantly, but not completely, inhibited the NANC‐i response of the pouch, suggesting involvement of NO in the NANC‐i neurotransmission.

5 The pouch relaxations to vagal stimulations were inhibited significantly after incubation with oxyHb indicating that NO was released.

6 The amount of methaemoglobin (metHb) formed from oxyhaemoglobin (oxyHb) during vagal stimulation was measured by spectrophotometry. Comparison of the values between the control and after nerve stimulation indicated a trend (P = 0.07) toward greater metHb formation in the pouch perfusate after nerve stimulation.

7 NANC‐i responses were not significantly inhibited by incubation of the pouch with either of the guanylate cyclase inhibitors, methylene blue or 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ). However, a trend toward significance (P ≤ 0.07) was observed.

8 This study demonstrated that NO is involved in NANC‐i neurotransmission. However, the findings did not conclusively support the contention that NO is the sole neurotransmitter of NANC inhibition. It is possible that NO produced relaxation of guinea‐pig trachea through a cGMP‐independent mechanism.
Species‐dependent effects of adenosine receptor agonists on contractile responses of vas deferens to ATP
Authors: Smith Andrew D. , Moloney Susan , Khoyi Mohammad A. , Westfall David P.
Published: March 2003

1 Experiments were carried out to examine the postjunctional actions of adenosine receptor agonists on the smooth muscle of the vas deferens of the guinea‐pig and rabbit.

2 Although they produced neither contraction nor relaxation by themselves, adenosine analogues enhanced contractions of the guinea‐pig vas deferens induced by 10 μm ATP. The rank order of potency was N6‐cyclopentyladenosine (CPA) > 5′‐N‐ethylcarboxamidoadenosine (NECA) > adenosine > CGS 21680. Dose–response curves for NECA were shifted to the right by the nonselective adenosine receptor antagonist 8(p‐sulphophenyl)theophylline (8‐SPT; 100 μm) and by the selective A1‐receptor antagonist 1,3‐dipropyl‐8‐cyclopentylxanthine (DPCPX; 1 m
m).

3 In the rabbit vas deferens, contractions induced by ATP (1 m
m) were inhibited rather than facilitated by NECA. Neither CPA, R(–)‐N6‐(2‐phenyl isopropyl)‐adenosine (R‐PIA) nor CGS 21680 had any effect.

4 The results indicate that the smooth muscle of the guinea‐pig vas deferens expresses facilitatory adenosine A1 receptors but not adenosine A2 receptors. In contrast, in rabbit there are postjunctional inhibitory adenosine A2A receptors but not adenosine A1 receptors.
Effect of hydroquinone, hydroxocobalamin and carboxy‐PTIO on non‐adrenergic non‐cholinergic nerve mediated relaxations of the rat duodenum
Authors: Correia N. A. , Cavalcanti P. M. S. , Oliveira R. B. , Ballejo G.
Published: March 2003

1 Relaxation induced by NANC‐nerve stimulation is reduced by nitric oxide synthase (NOS) inhibitors but not by superoxide generators or NO scavengers, casting doubts on the precise nature of the neurotransmitter being released by these nerves. The lack of effect of superoxide anion generators to inhibit nitrergic nerve‐mediated relaxations has been attributed to the protective action of high tissue levels of superoxide dismutase (SOD).

2 The effects of hydroquinone, hydroxocobalamin and carboxy‐PTIO, three NO inactivators which do not depend on superoxide anion generation, upon nitrergic nerve‐mediated relaxations of the rat proximal duodenum were determined in order to elucidate whether they are mediated by free NO.

3 GABA and nicotine caused relaxations of isolated segments of the rat proximal duodenum in a concentration‐dependent manner that were abolished by tetrodotoxin (TTX). Similarly, transmural electrical stimulation (TES) caused frequency‐dependent relaxations that were also abolished by TTX.

4 The NOS inhibitors L‐NAME and L‐NOARG reduced in a concentration‐dependent manner nerve‐mediated relaxations elicited by TES, nicotine and GABA. The effect of NOS inhibitors was prevented by
l‐arginine but not
d‐arginine.

5 NO caused concentration‐dependent relaxations that were not affected by TTX or L‐NOARG but were abolished by hydroquinone, hydroxocobalamin and carboxy‐PTIO. In contrast, these compounds failed to affect TES‐, nicotine‐ and GABA‐induced relaxations. The lack of effect of hydroquinone, hydroxocobalamin and carboxy‐PTIO upon nerve‐mediated relaxations was unaltered by pretreatment with the SOD irreversible inhibitor DETCA.

6 The present findings show that nitrergic nerve‐mediated relaxations of the rat duodenum are unaffected by NO inactivators that do not generate superoxide anion. It is suggested that either a NO‐containing molecule that is unreactive with the inactivators tested is the inhibitory neurotransmitter released by nitrergic nerves or that NOS activity fulfills another role in nitrergic nerves which could be related to the release of an still unidentified transmitter.
Effects of reduced sympathetic activity on myocardial metaiodobenzylguanidine (MIBG) washout
Authors: Gao D.‐W. , Talke P. O. , Dae M. W.
Published: March 2003

1 Increase in myocardial sympathetic activity contributes markedly to the pathophysiology of conditions such as congestive heart failure and is also associated with myocardial infarction. However, measurement of myocardial sympathetic activity in vivo is difficult.

2 The present study assesses the effectiveness of metaiodobenzylguanidine (MIBG) imaging to characterize modulation of sympathetic activity, as induced by dexmedetomidine, a highly specific α‐2 adrenoceptor agonist.

3 We imaged washout of [125I]‐MIBG from rabbit heart before and during two consecutive 45‐min intravenous infusions of dexmedetomidine (10 μg kg–1 followed by 16 μg kg−1) (n=9) or of saline (n=9).

4 Heart rate (HR), and mean blood pressure (BP) were measured before and at the end of each study period. Plasma noradrenaline (NA) was measured before and after study drug infusion. The hearts were then excised and biopsied for MIBG tissue concentration [MIBG] (%kg‐dose g−1).

5 Relative to saline controls, dexmedetomidine significantly decreased HR, BP, plasma NA and MIBG washout. There was an inverse correlation between MIBG washout and residual [MIBG] in the myocardium (r=−0.75, P < 0.01).

6 These data suggest that a reduction of sympathetic nervous system activity causes a decrease in myocardial MIBG washout in vivo in rabbits, and confirms the usefulness of MIBG scintigraphy as a non‐invasive tool to measure changes in myocardial sympathetic activity.
Contractile effects of tacrolimus in human and rat isolated renal arteries
Authors: Schwertfeger E. , Wehrens J. , Oberhauser V. , Katzenwadel A. , Rump L. C.
Published: March 2003

1 We tested the vasoactive properties of the immunosuppressive drug FK 506 (tacrolimus) in preconstricted rat and human isolated renal arteries in vitro.

2 In rat renal arteries, tacrolimus (3, 10 μM) showed a direct and dose‐dependent contractile effect by maximally 23 μm (10% of the noradrenaline effect), which was only observed in the presence of intact endothelium. Moreover, a lower concentration of tacrolimus (1 μM) potentiated pressor responses to the sympathetic neurotransmitter noradrenaline but not to ATP in this species. ATP‐ (0.01–10 μM) induced vasodilation was not affected by tacrolimus (1 μM).

3 In contrast, in human interlobar arteries, tacrolimus failed to induce direct vasoconstriction and did not significantly potentiate constrictor responses to noradrenaline. Acetylcholine‐(1 μM) induced vasodilation was much smaller in human than in rat renal arteries suggesting the lack of functional endothelium in the human preparation.

4 The findings suggest that tacrolimus releases an endothelium‐derived constricting factor in rat renal arteries to increase vascular tone and to potentiate pressor responses to noradrenaline. In human interlobar arteries, this effect of tacrolimus is not observed probably because of the absence of functional endothelium or the necessary mediator mechanism.
The savannization of moist forests in the Sierra Nevada de Santa Marta, Colombia
Authors: Cavelier J. , Aide T. , Santos C. , Eusse A. , Dupuy J.
Published: March 2003

In the Rio Ranchería watershed of the Sierra Nevada de Santa Marta, between 500 and 1500 m, savanna vegetation is interspersed with moist forests. The savannas are composed of native savanna grasses like Aristida adscensionis L., Arundinella sp., Panicum olyroides Kunth, and Schyzachyrium microstachyum (Desv.) Roseng., Arrill & Izag and the African Melinis minutiflora P. Beauv. There is also Curatella americana L. and Byrsonima crassifolia (L.) H.B.K., two typical tree species of the neotropical savannas. Although moist forest patches occur more often on lower slopes and narrow valley bottoms, they can also be found on mid‐ and upper‐slopes and less often on ridges. Thus, these forest patches are not gallery forests as are found throughout the neotropics, but the result of deforestation and fractionation of a continuous forest. A comparison of soil profiles between the savannas and remnant forest patches on the same slope, showed the disappearance of the A and B horizons (approx. 50 cm) under savanna vegetation. The sharp difference between the savanna and forest soils at the Rio Ranchería does not appear to be due to a change in soil water status along a toposequence or differences in the underlying bedrock. We hypothesize that the savannas of the Rio Ranchería watershed, are the result of deforestation and land practices on infertile soils derived from granite. The savannization process was likely initiated by Amerindians by means of the frequent use of fire or clearing lands for the cultivation of maize. The introduction of cattle by Spaniards (c. 1530) and the frequent use of fire to maintain grazing fields, contributed to further degradation of the habitat. While some tropical landscapes recovered their forest cover when human pressure was removed approximately 500 years ago, areas such as the Rio Ranchería watershed have suffered permanent damage. The savannas of this region are likely to remain unless fire is suppressed and soil restoration practices implemented.
Review of the biogeography of the genus Artemia (Crustacea, Anostraca)
Authors: Triantaphyllidis George , Abatzopoulos Theodore , Sorgeloos Patrick
Published: March 2003

In this study, we report on the known Artemia habitats worldwide. Recent literature information is incorporated about the taxonomic status of the various populations studied. The genus is composed of di‐, tri‐, tetra‐ and pentaploid parthenogenetic populations and of the following bisexual species: A. franciscana franciscana, A. franciscana monica, A. franciscana sp., A. persimilis, A. salina, A. urmiana, A. sinica and A. sp. from Kazakhstan. The problems of characterizing new brine shrimp populations are discussed. In view of the great importance of Artemia as part of the live food chain for the culture of fish and shellfish larvae and the present cyst shortage from the market, the need for commercial exploitation and development of new Artemia sources is now, more than ever, necessary.
Continuity or discontinuity? Vegetation change in the Hadrianic–Antonine frontier zone of northern Britain at the end of the Roman occupation
Authors: Dumayne‐Peaty Lisa
Published: March 2003

Aim The aim of this paper is to determine the nature of vegetation change in the Hadrianic‐Antonine frontier zone of northern Britain at the end of the Roman occupation. The concepts of continuity and change are important issues in palynological and archaeological studies and it has been assumed traditionally that large‐scale woodland regeneration occurred in the area at the end of the Romano‐British period.

Location Hadrianic–Antonine frontier zone of northern Britain.

Methods Pollen analysis of peat profiles, radiocarbon dating

Results and main conclusions The pollen diagrams suggest that woodland regeneration occurred around the time of the withdrawal of Roman troops at Fozy Moss, Northumbria; Glasson Moss, Cumbria; Bolton Fell Moss (marg), Cumbria; Letham Moss, Stirlingshire; Cranley Moss, Lanarkshire; Carsegowan Moss, Wigtonshire and Dogden Moss, Berwickshire. Regeneration started at Blairbech Bog, Dumbartonshire and Ellergower Moss, Dumfriesshire before the Roman occupation began. The landscape around Walton Moss, Cumbria remained open later and regeneration of woodland did not take place until the latter half of the sixth century AD. Woodland regeneration at each of the sites was also associated with a decline in agricultural production, and renewed clearance did not occur until Anglian, monastic or Scandinavian settlement took place.