bluuebunny/crossref_metadata_2025_split huggingface dataset:
When time is of the essence: choosing a currency for prey‐handling costs
Authors: Rovero Francesco , Hughes Roger N. , Chelazzi Guido 
Published: March 2003

1. Heartbeat rate was measured in shore crabs Carcinus maenas (L.) feeding on mussels Mytilus edulis L. in order to estimate the energetic cost of handling prey and to assess the relative importance of energy and time as costing currencies. 2. Energetic handling costs represented approximately 2% of corresponding gains. 3. The tendency of profitability (gain per unit handling time) to increase with prey size was weakened by including energetic handling costs. 4. Time was judged to be a more appropriate currency than energy for costing prey‐handling behaviour. 5. The importance of time as a costing currency, either through the principle of lost opportunity or through exposure to mortality risk, may extend to other behavioural systems, including aggression.
Flippers versus feet: comparative trends in aquatic and non‐aquatic carnivores
Authors: Bininda‐Emonds Olaf R.P. , Gittleman John L. , Kelly Colleen K. 
Published: March 2003

SummaryIt is commonly accepted that many adaptations characterize carnivores that live in water. However, no comparative tests have ever shown systematic differences between aquatic and terrestrial carnivore species as a whole. We examine numerous hypotheses that purport to distinguish aquatic and terrestrial carnivores using 20 morphological, life history, physiological and ecological traits. Using the method of independent contrasts with a complete species‐level phylogeny of extant carnivores, we found few differences between aquatic and terrestrial species. Compared to terrestrial sister taxa, aquatic carnivores are streamlined (increased head and body length for a given body weight), have larger brains, smaller litter sizes, shorter interbirth intervals, and shorter lifespans. Some of these differences are important functionally. Larger brain size may be related to increased cognitive and sensory needs required for an amphibious lifestyle; smaller litters are likely associated with increased neonatal survival amidst competition for suitable breeding sites and advantages accruing to increased precociality. We conclude that broad differentiation of carnivores into aquatic and terrestrial ecotypes is not useful given that adaptive differences between these groups are limited and seemingly no more numerous than those that occur within each ecological group.
Metapopulation structures affect persistence of predator–prey interactions
Authors: Bonsall Michael B. , French David R. , Hassell Michael P. 
Published: March 2003

SummaryWe investigate the metapopulation dynamics of an extinction‐prone host–parasitoid interaction.Single cell host–parasitoid interactions show diverging oscillations resulting in rapid extinction of both host and parasitoid. By linking cells together into metapopulations and controlling for increased availability of resource, persistence time of the trophic interaction is enhanced.Metapopulation persistence is influenced by spatial structure and local demographics. Using nonlinear mixed models, we show that the persistence time of these host–parasitoid metapopulations is determined by habitat size and local within‐patch population dynamics.We use a metapopulation model to show how the role of local demographic population structure and habitat size act concomitantly to affect persistence.
Denning ecology of the striped skunk in the Canadian prairies: implications for waterfowl nest predation
Authors: LariviÈre Serge , Messier FranÇois 
Published: March 2003

1.  From 1993 to 1995, we studied the summer denning ecology of 40 radio‐collared striped skunks Mephitis mephitis (32 females, eight males) during the waterfowl nesting season in Saskatchewan, Canada. 2.  Forty‐seven natal dens were used by 30 females. Natal den sites were either underground burrows (55%) or holes underneath buildings (45%), and were preferably located in farmsteads. 3.  Male and female striped skunks used similar resting sites which consisted of above‐ground retreats (57%), underground burrows (23%), buildings (17%) and culverts (3%). 4.  Habitat preferences for resting sites did not differ between males and females: both sexes preferred farmsteads and wetlands, whereas managed waterfowl nesting areas, woodland and miscellanous habitats were avoided. Cropland was avoided for both natal dens and resting sites. 5.  Females did not simultaneously share natal dens or resting sites, but both types of retreats were occupied by different females over time. Natal dens were occupied for 47 ± 3 days for females using a single den vs. 60 ± 3 days for females using >1 natal dens. Den switching may have been induced by a build‐up of faeces. 6.  Management of natal den sites such as abandoned farmsteads and buildings may provide an avenue of non‐destructive predator management that is less expensive and controversial than exclusion or control.
How does temporal variability affect predictions of weed population numbers?
Authors: Freckleton R.P. , Watkinson A.R. 
Published: March 2003

1.  Population models that are used to predict weed population dynamics or the impact of control measures on weed abundance typically ignore temporal variability in life‐history parameters and control measures, and utilize mean arithmetic population growth rates to predict population abundance. 2.  We demonstrate that the persistence of weeds in a stochastically varying environment depends on the geometric mean population growth rate being greater than zero, rather than the arithmetic mean population growth rate being greater than zero. 3.  In a stochastically varying environment we show that temporal variability in fecundity, germination and survivorship will tend to decrease population size, relative to predictions based on arithmetic means. Conversely, variability in competitive effects and weed control will tend to increase population size, relative to predictions based on arithmetic mean values. The distinction between these two sets of parameters is that increases in the former will increase population growth rate, whereas increases in the latter will decrease it. 4.  We argue that population models based on arithmetic mean population growth rates will tend to over‐estimate population size. Numerical simulations indicate that this bias may be considerable. 5.  Since short‐term studies cannot, in general, estimate the geometric mean growth rate of a population we suggest several approaches for estimating the degree of bias in the predictions of models owing to the effects of variability. Accounting for such variability is necessary since current models for the dynamics of weed populations are based on arithmetic mean measures of population growth and hence likely to be biased.
Effects of supplementary feeding on territoriality, breeding success and survival of pheasants
Authors: Hoodless A. N. , Draycott R. A. H. , Ludiman M. N. , Robertson P. A. 
Published: March 2003

1. The effects of supplementary food in spring on subsequent pheasant breeding in an intensively farmed area in southern England were assessed by a large‐scale, replicated field experiment. 2. Territorial cock pheasants were counted in April, and the breeding success and survival of radio‐tagged hens were monitored in six 1‐km2 plots during 1994 and 1995. Total numbers of young reared and post‐breeding pheasant densities were found by August counts. In 1994, three randomly selected plots were supplied with wheat grains via hoppers along woodland edges and hedgerows. The other three plots acted as controls and the treatments were reversed in 1995. 3. The density of cock territories increased significantly in food‐supplemented plots (44 ± 8 km−2) in relation to control plots (29 ± 8 km−2), and the presence of hoppers significantly affected the locations of territories. However, similar proportions of territorial males acquired harems in the control and food‐supplemented plots. Hen density did not increase and, consequently, the mean harem size was significantly lower with supplementary feeding. 4. Hens given supplementary food did not nest earlier and the number of nests initiated, clutch sizes and the proportion of successful nests did not differ significantly from those of controls. However, hens supplied with supplementary food re‐nested significantly more quickly following the loss of a nest or brood. 5. Radio‐tagged hens did not rear significantly more young with supplementary feeding. Hen survival was unchanged and post‐breeding pheasant densities were no higher. 6. On present evidence, spring feeding cannot be advocated as a management technique to improve the breeding success of pheasants surviving the winter.
A comparison of regeneration dynamics following gap creation at two geographically contrasting heathland sites
Authors: Britton A.J. , Carey P.D. , Pakeman R.J. , Marrs R.H. 
Published: March 2003

1. Lowland Calluna‐dominated heathlands are a high priority for conservation in Europe. As an anthropogenic subclimax community they require regular management intervention to maintain their conservation interest. 2. Increasingly, Calluna is disappearing from lowland heathlands and being replaced by grasses, especially in the Netherlands and more recently in south‐east England. While Calluna is highly competitive over much of its life cycle, its competitive ability is reduced during the regeneration phase that follows the death of stands or results from management activity. 3. We examined the influence of five factors on regeneration of vegetation in gaps in two broadly similar lowland dry heaths over a 3‐year period. These were: geographical location (combining a variety of environmental contrasts); dominant species (Calluna or grasses); management techniques; gap size; and seed source availability. 4. Site location had the greatest effect on patterns of regeneration. Regeneration on the Wirral (north‐west England) was faster and more dominated by Calluna than regeneration in Breckland (south‐east England), which was dominated by other species including grasses and annual plants. Addition of Calluna seed at the Breckland site failed to increase Calluna cover. It was concluded that climatic or other environmental factors were the most probable cause of poor regeneration. 5. Cover of grasses in regenerating areas was greatest in Breckland, where Deschampsia was able to establish in all gaps where there was a seed source (either in the surrounding vegetation or applied as a treatment). On the Wirral, Deschampsia establishment was limited, even in gaps where a seed source was applied. 6. This work has implications for the conservation management of heathlands, which currently follows a standard prescription throughout the UK. It is suggested that management regimes should be tailored to suit the conditions prevailing at individual sites as regeneration dynamics may be extremely variable.
Fire and biodiversity: responses of grass‐layer beetles to experimental fire regimes in an Australian tropical savanna
Authors: JÉrôme Orgeas , Andersen Alan N. 
Published: March 2003

Summary Up to 50% or more of the savanna landscapes of northern Australia are burnt each year, but the effects of these fires on savanna faunas are poorly known, especially for arthropods. We investigated the responses of grass‐layer beetles to three fire regimes (unburnt – fires excluded; early – annual fires lit early during the dry season; late – annual fires lit late during the dry season) as part of a landscape‐scale fire experiment at Kapalga in Australia’s Northern Territory, where replicated fire regimes were applied to 15–20‐km2landscape units over a 5‐year period. We also sought to identify beetle species that might act as indicators of particular fire regimes, and examined the extent to which analysis at the family level is sufficient to reveal patterns evident from species‐level analysis. Beetles were sampled using sweep nets during February (mid‐wet season) and May (end of wet season) each year, from 1989 (18 months prior to the imposition of fire treatments) to 1995 (after 5 years of treatments). A total of 3865 beetles from 233 species was recorded, with the dominant families Chrysomelidae (leaf beetles) and Curculionidae (weevils) contributing 91% of all beetles and 57% of total species. Total beetle abundance, species richness, family richness and the abundances of one of the 10 most common species were significantly affected by fire treatment according toanova. In all cases, beetle abundance and richness were similar in the two burning treatments, but greater than in the unburnt treatment. These differences were only apparent during the second half of the experiment. The responses were mirrored by changes in composition at species, family and guild levels, according to multivariate analysis. According to indicator analysis, five beetle species were significant indicators of late fires, and one of early fires. All these species were infrequently recorded and therefore of limited use for management. However, two common species were indicative of burnt habitats if early and late treatments are considered together. Family richness was highly correlated (r2 = 0·615) with species richness, and multivariate analysis of family‐level abundances revealed the compositional changes in relation to fire that were evident in species‐level analysis. Family was therefore a reliable surrogate of species for detecting beetle responses. Although we found significant effects of our experimental treatments, in the broader context of overall beetle dynamics the assemblages appeared to be remarkably resilient to fire. This reflects a long history of association with frequent fire, and is consistent with many other components of the northern Australian fauna, where fire appears to be of secondary importance to variation in rainfall and soil type. The lack of effect of fire timing on grass‐layer beetles calls into question a management paradigm that focuses largely on fire intensity, and suggests that fire management needs to be more mindful of fire frequency.
The interplay between culling and density‐dependence in the great cormorant: a modelling approach
Authors: Frederiksen M. , Lebreton J.‐D. , Bregnballe T. 
Published: March 2003

Summary The population of great cormorantsPhalacrocorax carbo sinensisbreeding in northern Europe has increased from 5000 pairs around 1970 toc. 100 000 pairs in the late 1990s, leading to serious conflicts with fishery and aquaculture interests. Management action, including widespread culling, has been taken in several countries. Since 1990, presumed density‐dependent declines in demographic performance have appeared in cormorant populations. We employed an extended Leslie matrix model to study the interaction between culls and density‐dependence in regulating breeding and autumn population sizes, with emphasis on evaluating the effects of culling. During 1979–92, the breeding population of great cormorants in northern Europe increased by 18% year−1, in accordance with observed life‐cycle parameters before the appearance of density‐dependent declines. We modelled six scenarios with varying assumptions about the strength of density‐dependence in adult survival and the proportions of breeding cormorants. A series of cull estimates was also included. Scenarios with moderate or strong levels of density‐dependence provided predictions that fit the observed numbers of breeding pairs, whereas scenarios without density‐dependence in survival overestimated real population growth. The most well‐supported scenarios indicated that the effect of culls at the present level (1998–99: 17 000 cormorants shot) was limited (< 10% reduction at equilibrium). Increasing the annual cull to 30 000 still had a limited effect, whereas shooting 50 000 birds year−1led to population extinction within 20–40 years. Shooting a fixed proportion of the population exceeding a threshold, through density‐dependent culling, could eliminate differences among scenarios and stabilize the population. We conclude that culls probably have had a limited effect on cormorant populations, but if carried out in a density‐dependent way they could stabilize numbers near a desired level. However, a reduction in the number of cormorants may not lead to a similar reduction in conflicts, and actions to control damage rather than cormorant populations are likely to be more cost‐effective. If culling is to be continued, we recommend the adoption of an adaptive and co‐ordinated management strategy across Europe. We also advocate the need to account for density‐dependent mechanisms in general culling strategies.
Inflammatory and motor responses by tachykinins in the guinea‐pig oesophageal sphincter
Authors: Conte B. , Parlani M. , Lopez G. , Cirillo R. , Maggi C. A. , Manzini S. 
Published: March 2003

1 The aim of this study was to characterize the tachykinin receptors involved in producing plasma protein extravasation and contractile responses of the guinea‐pig oesophageal sphincter. 2 In anaesthetized guinea‐pigs, the selective tachykinin NK‐1 receptor agonist [Sar9,Met(O2)11]substance P produced plasma protein extravasation (PPE) which was not affected by the treatment with the tachykinin NK‐2 receptor antagonist MEN 10627 (1 μmol kg−−1 i.v.) or the histamine H1‐receptor antagonist, diphenhydramine (34.5 μmol kg−−1 i.v.). However, the [Sar9,Met(O2)11]substance P‐induced PPE was blocked by the previous administration of the peptide tachykinin NK‐1 receptor antagonist FK 888 or by the non‐peptide antagonist SR 140333, yielding ED50 values of 1.1 ± 0.2 and 0.01 ± 0.004 μmol kg−−1 i.v., respectively. 3 The tachykinin NK‐2 or NK‐3 receptor agonists [β‐Ala8]neurokinin A (4–10) or [MePhe7]neurokinin B, respectively, produced a weak PPE at high doses. The effect of [MePhe7]neurokinin B‐induced PPE was inhibited by SR 140333. 4 In the guinea‐pig isolated oesophageal sphincter, [Sar9,Met(O2)11]substance P did not exert any contractile effect up to 10 μm. The selective tachykinin NK‐2 receptor agonist ([β‐Ala8]neurokinin A (4–10), produced concentration‐dependent contractions (pD2 = 7.6 ± 0.03) which were inhibited by the selective tachykinin NK‐2 receptor antagonist, MEN 10627 (pA2 = 8.6 ± 0.1). Also, the tachykinin NK‐3 receptor selective agonist [MePhe7]neurokinin B induced concentration‐dependent contractile responses, but these responses were inhibited by MEN 10627. 5 Altogether, these data indicate that the stimulation of tachykinin NK‐1 receptor produces a vascular inflammatory response, while activation of tachykinin NK‐2 receptors mediate the contraction of the guinea‐pig oesophageal sphincter.
Vascular responses to β‐adrenoceptor subtype‐selective agonists with and without endothelium in rat common carotid arteries
Authors: Chiba S. , Tsukada M. 
Published: March 2003

1 Using the cannula inserting method, vasodilator responses to β‐adrenoceptor agonists (isoprenaline, denopamine and procaterol) were investigated in isolated and perfused rat common carotid arteries. 2 Each β‐adrenoceptor agonist induced a vasodilation in preparations preconstricted by phenylephrine in a dose‐related manner. The potencies were in the order of isoprenaline > procaterol >> denopamine. 3 Denopamine‐induced dilations were significantly inhibited by 1 nmol betaxolol (a selective β1‐adrenoceptor antagonist), but it was not influenced by 1 nmol ICI 118,551 (a selective β2‐adrenoceptor antagonist). On the other hand, procaterol‐induced vasodilations were significantly inhibited by 1 nmol ICI 118,551 but not modified by 10 nmol betaxolol. 4 ACh‐induced vasodilations disappeared after intraluminal saponin injection to remove endothelium, but procaterol‐ and denopamine‐induced dilations were not modified by removal of the endothelium. 5 Pretreatment with L‐NG‐nitroarginine methyl ester (L‐NAME) readily inhibited ACh‐induced vasodilations. However, neither procaterol‐ or denopamine‐induced vasodilation was modified by L‐NAME treatment. 6 From these results, it is concluded that in the rat common carotid arteries (1) there are abundant β2‐ and a few β1‐adrenoceptors, and (2) there is no participation of the endothelium‐dependent mechanism in β‐adrenoceptor mediated vasodilations.
Effects of P5, a novel oxazolo(3,2‐a)pyridine derivative with a long‐acting antihypertensive activity, on different agonist‐mediated pressor responses in pithed rats
Authors: Martín E. , Sevilla M. A. , Morán A. , Martín M. L. , Román L. San 
Published: March 2003

1 An oxazolo(3,2‐a)pyridine derivative P5, described chemically as (±)‐ethyl‐7‐(3‐nitrophenyl)‐5,8a‐dimethyl‐6‐methoxycarbonyl‐2,3,8,8a‐tetrahydro‐7H‐oxazolo[3,2‐a]pyridin‐8‐carboxylate, is a novel compound that has been synthesized as a possible antihypertensive prodrug of the 1,4‐dihydropyridine type. Its antihypertensive activity was described in a previous study by the authors (Morán, Martin, Velasco, Martin, San Roman, Caballero, Puebla, Medarde & San Feliciano, 1997). 2 The aim of this work was to establish in vivo, the possible mechanisms participating in this antihypertensive action. Accordingly, we examined the effect of P5 on the pressor responses induced in pithed rats by noradrenaline (an α1‐, α2‐ and β‐adrenoceptor agonist), xylazine (an α2‐adrenoceptor agonist), methoxamine (an α1‐adrenoceptor agonist), angiotensin I, angiotensin II, L‐NAME (a nitric oxide synthase inhibitor) and BayK 8644 (a calcium channel agonist) and compared them with those of nifedipine, used as the reference drug. 3 Intravenous (i.v.) administration of P5 (2.5–10 mg kg–1) inhibited the pressor responses to noradrenaline (1 μg kg–1), xylazine (80 μg kg–1), angiotensin I (0.5 μg kg–1), angiotensin II (0.5 μg kg–1), BayK 8644 (30 μg kg–1) and L‐NAME (10 mg kg–1). Nifedipine (10 μg kg–1, i.v.) reduced the pressor responses to all these agonists and also to methoxamine (2 μg kg–1). 4 However, P5 was more effective than nifedipine in inhibiting these responses and its inhibitory effect lasted longer. Intravenous infusion of calcium gluconate (1 ml kg–1 min–1) reversed the reduction in the pressor responses as a result of nifedipine. The effects of P5 were only reversed at 2–3 h after administration. 5 These results suggest that P5 has a strong capacity to inhibit the pressor responses to several agonists after its i.v. administration and that such effects are related to its potent antihypertensive activity.
Changes of the responses of single sympathetic ganglionic neurones to substance P following desensitization
Authors: Simmons M. A. 
Published: March 2003

1 The neuropeptide substance P (SP) exerts an excitatory effect on sympathetic neurones by inhibiting a time‐ and voltage‐dependent potassium current. During prolonged application of SP, the response desensitizes. The changes in kinetics of the SP response in single neurones after desensitization have been studied in an attempt to gain some insight as to the molecular mechanism of desensitization in live, functioning neurones.2 Desensitization to SP resulted in subsequent SP responses being smaller, but the time course was unchanged in desensitized cells compared with non‐desensitized cells.3 Experimental manipulations were performed to decrease receptor and G protein function for comparison to desensitization. Intracellular application of GDPβS, to decrease G protein function, led to successive responses to agonist becoming smaller and slower. When functional muscarinic receptors were decreased by extracellular application of propylbenzilylcholine mustard (PrBCM), the response to muscarine became smaller, but the time course was unchanged compared with the change in time course produced by PrBCM vehicle alone.4 The results have also been compared with simulations from a mathematical model of drug‐receptor–G protein interactions. Under a constrained set of conditions, the model predicts that decreasing the size of the G protein pool will decrease both the magnitude and the time course of the response to agonist. Decreasing receptor levels results in a more efficient decrease in the magnitude of the response but no change in the time course of the response.5 These data provide evidence that desensitization of the response to SP in single neurones results from a decrease in functional receptors.