bluuebunny/crossref_metadata_2025_split huggingface dataset:
Validation of a spatial simulation model of a spreading alien plant population
Authors: Higgins Steven I. , Richardson David M. , Cowling Richard M. 
Published: March 2003

Summary Process‐based models, and spatially explicit models in particular, will play an important role in predicting the impacts of future environmental change. Enthusiasm for the rich potential of these models, however, is tempered by the realization that their parameterization is often challenging and time consuming. Moreover, these models are seldom validated; this makes their predictive value in applied contexts uncertain.In this paper we describe the process of parameterizing and validating a spatial demographic model of a spreading alien plant population. The model, a spatially explicit individual‐based simulation, has modest data requirements (for a spatial simulation model) in that it concentrates on simulating recruitment, dispersal, mortality and disturbance and ignores the environmental and biotic heterogeneity of the receiving environment.We tested the model using the invasion ofAcacia cyclopsandPinus pinasterinto fynbos, the mediterranean shrublands of South Africa, as a case study. Dispersal, recruitment and mortality data were collected for each species at six different sites. Aerial photographs from six independent sites (two sites forA. cyclopsand four sites forP. pinaster)were used to reconstruct the invasion histories of the two species between 1938 and 1989. Demographic data were used to parameterize the model, and the 1938 distribution of alien plants, derived from aerial photography, was used to initialize the model.The empirically estimated indices of rate and pattern of invasion fell within the range of model predictions made at all six sites studied. The indices of rate and pattern of invasion predicted by the model did not differ significantly from the empirically estimated indices for 76% of the model data comparisons made. These analyses suggested that the model predictions are good, given the variance in parameter estimates.The proportion of grid locations where the model correctly predicted alien plant distribution was typically above 0·75 and always above 0·5 for both species. A permutation test showed that locations of invasive plants predicted by the model were significantly better than random forP. pinaster, but not always forA. cyclops;this may be becauseA. cyclopsis bird dispersed, and its dispersal may be biased towards perch sites, whereasP. pinasteris wind dispersed.We conclude that, although spatial simulation models are often more difficult to parameterize and validate than statistical or analytical models, there are situations where such effort is warranted. In this case the validation process provides confidence to use the model as a tool for planning the control of invasive plants. In a more general sense we believe that the approach outlined here could be used for model parameterization and validation in situations where spatial simulation models seem appropriate.
Effects of ultraviolet‐B radiation and pH on early development of the moor frogRana arvalis
Authors: Pahkala Maarit , Laurila Anssi , Björn Lars Olof , Merilä Juha 
Published: March 2003

Summary Although the potential negative effects of increased ultraviolet‐B (UV‐B) radiation on early life stages of aquatic organisms are widely recognized, possible synergistic effects with other stressors have seldom been studied outside the laboratory. We investigated the effects of UV‐B radiation and pH on hatchability and early development of moor frogRana arvaliseggs in the field and in laboratory experiments conducted during April 1998 and April 2000 in central Sweden. In the field experiments, no evidence was found for reduced hatchability or increased frequency of developmental anomalies of embryos exposed to ambient levels of UV‐B compared with embryos shielded from UV‐B radiation. Hatchlings shielded from ambient UV‐B radiation did not grow larger than their exposed full‐sibs, giving no support to the hypotheses that (i) the repair of cellular UV‐B damage might be energetically costly nor (ii) that UV‐B‐induced photoproducts directly reduce growth. Although low pH (5·0) reduced hatchability, increased frequency of developmental anomalies and reduced early embryonic growth inR. arvalis, there was no evidence for synergistic effects of pH and UV‐B on any of these traits. The lack of UV‐B radiation effects on the development ofR. arvalisembryos cannot be ascribed to relatively low effective daily doses of radiation (c. 0·43 kJ m−2) during the field experiments, as in the laboratory even higher doses at UV‐B 1·25 kJ m−2and 1·58 kJ m−2(all DNA weighed) had no negative effects. These results suggest that current levels of UV‐B radiation in northern Europe are not likely to reduce fitness in natural populations of the moor frog, even in areas already stressed by acidity.
Predicting shorebird mortality and population size under different regimes of shellfishery management
Authors: Stillman R. A. , Goss‐Custard J. D. , West A. D. , Durell S. E. A. Le V. Dit , McGrorty S. , Caldow R. W. G. , Norris K. J. , Johnstone I. G. , Ens B. J. , Van Der Meer J. , Triplet P. 
Published: March 2003

Summary Human interests often conflict with those of wildlife. In the coastal zone humans often exploit shellfish populations that would otherwise provide food for populations of shorebirds (Charadrii). There has been considerable debate on the consequences of shellfishing for the survival of shorebirds, and conversely the effects of shorebird predation on the shellfish stocks remaining for human exploitation. Until now, it has been difficult to determine the impact of current shellfishery practices on birds or to investigate how possible alternative policies would affect their survival and numbers. One long‐running contentious issue has been how to manage musselMytilus edulisand cockleCerastoderma eduleshellfisheries in a way that has least effect on a co‐dependent shorebird, the oystercatcherHaematopus ostralegus, which also consumes these shellfish. This study used a behaviour‐based model to explore the effects that the present‐day management regimes of a mussel (Exe estuary, UK) and a cockle (Burry inlet, UK) fishery have on the survival and numbers of overwintering oystercatchers. It also explored how alternative regimes might affect the birds. The model includes depletion and disturbance as two possibly detrimental effects of shellfishing and some of the longer‐term effects on shellfish stocks. Importantly, model birds respond to shellfishing in the same ways as real birds. They increase the time spent feeding at low tide and feed in fields and upshore areas at other times. When shellfishing removes the larger prey, birds eat more smaller prey. The results suggest that, currently, neither shellfishery causes oystercatcher mortality to be higher than it would otherwise be in the absence of shellfishing; at present intensities, shellfishing does not significantly affect the birds. However, they also show that changes in management practices, such as increasing fishing effort, reducing the minimum size of shellfish collected or increasing the daily quota, can greatly affect oystercatcher mortality and population size, and that the detrimental effect of shellfishing can be greatly increased by periods of cold weather or when prey are unusually scarce. By providing quantitative predictions of bird survival and numbers of a range of alternative shellfishery management regimes, the model can guide management policy in these and other estuaries.
Pollen removal and deposition by honeybee and bumblebee visitors to apple and almond flowers
Authors: Thomson James D. , Goodell Karen 
Published: March 2003

Summary

To help evaluate the worth of alternative pollinators in agriculture, we present a theoretical framework for comparing the effectiveness of two or more pollinators by measuring pollen removal and deposition.
We report pollen removal and deposition data by Apis mellifera and Bombus spp. during single visits to four cultivars of apples (Golden Delicious, Starkrimson Delicious, Empire/MacIntosh and Rome) and Mission almond.
Apis and Bombus removed similar amounts of pollen from apple flowers but Bombus deposited more pollen on stigmas. Pollen‐collecting bees removed more pollen from apple anthers than nectar‐collecting bees. Apis that approached nectaries laterally deposited substantially less pollen than other visitors.
Apis and Bombus removed and deposited similar amounts of pollen on almond flowers. Apis tended to remove more during pollen‐collecting visits than nectar‐collecting visits. The type of resource sought did not significantly influence deposition.
Based on removal and deposition data, additions of Bombus may increase pollen delivery in apple orchards but reduce pollen delivery in almond orchards if Apis already serve as primary pollinators. Additional data on inter‐tree and inter‐row flights would be necessary to know how much these changes in pollen transfer might affect fertilization.
Measures of pollen‐transfer effectiveness do not provide a complete assessment of pollination value, but can serve as a general, inexpensive tool for pre‐screening possible alternative pollinators.
Are urban bird communities influenced by the bird diversity of adjacent landscapes?
Authors: Clergeau Philippe , Jokimäki Jukka , Savard Jean‐Pierre L. 
Published: March 2003

SummaryThe species diversity of adjacent landscapes influences the conservation or restoration of several animal groups in urban areas, but the effect on birds is unclear. To address this question, we compared bird species richness (BSR) and community composition between periurban (area surrounding the town) and urban (suburban and centre areas) landscapes across three spatial scales.At a large biogeographical scale (temperate and boreal climatic zone), relationships between the BSR of urban areas and their surrounding landscapes were examined in a meta‐analysis of 18 published studies. In general, BSR was negatively correlated with latitude and urbanization. The BSR of suburban and centre landscapes correlated positively with the BSR of periurban landscapes. However, latitudinal effects were also involved, as BSR in urban and periurban landscapes declined as town latitude increased. Similarity indices were low (50%) between periurban and centre bird communities.At a regional scale, we assessed winter bird data from several towns within three regions of temperate and boreal countries (western France, northern Finland and eastern Canada). The type of periurban landscape, number of inhabitants and town diameter did not affect BSR. BSR was similar between the cities of a given biogeographical area. Bird communities were more similar between similar habitat types of different cities than between different habitats of the same city.At a local scale, we tested the influence of proximity to the periurban landscape on BSR in parks of western French towns of different size. Neither BSR nor community similarity changed in relation to the distance of the park from the periurban landscape.Guild composition according to diet and feeding habitat did not vary between urban and periurban locations at regional or local scales.We conclude that, at regional and local scales, urban bird communities are independent of the bird diversity of adjacent landscapes, and that local features are more important than surrounding landscapes in determining BSR. Whatever the biodiversity quality of the periurban landscape, site‐specific actions such as shrub and tree planting, water restoration and increasing vegetation diversity can change bird diversity in towns and improve the quality of human–wildlife contacts.
The verification and application of bioindicators: a case study of dung beetles in a savanna ecosystem
Authors: McGeoch Melodie A. , Van Rensburg Berndt J. , Botes Antoinette 
Published: March 2003

Summary

Bioindicators of habitat quality and environmental change must be identified quantitatively and tested independently to confirm their usefulness. We used the indicator value (IndVal) method, which combines measures of habitat fidelity and specificity, to assess the indicator responses of dung beetles (Coleoptera: Scarabaeidae) in Tembe Elephant Park, South Africa. The indicator responses were verified by sampling in different areas of the Park, 2 years after the responses were originally quantified.
We postulated that terrestrial insect indicators with different combinations of habitat specificity and fidelity might fulfil different indicator roles. Indicator species with strong habitat specificity (characteristic species) are unlikely to provide information on the direction of ecological change despite high vulnerability. Rather, detector species that span a range of ecological states are likely to be better in this role. We used IndVal for selecting such detector species that indicate the direction of ecological change.
Sets of species were found to be robust bioindicators, i.e. reliably characteristic across the habitat of which they were indicative. The suite of indicators was refined by discarding those with IndVals that varied significantly across years, thus improving the confidence in the final suite of species selected. By clearly responding to a change in habitat between two ecological states, detector species provided information complementary to that provided by characteristic species.
The IndVal method enabled both the identification and testing of indicator (characteristic and detector) species. Because of its resilience to changes in abundance, IndVal is a particularly effective tool for ecological bioindication.
We conclude that both characteristic and detector species are useful bioindicators of habitat quality and conversion. We propose that bioindicators that are categorized and verified in this way will have valuable application in the monitoring of habitat integrity.
Can niche use in red and grey squirrels offer clues for their apparent coexistence?
Authors: Bryce Jenny , Johnson Paul J. , Macdonald David W. 
Published: March 2003

Summary

Introduced species are, world‐wide, one of the most serious threats to biodiversity. Grey squirrels Sciurus carolinensis are one of many introduced species to have threatened a native congener; they are thought to have replaced red squirrels Sciurus vulgaris throughout much of the UK as a result of competition. The rate of competitive replacement may be influenced by habitat composition, with some red squirrel populations persisting for prolonged periods in the presence of greys in predominantly coniferous forest.
Here the similarity of red and grey squirrels’ pattern of habitat use was investigated in Craigvinean forest in Scotland, UK, a site that has experienced apparent coexistence for up to 30 years. Overlap was examined in several dimensions: spatial overlap of home ranges, dynamic association and niche overlap. Habitat selection was examined at three levels: selection of core home range areas, selection of tree species within the home range, and the characteristics of patches used intensively by each squirrel species in comparison with random locations within their home range.
Although there was overlap between red and grey squirrel ranges, there were clear differences in the macrohabitats utilized, with red squirrels selecting areas of Norway spruce Picea abies and grey squirrels selecting riparian corridors of mixed woodland for their home ranges. Within their home ranges, habitat selection by individual red and grey squirrels was similar, but again with reds selecting Norway spruce and greys selecting patches of mixed conifers and broad‐leaved trees. As no habitat variables consistently affected the microdistribution of red and grey squirrels within blocks or ‘stands’ of trees, stands that were used were thought to constitute good and relatively homogeneous habitats for squirrels of either species.
There was no evidence to suggest that red and grey squirrels avoided using the same areas at the same time, and potential niche overlap was considerable (0·77). However, partitioning of habitats may have reduced competition between red and grey squirrels and hence have contributed to red squirrel persistence at this site.
This work (i) reinforces earlier proposals that forest management offers a promising tool to assist the conservation of red squirrels; (ii) raises the issue of determining the spatial scale at which coexistence operates; and (iii) offers an illustration of how the management of invasive species can be mediated through the manipulation of niche availability.
Effect of venlafaxine hydrochloride in different preparations of isolated guinea‐pig and rat organ tissues
Authors: Velasco A. , Arruza A. , Maroto M. , Carvajal A. , Del Busto E. Fernández ,   &, Del Pozo J. García 
Published: March 2003

1 A study was undertaken to know better the effects of venlafaxine hydrochloride on the responses of isolated rat vas deferens to noradrenaline and dopamine, those of isolated rat uterus to serotonin and histamine, and those of isolated guinea‐pig ileum to acetylcholine and histamine. 2 Venlafaxine hydrochloride increased the response of rat vas deferens to noradrenaline but not to dopamine. Venlafaxine did not alter the response of rat isolated uterus to serotonin. In rat uterus, venlafaxine did not modify the response to histamine but was able to increase it in guinea‐pig ileum. An anticholinergic effect was observed with the lowest concentration tested. 3 Although venlafaxine is a selective serotonine reuptake inhibitor in the central nervous system, serotonin uptake was not seen in the rat uterus. The anticholinergic effects observed in the present study might be consistent with some of the side‐effects associated with venlafaxine.
Autoregulation of neurotransmitter release at autonomic nerve terminals: a questionable theory
Authors: Kalsner S. 
Published: March 2003

1 The evidence for feedback regulation of neurotransmitter release by means of autoreceptors is questioned. 2 Autoreceptor function must meet the expectations for feedback loops. However, this concordance has not been observed in most neuroeffector systems. 3 The characteristics of per pulse transmitter release with changes in the parameters of stimulation in several autonomic systems do not support the ongoing operation of negative feedback loop mediated by locally released transmitter. Also, the effects of antagonists and agonists often do not comply with feedback expectations. 4 Evidence is provided that agonists and antagonists act at different loci to achieve their inhibiting and potentiating effects on transmitter release. 5 Future efforts should be directed to exploring the mechanism(s) of antagonist action and to a system‐by‐system analysis of the evidence for and against autoreceptor operation.
Comparison of IY81149 with omeprazole in rat reflux oesophagitis
Authors: Kil B. J. , Kim I. W. , Shin C. Y. , Jeong J. H. , Jun C. H. , Lee S. M. , Kim D. Y. , Huh I. H. , Sohn U. D. 
Published: March 2003

1 This study was aimed at evaluating the effects of IY81149{2‐[[(4methoxy‐3‐methyl)‐2‐pyridinyl]methylsulfinyl]‐5‐(1H‐pyrrol‐1‐yl)‐1H‐benzimidazole}, a new proton pump inhibitor, on the development of the surgically induced reflux oesophagitis, on gastric secretion and on lipid peroxidation which is a marker of oxidative stress. Omeprazole was used as a reference drug. We furthermore investigated the influence of quercetin and desferrioxamine (DFO) on the development of the surgically induced reflux oesophagitis in rats on gastric secretion and on lipid peroxidation. 2 IY81149 and omeprazole significantly prevented the development of reflux oesophagitis and gastric secretion in a dose‐dependent manner. The ED50 values of IY81149 for inhibition of oesophagitis and volume of gastric secretion were lower than of omeprazole (5.7 vs. 14.2 μmol, 15.3 vs. 24.0 μmol, respectively). IY81149 was also more potent in the acid output inhibition with an ED50 of 6.8 μmol compared with 20.8 μmol of omeprazole. 3 Malonyldialdehyde (MDA) content, the end product of lipid peroxidation, increased significantly in the oesophageal mucosa after the induction of reflux oesophagitis. IY81149 and omeprazole significantly and dose‐dependently prevented lipid peroxidation. Quercetin (200 mg kg−1, p.o.) and DFO (800 mg kg−1, i.d.) significantly prevented the development of reflux oesophagitis and inhibited the lipid peroxidation independent of their actions on gastric secretion. 4 This result suggests that IY81149 is comparable with omeprazole in the treatment of reflux oesophagitis.
Acute renal failure in 2K2C Goldblatt hypertensive rats during antihypertensive therapy: comparison of an angiotensin AT1 receptor antagonist and clonidine analogues
Authors: Sattar M. A. , Yusof A. P. M. , Gan E. K. , Sam T. W. , Johns E. J. 
Published: March 2003

1 This study compared the effect of a non‐peptide angiotensin II receptor antagonist and a series of clonidine analogues on blood pressure and renal function in a two‐kidney two‐clip Goldblatt rat model of hypertension subjected to 2 weeks of dietary sodium deprivation. 2 Animals received either vehicle, the angiotensin II antagonist, ZD7155 or structural analogues derived from clonidine (AL‐11, AL‐12 and CN‐10) at 10 mg kg−1 day−1 for 4 days. 3 All groups of rats had systolic blood pressure in the hypertensive range (160–180 mmHg). ZD7155 caused a 33‐mmHg fall in blood pressure (P < 0.05) and raised plasma urea and creatinine four‐ to six‐fold. 4 AL‐12 decreased blood pressure by 30 mmHg (P < 0.05), but had no effect on water intake, urine flow or plasma urea and creatinine. AL‐11 and CN‐10 had minimal effects on blood pressure and water intake and while CN‐10 decreased urine flow on the third treatment day, AL‐11 markedly reduced urine flow by some 70%. 5 These data show that in this sodium deficient renovascular model of hypertension, blockade of angiotensin II receptors normalizes blood pressure but causes renal failure, whereas the vasodepressor action of the clonidine analogue AL‐12 occurs without detriment to renal function. These findings imply that angiotensin II receptor antagonists could lead to renal failure if used as antihypertensive agents in renovascular hypertension whereas this would be avoided with the use of clonidine‐like analogues.
The influences of extremely low frequency magnetic fields on clonidine‐induced sleep in 2‐day‐old chicks
Authors: Min Y. S. , Jeong J. H. , Choi Y. M. , Lee B. C. , Huh I. H. , Lee S.‐Y. , Sohn U. D. 
Published: March 2003

1 It has been shown that magnetic fields (MFs) affect a variety of biological effects in animal brains. There have been few experiments on the effects of MFs on sleep. Therefore, we investigated whether extremely low frequency (ELF) MFs affect the sleep induced by clonidine, a central α2‐adrenoceptor agonist. Clonidine produced dose‐related increase of the sleeping time and dose‐related decrease of the onset time in 2‐day‐old chicks. 2 Exposure of chicks to MFs (5, 10, 20 G; for 3, 6, 9, 12 h) significantly increased the clonidine‐induced sleep time as a direct function of intensity and duration of MF application. Clonidine reduced noradrenaline or tyrosine in the brain, an effect which was not further changed in animals exposed to MF. 3 To determine whether the gamma amino butyric acid A (GABAA)/benzodiazepine (BZD) receptor system is involved in the decrease in clonidine‐induced sleep caused by activation of central α2‐adrenergic systems, we examined exposure of chicks to the effects of the BZD receptor antagonist flumazenil (0.5 mg kg−1, i.p.) and GABAA antagonist bicuculline (0.1 mg kg−1, i.p.) on clonidine‐induced sleep. Bicuculline and flumazenil inhibited the increase of clonidine‐induced sleep time by MFs. Clonidine or MFs did not change GABA levels in the brain. 4 These results suggest that MFs can increase clonidine‐induced sleep via a change of GABAA and BZD receptor system irrespective of the concentration of GABA or noradrenaline in the brain of 2‐day‐old chicks.