bluuebunny/crossref_metadata_2025_split huggingface dataset:
The diversity and abundance of ants in relation to forest disturbance and plantation establishment in southern Cameroon
Authors: Watt Allan D. , Stork Nigel E. , Bolton Barry 
Published: March 2003

Summary

Tropical biodiversity is seriously threatened by deforestation but few studies have quantified its impact. We aimed to measure the impact of forest clearance and different methods of establishing Terminalia ivorensis (Combretaceae) forest plantations on the abundance, richness and composition of ants, the most abundant group of arthropods in tropical forest canopies, in the Mblamayo Forest Reserve in Cameroon. For canopy ants, we quantified the effects of different methods of plantation establishment by sampling two sets of plots subjected to complete clearance, partial mechanical clearance and partial manual clearance relative to uncleared forest reference plots. For leaf‐litter ants, we quantified the impacts of different levels of forest disturbance along a gradient from near primary forest to complete forest clearance.
A total of 97 ant species was recorded from the canopy (from approximately 48 500 individuals), at an average of 213 (±45) ants m−2. Jack‐knife estimates of species richness showed that at one site, Bilik, 87% more species occurred in the partial manual clearance plot than the complete clearance plot, with the partial mechanical clearance plot intermediate. At the other site, Ebogo, ant richness did not vary between treatments. Ants were 20 times more abundant in the partial manual clearance plot in Ebogo than the partial manual clearance plot in Bilik, largely due to a numerous Technomyrmex species that might have reduced ant richness on this plot.
Cluster analysis of the similarities in ant species composition between plots, calculated by the Morisita index, showed that site and treatment affected species composition. Neither treatment nor site affected the relative number of species in different nesting categories.
A total of 111 ant species (from 3650 individuals) was recorded from the leaf litter, at an average of 52 (±4·6) ants m−2. Species numbers were greatest in the two partial clearance plots in Ebogo (52–53 species), lowest in the two complete clearance plots (37), and intermediate and most variable in the three uncleared forest plots (40–52). Cluster analysis showed that species composition was not affected by treatment, while neither treatment nor site affected the relative number of ant species in different feeding categories.
Despite some local effects by dominant species, our results support the view that deforestation can reduce arthropod species richness. This study is unique in showing that reforestation methods (using a single tree species) can have a marked effect on arthropod species richness and composition. Specifically, it reveals that ant species richness can be greater in plantations established after partial manual clearance than complete clearance.
Scale‐related effects of grazing on native plant communities in an arid rangeland region of South Australia
Authors: Landsberg J. , James C. D. , Maconochie J. , Nicholls A. O. , Stol J. , Tynan R. 
Published: March 2003

Summary

To explore how rangeland grazing affects native plant diversity at local and regional scales, we measured the frequency of occurrence of plant species along six transects spread across a large region of arid calcareous rangelands in north‐western South Australia. Four transects were in commercial sheep‐grazed paddocks and two were in otherwise similar lands that had never been developed for pastoralism. Each transect comprised four sites of area 0·5 km2, at distances of 1, 4, 7 and 10 km from the nearest stock watering point in a paddock, or from a nominal starting point > 10 km from water in the undeveloped lands.
Nearly 200 plant species were recorded, but distributions were patchy, with > 30% of species present at < 10% of sites.
The apparent influence of pastoral development and proximity to water varied with the scale of inquiry. At the regional level, pastoral development had a predominantly negative effect on the abundance of species: 16 species were less abundant in paddocks than in lands that had never been developed, and only one species was more abundant. Localized trends within paddocks were more positive: significantly more species showed trends of increasing abundance with increasing proximity to watering points and associated grazing activity.
The study results are consistent with a general pattern whereby pastoral development enhances richness of plant species at a local scale (by providing opportunities for more species to establish) but has the potential to decrease it at a regional scale (by removing the most grazing‐sensitive species from the regional species pool).
The results suggest there may be two fundamentally different mechanisms whereby species decline in abundance under grazing. Palatable, drought‐hardy, perennial species are more likely to decline in abundance with proximity to water and associated accumulated grazing pressure in paddocks. Uncommon or short‐lived species that are selectively grazed during very good seasons are more likely to decline everywhere in paddocks, regardless of the location of water points.
If both mechanisms contribute to species decline there may need to be a mix of strategies for protecting all species in any regional network of conservation reserves.
Biphasic responses of equine colonic vessel rings to vasoactive inflammatory mediators
Authors: Venugopalan C. S. , Moore R. M. , Holmes E. P. , Sedrish S. A. , Koch C. E. 
Published: March 2003

1 The role of endothelium in modulating equine colonic vessel responses to histamine (HST), 5‐hydroxytryptamine (5‐HT), bradykinin (BK) and acetylcholine (ACh) was evaluated in vitro. 2 Segments of mesenteric arteries and veins were collected from the left ventral colon of six adult horses destined for euthanasia for reasons unrelated to cardiovascular or gastrointestinal systems. Vessels were gently cleansed and cut into 4 mm wide rings. 3 Three vessel conditions namely endothelium intact, endothelium removed and Nω‐nitro‐L‐arginine methyl ester (L‐NAME)‐treated were used for both arterial and venous rings. Each ring was placed in an organ bath with oxygenated Tyrode’s solution. One side of the ring was fixed to the floor of the bath and the other side to a force‐displacement transducer interfaced with a polygraph. 4 An initial tension of 2 g was applied to rings which were allowed to equilibrate for 45 min. The bath solution was gently replaced every 15 min and tension was readjusted to 2 g each time except following the last wash. 5 Rings were precontracted with a single EC25 dose of noradrenaline and after the response plateaued, cumulative concentration (10−−12–10−−4 m) response curves were determined for each agent on separate rings. The relaxation from the precontracted level to the baseline was considered as 100% relaxation. Maximal relaxation and maximal contractions were statistically analyzed. 6 All agents induced a relaxation response initially, followed by a contractile phase as the concentrations increased in both arteries and veins, thus, making a biphasic concentration–response curve. In arteries, relaxation produced by ACh was significantly greater than 5‐HT. Endothelium removal and L‐NAME treatment significantly reduced relaxation in arteries. Only endothelium removal produced a significant reduction of relaxation in veins. 7 In both arteries and veins, HST and 5‐HT produced significantly greater contraction than ACh or BK. No significant change in contraction was observed in arteries either by endothelium removal or L‐NAME treatment, however, contraction was significantly reduced in veins by endothelium removal. 8 These findings suggest that the endothelium plays a major role in modulating equine colonic arterial relaxation via nitric oxide and venous contraction via endothelium‐derived contractile mediators, probably endothelin and/or arachidonates.
Regarding the unitary theory of agonist and antagonist action at presynaptic adrenoceptors
Authors: Kalsner S. , Abdali S. A. 
Published: March 2003

1 The linkage between potentiation of field stimulation‐induced noradrenaline release and blockade of the presynaptic inhibitory effect of exogenous noradrenaline by a presynaptic antagonist was examined in superfused rabbit aorta preparations. 2 Rauwolscine clearly potentiated the release of noradrenaline in response to 100 pulses at 2 Hz but reduced the capacity of noradrenaline to inhibit transmitter release to a questionable extent, and then only when comparisons were made with untreated, rather then to rauwolscine‐treated, controls. 3 Aortic preparations exposed for 60 min to rauwolscine followed by superfusion with antagonist‐free Krebs for 60 min retained the potentiation of stimulation‐induced transmitter release but no antagonism of the noradrenaline‐induced inhibition could be detected at either of two noradrenaline concentrations when comparisons were made with rauwolscine treated controls. 4 Comparisons of the inhibitory effect of exogenous noradrenaline (1.8 × 10–6 M) on transmitter efflux in the presence and absence of rauwolscine pretreatment revealed that the antagonist enhanced rather than antagonized the presynaptic inhibition by noradrenaline. 5 It is concluded that the unitary hypothesis that asserts that antagonist enhancement of transmitter release and its blockade of noradrenaline induced inhibition are manifestations of a unitary event are not supportable.
Racemic salbutamol administration to guinea‐pigs selectively augments airway smooth muscle responsiveness to cholinoceptor agonists
Authors: Loss James R. , Hock Rick S. , Farmer Stephen G. , Orzechowski Raymond F. 
Published: March 2003

1 An aim of this study was to investigate whether continuousin vivoadministration of a low dose of salbutamol to guinea‐pigs alters the responsiveness of airway smooth musclein vitro.2 Osmotic minipumps containing a solution of racemic salbutamol were implanted subcutaneouly in guinea‐pigs. The drug was infused at a dose of 0.2 mg kg−1 day−1for 10 days and, at the end of that time, the trachea was isolated and concentration–response relationships to several contractile agonists were examined.3 This treatment resulted in significant increases in the maximum tension developed by tracheal preparations in response to cholinoceptor agonists, carbachol and methacholine.4 Cumulative concentration–response curves for histamine, leukotriene D4, and KCl were similar in tracheal segments from saline‐control and salbutamol‐infused animals.5 Time course experiments showed that augmented airway contractile responsiveness to cholinoceptor agonists was reversible within 3 days after cessation of the 10 day salbutamol infusion.6 Our findings support the hypothesis that β2‐adrenoceptor agonist drugs, administered over timein vivo, induce a transient hyperresponsiveness of airway smooth muscle to cholinergic bronchoconstrictor stimuli.
On Udvardy's Insulantarctica province: a test from the weevils (Coleoptera: Curculionoidea)
Authors: Morrone Juan 
Published: March 2003

‘The scattered islands of the southern, cold ocean have clear affinities with one another . . . They are the basis for my Insulantarctica province.’Udvardy, 1987, p. 190Analyses of the distributional patterns of weevils (Coleoptera: Curculionoidea) from several Subantarctic islands, namely, Campbell, Auckland, Snares, Antipodes, Chatham, Falklands, Tierra del Fuego, Tristan da Cunha, Inaccessible, Nightingale, Gough, Marion, Prince Edward, Crozet, Kerguelen, and Heard, as well as South America and New Zealand, were carried out in order to determine their historical relationships, and to test the validity of Udvardy's (1987) Insulantarctica province. Three parsimony analyses of endemicity (PAE) considering (a) only species, (b) only supraspecific taxa, and (c) species and supraspecific taxa together, were undertaken. The following four groups emerged from the analyses: (1) New Zealand with the Snares, Auckland, Campbell, and Chatham Is., where New Zealand is the sister area to the Chatham Is., and the Auckland Is. are the sister area to Campbell I.; (2) South America with the Falkland Is. and Tierra del Fuego, where South America and Tierra del Fuego together are the sister area to the Falkland Is.; (3) Tristan da Cunha‐Gough group, with the islands following the sequence Gough, Tristan da Cunha, Inaccessible, and Nightingale Is.; and (4) Kerguelen, Heard, Crozet, Marion, and Prince Edward Is., with Kerguelen and Heard Is. being sister areas, and Marion and Prince Edward Is. together being the sister area to the Crozet Is. It is concluded that the weevil fauna does not support the existence of an Insulantarctica province; the similarities among the different Subantarctic islands are due more to similar environmental conditions rather than to a common history.
A biological basis for lichenometry?
Authors: McCarthy Daniel P. 
Published: March 2003

Summary Aim Develop a biologically defensible conceptual model to explain lichen population dynamics. Methods This work critically examines the biological basis for several of the key assumptions that are used to interpret lichen‐size age data. It then presents a biologically defensible conceptual model that can be used to develop computer based simulations of lichen population dynamics or to design alternative approaches to lichenometry. Main conclusions Most lichenometric ages are not verifiably accurate and are generated by methodologies that do not incorporate widely accepted biological principles. Polymodality in thallus‐size distributions is not always the product of discrete events. Polymodality could reflect continuous changes in the availability of inhabitable patches (gaps) in a heterogenous mosaic. Improvement in lichenometry could be realized by investigations that seek to quantify the temporal and perhaps density‐dependent onset of departures from statistical normality for certain lichen cohorts or species groupings. The study of lichen communities on substrates of known age may, in the short term provide some indication of the relative timing of age‐stage changes in lichen demographic structure.
Environmental constraints at the edge of a species distribution, the Eurasian badger (Meles meles L.): a biogeographic approach
Authors: Virgós Emilio , Casanovas Jorge G. 
Published: March 2003

Summary Aim This paper describes the distribution pattern (occurrence) of badgers (Meles meles L. 1758) in a Mediterranean mountain area of central Spain, in relation to landscape characteristics and climatic data. We test the fit of the badger occurrence pattern to the niche hypothesis predictions. Location We sampled twenty‐four survey plots randomly distributed in the mountains of central Spain (Sierra de Guadarrama, Madrid): ten in the north and fourteen in the south slopes. All habitat types and climatic conditions typical of central Spain can be found. Methods The ocurrence of badgers in the plots were recorded through an exhaustive search of setts and latrines in four different (and evenly spaced) points in each plot. The index of occurrence was made by dividing the number of positive points (badger presence) by the total number of points sampled (four in all plots). Landscape patterns (% type of habitat in each plot) were obtained from detailed maps and climate data from meteorological stations placed in the plot.We analyse the contribution of landscape variables and climate data to explain the differences in badger occurrence through Pearson correlations and fixed one‐way ANCOVA with climatic data as fixed factor, vegetation cover as covariates and badger occurrence as response variable. Additionally, we use an one‐way ANOVA to check the differences in occurrence between north and south plots with the location of each plot as fixed factor. Results The results indicate that the badger is more abundant in rainy areas of the mountains, and in open landscapes vegetated by ash‐tree forests than in closed landscapes vegetated by holm oak forests. In addition, the species is more abundant in the northern plots than in the southern ones. Northern plots were homogeneous areas characterized by their open landscape and wet climate, while southern plots were characterized by their dry climate and closed landscapes. In addition, climate (measured as summer rain) is more determinant than habitat type (holm oak cover) to explain the pattern of badger occurrence. Main conclusions Overall, we consider that the typical Mediterranean landscapes are poor habitats for badgers due to changes in the environmental conditions associated with concomitant changes in food resources. These data support the niche hypothesis to explain the changes in abundance or occurrence close to the edge of the distribution of species, and in particular, in Palearctic species in the Mediterranean area.
The influence of spatial scale on cross‐taxon congruence patterns and prediction accuracy of species richness
Authors: Pearson David L. , Carroll Steven S. 
Published: March 2003

SummaryA comparison of species richness patterns of butterflies and birds was made using data from two grids of squares (small squares 137.5 km on a side and large squares 275 km on a side) covering western North America. Using geostatistical procedures, we found that the spatial patterns of species richness of these two taxa were related. The influence of grain size on the strength of this relationship was investigated by analysing the two data sets. For both data sets, the number of butterfly species in a square was a statistically significant predictor of the corresponding number of bird species. However, cross‐validation techniques showed that the marginal improvement in prediction accuracy due to including butterflies as a predictor was greater in the large‐square data. We explored the effect of areal extent on cross‐taxon congruencies by investigating species richness patterns in four subsets of the small‐square data. In regions with smaller areal extent, the cross‐taxon congruence patterns were not substantially different from the pattern found in the full data set. Finally, using data‐splitting techniques, we explored the relationships between prediction accuracy of species richness, sample size, areal extent of the sample, and grain size.
Partitioning sources of variation in vertebrate species richness
Authors: Boone Randall B. , Krohn William B. 
Published: March 2003

AbstractAimTo explore biogeographic patterns of terrestrial vertebrates in Maine, USA using techniques that would describe local and spatial correlations with the environment.LocationMaine, USA.MethodsWe delineated the ranges within Maine (86,156 km2) of 275 species using literature and expert review. Ranges were combined into species richness maps, and compared to geomorphology, climate, and woody plant distributions. Methods were adapted that compared richness of all vertebrate classes to each environmental correlate, rather than assessing a single explanatory theory. We partitioned variation in species richness into components using tree and multiple linear regression. Methods were used that allowed for useful comparisons between tree and linear regression results. For both methods we partitioned variation into broad‐scale (spatially autocorrelated) and fine‐scale (spatially uncorrelated) explained and unexplained components. By partitioning variance, and using both tree and linear regression in analyses, we explored the degree of variation in species richness for each vertebrate group that could be explained by the relative contribution of each environmental variable.ResultsIn tree regression, climate variation explained richness better (92% of mean deviance explained for all species) than woody plant variation (87%) and geomorphology (86%). Reptiles were highly correlated with environmental variation (93%), followed by mammals, amphibians, and birds (each with 84–82% deviance explained). In multiple linear regression, climate was most closely associated with total vertebrate richness (78%), followed by woody plants (67%) and geomorphology (56%). Again, reptiles were closely correlated with the environment (95%), followed by mammals (73%), amphibians (63%) and birds (57%).Main conclusionsComparing variation explained using tree and multiple linear regression quantified the importance of nonlinear relationships and local interactions between species richness and environmental variation, identifying the importance of linear relationships between reptiles and the environment, and nonlinear relationships between birds and woody plants, for example. Conservation planners should capture climatic variation in broad‐scale designs; temperatures may shift during climate change, but the underlying correlations between the environment and species richness will presumably remain.
How to go extinct: lessons from the lost plants of Krakatau
Authors: Whittaker Robert J. , Field Richard , Partomihardjo Tukirin 
Published: March 2003

AbstractAimFew data sets exist that allow measurement of long‐term extinction and turnover rates for islands of the size of the three main islands of the Krakatau group. We test the reliability of previous estimates of plant species extinction and examine structure within the extinction data.LocationThe data analysed are for the three older Krakatau islands: Rakata, Sertung and Panjang in the Sunda Strait, Indonesia.MethodsOur analysis is based on a comprehensive database incorporating all species records for each island since recolonization began after the 1883 sterilization, plus attributes such as distribution, phylogeny, population status and dispersal mechanism for each species. We employ a combination of univariate and multi‐term analyses in analysing structure, and derive Minimal Adequate Models using binary logistic analyses of variance and covariance. We compare the 1883–1934 data set with the contemporary flora as represented by (1) 1979–83 records (as used in previous analyses) and (2) 1979–94 data (original).ResultsThe improved data for the contemporary flora reduces the number of missing species by one‐third. We show that a variety of estimates of extinction rate can be produced depending on what assumptions are made concerning the status of particular species groups. Structural features in the extinction data persist despite the reduction in overall numbers of losses. Losses relate to: (1) the number of islands on which a species originally occurred, (2) the primary dispersal mode, and (3) the original abundance of a species (e.g. whether it was known to have established a successful resident population, and whether it was in decline or increasing inc.1930). The ‘best’ descriptive model employs the variables denoted under (3). A high proportion of losses comprised species introduced by people and rare or ephemeral species. Losses of ‘residents’ that had colonized naturally could largely be accounted for by reference to (1) successional loss of habitat and, to a lesser degree, (2) other habitat disturbance or loss.Main conclusionsPrevious analyses, based on a more limited data set, have significantly over‐estimated extinction from the Krakatau flora. Few naturally colonizing and established species have become extinct. The findings indicate that caution is necessary in interpreting ‘headline’ island ecological rates, and in analysing and modelling such data. Examination of structural features of the data appear to be valuable both in providing ecological insights in their own right, and in enabling refinements to estimates of extinction and thus turnover.