bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of pea cultivar and water stress on root and shoot competition between vegetative plants of maize and pea
Authors: Semere Tzehaye , Froud‐Williams Robert J.
Published: March 2003

Improvements in intercrop yields may be achieved through an understanding of yield advantages due to above‐ground or below‐ground interactions.

Forage maize and two morphologically contrasting cultivars of pea (leafy cv. Bohatyr and semi‐leafless cv. Grafila) were grown alone and in additive mixtures, under two contrasting levels of soil moisture (± water stress).

The mechanism of competition between maize and pea was studied by separating the effects of root competition and shoot competition, using soil and aerial partitions. Plants were grown in rectangular tanks in a glasshouse.

Leafy pea cv. Bohatyr was as competitive as maize, both below‐ground and above‐ground, whereas semi‐leafless pea cv. Grafila was less competitive than maize or pea cv. Bohatyr. The greater competitive ability of the leafy pea, both above‐ and below‐ground, was probably due to its greater growth rate, associated with its greater leaf area.

The competitive ability of maize, relative to peas, was considerably reduced by water stress. Both the root and shoot competitive abilities of pea were greater under water stress, compared with those of maize.

Relative yield total (RYT) values were significantly greater when maize and pea were subjected to shoot competition only (RYT = 1·76) than when subjected to root competition (RYT = 1·17) or when subjected to both shoot and root competition (RYT = 1·13). This reflects the fact that the effects of root competition were greater than those of shoot competition.

Root competition decreased the shoot dry weights, plant height and leaf area of both maize and pea, whereas shoot competition had no significant effect on these attributes, indicating that soil resources, i.e. mineral nutrients and water, were more limiting than light.
Estimating deer abundance from line transect surveys of dung: sika deer in southern Scotland
Authors: Marques Fernanda F.C. , Buckland Stephen T. , Goffin David , Dixon Camilla E. , Borchers David L. , Mayle Brenda A. , Peace Andrew J.
Published: March 2003

Accurate and precise estimates of abundance are required for the development of management regimes for deer populations. In woodland areas, indirect dung count methods, such as the clearance plot and standing crop methods, are currently the preferred procedures to estimate deer abundance. The use of line transect methodology is likely to provide a cost‐effective alternative to these methods.

We outline a methodology based on line transect surveys of deer dung that can be used to obtain deer abundance estimates by geographical block and habitat type. Variance estimation procedures are also described.

As an example, we applied the method to estimate sika deer Cervus nippon abundance in south Scotland. Estimates of deer defecation and length of time to dung decay were used to convert pellet group density to deer density by geographical block and habitat type. The results obtained agreed with knowledge from cull and sightings data, and the precision of the estimates was generally high.

Relatively high sika deer densities observed in moorland areas up to 300 m from the forest edge indicated the need to encompass those areas in future surveys to avoid an underestimate of deer abundance in the region of interest.

It is unlikely that a single method for estimating deer abundance will prove to be better under all circumstances. Direct comparisons between methods are required to evaluate thoroughly the relative merits of each of them.

Line transect surveys of dung are becoming a widely used tool to aid management and conservation of a wide range of species. The survey methodology we outline is readily adaptable to other vertebrates that are amenable to dung survey methodology.
Restoring resources for an endangered butterfly
Authors: Schultz Cheryl B.
Published: March 2003

Recent changes in land use have resulted in dramatic habitat loss for numerous species. More than 99% of the habitat for Fender's blue butterfly Icaricia icarioides fenderi, an endangered butterfly in Oregon, USA, has been lost.

Fender's blue butterflies require larval host‐plants (Kincaid's lupine Lupinus sulphureus kincaidii) and nectar from native wildflowers.

An experiment was conducted at two degraded sites near Eugene, Oregon, to investigate methods for restoration of Fender's blue habitat. The experimental design included four soil treatments (tilling, reverse fertilization, solarization and a control) combined with two planting treatments (50% forb seed : 50% grass seed and 10% forb seed : 90% grass seed) and two weeding treatments (weeding or not weeding). Treatments were replicated in eight experimental blocks (9 × 28 m) at each site. Seeds from 12 native plant species were field collected and sown in September 1995.

Plant establishment was monitored in May 1996, 1997, 1998 and 1999. In 1999, flowers of all nectar species and leaves of Kincaid's lupine were counted.

Based on estimates of resource needs from previous work, resources were evaluated as insufficient, sufficient or ample.

Solarization combined with 50% forb : 50% grass planting promoted sufficient nectar to sustain butterflies at both sites. Control treatments provided insufficient nectar at both sites. None of the treatments produced sufficient larval resources.

This experiment demonstrates a method to quantitatively link habitat restoration to the resource needs of focal species. The results emphasize the importance of connecting restoration efforts to the life‐history features of focal species. In addition, they highlight the importance of using experiments conducted across a range of sites to test restoration methods before large‐scale efforts are implemented.
Short‐term effects of canopy openness on insect herbivores in a rain forest in Guyana
Authors: Basset Yves , Charles Elroy , Hammond David S. , Brown Valerie K.
Published: March 2003

A before/after–control/impact experiment (BACI) was used to examine the short‐term effects of canopy openness on insect herbivores foraging on the seedlings of five rain forest species in an unlogged forest in Guyana. During the first and second study years, insects were collected monthly from 250 sites, representing 9750 seedlings spread over a plot of 1 km2. At the onset of the second collecting year, half of the parent trees at the sites were felled, creating an average canopy openness of 26%.

Comparisons of the control and impact sites before and after the felling showed that overall insect abundance, particularly of psyllids, and species richness increased at the impact sites, whereas evenness decreased markedly. These responses were consistent with the prediction that intermediate disturbance promotes high diversity in tropical systems.

Twenty‐nine per cent of insect species analysed showed a significant response to felling, with some populations doubling or halving at the impact sites after felling. The abundance of most species increased, although responses varied even between congeners.

A canonical correspondence analysis at the impact sites after felling indicated that most species responded to an increase in leaf production by seedlings, not to canopy openness per se. Species declining at the impact sites were more likely to feed indiscriminately on young and mature foliage and probably reacted to changes in microclimate.

The study illustrates the difficulty in identifying higher taxa, umbrella or indicator species that adequately integrate the responses of insect herbivores to forest disturbance. Because the integrity of insect communities in the understorey of this forest depends more on minimizing damage to plant resources than on canopy openness, we found some support for the conservation value of reduced impact logging in tropical wet forests.
The effect of plant competition and simulated summer browsing by deer on tree regeneration
Authors: Harmer Ralph
Published: March 2003

During the last decade the use of natural regeneration has become an accepted method of restocking British woodlands after harvesting. However, in many broadleaved woodlands there are insufficient numbers of established tree seedlings of adequate size to ensure that restocking is successful. This lack of seedlings may be related to a number of factors, including competition from the ground flora and browsing by deer.

The numbers of deer (Capreolus capreolus,Cervus elaphusandDama dama) are rising throughout Britain and population densities frequently exceed those known to have a significant impact on broadleaved trees. This experiment, which took place at four sites over a 5‐year period, studied the effects of competition from the ground flora and severe, simulated, browsing by deer during summer, on the growth and mortality of naturally occurringAcer pseudoplatanus,Fraxinus excelsior,Fagus sylvaticaandQuercus roburseedlings.

The seedlings were initially 30–40 cm tall with stem diameters of 2·6–6·2 mm. Competition from the ground flora was removed by maintaining circular areas, 1 m in diameter, free of vegetation using a general herbicide. Browsing was simulated by clipping new shoots that were longer than 1 cm in June and August.

The control of the ground flora had little effect on the growth and survival of seedling trees.

In general, the number of tree seedlings producing sufficient growth to receive the simulated browsing treatment decreased with time, but for those seedlings that were clipped there were no consistent trends in either numbers or weights of shoots removed. Unclipped seedlings continued to grow. The height and stem diameter increments varied with species and site, but after 5 years unclipped plants were 50–200% taller with stem diameters 20–130% greater than at the start of the experiment.

The mortality of unclipped seedlings was low and 80% or more survived. Clipping significantly reduced the survival ofFraxinus excelsiorandA. pseudoplatanus, butQ. roburandFagus sylvaticawere unaffected. On an annual basis, there was no relationship between mortality and accumulated number or dry weight of shoots clipped, initial stem diameter or height, and whether or not the seedling was under the overstorey canopy.

The results from this study indicate that established seedlings ofA. pseudoplatanus,Fraxinus excelsior,Fagus sylvaticaandQ. roburthat are > 30 cm tall can survive several years of severe browsing under the shade provided by overstorey canopy covers of 50% or more. This suggests that management should aim to improve survival during the first 1–2 years of growth. This may be achieved by exclusion of animals by fencing, protection of individual seedlings using tree shelters, or culling to control herbivore numbers.
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

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

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.
An arsenic(III)-oxidizing bacterial population: selection, characterization, and performance in reactors
Authors: Battaglia-Brunet F. , Dictor M.-C. , Garrido F. , Crouzet C. , Morin D. , Dekeyser K. , Clarens M. , Baranger P.
Published: March 2003

Aims: To select an autotrophic arsenic(III)-oxidizing population, named CASO1, and to evaluate the performance of the selected bacteria in reactors. Methods and Results: An As(III)-containing medium without organic substrate was used to select CASO1 from a mining environment. As(III) oxidation was studied under batch and continuous conditions. The main organisms present in CASO1 were identified with molecular biology tools. CASO1 exhibited significant As(III)-oxidizing activity between pH 3 and 8. The optimum temperature was 25°C. As(III) oxidation was still observed in the presence of 1000 mg l−1 As(III). In continuous culture mode, the As(III) oxidation rate reached 160 mg l−1 h−1. The CASO1 consortium contains at least two organisms – strain b3, which is phylogenetically close to Ralstonia picketii, and strain b6, which is related to the genus Thiomonas. The divergence in 16S rDNA sequences between b6 and the closest related organism was 5·9%, suggesting that b6 may be a new species. Conclusions: High As(III)-oxidizing activity can be obtained without organic nutrient supply, using a bacterial population from a mining environment. Significance and Impact of the Study: The biological oxidation of arsenite by the CASO1 population is of particular interest for decontamination of arsenic-contaminated waste or groundwater.
Development of an enzyme assay for rapid assessment of Escherichia coli in seawaters
Authors: Caruso G. , Crisafi E. , Mancuso M.
Published: March 2003

Aims: An analytical protocol has been developed and applied for the detection of glucuronidase activity in marine waters as a rapid alternative approach to assess the microbiological quality of seawaters. Methods and Results: The fluorogenic substrate 4-methylumbelliferyl-β-d-glucuronide is cleaved to a fluorescent product, methylumbelliferone, by the enzyme β-glucuronidase, specificto Escherichia coli and closely related enterobacterial species (Shigella). The results suggest that this test is related to E. coli numbers, as estimated by immunofluorescence, more significantly than to faecal coliform numbers, obtained from culture media. Conclusions: The determination of the potential rate of glucuronidase activity may be used as a diagnostic tool for the indirect estimation of the presence of E. coli in seawaters. Significance and Impact of the Study: The method may be particularly useful in the early warning of seawater pollution, allowing the screening of coastal areas with different contamination levels in reduced time.
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.
BIOME 6000: reconstructing global mid‐Holocene vegetation patterns from palaeoecological records
Authors: Prentice I. Colin , Webb III Thompson
Published: March 2003

Global change research needs data sets describing past states of the Earth system. Vegetation distributions for specified ‘time slices’ (with known forcings, such as changes in insolation patterns due to the Earth's orbital variations, changes in the extent of ice‐sheets, and changes in atmospheric trace‐gas composition) should provide a benchmark for coupled climate‐biosphere models. Pollen and macrofossil records from dated sediments give spatially extensive coverage of data on vegetation distribution changes. Applications of such data have been delayed by the lack of a global synthesis. The BIOME 6000 project of IGBP aims at a synthesis for 6000 years bp. Success depends on community‐wide participation for data compilation and quality assurance, and on a robust methodology for assigning palaeorecords to biomes. In the method summarized here, taxa are assigned to one or more plant functional types (PFTs) and biomes reconstructed using PFT‐based definitions. By involving regional experts in PFT assignments, one can combine data from different floras without compromising global consistency in biome assignments. This article introduces a series of articles that substantially extend the BIOME 6000 data set. The list of PFTs and the reconstruction procedure itself are evolving. Some compromises (for example, restricted taxon lists in some regions) limit the precision of biome assignments and will become obsolete as primary data are put into community data bases. This trend will facilitate biome mapping for other time slices. Co‐evolution of climate‐biosphere modelling and palaeodata synthesis and analysis will continue.
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. 190

Analyses 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 comparison of species diversity and morphological diversity across the North American latitudinal gradient
Authors: Shepherd Ursula
Published: March 2003

There are vastly more plants and animals in the tropics than elsewhere. In the past 100 years, many hypotheses have been investigated, but no concise answer to what drives tropical diversity has emerged. One reason is that the usual way of examining diversity, species richness, is only one possible descriptor. Other measures, such as morphological diversity, may be equally revealing, and comparisons between measures may provide still better resolution. I performed the first explicit comparison of species richness and morphological diversity of terrestrial mammal communities across latitude. Mammal com‐ munities differed in diversity of both body sizes and body shapes. Tropical sites were less size diverse and more shape diverse than predicted by random models. Polar sites were more size diverse and less shape diverse than predicted. The analysis indicated that different evolutionary and ecological factors determine community structure at different points along this latitudinal gradient.
Alien and native species in Central European urban floras: a quantitative comparison
Authors: Pyšek Petr
Published: March 2003

The paper provides quantitative information on the occurrence of alien species in Central European cities and analyses factors determining the richness of alien and native floras in this habitat type. Data for 54 cities (25 Polish, 24 German, 4 Czech and 1 Austrian) were gathered, and the representation of archaeophytes (i.e. aliens introduced before 1500 ad), neophytes (introduced after that date) and native species was expressed. In an average city there were 87.4 archaeophytes (15.2% of the city flora) and 172.4 neophytes (25.2%) giving a total of 259.7 for alien species (40.3%). The number of native species averaged 386.5. The numbers of species in each category of immigration status increased significantly with city size. For neophytes, the species‐area relationship showed a higher slope (0.49) on log–log axes than for both archaeophytes (0.16) and native species (0.30). Not only the number, but also the relative contribution of neophytes to the total flora, increased with city size, indicating that neophytes are the group which are most closely associated with human activity. On the other hand, archaeophytes were better represented in smaller cities, as they were confined to rural environment. A step‐wise multiple regression was used to test for environmental variables acting as significant predictors, and explained between 40 and 65% of variation in the species numbers for particular categories of immigration status, providing the best fit for neophytes. City size was the best predictor for each characteristic, except of the proportion of total aliens, where the percentage of explained variability was low (8.2%), with latitude being the only significant predictor. Temperature was another highly significant predictor for the number of archaeophytes and total aliens, reflecting the origin of aliens in warmer areas. There was an effect of region on some flora characteristics. Polish cities had significantly higher proportion of archaeophytes and of total aliens than German cities. It is concluded that the occurrence of native and alien species in urban floras follows rather different pattern.
A biological basis for lichenometry?
Authors: McCarthy Daniel P.
Published: March 2003

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

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

A 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

AimTo 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

Aim

Few 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.

Location

The data analysed are for the three older Krakatau islands: Rakata, Sertung and Panjang in the Sunda Strait, Indonesia.

Methods

Our 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).

Results

The 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 conclusions

Previous 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.
A reconstruction of the history of a Holocene sand dune on Great Barrier Island, northern New Zealand, using pollen and phytolith analyses
Authors: Horrocks M. , Deng Y. , Ogden J. , Sutton D. G.
Published: March 2003

Aim  To reconstruct the history of a Holocene sand dune using pollen and phytolith analyses, and to identify the strengths, weaknesses and compatibility of these two methods in the interpretation of Quaternary coastal environments.

Location  Great Barrier Island, northern New Zealand.

Methods  Pollen and phytolith analyses were carried out on a sequence through a Holocene sand dune containing a palaeosol.

Results  Phytoliths were present throughout the sequence. Grass phytoliths increased at the expense of tree phytoliths following fire disturbance. Pollen (and spores) was preserved only in the palaeosol part of the profile. Pteridium fern spores increased at the expense of tall tree pollen following the fire disturbance.

Main conclusions  Lack of phytolith production by many species and problems of taxonomic specificity in many others restricts the usefulness of phytolith analysis to defining only broad vegetation types. In New Zealand, gymnosperms are invisible in the phytolith record and ferns are extremely under‐represented. In contrast, pollen analysis usually provides a great deal of information regarding the composition of a particular vegetation type. The loss of microscopic charcoal fragments during the phytolith extraction process is a disadvantage in the reconstruction of environments where fires have occurred. The greater durability of phytoliths compared with pollen means that phytoliths may be found in sediments where pollen has not been preserved. The phytolith record may also provide evidence of wetter environments that are not apparent in the pollen record. Unlike grass pollen, which is widely dispersed and therefore blurs the spatial record, the presence of grass phytoliths in sediments indicates a local source. The simultaneous application of both methods potentially provides a powerful tool in ecological interpretation and the reconstruction of Quaternary coastal environments.
Global distribution patterns of non‐halacarid marine intertidal mites: implications for their origins in marine habitats
Authors: Procheş Şerban , Marshall David J.
Published: March 2003

Aim

We investigated the taxonomic, ecological and global biogeographical trends of non‐halacarid marine mites with a view to understanding their origins in the marine environment. While halacarid mites are typically marine, numerous other mite taxa occupy littoral habitats, including rocky‐shores, boulder beaches, salt marshes and mangrove forest floors, and occur in most geographical regions.

Location

This study concerns the extant taxa of non‐halacarid marine mite from intertidal zones, worldwide.

Methods

A literature survey was undertaken to compile the records for localities and habitats of all the known species of non‐halacarid intertidal mite. Simple analyses were used to determine their taxonomic and geographical trends. A multivariate analysis was used to compare how closely the biogeography of selected faunas conformed with the generally accepted marine biogeographical zones.

Results

Although the species records are incomplete because of variable sampling intensities among regions, there is clear indication that these marine mite faunas are species‐poor (only 162 species were recorded in the literature). The records for some groups (ameronothroid and hyadesiid mites), some habitats (rocky‐shores) and some world regions (Eastern Atlantic‐Boreal, Sub‐Antarctic and Southern New Zealand) are apparently representative of actual faunas, whereas those for the mesostigmatid and non‐halacarid prostigmatid mites, and mangrove and salt marsh habitats, are clearly incomplete. The faunas comprise mites from four suborders, the Mesostigmata, Prostigmata, Oribatida and Astigmata. Structuring of the lower taxonomic levels differs markedly among the suborders; mesostigmatid and prostigmatid mites comprise low species to genus and species to family ratios, relative to oribatid and astigmatid mites. These mite groups also differ with respect to ecological and geographical attributes; ameronothroid (oribatid) and hyadesiid (astigmatid) mites exhibit wider generic geographical distributions and stronger marine trophic links.

Conclusions

The emerging trends suggest different geological time‐scales for the evolutionary incursions into the marine environment by the mesostigmatid and prostigmatid mite group and the oribatid and astigmatid mite group. They suggest that members of the latter have had longer associations with marine intertidal systems. The origins of both groups are also likely to differ from those of the typically marine halacarid mites.