bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modern pollen precipitation from an elevational transect in central Jordan and its relationship to vegetation
Authors: Davies Caroline P. , Fall Patricia L. 
Published: March 2003

AimTo explore the relationship between modern pollen precipitation and vegetation patterns in an arid region of the Middle East.LocationData come from the central Jordan Rift from 1700 m elevation in the highlands to 300 m below sea level in the Dead Sea basin.MethodsModern pollen samples and descriptive vegetation data were collected from twenty‐one locations at 100 m elevational intervals from the highest elevations on the eastern side of the rift valley, where woodlands grow, to the lowest elevation desert on earth, characterized by drought and salt tolerant plants. Pollen percentage data from each vegetation zone are compared descriptively and numerically using cluster and Principal Components Analyses (PCA).ResultsThree major vegetation zones: woodland, shrub steppe, and desert scrub, are identified by their dominant plant species. The widely spaced tree, Quercus calliprinos Webb, defines the Quercus L. woodland that grows above 1500 m elevation. The shrub steppe can be divided into two subzones found between about 1500 and 900 m elevation: Artemisia herba‐alba Asso shrub steppe and Artemisia L. shrub steppe with Juniperus phoenica L. Desert scrub dominates the lower elevation landscape with Hammada salicornia (Moq.) Iljin the dominant shrub between 900 and 200 m and Haloxylon persicum Bge. found below 200 m elevation.Pollen spectra reflect the elevational vegetation zones. In particular, Quercus L., Juniperus L. and Tamarix L. pollen are abundant where the trees grow. Highly variable amounts of non‐arboreal pollen taxa – primarily Artemisia L. and Chenopodiaceae Vent. – differentiate shrub steppe from desert scrub vegetation. Cluster and PCA of pollen data support the qualitative vegetation zonation.Main conclusionsThe main vegetation zones along the Jordan Rift from 1700 to –300 m elevation can be distinguished by their modern pollen precipitation. Open vegetation types, in particular, can be recognized by their pollen spectra. High amounts of Artemisia L. pollen distinguish the moister upper elevations where Artemisia L. steppe grows. In contrast, greater amounts of Chenopodiaceae Vent. pollen characterize the drier, lower elevation deserts.
Competitive ability, body size and geographical range size in small mammals
Authors: Glazier Douglas S. , Eckert Sara E. 
Published: March 2003

AimWhy are some species widespread and abundant while others are restricted and rare?Darwin (1859) and others have claimed that some species have become widespread because they are competitively dominant over related, geographically restricted species. An alternative hypothesis is that wide‐ranging species are ecological generalists that have been able to opportunistically colonize many kinds of new, disturbed and/or marginal habitats, whereas related narrow‐ranging species are ecological specialists that competitively dominate specific kinds of relatively stable habitats/resources. We tested these opposing hypotheses using small mammals, for which considerable data on competitive interactions and geographical range sizes are available.LocationNorth America, Europe, Asia, Africa and Australia.MethodsWe analysed data for forty‐three competitive interactions between congeneric species in twenty genera, seven families, and four orders of small mammals. Competitive dominance was identified from both field and laboratory experiments, which were lumped because they showed similar results.ResultsWe found that (1) when all studies were analysed as individual data points, species with smaller geographical ranges tended to be dominant over congeneric species with larger geographical ranges, (2) lumping of interaction pairs sharing one or more of the same species yielded a similar result, (3) lumping all interactions involving the same genus also showed the same result, although it was not statistically significant, probably because of the small sample size resulting from this attempt to remove phylogenetic effects. Examination of the taxonomic relationships of the studied genera revealed no obvious phylogenetic effects on the relationship of competitive dominance with geographical range size. Furthermore, although body‐size differences appeared to have played a role in the results observed, they cannot completely explain them.Main conclusionsWe tentatively conclude that Darwin's hypothesis is falsified for small mammals, while the alternative hypothesis that geographically restricted species are competitively dominant over related widespread species receives some support.
Winter bird communities in urban habitats: a comparative study between central and northern Europe
Authors: Jokimäki Jukka , Clergeau Philippe , Kaisanlahti‐Jokimäki Marja‐Liisa 
Published: March 2003

AimUrbanization can lead to uniformity in urban bird communities, and the general biogeographical patterns found in natural communities may not be found in urban ones. Thus, it is important to know if urbanization might be seen as contributing to a general pattern that modifies the biogeographical processes of wildlife communities.LocationWe studied differences in suburban bird assemblages in France and Finland. Birds in each town included in the study were surveyed using 30 ha suburban study plots located within single‐family housing area and apartment block area.MethodsThe wintering birds were surveyed using a single‐visit study plot method in January and February 1999. The level of urbanization was measured according to the general structure of the habitat by using the town maps and field notes. In addition, we counted active winter feeding stations during bird surveys.ResultsThe average number of species was higher in France than in Finland, both in single‐family house areas and in apartment block areas. The most abundant bird species occurred in most of the study sites. The urbanization level affected bird community composition more in northern Finland than in France. In Finland, the number of wintering species and their total biomass were higher in single‐house areas than in more urbanized areas. The total density and biomass of birds were higher in France than in Finland in areas of apartment blocks, but not in the areas of single‐houses. Urbanization level affected the total bird density only in France, being higher in areas of apartment blocks. In Finland, the total biomass of birds was higher in the single‐family house areas than in the areas of apartment blocks. Most of the bird species were more abundant in France than in Finland. The habitat factors associated with the bird community variables in France and in Finland differed from one another. Feeding tables increased the species richness and the abundance of birds in Finland.ConclusionsThe species decrease between France and Finland was mainly because of the large proportion of species in France that are migratory in northern Finland. The abundance of urban birds did not necessarily decrease northwards. Intensive winter feeding in northern latitudes may help birds to overcome natural range limitations. Our results differed from results obtained when studying town centres and they highlight the complexity of the urbanization process across a geographical gradient.
A revised cline theory that can be used for quantified analyses of evolutionary processes without parapatric speciation
Authors: Salomon Marc 
Published: March 2003

AimClassical cline theory interprets clines as speciation processes in two stages: (1) smooth clines, typical of species with no marked subspecies, and (2) stepped clines, characteristic of species with marked subspecies, separated by hybrid zones, where the clines are steeper than within the areas of the subspecies. (These steeping clines eventually become vertical clines—a situation, where the taxa turn into separate species, termed `parapatric speciation'.) This theory, dating from the late 1930s, still has a number of active supporters. But, because results from population genetics suggest that barriers are necessary for speciation to take place, most authors nowadays reject both parapatric speciation and classical cline theory, the former appearing to be the logical consequence of the latter. The theory presented here does not involve parapatric speciation, but provides a revised cline theory including a third stage, the broken cline, which corresponds to the stage at which speciation finally takes place. I suggest that a cline theory without the prerequisite of parapatric speciation can be very useful, for it provides both an evolutionary interpretation of a given geographical distribution and also a method of quantitative analysis.LocationAn example is taken within a species complex of the chiffchaff, Phylloscopus collybita‐ibericus (Aves, Sylviidae), using populations ranging from south Iberia to north Sweden for one variable and to south Belgium for three other variables.MethodsI used regression analyses to interpret clinal variations, and Student's t‐tests to evaluate the broken or continuous nature of the clines.ResultsIn this example, the cline is broken between the adjacent populations of P. ibericus and P. c. collybita, and is continuous and gradual elsewhere.Main conclusions(1) Phylloscopus ibericus and P. c. collybita are good examples of taxa undergoing current speciation; (2) the southern and northern populations of P. ibericus on one hand, and of P. c. collybita and of P. c. abietinus on the other hand, show cline patterns illustrating pairs of vicariant and isolated `weak' subspecies in the sense of Deuve (1994).
Predicted regional impacts of climate change on the geographical distribution and diversity of tropical forests in Costa Rica
Authors: Enquist C. A. F. 
Published: March 2003

AimSpatial models generated in a geographical information system (GIS) are utilized to predict shifts in the distribution and diversity of tropical forests in Costa Rica in response to climate change.LocationAnalyses were conducted using the Holdridge life zone classification system for the Central American country of Costa Rica.MethodsMean annual precipitation and temperature ranges were varied to reflect different magnitudes of climate change and then used to predict the distributions of nineteen forest types (life zones). Holdridge et al.'s (1971) field survey data of species richness and endemism for ten Costa Rican life zones were also analysed and considered in view of the climate change scenarios.ResultsThe scenarios indicated that shifts in the distribution of tropical forest life zones are likely to occur as a result of climatic changes. High elevation life zones were shown to be more sensitive to changes in temperature, while lower elevation life zones tended to be more sensitive to changes in precipitation. Regional life zone diversity was greatly reduced in an extreme wet and warm climate scenario. Three elevation‐associated life zones (lower montane rain forest, montane rain forest, and premontane rain forest) ranked in the top four in percentage number of endemic species. The lowland seasonally dry forest life zone ranked second in this group, suggesting that this life zone has a unique species composition in comparison with other lowland Holdridge life zones. Of the nineteen life zones, these four life zones displayed particular sensitivity to the climate changes modelled here.Main conclusionsElevation‐associated life zones may be particularly vulnerable to future climatic changes. This is also true of lowland seasonally dry forest. Geographical regions in Costa Rica that contain these life zones are likely to warrant special management and conservation attention in the event of predicted climate change.
Potential disruptions to seed dispersal mutualisms in Tonga, Western Polynesia
Authors: Meehan Hayley J. , McConkey Kim R. , Drake Donald R. 
Published: March 2003

AimAs a result of the extinctions of several large frugivorous birds (and one flying fox) and the diminished ranges of others, Tonga now has a relatively small number of effective seed dispersers, especially for large‐seeded plants. We estimate the bill width and gape of the two largest known extinct pigeon species (Ducula) present in Tonga prior to human arrival. We then estimate which native rain forest species had fruits that would have probably been included in the diets of these extinct birds but which may not be dispersed regularly by the smaller frugivores present today.MethodsBill width for the two largest extinct pigeons was derived by extrapolating from the size of fossil bones and measurements of skeletons of extantDuculaspecies.DuculaandPtilinopusspecies have distensible jaws, and therefore their gape allows them to swallow objects broader than their bill width. We estimated the gape width and maximum ingestible fruit size that both the extinct and extant species could consume, by extrapolating from feeding observations of extantDuculaandPtilinopusspecies (using known bill widths and fruit sizes). We determined whether those plant species whose fruit diameters exceed the mean gape width of the largest remaining avian frugivore in Tonga (Ducula pacificaGmelin) appeared adapted for dispersal by birds or flying foxes.ResultsApproximately 79% of the native rain forest trees and lianas in Tonga produce fruits whose morphology suggests that they are adapted to vertebrate dispersal. Bill width estimates derived from the bones of the extinctDuculasp. nova suggest that this pigeon could swallow fruit up to 48 mm in diameter, whilst the smallerDuculacf.davidBalouet & Olson is estimated to have been able to swallow fruit up to 36 mm in diameter. Plant species whose fruits are too large to be swallowed by Tonga's largest extant frugivorous bird (D. pacifica) yet display fruit characteristics suggesting birds were likely to have been their predominant vertebrate disperser in pre‐human times include:Calophyllum inophyllumL., Cerbera odollamGaertn,Planchonella garberiChristophersen, P. membranaceaLam., Pometia pinnataJ. R. & G. Forst.,Syzygium quandrangulatum(A. Gray) Merr. & Perry, Syzygium richii(A. Gray) Merr. & Perry andTerminalia catappaL.Main conclusionsThere is now no avian disperser in Tonga for plant species whose fruits measure >28 mm in diameter (the maximum gape ofD. pacifica). Although frugivorous flying foxes (Pteropus tonganusQuoy & Gaimard) may eat the fruit and disperse the seeds of the eight plant species identified with large fruits, the frequency of dispersal by birds was probably much higher in the past. Species that once relied on the large extinct pigeons for dispersal may have become reduced in abundance in their absence.
Floristic exchange between mainland Africa and Madagascar: case studies in Apocynaceae– Asclepiadoideae
Authors: Meve Ulrich , Liede Sigrid 
Published: March 2003

AimThe Apocynaceae–Asclepiadoideae (c. 125 species) of Madagascar's flora are highly endemic, and floristic conformity between Madagascar and Africa (and Asia) is low. Of thec. 1250 Old World Asclepiadoideae species, only ten species are shared between mainland Africa and Madagascar. Our comprehensive data elaborated during the last 15 years of systematic research in Asclepiadoideae were used to (1) examine Leroy's hypothesis that Madagascar's flora resulted from an autochthonous Gondwanean stock and natural introduction of taxa in time, (2) check the probability of our phylogentic considerations against the direction of the floristic exchange traced, and (3) present evidence for successful long‐distance dispersal events.LocationAfrica, Madagascar, Asia.MethodsPublished and unpublished data on distribution, morphology, chromosome numbers and DNA sequence analysis of Asclepiadoideae taxa distributed in both Africa and Madagascar (Asia and Madagascar) were reviewed and evaluated.ResultsTen species belonging to the generaCeropegia, Cynanchum(incl.Sarcostemma),Gomphorcarpus, Gymnema, Microloma, Pentatropis, Pleurostelma, TelosmaandTylophoraare shared between mainland Africa and Madagascar, three species extend to Asia. In most of the cases presented, evidence points to long‐distance dispersal from Africa to Madagascar; only in theCynanchumcomplex dispersal events from Madagascar to Africa are corroborated.MainconclusionsAn exchange of asclepiadaceous flora between mainland Africa and Madagascar andvice versatook place in at least ten cases. However, <1% of the Malagasy species is involved, meaning that the speciose autochthonous Malagasy Asclepiadoideae flora is only inconspicuously influenced by these presumably rather recent introductions. The African–Malagasy distributions can only be explained by long‐distance dispersal events effected by anemochorous seeds.
Effects of natural disturbance and selective logging onNothofagusforests in south‐central Chile
Authors: Pollmann William 
Published: March 2003

AimChanges in stand structure, floristic composition and tree population dynamics during the last four centuries were described in southern temperate rain forests. The impacts of natural and anthropogenic disturbance since the late 1560s were examined for old‐growth and logged forests.LocationThe study was conducted in montaneNothofagus alpinaforests in the Andean Range of south‐central Chile. Study sites were located at a range of altitudes between 1000 and 1250 m a.s.l.MethodsTemporal variation in species recruitment and annual dendroecological data were used to determine the historical development and disturbance history of three old‐growth forests, and three stands after selective logging in the late 1880s to early 1900s. Considering the spatial structure of evergreen vs. deciduous elements, the forests are a mixture of deciduous and evergreen tree species.ResultsStem density, maximum stem diameter and basal area differed between the old‐growth and logged stands, but species composition did not. At lower altitudes,N. alpinawas the dominant canopy species in both old‐growth and logged stands, but regeneration ofN. alpinawas significantly different in these stands. At higher altitudes,N. alpinaandN. dombeyiwere the dominant canopy species in both old‐growth and logged stands, and here regeneration patterns of theseNothofagusspecies were similar. After selective logging, in mixed forests of shade‐intolerantNothofagusand more shade‐tolerant trees (such asLaurelia philippiana) there has been a shift in regeneration from more shade‐tolerant resprouting species towardsNothofagus. Major and moderate releases in radial growth, indicative of disturbance, occurred in most of the older trees during the last four centuries, and especially during the last 100 years. Growth rates ofN. alpinaare higher than those of associated shade‐tolerant trees, and apparently increase after disturbances.Main conclusionsResults suggest that under disturbance regimes dominated by treefall gaps, and additionally canopy openings by selective logging, maintenance ofNothofagusspecies appears to be associated with complementary differences in growth rate, sprouting capacity, canopy residence time, and longevity. Such small‐scale canopy openings may help explain the relative abundance ofN. alpinain montane mixed rain forests in the Andean Range, where the maintenance ofNothofagusspecies in many stands has been attributed to a high frequency of coarse‐scale disturbance. My results serve to emphasize that understanding the species coexistence and forest dynamics inNothofagusforests may require attention to interspecific differences in life‐history characteristics.
Ravens (Corvus corax corax L.) in the British landscape: a thousand years of ecological biogeography in place‐names
Authors: Moore P. G. 
Published: March 2003

Abstract Aim To investigate the information content of place‐names regarding the habits, habitat and biogeography of ravens in Britain over the past millennium.Location England, Scotland and Wales.Methods Linguistic and ecological analysis of over 400 British place‐names that have a putative ‘raven’ derivation.Results Most of the ‘raven’ place‐names are Old English in origin. Some of these (a minority), however, derive from personal names. The derivations of most names reflect landscape rather than man‐made features; the majority relating to high, craggy ground or coastal features, a minority to wooded situations or human habitations. In lowland Scotland and the Scottish borders the colloquial name corbie dominates ‘raven’ place‐names, perhaps reflecting French influence. In the Highlands and the Western Isles the Gaelic fitheach and its derivatives are predominant. Relatively fewer place‐names that have ‘raven’ roots have been educed in other parts of the Celtic West, i.e. Wales and Cornwall (only one traced in the latter).Main conclusions Comparison of the geographical distribution of ‘raven’‐derived place‐names with the present‐day distribution of the species in Britain reveals the extent of the contraction in the raven's range to the West over historical time, most notably during theprevious two centuries, associated with changed land‐management practices in particular.
Nested communities of alpine plants on isolated mountains: relative importance of colonization and extinction
Authors: Bruun Hans Henrik , Moen Jon 
Published: March 2003

AbstractAim  This paper seeks to investigate whether alpine floras on isolated mountains in boreal forest show nestedness, and, if that is the case, to determine whether selective extinction or colonization is the likely cause of the observed patterns.Location  Isolated mountains in the boreal coniferous forests of northern Sweden (province of Norrbotten, c. 66°N; 18°E). The timberline in the region probably has been 300–400 m above the present some thousands of years before present, potentially covering these mountains.Methods  A data matrix of twenty‐seven alpine plant species on twenty‐seven isolated mountains was subjected to nested subsets analysis. Extinction probability was assumed to increase with decreasing area, and colonization probability was assumed to decrease with increasing isolation. By sorting the data matrix by these factors and sequentially computing the degree of nestedness, we were able to determine whether the alpine floras were structured mainly by selective extinction or mainly by differential colonization.Results  When ordered by decreasing area the data matrix was significantly more nested than random, but that was not the case when ordered by decreasing isolation. Ordering by maximum altitude also produced significant nestedness.Main conclusions  Contrary to the conventional view that isolated mountains were completely covered with boreal forest some thousands of years ago, the nestedness patterns of alpine plants indicate that many of them survived the forest period on the isolated mountains, probably on cliffs and slopes too steep for the formation of closed forest.
Are we facing a `post‐antibiotic era'? – a review of the literature regarding antimicrobial drug resistance
Authors: TRNOBRANSKI PHILIPPA H. 
Published: March 2003

• Since the introduction of antibiotics in the 1940s, antibiotic resistance has become an increasing problem.• Today, multiple‐antibiotic resistance is commonly associated with a number of clinically important pathogens and is therefore an important issue in clinical nursing practice.• Epidemiological studies identify a number of important factors associated with increases in antimicrobial resistance. These include patterns of antimicrobial use, changes in medical and veterinary care and social practices affecting the transmission of microbes.• Bacterial mechanisms of antibiotic resistance and the genetics of resistance‐gene transfer are explored, with the intention of developing nurses' knowledge and understanding of control measures.