bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plant dispersal in boreal rivers and its relation to the diversity of riparian flora
Authors: Andersson Elisabet , Nilsson Christer , Johansson Mats E. 
Published: March 2003

AbstractAimThe paper has four major objectives: (1) to determine whether diaspore mimics accurately represent dispersal dynamics of real diaspores in a free‐flowing river; (2) to estimate distance travelled and reasons for stranding of floating diaspores along a free‐flowing river; (3) to test if species composition and seedling recruitment vary with the ability of the riverbank to trap waterborne drift; and (4) to compare diaspore dispersal in a free‐flowing river with that in a regulated river where current velocity has been reduced.LocationThe field work was conducted in two 7th‐order boreal rivers in northern Sweden, the free‐flowing Vindel River and the regulated Ume River.MethodsWe performed a series of dispersal experiments. We tested the usefulness wooden cubes of diaspore mimics for performing dispersal experiments by releasing cubes and achenes ofHelianthus annuusand compare their dispersal patterns in the free‐flowing Vindel River. We used the cubes to identify 50‐m long sections along the river with different trapping capacity, i.e. the number of stranded diaspore mimics within a 50‐m section. We then related the number of stranded diaspore mimics to the vascular plant flora, the proportions of species with long or short floating times (i.e. more than or less than 2 days, respectively), the number of seedlings, and to environmental variables within the sections. We also released wooden cubes in a run‐of‐river impoundment to determine the dispersal capacity of diaspores in a regulated river.ResultsThe cubes were useful as diaspore mimics. They dispersed similarly to achenes ofH. annuus. The stranding pattern of diaspore mimics was significantly associated with water current. Species richness of vascular plants per 50‐m section increased with the number of stranded mimics. Seedling recruitment, and the proportions of species with short‐floating and long‐floating diaspores, did not vary with the number of stranded mimics. The ability of a river to transport diaspores downstream was strongly reduced by impoundment.Main conclusionsWe conclude that patterns of species richness of riparian vegetation is in part determined by the ability of the riverbank to trap waterborne diaspores, but differences in floating ability among species did not affect the species composition along free‐flowing rivers.
Does the phylogeny of pelomedusoid turtles reflect vicariance due to continental drift?
Authors: Noonan Brice P. 
Published: March 2003

AbstractAimThe turtle hyperfamily Pelomedusoides has been long regarded as one of the best reptilian examples of the shared biological history of Africa and South America, and of vicariance due to continental drift. The currently accepted phylogeny of the Pelomedusoides is based on morphological and serological evidence. This study uses molecular data to examine the relationships within the Pelomedusoides and tests the hypothesis that the speciation within this group was caused by the separation of the Gondwanan continents.MethodsPhylogenetic analysis of 921 bp of 12S and 16S mitochondrial rRNA obtained from GenBank.ResultsOur analysis resulted in a well‐supported phylogenetic hypothesis for the extant Pelomedusoides that does not agree with previous hypotheses based on morphology and serology. The new hypothesis of pelomedusoid relationships is (Pelusios + Pelomedusa) (Peltocephalus[Erymnochelys + Podocnemis]). The molecular evidence supports the monophyly of the Podocnemidae and Pelomedusidae of de Broin (1988). However, the relationships within the Podocnemidae differ in that the Madagascan Erymnochelys is the sister taxon of the neotropical Podocnemis.Main conclusionThis result is in conflict with the hypothesis of pelomedusoid speciation being a result of the continental drift of South America and Africa/Madagascar, with the separation of those three continents resulting in three separate evolutionary groups. Based on an extensive fossil record, the Pelomedusoides are known to have been a wide‐ranging group. This latest phylogenetic hypothesis, combined with that of Meylan (1996) for the Pelomedusoides, suggests that current pelomedusoid distributions and relationships could be the result of large‐scale extinctions with extant taxa being relicts of this widespread group.
Effects of postsettlement human activities on forest composition in the north‐eastern United States: a comparative approach
Authors: Bürgi Matthias , Russell Emily W. B. , Motzkin Glenn 
Published: March 2003

AbstractAimThis study compares human impacts and forest ecosystem response across geographical regions. Such a comparison allows us to evaluate the relationship between regional changes in forest composition and regional patterns of human activity.LocationFour study areas in the north‐eastern USA were investigated, two of which were dominated by oak‐pine forests at the time of European settlement (Central Massachusetts, MA; Pike County, PA), and two of which were dominated by beech and hemlock (South Berkshire, MA; Wayne County, PA).MethodsTrees recorded in early land survey records were compiled and compared with data on modern forest composition obtained from recent forest inventories. To assess the similarity of the four regions with regard to species composition, Euclidean Distances (ED) were calculated between the colonial and modern forest composition for each of the four regions. Information about the history of human impacts in the four study regions was used to interpret the changes in forest composition.ResultsGeneral changes in forest composition through the historical period include a decline in beech, hemlock and chestnut, and an increase in maple and birch. Changes in pine and oak were minor by comparison. Supraregional human impacts are generally linked with supraregional trends in species composition, whereas regional patterns of land use caused regional patterns of change in species composition.Main conclusionsThese results suggest that human activities do not necessarily lead to more similar species composition between regions, especially if these activities show clear spatial patterns at about the same resolution that species composition is evaluated. Comparing species‐specific changes in forest composition with species‐specific human activities on the same spatial scale is crucial in order to evaluate human impacts on ecosystems and to make more robust generalizations about the temporal dynamics of landscapes.
Molluscan successions from two Holocene tufas near Northampton, English Midlands
Authors: Meyrick R.A. , Preece R.C. 
Published: March 2003

AimTo investigate the molluscan successions from two Holocene tufa sequences in the English Midlands to establish whether similar patterns of colonization occur and to document how they relate to other successions reported from southern Britain and elsewhere.LocationCourteenhall and Weston Favell near Northampton, English East Midlands.MethodsClose serial sampling and quantitative analyses have allowed detailed faunal successions to be reconstructed for each site. Radiocarbon dating ofCepaeashells by AMS has provided a chronology for each site.ResultsRemarkable similarities were found to exist between the two sites. The record from Courteenhall extended back to the end of the Devensian late‐glacial and continued until about 6000 yr BP. The sequence from Weston Favell was shorter, commencing at the beginning of the Holocene and ending about 7500 yr BP. Both successions show a progressive replacement of open country assemblages by those of woodland. At Courteenhall arctic‐alpine species, such asColumella columella(Martens) andVertigo genesii(Gredler), were present in these early open‐ground communities. Both sites supported extremely rich (> 30 species) land snail assemblages during the mid Holocene. This richness cannot be matched at any single site in Britain today. These mid Holocene assemblages include species such asSpermodea lamellata(Jeffreys),Leiostyla anglica(Wood) andVertigo alpestrisAlder that are rare or absent today in southern Britain.Discus ruderatus(Férussac), which has a modern boreo–montane range, occurred at Courteenhall between about 9700 and 8750 yr BPbut was also present in two consecutive samples just below a level dated at about 7000 yr BP, its latest known occurrence in Britain. These assemblages have no modern analogue because the ranges of several species (e.g.Discus ruderatusandLeiostyla anglica) never overlap today.General conclusionsDuring the Holocene land snails appear to have colonized southern Britain in a relatively ordered sequence. The history of some species is unpredictable and they may occur at different sites at different times. For others, the general pattern shows greater consistency, enabling the recognition of a series of mollusc zones applicable over large areas of southern Britain. These Northamptonshire sites also contribute to the debate surrounding the notion of a ‘late Holocene tufa decline’. Tufa formation began unusually early (c. 10,280 yr BP) at Courteenhall but it had ceased to form at both sites by 6000 year (maybe by 7500 yr BPat Weston Favell). There is no evidence for late Holocene tufa formation at either site, a pattern consistent with many other British sites. Rates of tufa growth from 2.7 to 7.0 cm 100 years–1, calculated from the radiocarbon dates from Courteenhall, are comparable with accumulation rates established from other Holocene tufas.
A contribution to the discussion of biota dispersal with drift ice and driftwood in the North Atlantic
Authors: Johansen S. , Hytteborn H. 
Published: March 2003

AimThe present work aims to review the early proposed hypothesis of biota dispersal by driftwood and drift ice.LocationThe North Atlantic region.MethodsNew knowledge gained about drift ice patterns and sources and transport routes of ice‐rafted debris and dendrochronologically dated driftwood is used to investigate chance dispersal of diaspores. In addition, the extremely disjunct distribution patterns of some vascular plants in Scandinavia and East Greenland are examined in the light of this new data.ResultsBoth drift ice and driftwood are thought to be important in the chance dispersal of diaspores from Siberia and North‐west Russia to parts of the North Atlantic region, in the Late Weichselian or early Holocene. It is proposed that the extremely disjunct distribution of some vascular plants in northern Scandinavia and East Greenland (e.g. Draba sibirica, Oxytropis deflexa ssp. norvegica, Potentilla stipularis and Trisetum subalpestre) are examples of this type of long‐distance dispersal.Main conclusionsThe concentration of extremely disjunct distributed vascular plant species in parts of northern Norway and East Greenland is suggested to relate to the Late Weichselian ice free conditions and the topography and exposure of the coastline in these areas, allowing accumulation of ice‐rafted debris and driftwood. A systematic survey of debris samples obtained from drift ice and driftwood trees is needed to evaluate the significance of these vectors for dispersal of biota to the North Atlantic region.
Genetic diversity in New Zealand Galaxias vulgaris sensu lato (Teleostei: Osmeriformes: Galaxiidae): a test of a biogeographic hypothesis
Authors: Wallis Graham P. , Judge Karen F. , Bland Julie , Waters Jonathan M. , Berra Tim M. 
Published: March 2003

AimTo test whether a geologically recent region with low endemism shows low genetic diversity in a freshwater fish species complex, in contrast to an adjacent area with high diversity. The low endemism is generally postulated to be the combined effect of Pleistocene glaciations and the unstable nature of the recent gravel outwash from young mountains to the west. This rock aggradation has formed a plain, crossed by several braided rivers. The faunas of these rivers have the potential to interchange through flooding or course changes.LocationSouthern and central South Island, New Zealand (NZ). We define the boundary of these two biogeographical regions as the Waitaki River, the most southerly braided river. To the north lies the Canterbury Plain, formed from coalesced alluvial fans; to the south is the Otago peneplain and associated mountain ranges.MethodsPrevious work has revealed considerable genetic structuring in the stream‐resident fish Galaxias vulgaris Stokell sensu lato, including a species complex in the southern region of South Island, NZ. Using isozyme electrophoresis, we have now examined genetic variation among a total of 58 samples of non‐migratory river galaxias from 24 river systems in South Island: 16 in the central region and eight to the south.ResultsWhereas samples from the central region do exhibit significant genetic structuring (Wright’s FST=0.331), they are more genetically homogeneous (mean Nei’s D= 0.032) than populations to the south of the Waitaki River (FST=0.826, mean D=0.374).Main conclusionsThe results concur with our expectations of differences between the central and southern regions. We suggest that the divergence in the south reflects geological stability, whereas relatively shallow divergences within the central region reflects the more recent formation of the Canterbury Plain and its unstable braided rivers. The genetic structuring of this group has been promoted by the absence of the marine juvenile phase that is found in five other members of the genus native to NZ. This diversity of the southern region mirrors its diverse flora and invertebrate fauna, and has conservation implications that parallel those resulting from our improved knowledge of the NZ herpetofauna through the application of genetic analysis.
Regional gradient analysis of freshwater biota: do similar biogeographic patterns exist among multiple taxonomic groups?
Authors: Heino Jani 
Published: March 2003

AimTo examine if different groups of freshwater organisms show concordant distribution patterns at large spatial scales.LocationNorthern Europe: Denmark, Sweden, Norway, Finland.MethodsI analysed provincial distribution records of macrophytes, dragonflies, stoneflies, dytiscid beetles and teleost fishes in northern Europe. I conducted multivariate analyses, including two‐way indicator species analysis (TWINSPAN), canonical correspondence analysis (CCA) and Mantel test to reveal biogeographical patterns and the degree of concordance in the distribution patterns among taxa.Results TWINSPAN and Mantel tests indicated that broadly similar biogeographical patterns existed among the taxonomic groups. The results of CCA confirmed that variation in provincial species composition was generally related to climatic variation along latitudinal and altitudinal gradients. However, variation partitioning revealed that less than 50% of variation in the distribution patterns of each taxonomic group was accounted for by the climatic and geographical variables.Main conclusionsThe distribution patterns of most taxonomic groups were strongly concordant and related to provincial climate and geographical location. Such patterns suggest that large‐scale factors determine not only provincial species combinations, but also express severe constraints on the composition of local communities. Therefore, these factors should also be considered in studies on the structure and conservation of local freshwater systems.
Phylogeography in coastal marine animals: a solution from California?
Authors: Dawson Michael N 
Published: March 2003

AimRecently discovered deep phylogenetic gaps in coastal California marine taxa are geographically discordant with the provincial biogeographic boundary at Point Conception. This discordance runs contrary to the phylogeographic hypotheses that were derived from studies of coastal marine taxa in south‐eastern North America. Here, I investigate the nature of the discrepant phylogeographic and biogeographic patterns in coastal California.LocationCoastal south‐western North America.MethodsThe scientific literature describing the phylogeography and biogeography of coastal California taxa was reviewed. Data describing life‐history characteristics, habitat, and degree of phylogeographic structure were extracted and compared. The geographical distribution of phylogenetic breaks was compared with regional biogeographic data.ResultsAll taxa were genetically variable. Those with greater dispersal ability generally had less phylogeographic structure. Although few taxa had very limited dispersal ability, many exhibited phylogeographic breaks within the California Transition Zone, a region of gradual species replacement between Oregonian and Californian biogeographic provinces. The most precisely resolved phylogeographic breaks were geographically concordant with peaks in the distribution of edge‐effect species, which are strong indicators of environmental discontinuities, or ecotones. Moreover, these phylogeographic gaps, edge‐effect species, and ecotones coincide geographically with Late Pleistocene faunal discontinuities and probable long‐term physical barriers to gene flow.Main conclusionsContrary to prior inference, phylogeographic patterns in coastal California marine taxa are consistent with the phylogeographic hypotheses. The concordance of phylogeographic and biogeographic patterns in the coastal marine faunas of south‐eastern and south‐western North America, and also the Indo‐Pacific, suggests that the phylogeographic hypotheses are generally applicable to many coastal marine settings. As such, they provide a framework for investigating and comparing patterns of evolution in disparate coastal marine faunas.
Ichthyofaunistic biogeography of the Japan (East) Sea: the comparison of various rank taxa for zoning
Authors: Kafanov Alexander I. , Volvenko Igor V. 
Published: March 2003

AimThe aim of the present study is the analysis of the latitudinal distribution of taxonomic richness (number of genera and families) of ichthyofauna at the western and eastern coasts of the Japan Sea for the purpose of identification of natural boundaries, and subsequent comparison with results obtained using the distribution analysis of species richness.LocationJapan Sea (Korean – East Sea).MethodsAll statistical procedures were based on well‐tried and widely accepted numerical methodology and the STATISTICA program package. For identifying the statistically meaningful (non‐random) maxima and minima in taxonomic richness (n), arithmetic differences in the number of taxa at ith and i − 1th geographical latitudes and the measurements of as well as residuals in polynomial trends and clustering (Ward’s method) of genera and family lists, were analysed. The relationship between the number and the scope of taxa was approximated by Zipf–Pareto–Mandelbrot frequency distribution: p(N)=k/N1+k, where p(N) is a relative number of taxa, each of them includes N taxa of the next lower rank; k is a constant. The determination of the constant was made by a nonlinear estimation procedure using quasi‐Newton algorithms approximating the second‐order derivatives of the loss function to guide the search for estimation of the minimum/best parameter estimates.ResultsThe comparison between all the types of analysis gives similar results and the boundaries of faunistic units identified from taxonomic lists of species, genera and families are practically coincident at herein accepted regional biogeographical scaling. The relation between the number and the scope of taxa is approximated satisfactorily by Zipf–Pareto–Mandelbrot model.Main conclusionsThe differences obtained by other authors in the results of zoning by species, genera and family lists are largely pre‐determined by commonly used quantitative analytical methods: theoretical‐and‐graph methods and clustering procedures. The distribution analysis of species and superspecific taxa gives closely approaching results for relatively high latitudes and sharply diverging results for relatively low latitudes. The Zipf–Pareto–Mandelbrot distribution describing the relation between the number and the scope of taxa uniquely pre‐supposes definite quantitative relationships between various rank taxa. So, the predicted species number S may be calculated on observed genera number G. If the values of species/genus ratios (S/G) are tabulated for various G, it turns out that the relationship S/G shows an almost linear variation (between 1.78 and 2.50) in the interval between twenty and 1000 species, abruptly rising with further increase in the length of species list. Therefore, the S/G ratios widely used and considered important by various ecological and biogeographical concepts are a statistical artefact. Variation analysis of taxonomic richness is a basic operational procedure in faunistic biogeography.
Holocene landscape development and human impact in the Connemara Uplands, Western Ireland
Authors: Huang Chun Chang 
Published: March 2003

AimAim Investigate: (1) the role of human impact in shaping the landscape and particularly the initiation of blanket bog; (2) the short‐lived abrupt changes and their causation; (3) the phenomenon of large‐scale upland peat erosion to answer the question of when and why erosion of upland blanket peat commenced in the Connemara uplands.LocationLough Maumeen in the Maumeen Gap, Connemara, Western Ireland.MethodsPollen, sedimentary analysis and 14C dating on the lake sediment cores.ResultsPollen diagrams, charcoal fragments, bulk and dry densities, mineral content (or loss‐on‐ignition), whole core magnetic susceptibility, specific magnetic susceptibility for the core profile.Main conclusionsPine‐dominated woodland developed from 9250 BP. Human activities effected the deforestation between 5050–4000 BP. Peat bog initiated on the wet hollow ground in the gap during the elm decline. The major expansion of blanket bog landscape in the upland commenced at 4000 BP following immediately the Taxus decline. Human impact was the dynamic force responsible for the destruction of the woodland and the formation of blanket bog in the upland. Three episodes of short‐lived erosion events were identified between 8650–8400 BP, 5450–5250 BP, and 600–200 cal. BP, respectively. They are very different from each other in their causation. Large‐scale peat erosion is a recent phenomenon. It has been caused by intensive sheep grazing, which has been extended to the upland blanket bogs since the late eighteen century.