Distribution of plant species in Israel in relation to spatial variation in rainfall

Abstract. Relations between the distribution of herbaceous and woody species from the flora of Israel and the variation (25–900 mm) in mean annual rainfall are described using a grid-based approach integrating multivariate techniques (cluster analysis and DCA-ordination) and GIS. The analysis was based on an extensive data base of vascular plant records in 10 km × 10 km grid cells representing the climatic zones of Israel. Cluster analysis revealed three geographically distinct clusters of grid cells which could be arranged along the main rainfall gradient in the study area. The main subdivision is between cells from the Mediterranean region and cells from the more arid region. The second subdivision separated cells from the arid region into two distinct groups which differed significantly in rainfall. Clustering of herbaceous and woody species was similar, but boundaries separating adjacent clusters based on woody species were consistently linked to more rainy areas. Cell scores on the first DCA-axis were significantly correlated with mean annual rainfall, but this relationship was not linear. Log-transformation of the rainfall data resulted in a higher correlation between the DCA-scores and rainfall, indicating that variation in rainfall had a stronger effect on species composition in relatively dry than in more mesic regions. Slopes of linear regression models relating cell scores on the first DCA-axis to mean annual rainfall, as well as the corresponding R²-values, were highest in the desert, intermediate in the dry Mediterranean, and lowest in the mesic Mediterranean territory. These results indicate that both the per-unit effect of rainfall on plant species composition and its relative importance as a determinant of compositional variation decreased from relatively dry to more mesic regions. The length of the first axis, as well as the slopes of regression models relating cell scores on the first DCA-axis to mean annual rainfall were consistently higher in the case of woody species which are characterized by a higher rate of compositional variation. Due to lack of comparable data, it is difficult to evaluate whether our results can be generalized to other regions. However, an analysis of data obtained from different parts of the world points to a considerable variability in the degree to which rainfall affects patterns of floristic variation. Our findings that compositional responses to rainfall may vary between different groups of species and may depend on the part of the rainfall range which is being considered may partially explain this inconsistency.     

A numerical analysis of the mesoscale distribution patterns of vascular plants in the subarctic Kevo Nature Reserve, northern Finland

Different numerical techniques were used to detect and describe the major ecological-biogeographical patterns of vascular plant distributions at the meso-scale level in a subarctic region in Finland. The distribution patterns of 231 native taxa in 362 1 km² grid squares of the Kevo Nature Reserve were analysed by two-way indicator species analysis and detrended correspondence analysis, and were subsequently related to twenty-eight geographical, topographical, geological, and vegetational variables using simple discriminant functions and canonical correspondence analysis with associated Monte Carlo permutation tests.
The floristic variation detected reflects variations in environmental factors operative at the regional and local scales. No major broad-scale coherent geographical patterns were detected; instead, the spatial distribution of the grids with a similar floristic composition shows a scattered distribution. All the numerical techniques reveal a major gradient from alpine areas to lowland sites with rivers and rocky outcrops, and the most important explanatory variables for predicting the main floristic variation are all associated with altitude. The floristic patterns represented by the second ordination gradient mainly correlate with the abundance of mires. Partial ordinations indicate that both the geographical and geological variables explain relatively little of the species distributional patterns.
Although the meso-scale approach reveals much about the plant-environment relationships in the study area, the floristic variation appears to be determined mainly by fine-scale factors. In the most heterogeneous grids, the grid size used fails to detect accurately the ecological patterns of the species present.     

Structure in temperate predaceous diving beetle communities (Coleoptera: Dytiscidae)

Collection records of adult dytiscid beetles (Coleoptera, Dytiscidae) from 312 sites within the province of Alberta, Canada, were analyzed for patterns of similarity in species distribution. Sites compared on the basis of species occurrence (Jaccard coefficient of similarity and group average cluster analysis) separated into 12 principal clusters, interpreted as communities. However, cluster inclusion occurred at very low levels of similarity and 30% of sites were unclustered outliers. Ecological charade us tics of sites that were recognized as varying between dusters were salinity, productivity, stability, water temperature, substrate type, flow and vegetation. An index relating these qualitatively defined variables to species numbers is presented. An analysis of co-occurrence patterns of species was conducted as an alternative approach to definition of multispecies associations. Each possible combination of co-occurrence between pairs of species occurring in more than 5 collections each was tested for significance (p = 0.005) by means of Yates corrected χ² tests. Results of tests were expressed in binary terms, blank – no significance, x - significant. Species were then clustered on the basis of patterns of significant co-occurrences as above. This analysis was used as the basis for ordination of species in a symmetrical matrix with species ordered so as to maximize density of points of significant co-occurrence (x) around the principal diagonal. Areas in the matrix showing high densities of co-occurrence were interpreted as representing communities. The cluster analysis of species produced a better cluster pattern than obtained for sites but while generally similar, the species clustering pattern was less fine. The principal species groups consisted of those of saline water, alpine/subalpine lotic sites, other lotic habitats, and lentic habitats with two subgroups, species in forest areas and grassland species. The ordination, while reflecting this grouping of species, demonstrated that each group graded into others through loss of certain species and acquisition of others and thus showed the continuum nature of these communities. Restricting ordination to congeneric species indicated that these do not usually show identical patterns of co-occurrence but neither are patterns coincident with mutual exclusion. Within genera, considerable overlap in occurrence between species is the norm but species tend to occupy slightly different positions relative to one another along qualitatively defined ecological gradients. Relative position of species in these ordinations shows good correlation with patterns of geographical distribution lending support to the interpretation of ordination patterns reflecting relative ecological segregation. The dytiscid beetle fauna of north temperate regions is especially rich. Also, the large number of significant co-occurrences observed between species shows that species packing in many habitats of this region is dense. It is speculated that this species richness is possible because of the seasonality of habitats at these latitudes which reduces competition and predation from other groups and produces seasonal pulses of high productivity permitting a species rich fauna to develop because of abundant resources. It is likely that factors other than interspecific competition for resources are important in shaping dytiscid communities in habitats with strong nutrient pulses.     

Ordination and classification of operational geographic units in Southwest Sweden

The vascular plant distributions of Dalsland and northern Bohuslän (Southwest Sweden) were subjected to multivariate analyses in order to delimit geographically coherent floristic zones. 271 squares of 5×5 km were the Operational Geographic Units; the data matrix comprises presence/absence species records for each OGU. Different ordination and classification methods were tested and detailed results are presented for detrended correspondence analysis (DCA), UPGMA and ordination space partitioning (OSP). A weighting procedure, neighbour-weighting, which gives pseudo-frequency scores along the nominal scale 0–9 depending on the species' distribution patterns, is introduced. The superior method for delimiting geographically coherent floristic zones was judged to be ordination space partitioning, using DCA and neighbour-weighted species scores.Abbreviations DCA Detrended Correspondence Analysis - OGU Operational Geographical Unit - OSP Ordination Space Partitioning - UPGMA Unweighted Pair-Group Method using Arithmetic Averages     

A hierarchical classification of freshwater mussel diversity in North America

Aim North America harbours the most diverse freshwater mussel fauna on Earth. This fauna has high endemism at the continental scale and within individual river systems. Previous faunal classifications for North America were based on intuitive, subjective assessments of species distributions, primarily the occurrence of endemic species, and do not portray continent‐wide patterns of faunal similarity. The aim of this study is to provide an analytical portrayal of patterns of mussel diversity in a hierarchical framework that informs the biogeographical history of the fauna. Location The study considered the mussel fauna of North America from the Rio Grande system northwards. Methods Patterns of mussel faunal similarity in 126 river systems or lake watersheds across North America were examined. The dataset was developed from the literature and consisted of recent species presence/absence (282 species) in each drainage unit; subspecies were not included. Patterns of mussel diversity were examined with hierarchical cluster analysis, based on a pairwise distance matrix between all drainage units. Results Cluster analysis revealed 17 faunal provinces within four major faunal regions: Mississippian, Atlantic, Eastern Gulf and Pacific. The Mississippian Region dominates the North American fauna with 11 provinces, including five not recognized by previous classifications: Mississippi Embayment, Upper Mississippi, Great Plains, Ohioan and Pontchartrain–Pearl–Pascagoula. Within the Eastern Gulf Region (containing three provinces), the Escambia–Choctawhatchee Province is distinctive from the Apalachicolan Province, under which it was previously subsumed. Patterns of diversity in the Atlantic Region (two provinces) and Pacific Region (one province) were similar to previous classifications. Main conclusions The classification proposed in this study largely corroborates earlier schemes based on the occurrence of endemic species but identifies additional heterogeneity that reflects unique assemblages of widely distributed species. The study proposes a hierarchical structure that illustrates relationships among these provinces. Although some provinces in the Mississippian Region have high endemism, all Mississippian provinces share a group of widely distributed species. The Atlantic and Eastern Gulf regions have distinctive, endemic faunas suggesting limited past connectivity with the Mississippian Region. The Pacific Region is the most distinct fauna in North America and bears close affinity to the Eurasian mussel fauna.     

The ecology of two intermittent streams in Victoria, Australia

1. We compared aquatic macroinvertebrate assemblage composition within and between habitats (pools and riffles) at four sites on two intermittent streams in Victoria, Australia during a drought year followed by a wetter year to see how different spatial and temporal scales influenced patterns of community structure detected by multivariate techniques of ordination and classification. We also examined the fit between faunal groups and ‘flow phases’ characterized by multivariate analyses of physicochemical variables in an earlier paper. 2. Pools contained more taxa and individuals than riffles. At the more temporary site, there was considerable overlap between the faunal composition of pools and riffles, whereas habitat-specific assemblages consistently occurred at the more permanent sites. Most taxa were either tolerant, permanent stream forms able to persist in streams that dry briefly, or facultative species that occur in lotic or lentic habitats. Few species appeared specifically adapted to temporary waters. 3. Within habitats, there were some matches between faunal groups and flow phases, especially with the onset of the ‘diminishing flow’ phase, characterized by rising water temperature and conductivity, and declining pH and dissolved oxygen. However, disjunctions among faunal groups were less marked than those between flow phases, and were absent at an intermediate scale when habitats were pooled within sites. At the broadest scale of analysis (within habitats between sites and years), historical events (e.g. whether pools upstream dried completely during the previous summer) apparently influenced community composition as much as site-specific abiotic differences.     

The distribution of micro-arthropods in some southern English streams: the influence of physicochemistry

SUMMARY. 1. Micro-arthropods were surveyed during October 1986 at thirty stony, stream riffle sites in the Ashdown Forest, southern England.
2. The importance of a number of physicochemical variables in determining both the distribution of micro-arthropod taxa and community structure was assessed.
3. Acidic sites had an impoverished fauna. Total micro-arthropod species richness and densities were highest under circumneutral conditions. and the same patterns were shown by the Hydrachnellae, Harpucticoida and Cladocera. A number of species seemed indifferent to acidic conditions and were widespread and, as a group, the cyclopoid copepods showed no relationship with pH.
4. Multiple regression showed that other environmental variables, in particular annual mean temperature and maximum discharge, were also important in explaining the between-site distribution of separate micro-arthropod groups and individual species.
5. Other multivariate techniques (ordination, classification and multiple discriminant analysis) showed that impoundment linkage, source distance and conductivity, along with pH, were the most important variables in explaining patterns of species composition between sites.     

Biogeographical patterns of benthic macroinvertebrates in the Southeastern Pacific littoral

Aim To use new collections and taxonomic reviews of the Chilean coastal biota, and studies on biodiversity on a reappraisal of Southeastern Pacific littoral biogeography. Location The temperate coastline of the Southeastern Pacific, extending over 6000 km from northern Peru to the southern tip of Chile. Methods Records of coastal macroinvertebrates were assigned to ten geographic zones along the Chilean coast. The Spearman rank correlation coefficient, ρ, was used to establish the relationship between the total number of species and the number of single records for each zone. Regions and underlying faunal gradient were verified via an unweighted paired group method using arithmetic averages (UPGMA), and ordination non-metric multidimensional scaling (nMDS) analysis based on a disagreement distance matrix of presence/absence data. Abundance down-weighting was preferred to rare species down-weighting, owing to the nature of the records, where a larger number of references for a given taxon did not necessarily indicate a greater abundance or commonness. The dissimilarity matrices between the different zones were used to establish the degree of agreement between the different levels of analysis, using a weighted Spearman rank correlation coefficient ρ_w. Statistical significance was established using a randomization (permutation) test. Main conclusions Analysis of new macroinvertebrate data and taxonomic reviews of the Chilean coastal fauna indicates a Transitional-Temperate Region for the Southeastern Pacific littoral, located between 35°S and 48°S where a gradual mixing and replacement of species negates previous hypotheses on the existence of a marked distributional break at 42°S.     

Analysis of factors implicated in the recent decline of Australia's mammal fauna

Aim To assess whether eight factors thought to be involved in the extinction process can explain the pattern of recent decline in Australia's mammal fauna. Location Australia. Methods We compiled the first comprehensive lists of mammal species extant at the time of European settlement in each of Australia's 76 mainland regions, and assigned a current conservation status to each species in each region to derive an index of faunal attrition. We then sought to explain the observed region‐to‐region variation in attrition (the dependent variable) by building a series of models using variables representing the eight factors. Results A strong geographically based pattern of attrition emerged, with faunal losses being greatest in arid regions and least in areas of high rainfall. The Akaike information criterion showed support for one model that explained 93% of the region‐to‐region variation in attrition. Its six variables all made independent contributions towards explaining the observed variation. Two were environmental variables, namely mean annual rainfall (a surrogate for regional productivity) and environmental change (a measure of post‐European disturbance). The other four were faunal variables, namely phylogenetic similarity, body‐weight distribution, area (as a surrogate for extent of occurrence), and proportion of species that usually shelter on the ground (rather than in rock piles, burrows or trees). Main conclusions In combination with historical evidence, the analysis provides an explicit basis for setting priorities among regions and species. It also shows that the long‐term recovery of populations of many species of Australian mammals will require introduced predator suppression as well as extensive habitat management that includes controlling feral herbivores. Specifically, habitat management should restore aspects of productivity relevant to the types of species at risk and ensure the continual availability of suitable refuges from physiological stressors.     

When the method for mapping species matters: defining priority areas for conservation of African freshwater turtles

Aim Defining priority areas for conservation is essential to minimize biodiversity loss, but the adoption of different methods for describing species distributions influences the outcomes. In order to provide a robust basis for the conservation of freshwater turtles in Africa, we compared the effect that different species‐mapping approaches had on derived patterns of species richness, species vulnerability and protected‐area representativeness. Location Africa. Methods We adopted three different approaches with increasing complexity for generating species distribution maps. The first approach was based on the geographic intersection of species records and grid squares; the second on the union of local convex polygons; and the third on inductive distribution modelling techniques. We used distribution maps, generated using these three approaches, to determine conservation priorities based on geographic patterns of species richness and vulnerability, as well as for conducting gap and irreplaceability analyses. Results We obtained markedly different distribution maps using the three methods, which in turn caused differences in conservation priorities. The grid‐square approach underestimated range sizes and species richness, while the polygon approach overestimated these attributes. The distribution modelling approach provided the most realistic outcome in terms of diversity patterns, by minimizing both commission and omission errors. An integrated map of conservation priority – derived by combining individual measures of priority based on the distribution modelling approach – identified the Gulf of Guinea coast and the Albertine Rift as major priority areas. Main conclusions Each species‐mapping approach has both advantages and disadvantages. The choice of the most appropriate approach in any given situation depends on the availability of locality records and on the relative importance of mitigating omission and commission errors. Our findings suggest that in most circumstances, the use of distribution modelling has many advantages relative to the other approaches. The priority areas identified in this study should be considered for targeting efforts to conserve Africa freshwater turtles in the coming years.     

Finding essential scales of spatial variation in ecological data: a multivariate approach

The identification of spatial structures is a key step in understanding the ecological processes structuring the distribution of organisms. Spatial patterns in species distributions result from a combination of several processes occuring at different scales: identifying these scales is thus a crucial issue. Recent studies have proposed a new family of spatial predictors (PCNM: principal coordinates of neighbours matrices; MEMs: Moran's eigenvectors maps) that allow for modelling of spatial variation on different scales. To assess the multi-scale spatial patterns in multivariate data, these variables are often used as predictors in constrained ordination methods. However, the selection of the appropriate spatial predictors is still troublesome, and the identification of the main scales of spatial variation remains an open question. This paper presents a new statistical tool to tackle this issue: the multi-scale pattern analysis (MSPA). This ordination method uses MEMs to decompose ecological variability into several spatial scales and then summarizes this decomposition using graphical representations. A canonical form of MSPA can also be used to assess the spatial scales of the species-environment relationships. MSPA is compared to constrained ordination using simulated data, and illustrated using the famous oribatid mites dataset. The method is implemented in the free software R.     

Biodiversity and biogeography of Southern Ocean pycnogonids

The pycnogonids of the Southern Ocean have been studied for almost two centuries and have played a key role in shaping previous biogeographic regions for the Antarctic benthos. The aim of this study was to assess the biogeographic patterns derived from the most current sample records of pycnogonids from the Southern Ocean and neighbouring areas. 332 species of pycnogonids from 1837 sample locations were analysed using 279 3° by 3° grid cells. We investigated richness patterns and the effect of sampling intensity at both local and regional scales, and used multivariate analysis of distribution patterns and species assemblages to define biogeographic trends. These analyses identified a distinct and isolated Antarctic pycnogonid shelf fauna which was different to that of the deep‐sea around Antarctica, the Sub‐Antarctic islands, South America or New Zealand. Within the Antarctic, we found the South Shetland Islands to be the most speciose region and a probable center of radiation for the pycnogonids. No latitudinal gradients in species richness were detected. We note that the distribution patterns observed are based upon classical taxonomy and discuss the potential for changes to these patterns with new insights from molecular techniques. We conclude that, even with the potential for cryptic species, the large‐scale biogeographic trends observed in the pycnogonids should hold true.     

Relevance of abiotic criteria used in German lake typology for macroinvertebrate fauna

For lake characterisation, top-down typologies are mostly used throughout Europe, including type criteria such as climate, lake area, catchment geology and conductivity. In Germany, a lake typology was applied comprising ecoregion, calcium concentration, Schindler’s ratio, stratification type and residence time. However, the relevance of these criteria for the macroinvertebrate fauna has not been conclusively demonstrated till now. Benthic invertebrate community data and related environmental parameters of pristine or near-pristine lakes in Germany were analysed by multivariate analysis techniques to elucidate which environmental parameters are reflected by invertebrate composition. Moreover, benthic invertebrate data were transformed to metrics expressing ecological attributes and species richness (summarising functional composition, diversity and sensitivity measures). Multivariate statistics were used to test whether information relevant to ordination was lost and whether variation decreases using metrics which combine data with ecological attributes. Analysis of lake-type criteria revealed that ecoregions and prevailing substrates were characterized by different taxonomic compositions of macroinvertebrates. In addition, a relationship was found between community composition and lake size. Creating a novel bottom-up lake typology based on ecoregions, lake size and prevailing substrate gives better separation of distinct macroinvertebrate communities and a higher level of homogeneity within groups compared to top-down typology or single environmental parameters alone, both on species and metrics data. Despite some data variation due to methodological differences (e.g. different sampling and sorting techniques) and interannual and seasonal variation in the data set, NMDS ordination presented well-separated groups of bottom-up lake types. Lake types were more precisely separated by species data than by metric data in both top-down and bottom-up typology. However, as information loss from species lists to calculated metrics is marginal, type-specific benthic invertebrate assemblages are reflected both on the species level and on the metric level. Species and metric data are both suitable for data ordination, while single environmental parameters affecting macroinvertebrate composition can best be obtained using metrics.     

Brittle stars from Southern Ocean (Echinodermata: Ophiuroidea)

The present biogeographic study on the ophiuroid fauna from the Southern Ocean (SO) contains an updated checklist, based on a compilation of all the published information provided for the Antarctic and sub-Antarctic regions as well as the information available in SCAR-MarBIN database. Faunal composition and geographical and bathymetric distribution are included. So far, 219 species have been recorded, of which 126 are endemic to the SO, 76 are exclusive to Antarctic waters, and 30 are exclusive to sub-Antarctic waters. This study corroborated the circumpolar and eurybathic character of the ophiuroid fauna of the SO, but some differences are discussed when considering shelf and deep-sea fauna in the whole SO, or in the Antarctic and sub-Antarctic regions separately. The biogeographic affinities of 17 areas considered in the SO are revised, based on a presence/absence datamatrix of the 219 species. This similarity analysis shows three main groups, two of them including sub-Antarctic areas and one for Antarctic areas. The faunal movement patterns between the main geographical connections have been based on historical site records of each species. These movements have a level of faunal exchange that exceeds that of other Antarctic benthic groups. Such movements are mainly from Antarctic and sub-Antarctic regions to the subtropical waters of South America, and from New Zealand and southern Australian waters to sub-Antarctic areas. In this context, the origin of the ophiuroid Antarctic fauna is discussed.     

荒漠草原土壤动物与降雨关系研究现状

在全球性气候变化背景下,极端降雨事件频发,总结土壤动物多样性与降雨变化间的关系及其响应机制,有助于理解全球变化对土壤生态系统结构与功能的作用过程,对于探讨陆地生态系统应对全球变化具有重要科学意义。荒漠草原生态系统极度脆弱,对气候变化敏感,但是关于荒漠草原土壤动物与降雨变化间关系的研究报道比较少,严重制约了对荒漠草原生态系统的有效管理和可持续利用。本文从地上、地面和地下3个方面总结了土壤动物和降雨变化间的关系,并就荒漠草原土壤动物应对气候变化研究提出了一些建议。研究表明,降雨变化直接影响土壤动物群落结构;土壤动物对降雨变化反应强烈,不同动物类群产生了积极的响应规律;某些土壤动物类群对于降雨变化还具有重要指示作用。在荒漠草原生态系统中,今后需要从降雨变化对土壤动物产生的长期影响、土壤动物对降雨变化的适应方式和某些动物类群对土壤水分敏感性以及土壤动物与气候变化间的互为反馈关系等方面加强研究。     

Differential Response of Benthos to Natural and Anthropogenic Disturbances in 3 Lowland Streams

The macroinvertebrate faunal assemblages of 8 sites on three small streams in SE England were examined annually in spring between 1987 and 1993. Considerable ‘natural’ variability was observed in the sites superimposed over a background of low-intensity anthropogenic disturbance such as farming, quarrying, and urban influences. Landscape changes and activities in the catchment (saline drainage, removal of topsoil, pipeline crossings of streams) associated with the construction of the UK terminal for the Channel Tunnel, resulted in further temporary disturbance at some of the sites. Most changes in faunal composition were related to natural and anthropogenically induced modifications of the stream substrate. The response and recovery time of sites to disturbances was very variable and was related to the hydraulic and substrate characteristics of the stream bed, with least change and quickest recovery at sites with coarse substrates and high slope. Variations between years in the occurrence of taxa were generally more apparent with species data than with family data except where environmental change was great. Despite the observed differences in faunal composition the main elements of the fauna were fairly constant throughout the study period. Analyses of the data with biotic indices, the predictive RIVPACS system and ordination analyses have all shown clearly the annual variability of faunal parameters used to measure environmental quality. The study has shown that very basic rapid assessment techniques can provide insights into faunal responses to disturbance, especially if the work is long-term and that before authoritative statements concerning environmental impact can be made it is essential to have knowledge of the natural variation to be expected in streams of differing characteristics.     

The Macrobenthos of Sites within Prince William Sound,Alaska, Prior to the Exxon Valdez Oil Spill

Benthic fauna within three bays (Rocky and Zaikof Bays, and Port Etches) of outer Prince William Sound, Alaska are examined. The data represent the only detailed benthic faunal information available for the period prior to a major oil spill by the tanker Exxon Valdez within the Sound. The spatial distribution of fauna determined by classification and ordination resulted in eight station groups. Stepwise multiple discriminant analysis demonstrated a relationship between station groups, sediment grain size and nitrogen. Major faunal differences were observed within Rocky and Zaikof Bays between 1982 and 1990. The faunal differences between the two time periods demonstrate the extreme temporal variability that might be expected within Prince William Sound. The study serves as a cautionary note to avoid conclusions about the effects of disturbance to the benthos on a single data set. An explanation for temporal differences within the bays is presented.     

Analyzing floristic inventories with multiple maps

Spatial observations of plant occurrences contain a wealth of information on relations among species and on the relation between species and environmental conditions. Typically, inventory data of this kind are large co-occurrence matrices, and hence, direct ecological interpretations based on expert knowledge are often very difficult. Hitherto, ordination approaches have been used to construct a virtual ordination space (represented as one or multiple scatter plots) in which species that often co-occur are situated close together, whereas species that hardly co-occur are found far apart. In this study, we investigate a recently proposed ordination approach, multiple maps t-SNE, that constructs multiple, independent ordination spaces in order to reveal and visualize complementary structure in the data. We compare multiple maps t-SNE to several conventional ordination approaches, exploring a large inventory of vascular plant occurrences (FLORKART). Our results reveal that multiple maps t-SNE is well suited for the analysis of floristic inventories. In particular, multiple maps t-SNE uncovers the major dependencies of species co-occurrences on climate and soil biogeochemical preconditions.     

Morphological diversity among fishes in a Great Plains river drainage

Longitudinal succession of stream fish faunas is commonly related to increasing stream size and stability. However, effects of succession on assemblage morphology are seldom quantified. We used an ecomorphological approach to determine differences in faunal structure among distinct stream types of the Cheyenne River drainage in South Dakota, USA. During May–October 2004 we collected fishes monthly from five streams. We examined 28 morphological traits of the dominant fish species and compared morphological structure among faunas using univariate analysis of variance (ANOVA) tests and multivariate ordination and distance calculation techniques. Species richness and composition varied between smaller creeks and larger rivers. Morphological diversity increased with richness, but richer assemblages were also more tightly packed in morphospace, partly because of increased cyprinid richness. Some morphological differences were predicted by variation in mean discharge and discharge flashiness (flow stability). Fishes of more stable or larger river stations characteristically had smaller heads and mouths and longer intestines. Larger mean standard length was also associated with less flashy flow regimes and higher mean discharge. All assemblages were hyperdispersed in morphological space, consistent with the harsh zoogeographical history of the region and suggesting the presence of open niches. Increasing species and morphological diversity despite increasing discharge flashiness suggests higher niche diversity in Great Plains rivers compared to adjacent creeks. Handling editor: J. A. Cambray     

BIOMETRIC ANALYSIS OF GEOGRAPHIC VARIATION AND RACIAL AFFINITIES

1. The study of geographic variation and the racial affinities between populations is of central importance to systematics and evolutionary theory. When using phenotypic variation to measure the similarity between the populations of a species one should analyse the variation in several characters simultaneously. This is a statistical procedure and is known as multivariate analysis. Multivariate analysis of phenotypic variation, unlike some other methods, has the advantage of not being dependent on living specimens. 2. To obtain an adequate sample at each locality, and an adequate distribution of localities within a given geographic area, can be a major problem. The pooling of data from adjacent localities is discussed. 3. There are several sources of phenotypic variation within a species, e.g. sexual and ontogenetic variation. Failure to eliminate the non-geographic sources of variation can confuse the assessment of the similarity between populations. 4. Correlation between characters can reflect similar genetic control and/or similar patterns of geographic variation, the biological interpretation being influenced by whether the data come from one locality or many. 5. The influences of environmental induction and genetic control cannot easily be separated. Also, some characters may not be entirely homologous throughout the range of the species. 6. Most studies rely on far too few characters of a too restricted type to give an ‘overall’ assessment of the phenotypic similarity. This is one of the most neglected aspects of the study of geographic variation. 7. The various forms of clinal and categorical variation, the precise nature and position of sharp transition (hybrid) zones, the relationship between non-adjacent as well as adjacent populations and the phenotypic divergence between island populations, etc., all come under the heading of geographic variation. The ideal technique should be able to elucidate all types of geographic variation but some techniques can only be used effectively with a few of them. Moreover, techniques may be limited in their application because they require the data to conform to certain models, e.g. normal distribution. 8. The degree of phenotypic similarity between populations can be measured by a wide range of similarity coefficients. Comparison between even a small series of populations produces a large set (or matrix) of similarity coefficients that is difficult to interpret. However, the relationships between populations can be summarized in several ways and these may be loosely grouped into four categories; (i) network diagrams, (ii) contours and isometric plots, (iii) hierarchical clusters, and (iv) ordination methods. These methods are explained and their advantages and limitations discussed. 9. The hierarchical (dendritic) model of cluster analysis is unsuitable for analysing all but a few types of geographic variation. 10. There are several types of ordination technique. They all aim to summarize the variation of many characters in a reduced number of axes. One can either emphasize the biological interpretation of each separate axis, or treat the analysis as a classifying technique and assess the grouping of the populations in the space defined by the axes. Considerable care is needed in interpreting the results of both of these approaches. If correctly applied, ordination techniques generally can be used to analyse all the forms of geographical variation and are therefore recommended. Contrary to current practice they can be used with a large number of characters. The advantages and limitations of the various ordination techniques are discussed. 11. Contours and their three-dimensional isometric plots can be used to portray geographic variations in the information obtained from a multivariate analysis. However, contours and isometric plots are limited in their applicability and the amount of information they can convey. 12. The sophistication of some multivariate methods should not be allowed to cloak the scientific inadequacies of a study. The use of more than one technique and variety in the choice of pertinent parameters may be of value in indicating the reliability of the results.