Showing papers in "Global Ecology and Biogeography in 2003"

Predicting the impacts of climate change on the distribution of species: are bioclimate envelope models useful?

Abstract: Modelling strategies for predicting the potential impacts of climate change on the natural distribution of species have often focused on the characterization of a species’ bioclimate envelope. A number of recent critiques have questioned the validity of this approach by pointing to the many factors other than climate that play an important part in determining species distributions and the dynamics of distribution changes. Such factors include biotic interactions, evolutionary change and dispersal ability. This paper reviews and evaluates criticisms of bioclimate envelope models and discusses the implications of these criticisms for the different modelling strategies employed. It is proposed that, although the complexity of the natural system presents fundamental limits to predictive modelling, the bioclimate envelope approach can provide a useful first approximation as to the potentially dramatic impact of climate change on biodiversity. However, it is stressed that the spatial scale at which these models are applied is of fundamental importance, and that model results should not be interpreted without due consideration of the limitations involved. A hierarchical modelling framework is proposed through which some of these limitations can be addressed within a broader, scale-dependent

A tribute to Claude Shannon (1916-2001) and a plea for more rigorous use of species richness, species diversity and the 'Shannon-Wiener' Index

Abstract: In the literature, the terms species richness and species diversity are sometimes used interchangeably. We suggest that at the very least, authors should define what they mean by either term. Of the many species diversity indices used in the literature, the Shannon Index is perhaps most commonly used. On some occasions it is called the Shannon‐Wiener Index and on other occasions it is called the Shannon‐Weaver Index. We suggest an explanation for this dual use of terms and in so doing we offer a tribute to the late Claude Shannon (who passed away on 24 February 2001).

Spatial autocorrelation and red herrings in geographical ecology

Abstract: Aim Spatial autocorrelation in ecological data can inflate Type I errors in statistical analyses. There has also been a recent claim that spatial autocorrelation generates 'red herrings', such that virtually all past analyses are flawed. We consider the origins of this phenomenon, the implications of spatial autocorrelation for macro-scale patterns of species diversity and set out a clarification of the statistical problems generated by its presence. Location To illustrate the issues involved, we analyse the species richness of the birds of western/central Europe, north Africa and the Middle East. Methods Spatial correlograms for richness and five environmental variables were generated using Moran's I coefficients. Multiple regression, using both ordinary least-squares (OLS) and generalized least squares (GLS) assuming a spatial structure in the residuals, were used to identify the strongest predictors of richness. Autocorrelation analyses of the residuals obtained after stepwise OLS regression were undertaken, and the ranks of variables in the full OLS and GLS models were compared. Results Bird richness is characterized by a quadratic north-south gradient. Spatial correlograms usually had positive autocorrelation up to c. 1600 km. Including the environmental variables successively in the OLS model reduced spatial autocorrelation in the residuals to non-detectable levels, indicating that the variables explained all spatial structure in the data. In principle, if residuals are not autocorrelated then OLS is a special case of GLS. However, our comparison between OLS and GLS models including all environmental variables revealed that GLS de-emphasized predictors with strong autocorrelation and long-distance clinal structures, giving more importance to variables acting at smaller geographical scales. Conclusion Although spatial autocorrelation should always be investigated, it does not necessarily generate bias. Rather, it can be a useful tool to investigate mechanisms operating on richness at different spatial scales. Claims that analyses that do not take into account spatial autocorrelation are flawed are without foundation.

Global synthesis of leaf area index observations: implications for ecological and remote sensing studies

Abstract: Aim We present the first global synthesis of plant canopy leaf area index (LAI) measurements from more than 1000 published estimates representing ∼ 400 unique field sites. LAI is a key variable for regional and global models of biosphereatmosphere exchanges of energy, carbon dioxide, water vapour, and other materials. Location The location is global, geographically distributed. Results Biomes with LAI values well represented in the literature included croplands, forests and plantations. Biomes not well represented were deserts, shrublands, tundra and wetlands. Nearly 40% of the records in the database were published in the past 10 years (1991‐2000), with a further 20% collected between 1981 and 1990. Mean ( ± SD) LAI, distributed between 15 biome classes, ranged from 1.3 ± 0.9 for deserts to 8.7 ± 4.3 for tree plantations, with temperate evergreen forests (needleleaf and broadleaf) displaying the highest average LAI (5.1‐6.7) among the natural terrestrial vegetation classes. Following a statistical outlier analysis, the global mean ( ± SD) LAI decreased from 5.2 (4.1) to 4.5 (2.5), with a maximum LAI of 18. Biomes with the highest LAI values were plantations > temperate evergreen forests > wetlands. Those with the lowest LAI values were deserts < grasslands < tundra. Mean LAI values for all biomes did not differ statistically by the methodology employed. Direct and indirect measurement approaches produced similar LAI results. Mean LAI values for all biomes combined decreased significantly in the 1990s, a period of substantially more studies and improved methodologies. Main conclusions Applications of the LAI database span a wide range of ecological, biogeochemical, physical, and climate research areas. The data provide input to terrestrial ecosystem and land-surface models, for evaluation of global remote sensing products, for comparisons to field studies, and other applications. Example uses of the database for global plant productivity, fractional energy absorption, and remote sensing studies are highlighted.

Six types of species‐area curves

Abstract: Macroecological studies infer ecological processes based on observed patterns. An often used measure of pattern is the species-area curve. Insufficient attention has been paid to the variety of methods used to construct those curves. There are six different methods based on different combinations of: (1) the pattern of quadrats or areas sampled (nested, contiguous, noncontiguous, or island); (2) whether successively larger areas are constructed in a spatially explicit fashion or not; and (3) whether the curve is constructed from single values or mean values. The resulting six types of curves differ in their shapes, how diversity is encapsulated, and the scales encompassed. Inventory diversity (x) can either represent a single value or a mean value, creating a difference in the focus of the measure. Differentiation diversity (P) can vary in the extent encompassed, and thus the spatial scale, depending on the pattern of quadrat placement. Species-area curves are used for a variety of purposes: extrapolation, setting a common grain, and hypothesis testing. The six types of curves differ in how they are used or interpreted in these contexts. A failure to recognize these differences can result in improper conclusions. Further work is needed to understand the sampling and measurement properties of the different types of speciesarea curves.

Above-ground biomass estimation in closed canopy Neotropical forests using lidar remote sensing: factors affecting the generality of relationships

Abstract: Aim Previous studies have developed strong, site-specific relationships between canopy metrics from lidar (light detecting and ranging) remote sensing data and forest structural characteristics such as above-ground biomass (AGBM), but the generality of these relationships is unknown. In this study, we examine the generality of relationships between lidar metrics and forest structural characteristics, including AGBM, from two study areas in Central America with different precipitation patterns. Location A series of tropical moist forest sites in Panama and a tropical wet forest in Costa Rica. Methods Canopy metrics (e.g. canopy height) were calculated from airborne lidar data. Basal area, mean stem diameter and AGBM were calculated from measurements taken as a part of ongoing forest dynamics studies in both areas. We examined the generality of relationship between lidar metrics and forest structure, and possible environmental effects (e.g. leaf phenology). Results We found that lidar metrics were strongly correlated ( R 2 : 0.65‐0.92) with mean stem diameter, basal area and AGBM in both regions. We also show that the relationships differed between these regions. Deciduousness of canopy trees in the tropical moist forest area accounted for the differences in predictive equations for stem diameter and basal area. The relationships between lidar metrics and AGBM, however, remained significantly different between the two study areas even after adjusting for leaf drop. We attribute this to significant differences in the underlying allometric relationships between stem diameter and AGBM in tropical wet and moist forests. Conclusions Important forest structural characteristics can be estimated reliably across a variety of conditions sampled in these closed-canopy tropical forests. Environmental factors such as drought deciduousness have an important influence on these relationships. Future efforts should continue to examine climatic factors that may influence the generality of the relationships between lidar metrics and forest structural characteristics and assess more rigorously the generality of field-derived allometric relationships.

Variation in plant species richness of different life forms along a subtropical elevation gradient in the Himalayas, east Nepal

Abstract: Aim To explore the variation in species richness along a subtropical elevation gradient, and evaluate how climatic variables explain the richness of the different life forms such as trees, shrubs, climbers, herbs and ferns. Location The study was made in a subtropical to warm temperate region in the south-eastern part of Nepal, between 100 and 1500 m above sea level (a.s.l.). Methods The number of species was counted in six plots (50 〈 20 m) in each of the 15 100 m elevation bands covering the main physiognomic structures along an imaginary transect. Each species recorded was assigned to a life form. Potential evapotranspiration (PET, i.e. energy), mean annual rainfall (MAR), and their ratio (MI = moisture index) were evaluated as explanatory variables by means of generalized linear models (GLM). Each variable was tested individually, and in addition MAR and PET were used to test the water-energy dynamics model for each life form. Results The richness of herbaceous species, including herbaceous climbers, was unrelated to any of the climate variables. PET was strongly negatively correlated with elevation, and the following relationships were found between increasing PET and richness: (i) shrubs, trees and total species (sum of all life forms) showed unimodal responses (ii) ferns decreased monotonically, and (iii) woody climbers increased monotonically. Richness of all woody groups increased monotonically with MAR and MI. The water-energy dynamics model explained 63% of the variation in shrubs, 67% for trees and 70% for woody species combined. Main conclusions For the various herbaceous life forms (forbs, grasses, and herbaceous climbers) we found no significant statistical trends, whereas for woody life forms (trees, shrubs, and woody climbers) significant relationships were found with climate. E.M. O’Brien’s macro-scale model based on water-energy dynamics was found to explain woody species richness at a finer scale along this elevational-climatic gradient.

The coincidence of people and biodiversity in Europe

Abstract: A positive correlation between human population density and species richness has been recorded across the tropics. Here I investigate whether this correlation holds true for Europe. Analyses reveal a positive correlation between human population density and plant (rho = 0.505), mammal (rho = 0.471) and reptile and amphibian (rho = 0.556) species richness. The results are largely concordant with those obtained in similar studies for Africa. However, contrary to previous analyses, the correlation found between people and breeding bird species richness (rho = 0.186) was weak. Of three measures of endemism used, only combined European endemic species richness correlated with human density (rho = 0.437). Richness among combined restricted-range European endemics was not correlated (rho = 0.095) with human density, while richness among all combined restricted-range species was only weakly correlated with human density (rho = 0.167). The results partially support the idea of a correlation between people and biodiversity, although there are some important exceptions. Discussion of possible mechanisms underling the observed patterns is undertaken.

Native and alien plant species richness in relation to spatial heterogeneity on a regional scale in Germany

Abstract: Aim The aim of our study was to reveal relationships between richness patterns of native vs. alien plant species and spatial heterogeneity across varying landscape patterns at a regional scale. Location The study was carried out in the administrative district of Dessau (Germany), covering around 4000 km2. Methods Data on plant distribution of the German vascular flora available in grid cells covering 5′ longitude and 3′ latitude (c. 32 km2) were divided into three status groups: native plants, archaeophytes (pre 1500 AD aliens) and neophytes (post 1500 AD aliens). Land use and abiotic data layers were intersected with 125 grid cells comprising the selected area. Using novel landscape ecological methods, we calculated 38 indices of landscape composition and configuration for each grid cell. Principal components analysis (PCA) with a set of 29 selected, low correlated landscape indices was followed by multiple linear regression analysis. Results PCA reduced 29 indices to eight principal components (PCs) that explained 80% cumulative variance. Multiple linear regression analysis was highly significant and explained 41% to 60% variance in plant species distribution (adjusted R2) with three significant PCs (tested for spatial autocorrelation) expressing moderate to high disturbance levels and high spatial heterogeneity. Comparing the significance of the PCs for the species groups, native plant species richness is most strongly associated with riverine ecosystems, followed by urban ecosystems, and then small-scale rural ecosystems. Archaeophyte and neophyte richness are most strongly associated with urban ecosystems, followed by small-scale rural ecosystems and riverine ecosystems for archaeophytes, and riverine ecosystems and small-scale rural ecosystems for neophytes. Main conclusions Our overall results suggest that species richness of native and alien plants increases with moderate levels of natural and/or anthropogenic disturbances, coupled with high levels of habitat and structural heterogeneity in urban, riverine, and small-scale rural ecosystems. Despite differences in the order of relevance of PCs for the three plant groups, we conclude that at the regional scale species richness patterns of native plants as well as alien plants are promoted by similar factors.

Uphill shifts in distribution of butterflies in the Czech Republic: effects of changing climate detected on a regional scale

Abstract: Aim To assess whether altitude changes in the distribution of butterflies during the second half of the 20th century are consistent with climate warming scenarios. Location The Czech Republic. Methods Distributional data were taken from a recent butterfly distribution atlas, which maps all Czech butterflies using a grid of 10 ′ longitude to 6 ′ latitude, equivalent to about 11.1 × 12 km. Cell altitude was used as an independent variable, and altitudinal ranges of individual species (less migrants, extinct species, recent arrivals and extremely rare species) in 1950‐80 vs. 1995‐2001 and in 1950‐80, 1981‐94, 1995‐ 2001 were compared using U -tests and linear regressions. Results Of 117 ( U -tests) and 119 (regressions) species, we found significant uphill increases in 15 and 12 species, respectively. The two groups were nested; none ( U -test) and one (regression) species showed a significant altitudinal decrease. Binomial tests of frequencies of signs of the U -tests and regression coefficients, including nonsignificant ones, also showed that the increases prevailed. The mean and median of the significant shifts were 60 and 90 m, respectively, and the maximum shift per species was 148 m. The recording effort in individual time periods was not biased with respect to altitude. Main conclusion Altitude shifts in the distribution of Czech butterflies are already detectable on the coarse scales of standard distribution maps. The increasing species do not show any consistent pattern in habitat affiliations, conservation status and mountain vs. nonmountain distribution, which renders climatic explanation as the most likely cause of the distributional shifts.

Three challenges for a real people-centred conservation

Abstract: Many commentators attest to a paradigm shift in biodiversity conservation, away from exclusive protected areas towards more people-centred or community-based conservation. This has been referred to as 'new conservation'. However, new conservation could be thought of as an attempt to re-label and re-package conservation and to 'get people on board' existing strategies. According to its critics even so-called new conservation policy, practice and institutions remain expert-driven, undemocratic and autocratic. I argue that for new conservation to become reality, then more fundamental changes in priority-setting, decision-making and organization are required. This paper presents three challenges for a real people-centred conservation: a more pluralist approach to understanding knowledge and values of different actors, greater deliberation and inclusion in decision-making, and a remodelling of institutions to support conservation.

Glacial refugia of temperate, Mediterranean and Ibero‐North African flora in south‐eastern Spain: new evidence from cave pollen at two Neanderthal man sites

Abstract: Aim To locate glacial refugia of thermophilous plant species in Spain. Methods We use pollen found in cave sediments as a source of palaeobotanical and palaeoecological information. The findings are discussed with regard both to animal remains from both sites, and also to other refugia in south-eastern Spain and elsewhere in the Iberian Peninsula. Results Both sequences show persistence of abundant mes- othermophilous trees during the last glacial stage, suggesting both localities were reservoirs of phytodiversity and wood- land species. At both sites, deciduous and evergreen oaks are the most abundant components, followed by a wide variety of deciduous trees and sclerophyllous shrubs, including Ibero- North African xerothermic scrub near the coast. Conclusions Incomplete information underlies a common misapprehension that Iberian glacial refugia were confined to southernmost parts of the peninsula. A rather different picture of Quaternary refugia emerges from consideration of pollen sequences from caves (and other inputs such as macroscopic charcoal, spatial genetic structure of present-day populations, faunal remains, and present-day distribution of thermophilous species). This picture offers a view of numer- ous viable areas for woodland species in southern Spain, in addition to others in the mountain ranges, both in continental central Spain and those of northern Spain: these stretch from the Mediterranean coast of Catalonia to the westernmost extent of the Bay of Biscay.

Patterns of ant species richness along elevational gradients in an arid ecosystem

Abstract: Aim In this study, we examine patterns of local and regional ant species richness along three elevational gradients in an arid ecosystem. In addition, we test the hypothesis that changes in ant species richness with elevation are related to elevation-dependent changes in climate and available area. Location Spring Mountains, Nevada, U.S.A. Methods We used pitfall traps placed at each 100-m eleva- tional band in three canyons in the Spring Mountains. We compiled climate data from 68 nearby weather stations. We used multiple regression analysis to examine the effects of annual precipitation, average July precipitation, and maximum and minimum July temperature on ant species richness at each elevational band. Results We found that patterns of local ant species richness differed among the three gradients we sampled. Ant species richness increased linearly with elevation along two transects and peaked at mid-elevation along a third transect. This suggests that patterns of species richness based on data from single transects may not generalize to larger spatial scales. Cluster analysis of community similarity revealed a high- elevation species assemblage largely distinct from that of lower elevations. Major changes in the identity of ant species present along elevational gradients tended to coincide with changes in the dominant vegetation. Regional species rich- ness, defined here as the total number of unique species within an elevational band in all three gradients combined, tended to increase with increasing elevation. Available area decreased with increasing elevation. Area was therefore correlated negatively with ant species richness and did not explain elevational patterns of ant species richness in the Spring Mountains. Mean July maximum and minimum temperature, July precipitation and annual precipitation combined to explain 80% of the variation in ant species richness. Main conclusions Our results suggest that in arid eco- systems, species richness for some taxa may be highest at high elevations, where lower temperatures and higher precipita- tion may support higher levels of primary production and cause lower levels of physiological stress.

Relative influences of current and historical factors on mammal and bird diversity patterns in deglaciated North America

Abstract: Aim To investigate the relative contributions of current vs. historical factors in explaining broad-scale diversity gradients using a combination of contemporary factors and a quantitative estimate of the temporal accessibility of areas for recolonization created by glacial retreat following the most recent Ice Age. Location The part of the Nearctic region of North America that was covered by ice sheets during the glacial maximum 20 000 BP. Methods We used range maps to estimate the species richness of mammals and terrestrial birds in 48 400 km(2) cells. Current conditions in each cell were quantified using seven climatic and topographical variables. Historical conditions were estimated using the number of years before present when an area became exposed as the ice sheets retreated during the post-Pleistocene climate warming. We attempted to tease apart contemporary and historical effects using multiple regression, partial regression and spatial autocorrelation analysis. Results A measure of current energy inputs, potential evapotranspiration, explained 76-82% of the variance in species richness, but time since deglaciation explained an additional 8-13% of the variance, primarily due to effects operating at large spatial scales. Because of spatial covariation between the historical climates influencing the melting of the ice sheet and current climates, it was not possible to partition their effects fully, but of the independent effects that could be identified, current climate explained two to seven times more variance in richness patterns than age. Main Conclusions Factors acting in the present appear to have the strongest influence on the diversity gradient, but an historical signal persisting at least 13 000 years is still detectable. This has implications for modelling changes in diversity patterns in response to future global warming.

Large-scale environmental correlates of forest tree distributions in Catalonia (NE Spain)

Abstract: Aim To explore the environmental correlates of tree species distributions in Catalonia according to the chorological status of the species. Location The study area is the region of Catalonia, in northeastern Spain. Methods We used presence-absence data for 24 species, sampled in random plots distributed throughout forests of Catalonia. A climate model for the Catalonia region provided environmental variables. We used classification tree analysis to explore the environmental correlates of the realized niches of tree species. The predictive accuracy of the models was assessed using the ROC curve approach. Potential distribution maps of tree species were generated for the whole Catalonia region. Results Models were ranked from low to high accuracy for the 24 species. Differences in accuracy among species were related to the chorological status of species. Zonal species, or species at the core of their range (Mediterranean and SubMediterranean species), were generally well predicted, while extrazonal species, or species at the edge of their range, were predicted only moderately well. Mediterranean species distributions showed good correlations with extreme temperatures and annual precipitation. Main conclusions The above trends confirmed the difficulty of identifying the realized niche of species at the edges of their ranges. In contrast, Mediterranean and Sub-Mediterranean species, which were at the core of their range, were well-predicted, confirming the importance of extremes of temperature and annual precipitation as effective surrogates for variables having more direct physiological roles in limiting the ability of plants to survive and grow. Maps of potential tree distributions allowed us to define suitable habitats and to highlight areas where species have been planted outside their natural distribution.

How important are large vs. small forest remnants for the conservation of the woodland flora in an urban context

Abstract: Aim To test whether, in an urban area, small forest fragments are more important than large ones, the present study aimed at firstly exploring the relationship between plant functional groups or individual species and urban woodlot characteristics such as patch area and isolation, and secondly investigating whether equal-sized combinations of islands tend to differ in species richness. Location The city of Brussels. Methods We considered the relationship between size, species richness and plant functional groups among one very large (1666 ha) and 11 rather small (2‐123 ha) woodlots. Results The largest woodlot harboured species missing in the smaller ones. The species-area relationship plotted for these wooded patches fitted the semilog model very well. Twenty-three species had a significantly higher frequency in the main forest. Only six species had a significantly higher frequency in smaller woodlots. The occurrence of species groups with high conservation value (e.g. ancient forest species, rare species) was higher in large patches. However, a SLOSS analysis showed that habitat subdivision appeared to be associated with increased species counts. A marginally nonsignificant effect of distance to the main forest became significant when matrix species were removed from the patch samples. Conclusions Although overall the data showed a higher conservation value for large woods, some plant functional groups (e.g. woodland species vs. ancient forest species) responded differently to fragmentation. This illustrates that, for conservation strategies, studies considering the biotic characteristics of remnants should focus on the species number of particular plant functional groups, especially those with high conservation value. Furthermore, matrix species should be removed from the analysis in order not to mask underlying patch size and distance effects.

Passive internal transport of aquatic organisms by waterfowl in Doñana, south-west Spain

Abstract: Aim Waterbirds may play an important role in the maintenance of aquatic ecosystem biodiversity by transporting plants and invertebrate propagules between different wetlands. The aim of this study is to provide the first quantitative analysis of the transport of plant and animal propagules by a community of waterbirds. Location Donana marshes in south-west Spain. Methods We quantified the number of intact seeds and invertebrate eggs in 386 faecal samples from 11 migratory waterfowl species (10 ducks and coot), collected from 3 November to 3 December 1998 (when birds were arriving from further north), and 22‐25 February 1999 (when birds were leaving Donana). Results Intact seeds of at least 7 plant genera, and invertebrate eggs (ephippia of at least 2 crustacea, statoblasts of at

Are there latitudinal gradients in species turnover

Abstract: Aim To examine the effect on the observed relationship between spatial turnover and latitude of both the measure of beta diversity used and the method of analysis. Location The empirical analyses presented herein are for the New World. Methods We take the spatial distributions of the owls of the New World as an exemplar data set to investigate the patterns of beta diversity across latitudes revealed by different analytical methods. To illustrate the strengths and weaknesses of alternative measures of beta diversity and different analytical approaches, we also use a simple random distribution model, focusing in particular on the influence of richness gradients and landmass geometry. Results Our simple spatial model of turnover demonstrates that different combinations of analytical approach and measure of beta diversity can give rise to strikingly different relationships between turnover and latitude. The analyses of the bird data for the owls of the New World demonstrate that this observation extends to real data. Conclusions For the particular assemblage considered, we present strong evidence that species richness declines at higher latitudes, and there is also some evidence that species turnover is greater nearer the equator, despite conceptual and practical difficulties involved in analysing spatial patterns of species turnover. We suggest some ways of overcoming these difficulties.

Values-led conservation

Abstract: In international nature conservation policy, value-arguments based on science and economic rationalism increasingly overshadow the aesthetic and ethical arguments that originally inspired the conservation movement. We argue that this trend risks removing conservation from the public realm, in part because it facilitates the adoption by nongovernment conservation bodies of corporate values and/or their integration with government bureaucracies. By contrast, the explicit recognition of aesthetic and ethical values would complement arguments based on science and economic utility. We subscribe to a reformist view of globalization that accepts the inevitability of a globalizing world but argues that the process needs humanizing by incorporating quality of life values in the policy process. We argue that re-emphasis of aesthetic and ethical arguments in international conservation policy would contribute to this goal by reasserting links between conservation bodies and the public, thereby leading to more effective action on the ground.

Does climate determine broad‐scale patterns of species richness? A test of the causal link by natural experiment

Abstract: Aim Broad-scale spatial patterns of species richness are very strongly correlated with climatic variables. If there is a causal link, i.e. if climate directly or indirectly determines patterns of richness, then when the climatic variables change, richness should change in the manner that spatial correlations between richness and climate would predict. The present study tests this prediction using seasonal changes in climatic variables and bird richness. Location We used a grid of equal area quadrats (37 000 km2) covering North and Central America as far south as Nicaragua. Methods Summer and winter bird distribution data were drawn from monographs and field guides. Climatic data came from published sources. We also used remotely sensed NDVI (normalized difference vegetation index — a measure of greenness). Results Bird species richness changes temporally (between summer and winter) in a manner that is close to, but statistically distinguishable from, the change one would predict from models relating the spatial variation in richness at a single time to climatic variables. If one further takes into account the seasonal changes in NDVI and within-season variability of temperature and precipitation, then winter and summer richness follow congruent, statistically indistinguishable patterns. Main conclusions Our results are consistent with the hypothesis that climatic variables (temperature and precipitation) and vegetation cover directly or indirectly influence patterns of bird species richness.

The impact of cropland cover on river nutrient levels in the Mississippi River Basin

Abstract: Aim This study developed high-resolution datasets of the area of maize, soybean and wheat cultivation in the United States for 1950, 1970 and 1992. The datasets were used to examine the relationship between individual crop cover and nutrient levels in rivers across the Mississippi River Basin. Location This study was conducted in the United States, with focus on the Mississippi River Basin. Methods County and state-level estimates of the planted area of maize, soybean and wheat were integrated with a satellite-derived pattern in total cropland to develop 5′ × 5′ resolution datasets of the fractional area of maize, soybean and wheat in the United States for 1950, 1970 and 1992. Regression analysis was used to determine the relationships between mean levels of nitrogen, phosphorous and silica in 25 rivers across the Mississippi Basin, and the extent of maize, soybean and wheat cultivation in the watersheds. Results The crop datasets provide a spatially explicit representation of the area of the three primary crops in 1950, 1970 and 1992. The datasets clearly depict the rapid expansion of soybean cultivation, the increased specialization of individual agricultural regions, and the accompanying reduction in agricultural biodiversity since 1950. The statistical analysis identified strong correlations between the extent of maize and soybean cover in a watershed and the level of nitrogen (N) and phosphorous (P) at the watershed outlet. In particular, the area of maize appears to be strongly related to the concentration of total-N and the ratio of dissolved inorganic-N and organic-N at the watershed outlet. Conclusions The intensification of cultivation of the three primary crops — maize, soybean and wheat — has altered land cover and water quality across the U.S. since 1950. The high present-day rate of fertilizer use on maize and the expansion of soybean cultivation could be largely responsible for the change in nutrient ratios in the Mississippi River since 1950.

Land use and cover with intensity of agriculture for Canada from satellite and census data

Abstract: Aim To develop the first national databases on land use and agricultural land use intensity in Canada for a wide variety of environmental monitoring applications. Location Canada. Methods In this paper, we describe a new system for the construction of both land use and land use intensity (within agricultural regions) called LUCIA (land use and cover with intensity of agriculture). Our methodology combines the highly detailed Canadian Census of Agriculture and recent growing season composites derived from the SPOT4/ VEGETATION sensor. Census data are of much coarser resolution than the remotely sensed data but, by removing non-agricultural pixels from each census sampling area, we were able to refine the census data sufficiently to allow their use as ground truth data in some areas. The ‘refined’ census data were then used in the final step of an unsupervised classification of the remotely sensed data. Results and main conclusions The results of the land use classification are generally consistent with the input census data, indicating that the LUCIA output reflects actual land use trends as determined by national census information. Land use intensity, defined as the principal component of census variables that relate to agricultural inputs and outputs (e.g. chemical inputs, fertilizer inputs and manure outputs), is highest in the periphery of the great plains region of central Canada but is also very high in southern Ontario and Quebec.

Environmental factors and vegetation composition, Lefka Ori massif, Crete, S. Aegean

Abstract: Aim The aim of this study was to explore the environmental factors that determine the spatial distribution of oro-mediterranean and alti-mediterranean plant communities in Crete. Location The paper provides a quantitative analysis of vegetation-environment relationships for two study areas within the Lefka Ori massif Crete, a proposed Natura 2000 site. Methods Eleven environmental variables were recorded: altitude, slope, aspect, percentage of bare rock, percentage of unvegetated ground, soil depth, pH, organic matter content and percentages of sand, silt and clay content. Classification of the vegetation was based on twinspan, while detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) were used to identify environmental gradients linked to community distribution. Results One hundred and twenty-five species were recorded from 120 plots located within the two study areas. Forty-seven of the recorded species are endemic, belonging to 35 families. Hemicryptophytes and chamaephytes were the most frequent, suggesting a typical oro-mediterranean life form spectrum. The samples were classified into five main community types and one transitional. The main gradients, identified by CCA, were altitude and surface cover type in the North-west site, while in the Central site the gradients were soil formation-development and surface cover type. Main conclusions The use of classification in combination with ordination techniques resulted in a good discrimination between plant communities and a greater understanding of controlling environmental factors. The methodology adopted can be employed for improving baseline information on plant community ecology and distribution in Mediterranean mountain zones.

Prairie dog towns as islands: applications of island biogeography and landscape ecology for conserving nonvolant terrestrial vertebrates

Abstract: Aim To evaluate the utility of island biogeography theory as a model for understanding and conserving native communities of nonvolant terrestrial vertebrates at prairie dog towns. Location Oklahoma Panhandle, USA. Methods We surveyed mammal, reptile and amphibian communities on 36 black-tailed prairie dog (Cynomys ludovicianus) towns during the summers and falls of 1997 to 1999. We used a Geographic Information System (GIS) to characterize the landscape within 10 km of each town. We used Principal Components Analysis (PCA), Correlation Analysis, and Linear Regression to test for patterns in species richness relative to area and isolation of towns, local habitat characteristics, and characteristics of the adjacent landscape. Results Species richness was not significantly correlated with town size, town isolation, or local habitat characteristics. On the other hand, species richness was significantly correlated with characteristics of the landscape within 10 km of the focal town. In addition, species richness of mammals at prairie dog towns during the summer increased in a northerly direction, while richness of mammals at towns during fall increased to the west. Main conclusions These results, albeit contrary to traditional island biogeography theory, are consistent with an emerging view that communities on relatively small islands are strongly influenced by characteristics of the adjacent landscape (or seascape). We recommend that to the extent possible, networks of reserves for prairie dogs and their associated species should include clusters of large towns (i.e. larger than those studied here), as well as large but isolated towns, and that conservation efforts should include management of the intervening matrix of anthropogenic habitats.

Climate-driven changes in shoot density and shoot biomass in Leymus chinensis (Poaceae) on the North-east China Transect (NECT)

Abstract: Aim Climate-driven changes affecting ecosystem primary production have been well documented for many vegetation types, while the effects of climate on plant populations remains unclear Herein, we address the relationships between climatic variables and shoot density, reproductive allocation and shoot biomass in Leymus chinensis on a large-scale climatic gradient in 2000 Location Nine sites experiencing similar light regimes, but differing in longitude, precipitation and altitude were selected on the North-east China Transect (NECT) from 115° to 124°E, around a latitude of 435°N Methods Densities of total, vegetative and reproductive shoots and of shoot biomass were measured twice over the growing season in each site Climatic data were taken from the climate database of the Laboratory of Quantitative Vegetation Ecology, Institute of Botany, Chinese Academy of Sciences and from the local weather stations throughout the NECT Results Densities of total, vegetative and reproductive shoots increased significantly from the west to the east and from dry to moist along the NECT, and were strongly correlated with annual precipitation (r2 = 0934, 0943 and 0863, respectively) and an aridity index (r2 = 0809, 0816 and 0744, respectively) The average total shoot density at the east end (470/m2) was about three times that at the west (160/m2) Reproductive allocation and shoot biomass for both vegetative and reproductive shoots increased with precipitation and declined with the aridity index along the NECT There were positive correlations between shoot biomass and annual precipitation for vegetative shoots (P < 005, R2 = 0604) and March precipitation for reproductive shoots (P < 005, R2 = 0533), respectively Main conclusions These findings suggest that L chinensis adjusts to decreasing precipitation/increasing aridity by alterations in shoot density, reproductive allocation and shoot biomass along the drought gradient of the NECT

Elevational gradients of small mammal diversity on the northern slopes of Mt. Qilian, China

Abstract: Aim Small mammal species richness and relative abundance vary along elevational gradients, but there are different patterns that exist. This study reports the patterns of distribution and abundance of small mammals along the broader elevational gradient of Mt. Qilian range. Location The study was conducted in the Mt. Qilian range, north-western China, from June to August 2001. Methods Removal trapping was conducted using a standardized technique at 7 sites ranging between 1600 and 3900 m elevation within three transects. Correlation, regression and graphical analyses were used to evaluate the diversity patterns along this elevational gradient. Results In total, 586 individuals representing 18 nonvolant small mammal species were collected during 20 160 trap nights. Species composition was different among the three transects with 6 (33%) of the species found only within one transect. Elevational distribution and relative abundance of small rodents showed substantial spatial variation, with only 2 species showing nonsignificant capture frequencies across elevations. Despite these variations, some general patterns of elevational distribution emerged: humped-shape relationships between species diversity and elevation were noted in all three transects with diversity peaks at middle elevations. In addition, relative abundance was negatively correlated with elevation.

Dispersal and the interspecific abundance‐occupancy relationship in British birds

Abstract: Aim To test the prediction that deviations of species from the positive interspecific relationship between abundance and occupancy (a measure of geographical range size) are related to differences in dispersal. Location Great Britain. Methods Quantitative data on the abundances, occupancy and dispersal distances of British birds are compared using phylogenetic comparative methods. Results Measures of natal and adult dispersal distance, and the intraspecific variance in these parameters, explain little variation in occupancy in addition to that accounted for by population size. Individual dispersal variables failed to explain significant variance when added individually to a model with population size as a predictor. Migrants and species using wet habitats tend to disperse further than residents and dry habitat species. Analysing these four groups separately revealed effects of dispersal only on the occupancy attained by dry habitat species. Conclusions The only consistent predictor of occupancy in these analyses was population size.

The bioclimatic model: a method of palaeoclimatic qualitative inference based on mammal associations

Abstract: Aim The bioclimatic model is a new method for palaeoclimatic reconstruction built on the assumption of a significant correlation between climate and mammal community composition. The goal of this approach is to infer past climatic conditions using mammal fossil associations as source data. Location The study used mammal faunas from all over the world to develop the bioclimatic model. As an example of the potential of the model, we have applied it to Quaternary faunas from Eurasia. Methods The proposed model was constructed by applying multivariate discriminant analysis to modern mammal faunas and climates from throughout the world. The model was validated with a different set of modern faunas than those used in the discriminant analysis, including some from transitional zones between different climates (ecotones). To test the reliability of the method in the Pleistocene, the results have been compared to those obtained with data from other disciplines, such as palaeobotany. Results The results obtained in the validation of the model show that more than 90% of the localities have been classified correctly. Comparisons of results in the late Pleistocene-Holocene of Barova between a palaeobotanical study and the bioclimatic analysis show the latter to be highly accurate. The results for early Pleistocene faunas show somewhat drier and more open climatic conditions for Europe than the present day, with larger areas of steppe environments. Main Conclusions The bioclimatic model could be used to infer climatic conditions from mammal faunas. The results presented in this work provide a preliminary example of the potential that bioclimatic analysis has as a tool for palaeoclimatic inference. Finally, this method offers the opportunity to standardize data coming from vertebrate palaeontology for use in the construction and evaluation of climatic models.

Colonization front of the understorey palm Astrocaryum sciophilum in a pristine rain forest of French Guiana

Abstract: Aims Astrocaryum sciophilum (Miq.) Pulle (Arecaceae) is an understorey palm, endemic to north-eastern South America with a patchy distribution. We tested the hypothesis that the spatial distribution of this palm species is not in equilibrium but is slowly colonizing the forest understorey. Location Inventories and seed dispersal studies were conducted in the undisturbed tropical forest close to the Nouragues research station, French Guiana. Additional data were collected in the entire territory of French Guiana. Methods We studied the demography of A. sciophilum on a 20-ha plot located at the edge of its distribution. The age of the palms was estimated by postulating an exponentially decreasing abundance by age class. Direct seed dispersal experiments were also conducted, to estimate dispersal parameters. The seeds of A. sciophilum were dispersed only by rodents. This information was used to parameterize a forest growth simulator, to study the spatial spread of this species. Results Within the sampling plot, the density of A. sciophilum dropped sharply from about 500 individuals per hectare to zero. The maturation age was estimated to be 170 ± 70 years, and over 55 years with 95% confidence. Seed-dispersal experiments yielded an average seed dispersal distance of 11 m and a maximum estimated dispersal distance of 125 m across a generational span of 55 years to maturity. Therefore, the maximal estimated colonization speed is 2.3 m/y. Conclusions Empirical results and numerical simulations suggest that the boundary of the A. sciophilum population is a colonization front, and that the range of this species is slowly expanding. The implications of this result in respect of palaeoenvironmental changes in this region are discussed.

The Early Holocene treeline in the southern French Alps: new evidence from travertine formations

Abstract: Aims The present paper concerns the analysis of macroremains (plant imprints) from high altitude travertine deposits dating back to the early Holocene (9800 BP ). Our results allow us to discuss treeline location and ecology, and to supplement previous data based on pollen from natural sediments and charcoal from natural soil. Location The travertine under study is located in the Queyras massif, in the southern French Alps, along the Italian border. The site is situated on a south-facing slope. Methods The travertine deposit has been dated by 230 Th/ 234 U. Taxonomic identification of plant imprints was achieved by comparison of the morphology of fossil specimens with extant material. Results Imprints of Pinus uncinata (cones and needles), broad-leaved trees ( Betula cf. pubescens , Populus tremula and Salix spp.), and unidentified trunks have been found. The plant assemblage records the existence at a high altitude (2200 m) of shade-intolerant vegetation at around 9800 BP . Our data indicate that the treeline limit was at least 100 m higher than previously thought. The morphological features of the travertine, the plant assemblage and trunk diameters indicate that during the travertinization process, vegetation around the site was probably dense with tall upright trees. Main conclusions Our data show that Pinus uncinata and broad-leaved trees developed at 2200 m, while regional pollen analyses locate the treeline at lower altitudes. Different research methods appear to provide different results. Around 9800 BP tree regeneration and growth were made possible up to at least 2200 m a.s.l., probably as a result of warmer and wetter summers. Warmer conditions are inferred from the predicted increase in incoming solar radiation based on calculated orbital variations, and wetter conditions are inferred from the build-up of the travertine.