Coarse‐scale plant species richness in relation to environmental heterogeneity

Abstract. We test to what extent mean environmental conditions and environmental heterogeneity are related to species richness in a regular geographical grid system (UTM) of 10 km × 10 km in the NE Iberian Peninsula (i.e. Catalonia, ca. 31 900 km²). Species richness of each UTM quadrat was estimated by compiling a large database (more than a million records) from bibliographic references and atlases. Mean environmental conditions of each quadrat were derived from climatic maps. Environmental heterogeneity was estimated from the diversity of geological substrates and climatic classes in each quadrat. The increase in effective (real) area due to topographic complexity was also considered (derived from the digital elevation model). The statistical analysis was performed by a weighted analysis of deviance assuming a negative binomial error distribution. The results suggest that species richness in the study area is a function of both within‐quadrat heterogeneity (specifically, effective area, heterogeneity of geological substrates, heterogeneity of January temperature) and mean environmental conditions (mean annual temperature, Thornthwaite moisture index and aspect). All these parameters showed a positive relationship with species richness. Quadrat heterogeneity accounted for ca. 2/3 of the explained deviance, suggesting the importance of environmental heterogeneity when using a geographical grid system. The study fits well with earlier results on the importance of climatic parameters on plant species richness and provides one of the few rigorous, quantitative, coarse‐scale studies testing environmental heterogeneity in plant species richness.     

Predicting patterns of plant species richness in megadiverse South Africa

Using new tools (boosted regression trees) in predictive biogeography, with extensive spatial 23 distribution data for >19 000 species, we developed predictive models for South African plant species richness patterns. Further, biome level analysis explored possible functional determinants of country‐wide regional species richness. Finally, to test model reliability independently, we predicted potential alien invasive plant species richness with an independent dataset. Amongst the different hypotheses generally invoked to explain species 30 diversity (energy, favorableness, topographic heterogeneity, irregularity and seasonality), results revealed topographic heterogeneity as the most powerful single explanatory variable for indigenous South African plant species richness. Some biome‐specific responses were observed, i.e. two of the five analyzed biomes (Fynbos and Grassland) had richness best explained by the “species‐favorableness” hypothesis, but even in this case, topographic heterogeneity was also a primary predictor. This analysis, the largest conducted on an almost exhaustive species sample in a species‐rich region, demonstrates the preeminence of topographic heterogeneity in shaping the spatial pattern of regional plant species richness. Model reliability was confirmed by the considerable predictive power for alien invasive species richness. It thus appears that topographic heterogeneity controls species richness in two main ways: firstly, by providing an abundance of ecological niches in contemporary space (revealed by alien invasive species richness relationships) and secondly, by facilitating the persistence of ecological niches through time. The extraordinary richness of the South African Fynbos biome, a world‐renowned hotspot of biodiversity with the steepest environmental gradients in South Africa, may thus have arisen through both mechanisms. Comparisons with similar regions of the world outside South Africa are needed to confirm the generality of topographic heterogeneity and favorableness as predictors of plant richness.     

Patterns of species richness for vascular plants in China's nature reserves

Explaining the heterogeneous distribution of biodiversity across the Earth has long been a challenge to ecologists and biogeographers. Here, we document the patterns of plant species richness for different taxonomic groups in China's nature reserves, and discuss their possible explanations at national and regional scales, using vascular plant richness data coupled with information on climate and topographical variables. We found that water deficit, energy and elevation range (a surrogate of habitat heterogeneity) represent the primary explanations for variation in plant species richness of the nature reserves across China. There are consistent relationships between species richness and climate and habitat heterogeneity for different taxonomic vascular plant groups at the national scale. Habitat heterogeneity is strongly associated with plant richness in all regions, whereas climatic constraints to plant diversity vary regionally. In the regions where energy is abundant or water is scarce, plant richness patterns were determined by water and habitat heterogeneity, whereas in the region with low energy inputs, water interacting with energy, and habitat heterogeneity determined its species richness pattern. Our results also suggest that energy variables alone do not represent the primary predictor of plant richness.     

Net primary productivity and seasonality of temperature and precipitation are predictors of the species richness of the Damselflies in the Amazon

Several hypotheses have been proposed to explain the mechanisms that generate temporal and spatial species richness patterns. We tested four common hypotheses (water, energy, climatic heterogeneity and net primary productivity) to evaluate which factors best explain patterns of Zygoptera species richness. Of these, we predicted that climatic heterogeneity would be the most important predictor for Zygoptera richness patterns. We sampled communities of adult Zygoptera in 100 small Amazonian streams. Based on generalized linear mixed models (GLMM), we found that net primary productivity and climatic heterogeneity comprised the best model of Zygoptera species richness in Amazonian streams, with an pseudo r² of 39.5%. Results indicate that species richness increases by one species per 1 kg of biomass per square meter in NPP, or with an increase of 2 °C in air temperature variability. Our work corroborates a recent study with other taxa in Brazilian Bioms. This suggests that temporal variation in climate and net primary productivity are important predictors of the macroecological patterns of richness for aquatic organisms in tropical regions.     

Energy–water and seasonal variations in climate underlie the spatial distribution patterns of gymnosperm species richness in China

Studying the pattern of species richness is crucial in understanding the diversity and distribution of organisms in the earth. Climate and human influences are the major driving factors that directly influence the large‐scale distributions of plant species, including gymnosperms. Understanding how gymnosperms respond to climate, topography, and human‐induced changes is useful in predicting the impacts of global change. Here, we attempt to evaluate how climatic and human‐induced processes could affect the spatial richness patterns of gymnosperms in China. Initially, we divided a map of the country into grid cells of 50 × 50 km² spatial resolution and plotted the geographical coordinate distribution occurrence of 236 native gymnosperm taxa. The gymnosperm taxa were separated into three response variables: (a) all species, (b) endemic species, and (c) nonendemic species, based on their distribution. The species richness patterns of these response variables to four predictor sets were also evaluated: (a) energy–water, (b) climatic seasonality, (c) habitat heterogeneity, and (d) human influences. We performed generalized linear models (GLMs) and variation partitioning analyses to determine the effect of predictors on spatial richness patterns. The results showed that the distribution pattern of species richness was highest in the southwestern mountainous area and Taiwan in China. We found a significant relationship between the predictor variable set and species richness pattern. Further, our findings provide evidence that climatic seasonality is the most important factor in explaining distinct fractions of variations in the species richness patterns of all studied response variables. Moreover, it was found that energy–water was the best predictor set to determine the richness pattern of all species and endemic species, while habitat heterogeneity has a better influence on nonendemic species. Therefore, we conclude that with the current climate fluctuations as a result of climate change and increasing human activities, gymnosperms might face a high risk of extinction.     

黄河流域被子植物和陆栖脊椎动物丰富度格局及其影响因子

生物多样性的大尺度空间分布格局及其形成机制一直是生态学和生物地理学的核心内容。黄河流域是我国重要的生态屏障, 明确该区域动植物多样性分布格局及其影响因素, 对我国黄河流域生态保护和高质量发展具有重要意义。本研究通过收集黄河流域被子植物和陆栖脊椎动物分布数据, 结合气候、环境异质性和人类活动等信息, 探讨了黄河流域被子植物和陆栖脊椎动物物种丰富度格局及其主要影响因素。结果表明, 黄河流域被子植物和陆栖脊椎动物物种丰富度在区域尺度具有相似的分布格局: 南部山地动植物物种丰富度最高, 而东部高寒区和北部干旱区物种丰富度最低。回归树模型表明, 冠层高度范围和净初级生产力范围分别是黄河流域被子植物和陆栖脊椎动物物种丰富度最重要的预测因子; 当移除空间自相关影响后, 环境异质性和气候因子依然对区域尺度的动植物物种丰富度具有较高且相似的解释度。表明环境异质性和气候共同决定了黄河流域被子植物和陆栖脊椎动物物种丰富度格局, 而人类使用土地面积并不是影响黄河流域动植物物种丰富度格局的主要因子。因此, 在未来的研究中若针对不同区域筛选出更精准的环境驱动因子或选用更多不同类别的环境异质性因子进行分析, 将有助于更深入理解物种多样性格局的成因。     

Leaf miner and plant galler species richness on Acacia: relative importance of plant traits and climate

Diversity patterns of herbivores have been related to climate, host plant traits, host plant distribution and evolutionary relationships individually. However, few studies have assessed the relative contributions of a range of variables to explain these diversity patterns across large geographical and host plant species gradients. Here we assess the relative influence that climate and host plant traits have on endophagous species (leaf miners and plant gallers) diversity across a suite of host species from a genus that is widely distributed and morphologically variable. Forty-six species of Acacia were sampled to encapsulate the diversity of species across four taxonomic sections and a range of habitats along a 950 km climatic gradient: from subtropical forest habitats to semi-arid habitats. Plant traits, climatic variables, leaf miner and plant galler diversity were all quantified on each plant species. In total, 97 leaf mining species and 84 plant galling species were recorded from all host plants. Factors that best explained leaf miner richness across the climatic gradient (using AIC model selection) included specific leaf area (SLA), foliage thickness and mean annual rainfall. The factor that best explained plant galler richness across the climatic gradient was C:N ratio. In terms of the influence of plant and climatic traits on species composition, leaf miner assemblages were best explained by SLA, foliage thickness, mean minimum temperature and mean annual rainfall, whilst plant gall assemblages were explained by C:N ratio, %P, foliage thickness, mean minimum temperature and mean annual rainfall. This work is the first to assess diversity and structure across a broad environmental gradient and a wide range of potential key climatic and plant trait determinants simultaneously. Such methods provide key insights into endophage diversity and provide a solid basis for assessing their responses to a changing climate.     

The relationship between the spectral diversity of satellite imagery,habitat heterogeneity,and plant species richness

Assessment of habitat heterogeneity and plant species richness at the landscape scale is often based on intensive and extensive fieldwork at great cost of time and money. We evaluated the use of satellite imagery as a quantitative measure of the relationship between the spectral diversity of satellite imagery, habitat heterogeneity, and plant species richness. A 16 km² portion of a military training area in Germany was systematically sampled by plant taxonomic experts on a grid of one hundred 1-ha plots. The diversity of disturbance types, resulting habitat heterogeneity, and plant species richness were determined for each plot. Using an IKONOS multispectral satellite image, we examined 168 metrics of spectral diversity as potential indicators of those independent variables. Across all potential relationships, a simple count of values per spectral band per plot, after compressing the data from the original 11-bit format with 2048 potential values per band into a maximum of 100 values per band, resulted in the most consistent predictor for various metrics of habitat heterogeneity and plant species richness. The count of values in the green band generally out-performed the other bands. The relationship between spectral diversity and plant species richness was stronger than for measures of habitat heterogeneity. Based on the results, we conclude that remotely sensed assessment of spectral diversity, when coupled with limited ground-truthing, can provide reasonable estimates of habitat heterogeneity and plant species richness across broad areas.     

Ice age legacies in the geographical distribution of tree species richness in Europe

Aim This study uses a high‐resolution simulation of the Last Glacial Maximum (LGM) climate to assess: (1) whether LGM climate still affects the geographical species richness patterns in the European tree flora and (2) the relative importance of modern and LGM climate as controls of tree species richness in Europe. Location The parts of Europe that were unglaciated during the LGM. Methods Atlas data on the distributions of 55 tree species were linked with data on modern and LGM climate and climatic heterogeneity in a geographical information system with a 60‐km grid. Four measures of species richness were computed: total richness, and richness of the 18 most restricted species, 19 species of medium incidence (intermediate species) and 18 most widespread species. We used ordinary least‐squares regression and spatial autoregressive modelling to test and estimate the richness–climate relationships. Results LGM climate constituted the best single set of explanatory variables for richness of restricted species, while modern climate and climatic heterogeneity was best for total and widespread species richness and richness of intermediate species, respectively. The autoregressive model with all climatic predictors was supported for all richness measures using an information‐theoretic approach, albeit only weakly so for total species richness. Among the strongest relationships were increases in total and intermediate richness with climatic heterogeneity and in restricted richness with LGM growing‐degree‐days. Partial regression showed that climatic heterogeneity accounted for the largest unique variation fraction for intermediate richness, while LGM climate was particularly important for restricted richness. Main conclusions LGM climate appears to still affect geographical patterns of tree species richness in Europe, albeit the relative importance of modern and LGM climate depends on range size. Notably, LGM climate is a strong richness control for species with a restricted range, which appear to still be associated with their glacial refugia.     

Patterns of woody plant species richness in the Iberian Peninsula: environmental range and spatial scale

Aim Climate‐based models often explain most of the variation in species richness along broad‐scale geographical gradients. We aim to: (1) test predictions of woody plant species richness on a regional spatial extent deduced from macro‐scale models based on water–energy dynamics; (2) test if the length of the climate gradients will determine whether the relationship with woody species richness is monotonic or unimodal; and (3) evaluate the explanatory power of a previously proposed ‘water–energy’ model and regional models at two grain sizes. Location The Iberian Peninsula. Methods We estimated woody plant species richness on grid maps with c. 2500 and 22,500 km² cell size, using geocoded data for the individual species. Generalized additive models were used to explore the relationships between richness and climatic, topographical and substrate variables. Ordinary least squares regression was used to compare regional and more general water–energy models in relation to grain size. Variation partitioning by partial regression was applied to find how much of the variation in richness was related to spatial variables, explanatory variables and the overlap between these two. Results Water–energy dynamics generate important underlying gradients that determine the woody species richness even over a short spatial extent. The relationships between richness and the energy variables were linear to curvilinear, whereas those with precipitation were nonlinear and non‐monotonic. Only a small fraction of the spatially structured variation in woody species richness cannot be accounted for by the fitted variables related to climate, substrate and topography. The regional models accounted for higher variation in species richness than the water–energy models, although the water–energy model including topography performed well at the larger grain size. Elevation range was the most important predictor at all scales, probably because it corrects for ‘climatic error’ due to the unrealistic assumption that mean climate values are evenly distributed in the large grid cells. Minimum monthly potential evapotranspiration was the best climatic predictor at the larger grain size, but actual evapotranspiration was best at the smaller grain size. Energy variables were more important than precipitation individually. Precipitation was not a significant variable at the larger grain size when examined on its own, but was highly significant when an interaction term between itself and substrate was included in the model. Main conclusions The significance of range in elevation is probably because it corresponds to several aspects that may influence species diversity, such as climatic variability within grid cells, enhanced surface area, and location for refugia. The relative explanatory power of energy and water variables was high, and was influenced by the length of the climate gradient, substrate and grain size of the analysis. Energy appeared to have more influence than precipitation, but water availability is also determined by energy, substrate and topographic relief.     

Experimental tests of the dependence of arthropod diversity on plant diversity

ABSTRACT Because a diversity of resources should support a diversity of consumers, most models predict that increasing plant diversity increases animal diversity. We report results of a direct experimental test of the dependence of animal diversity on plant diversity. We sampled arthropods in a well-replicated grassland experiment in which plant species richness and plant functional richness were directly manipulated. In simple regressions, both the number of species planted ([Formula: see text] transformed) and the number of functional groups planted significantly increased arthropod species richness but not arthropod abundance. However, the number of species planted was the only significant predictor of arthropod species richness when both predictor variables were included in ANOVAs or a MANOVA. Although highly significant, arthropod species richness regressions had low [Formula: see text] values, high intercepts (24 arthropod species in monocultures), and shallow slopes. Analyses of relations among plants and arthropod trophic groups indicated that herbivore diversity was influenced by plant, parasite, and predator diversity. Furthermore, herbivore diversity was more strongly correlated with parasite and predator diversity than with plant diversity. Together with regression results, this suggests that, although increasing plant diversity significantly increased arthropod diversity, local herbivore diversity is also maintained by, and in turn maintains, a diversity of parasites and predators.     

Relationships between species richness of vascular plants and terrestrial vertebrates in China: analyses based on data of nature reserves

The relationship between plant diversity and animal diversity on a broadscale and its mechanisms are uncertain. In this study, we explored this relationship and its possible mechanisms using data from 186 nature reserves across China on species richness of vascular plants and terrestrial vertebrates, and climatic and topographical variables. We found significant positive correlations between species richness in almost all taxa of vascular plants and terrestrial vertebrates. Multiple regression analyses indicated that plant richness was a significant predictor of richness patterns for terrestrial vertebrates (except birds), suggesting that a causal association may exist between plant diversity and vertebrate diversity in China. The mechanisms for the relationships between species richness of plants and animals are probably dependent on vertebrate groups. For mammals (endothermic vertebrates), this relationship probably represents the integrated effects of plants on animals through trophic links (i.e. providing foods) and non-trophic interactions (i.e. supplying habitats), whereas for amphibians and reptiles (ectothermic vertebrates), this may be a result of the non-trophic links, such as the effects of plants on the resources that amphibians and reptiles require.     

Local diversity of arable weeds increases with landscape complexity

Patterns of plant diversity are often related to local site conditions and to competitive interactions, but landscape context may also be important for local plant species richness. This is shown here by analysing the relationship between landscape complexity and local species richness of arable weeds in wheat fields. The fields were located in 18 landscapes characterised by a gradient in landscape complexity from structurally complex to structurally simple (39–94% arable land). We quantified local site conditions, field management intensity and landscape characteristics, and used principle component analyses to ordinate the environmental variables. The percentage of arable land was negatively correlated with perimeter–area ratio, habitat-type diversity and topographical heterogeneity, but landscape characteristics did not correlate with local site conditions and field management intensity. The number of plant species was mainly related to landscape characteristics and to a lesser extent to field management intensity (nitrogen fertilisation), whereas local soil characteristics did not contribute to the explanation of arable weed richness. In a geographic scale analysis using circular landscape sectors ranging from 1 km up to 5 km diameter, the predictive power of landscape complexity for local plant species richness was strongest at 2 km indicating a scale-dependent relationship between landscape context and plant species richness. Our results support the hypothesis that local plant species richness in arable fields is greatly influenced by processes operating at the landscape scale. Seed rain from ruderal source habitats and disturbed edges may be the most important underlying process.     

Evidence for indirect effects of plant diversity and composition on net nitrification

Abiotic controls on net nitrification rates are well documented, but the potential effects of plants on this important ecosystem process are poorly understood. We evaluated four structural equation models to determine the relative importance of plant community composition, aboveground herbaceous production, and plant species richness on nitrifier abundance and net nitrification following restoration treatments in a ponderosa pine forest. Model selection criteria indicated that species richness was the best predictor of nitrifier abundance, but a model that included community composition effects also had some support in the data. Model results suggest that net nitrification was indirectly related to plant species richness via a positive relationship between species richness and nitrifier abundance. Community composition was indirectly related to nitrifier abundance through its relationship with species richness. Our model indicates that species-rich plant communities dominated by C₃ graminoids and legumes are associated with soils that have high abundances of nitrifiers. This study highlights the complexity of deciphering effects of ecological treatments on a system response when multiple interacting factors are simultaneously affected. Our results suggest that plant diversity and composition can both respond to forest thinning, prescribed fire and fuel manipulations, and can be factors that might indirectly influence an ecosystem process such as nitrification. Ecological restoration treatments designed to increase plant diversity and alter community composition may have cascading effects on below-ground processes.     

Spatial patterns of woody plant and bird diversity: functional relationships or environmental effects?

Aim To understand cross‐taxon spatial congruence patterns of bird and woody plant species richness. In particular, to test the relative roles of functional relationships between birds and woody plants, and the direct and indirect environmental effects on broad‐scale species richness of both groups. Location Kenya. Methods Based on comprehensive range maps of all birds and woody plants (native species > 2.5 m in height) in Kenya, we mapped species richness of both groups. We distinguished species richness of four different avian frugivore guilds (obligate, partial, opportunistic and non‐frugivores) and fleshy‐fruited and non‐fleshy‐fruited woody plants. We used structural equation modelling and spatial regressions to test for effects of functional relationships (resource–consumer interactions and vegetation structural complexity) and environment (climate and habitat heterogeneity) on the richness patterns. Results Path analyses suggested that bird and woody plant species richness are linked via functional relationships, probably driven by vegetation structural complexity rather than trophic interactions. Bird species richness was determined in our models by both environmental variables and the functional relationships with woody plants. Direct environmental effects on woody plant richness differed from those on bird richness, and different avian consumer guilds showed distinct responses to climatic factors when woody plant species richness was included in path models. Main conclusions Our results imply that bird and woody plant diversity are linked at this scale via vegetation structural complexity, and that environmental factors differ in their direct effects on plants and avian trophic guilds. We conclude that climatic factors influence broad‐scale tropical bird species richness in large part indirectly, via effects on plants, rather than only directly as often assumed. This could have important implications for future predictions of animal species richness in response to climate change.     

Relationships between spatial environmental heterogeneity and plant species diversity on a limestone pavement

No empirical studies have examined the relationship between diversity and spatial heterogeneity across unimodal species richness gradients. We determined the relationships between diversity and environmental factors for 144 0.18 m² plots in a limestone pavement alvar in southern Ontario, Canada, including within-plot spatial heterogeneity in soil depth, microtopography and microsite composition. Species richness was unimodally related to mean soil depth and relative elevation. Microsite heterogeneity and soil depth heterogeneity were positively correlated with species richness, and the richness peaks of the unimodal gradients correspond to the maximally spatially heterogeneous plots. The best predictive models of species richness and evenness, however, showed that other factors, such as ramet density and flooding, are the major determinants of diversity in this system. The findings that soil depth heterogeneity had effects on diversity when the effects of mean soil depth were factored out, and that unimodal richness peaks were associated with high spatial heterogeneity in environmental factors represent significant contributions to our understanding of how spatial heterogeneity might contribute to diversity maintenance in plant communities.     

Scale-specific correlations between habitat heterogeneity and soil fauna diversity along a landscape structure gradient

Habitat heterogeneity contributes to the maintenance of diversity, but the extent that landscape-scale rather than local-scale heterogeneity influences the diversity of soil invertebrates—species with small range sizes—is less clear. Using a Scottish habitat heterogeneity gradient we correlated Collembola and lumbricid worm species richness and abundance with different elements (forest cover, habitat richness and patchiness) and qualities (plant species richness, soil variables) of habitat heterogeneity, at landscape (1 km²) and local (up to 200 m²) scales. Soil fauna assemblages showed considerable turnover in species composition along this habitat heterogeneity gradient. Soil fauna species richness and turnover was greatest in landscapes that were a mosaic of habitats. Soil fauna diversity was hump-shaped along a gradient of forest cover, peaking where there was a mixture of forest and open habitats in the landscape. Landscape-scale habitat richness was positively correlated with lumbricid diversity, while Collembola and lumbricid abundances were negatively and positively related to landscape spatial patchiness. Furthermore, soil fauna diversity was positively correlated with plant diversity, which in turn peaked in the sites that were a mosaic of forest and open habitat patches. There was less evidence that local-scale habitat variables (habitat richness, tree cover, plant species richness, litter cover, soil pH, depth of organic horizon) affected soil fauna diversity: Collembola diversity was independent of all these measures, while lumbricid diversity positively and negatively correlated with vascular plant species richness and tree canopy density. Landscape-scale habitat heterogeneity affects soil diversity regardless of taxon, while the influence of habitat heterogeneity at local scales is dependent on taxon identity, and hence ecological traits, e.g. body size. Landscape-scale habitat heterogeneity by providing different niches and refuges, together with passive dispersal and population patch dynamics, positively contributes to soil faunal diversity. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Relation between environmental variables and aquatic megafauna in a first order stream of the Atlantic Forest, southern Brazil

The study was done in a first order stream in the southern portion of the Brazilian Atlantic Rain Forest. Samples of the aquatic megafauna (amphibians, crustaceans and fishes) were taken with the aim of describing spatial (longitudinal) and temporal (seasonal) patterns in species composition and abundance. Thirty four structural and limnological variables at macro and mesoscales from three sampling reaches were analysed. The spatio-temporal analysis of species richness and diversity indicated a gradient in which values increased in an upstream–downstream direction, independently of the season of the year. The results showed a strong influence of structural environmental variables on community structure. Furthermore, they revealed a hierarchical relation between macroscale and mesoscale variables and their influence on community abundance and composition in the various spatio-temporal sampling units analysed. The spatial distribution of species richness and diversity in the Carvão creek was strongly influenced by the presence of waterfalls, being progressively richer and more diverse downstream. Waterfalls seem to function as selective filters more than as absolute barriers, presenting different efficiencies for different species.     

Relationships between the density and diversity of floral resources and flower visitor activity in a temperate grassland community

Abstract 1. Does the diversity and abundance of one trophic level affect another? Several studies at the landscape level have found a positive relationship between the diversity of floral resources and the diversity and abundance of pollinators. However, little is known about the relationship between these trophic levels on a smaller spatial scale, and the importance of blossom density relative to plant species richness in predicting abundance and richness of different flower visitor groups. 2. This study used a small‐scale approach to investigate how, and if, the diversity and abundance of floral resources in study plots affected the visitation activity of different flower visitor groups. During 201 observation periods between late May and mid‐August 2003, 3682 visits were observed. Bumblebees (60%), muscoids (17%), syrphids (9%), and beetles (5%) were the most abundant flower visitors. 3. Regression analysis was used to investigate the relationship between blossom density and plant species richness with visitation activity, including the probability of presence in plots, the visits within plots, and the visitor richness of the most abundant pollinator groups. 4. The activity of beetles, bumblebees, and muscoids was positively predicted by the variation in blossom density, while syrphid activity was better predicted by plant species richness. Overall, the models for beetles and bumblebees explained much more of the variation in activity compared with the models for the dipterans, and blossom density was a better predictor of both flower visitor richness and activity than was plant species richness.     

Plant species richness–environment relationships across the Subantarctic–Patagonian transition zone

Aim To evaluate the relative importance of climate, productivity, environmental heterogeneity, biotic associations and habitat use by cattle to account for the species richness of trees, shrubs and herbs across the Subantarctic–Patagonian transition. Location An area of c. 150 × 150 km, within the transition zone between the Subantarctic and Patagonian subregions on the eastern slope of the Andes (c. 39–42° S, 70–72° W). Methods All vascular plants found at each one of 50 (10 × 10 m) sampling plots were counted to estimate the local tree, shrub and herb species richness. Path analysis was used to evaluate the relationship between the richness of the three life‐forms and plant cover, dried litter biomass, mean annual temperature, annual precipitation, daily temperature range, substrate heterogeneity and number of faecal pats. Principal coordinates of neighbour matrices was used to model the spatial autocorrelation of the data. Results Total plant species richness showed a unimodal pattern of spatial variation across the transition. Richness responded positively to indirect effects of precipitation mediated through plant cover, but there was a negative overall effect of precipitation on richness towards the west of the transition, most strongly for trees. An increase in substrate heterogeneity promoted a local increase in herb and shrub richness; the richness of trees increased in sites with steeper slopes. Canopy closure had a direct negative impact on herb richness; it also increased the local accumulation of litter, which negatively affected shrub and herb richness. The impact of habitat use by cattle negatively affected herb richness in areas to the east of the biogeographical transition. Main conclusions We suggest that the importance of indirect climatic effects mediated by vegetation cover can account for species richness patterns across this transition, most strongly for woody species, which supports the productivity hypothesis. The southern temperate forests towards the west may represent a deviation from the predictions of the water–energy dynamics hypothesis. Dissimilar spatial patterns of variation in the richness of woody and herbaceous species, and their different responses to climatic and heterogeneity variables across the transition, suggest that plant life‐form influences the plant species richness–environment relationships.