Spatial and Temporal Patterns in Macrofaunal Diversity Components Relative to Sea Floor Landscape Structure

We examined temporal changes in macrofaunal α- and β-diversity over several spatial scales (within patches, among patches, across landscapes and across regions) in Long Island Sound on the northeast USA coast. Regional ε-diversity was estimated at 144 taxa, however γ-diversity fluctuated over time as did α- and β-diversity components. Based on additive partitioning, patch- and region-scale β-diversity components generally had the highest contributions to γ-diversity; lower percentages were found at within-patch and landscape scales. Multiplicative diversity partitioning indicated highest species turnover at within- and among patch scales. For all partition results, within-patch and patch-scale β-diversity increased sharply when hypoxia impacted benthic communities. Spatial variation in diversity components can be attributed to the collection of different patch types at varying spatial scales and their associated habitats across the benthic landscapes, as well as gradients in depth and other estuarine-scale characteristics. Temporal variation in diversity components across spatial scales may be related to seasonal changes in habitat heterogeneity, species population dynamics, and seasonal disturbances. Rare species were significant and temporally consistent components of macrofaunal diversity patterns over different spatial scales. Our findings agree with other marine and terrestrial studies that show diversity components vary significantly over different spatial scales and the importance of habitat/landscape heterogeneity in supporting diversity. However, our results indicate that the relative contributions of scale-specific β-diversity components can also change significantly over time. Thus, studies of diversity patterns across patches and landscapes based on data collected at one time, or assembled into a single data set from different times, may not capture the full suite of diversity patterns that occur over varying spatial scales and any time-specific determinants of those patterns. Many factors that shape and maintain sedimentary communities vary temporally, and appear to play an important role in determining and maintaining macrofaunal diversity over different spatial scales.     

退化高寒草甸狼毒发生区土壤真菌多样性的空间变异

狼毒是青藏高原危害最严重的毒草种类之一,其快速蔓延对高寒草甸生态系统的影响日益严重。选取祁连山中段退化高寒草甸为研究区,综合采用高通量测序技术、地统计学和GIS空间分析方法,分析狼毒发生区土壤真菌多样性的空间变异特征,研究狼毒群落与土壤真菌多样性的空间相关性。结果表明: 与非发生区相比,狼毒发生区土壤真菌群落物种丰富度下降而优势度显著增加,α多样性降低;土壤真菌群落物种构成差异增强,β多样性明显升高。狼毒入侵对土壤真菌多样性的空间格局有一定扰动,发生区各多样性指数的斑块破碎化程度增加,土壤真菌群落物种构成的空间异质性明显增强,α和β多样性的空间稳定性降低。狼毒盖度与土壤真菌α和β多样性指数呈现显著正相关及显著负相关的区域交错镶嵌分布,空间相关性规律不明显,表明狼毒入侵草甸土壤真菌多样性的空间变异可能受地上植被和土壤环境的共同作用。     

Computing β-diversity with Rao's quadratic entropy: a change of perspective

Ecologists have traditionally viewed β-diversity as the ratio between γ-diversity and average α-diversity. More recently, an alternative way of partitioning diversity has been proposed for which β-diversity is obtained as the difference between γ-diversity and average α-diversity. Although this additive model of diversity decomposition is generally considered superior to its multiplicative counterpart, in both models β-diversity is a formally derived quantity without any self-contained ecological meaning; it simply quantifies the diversity excess of γ-diversity with respect to average α-diversity. Taking this excess as an index of β-diversity is a questionable operation. In this paper, we show that a particular family of α-diversity measures, the most celebrated of which is Rao's quadratic entropy, can be adequately used for summarizing β-diversity. Our proposal naturally leads to a new additive model of diversity for which, given two or more sets of plots, overall plot-to-plot species variability can be additively partitioned into two non-negative components: average variability in species composition within each set of plots and the species variability between the set of plots. For conservation purposes, the suggested change of perspective in the summarization of β-diversity allows for a flexible analysis of spatial heterogeneity in ecological diversity so that different hierarchical levels of biotic relevance (i.e. from the genetic to the landscape level) can be expressed in a significant and consistent way.     

Additive Partitioning of Coral Reef Fish Diversity across Hierarchical Spatial Scales throughout the Caribbean

There is an increasing need to examine regional patterns of diversity in coral-reef systems since their biodiversity is declining globally. In this sense, additive partitioning might be useful since it quantifies the contribution of alpha and beta to total diversity across different scales. We applied this approach using an unbalanced design across four hierarchical scales (80 sites, 22 subregions, six ecoregions, and the Caribbean basin). Reef-fish species were compiled from the Reef Environmental Education Foundation (REEF) database and distributions were confirmed with published data. Permutation tests were used to compare observed values to those expected by chance. The primary objective was to identify patterns of reef-fish diversity across multiple spatial scales under different scenarios, examining factors such as fisheries and demographic connectivity. Total diversity at the Caribbean scale was attributed to β-diversity (nearly 62% of the species), with the highest β-diversity at the site scale. α¯-diversity was higher than expected by chance in all scenarios and at all studied scales. This suggests that fish assemblages are more homogenous than expected, particularly at the ecoregion scale. Within each ecoregion, diversity was mainly attributed to alpha, except for the Southern ecoregion where there was a greater difference in species among sites. β-components were lower than expected in all ecoregions, indicating that fishes within each ecoregion are a subsample of the same species pool. The scenario involving the effects of fisheries showed a shift in dominance for β-diversity from regions to subregions, with no major changes to the diversity patterns. In contrast, demographic connectivity partially explained the diversity pattern. β-components were low within connectivity regions and higher than expected by chance when comparing between them. Our results highlight the importance of ecoregions as a spatial scale to conserve local and regional coral reef-fish diversity.     

Illumina Sequencing of 16S rRNA Tag Revealed Spatial Variations of Bacterial Communities in a Mangrove Wetland

The microbial community plays an essential role in the high productivity in mangrove wetlands. A proper understanding of the spatial variations of microbial communities will provide clues about the underline mechanisms that structure microbial groups and the isolation of bacterial strains of interest. In the present study, the diversity and composition of the bacterial community in sediments collected from four locations, namely mudflat, edge, bulk, and rhizosphere, within the Mai Po Ramsar Wetland in Hong Kong, SAR, China were compared using the barcoded Illumina paired-end sequencing technique. Rarefaction results showed that the bulk sediment inside the mature mangrove forest had the highest bacterial α-diversity, while the mudflat sediment without vegetation had the lowest. The comparison of β-diversity using principal component analysis and principal coordinate analysis with UniFrac metrics both showed that the spatial effects on bacterial communities were significant. All sediment samples could be clustered into two major groups, inner (bulk and rhizosphere sediments collected inside the mangrove forest) and outer mangrove sediments (the sediments collected at the mudflat and the edge of the mangrove forest). With the linear discriminate analysis scores larger than 3, four phyla, namely Actinobacteria, Acidobacteria, Nitrospirae, and Verrucomicrobia, were enriched in the nutrient-rich inner mangrove sediments, while abundances of Proteobacteria and Deferribacterias were higher in outer mangrove sediments. The rhizosphere effect of mangrove plants was also significant, which had a lower α-diversity, a higher amount of Nitrospirae, and a lower abundance of Proteobacteria than the bulk sediment nearby.     

Niche and metabolic principles explain patterns of diversity and distribution: theory and a case study with soil bacterial communities

The causes of biodiversity patterns are controversial and elusive due to complex environmental variation, covarying changes in communities, and lack of baseline and null theories to differentiate straightforward causes from more complex mechanisms. To address these limitations, we developed general diversity theory integrating metabolic principles with niche-based community assembly. We evaluated this theory by investigating patterns in the diversity and distribution of soil bacteria taxa across four orders of magnitude variation in spatial scale on an Antarctic mountainside in low complexity, highly oligotrophic soils. Our theory predicts that lower temperatures should reduce taxon niche widths along environmental gradients due to decreasing growth rates, and the changing niche widths should lead to contrasting α- and β-diversity patterns. In accord with the predictions, α-diversity, niche widths and occupancies decreased while β-diversity increased with increasing elevation and decreasing temperature. The theory also successfully predicts a hump-shaped relationship between α-diversity and pH and a negative relationship between α-diversity and salinity. Thus, a few simple principles explained systematic microbial diversity variation along multiple gradients. Such general theory can be used to disentangle baseline effects from more complex effects of temperature and other variables on biodiversity patterns in a variety of ecosystems and organisms.     

Contrasting diversity patterns of epigeic arthropods between grasslands of high and low agronomic potential

Increasing demand for food, fuel and fibre promotes the intensification of land-use, particularly in areas favourable for agricultural production. In less-favourable areas, more wildlife-friendly farming systems are often either abandoned or under pressure of conversion, e.g. for bioenergy production. This raises the question, to which extent areas of different agronomic potential contribute to regional biodiversity. To approach this question on a regional scale, we established our study within a region where sites of high and low agronomic potential (AP) alternate on a small spatial scale. We selected 13 high-AP and 13 low-AP grasslands to quantify the contribution of these classes to the regional diversity of four epigeic arthropod taxa (ants, springtails, functional groups of ground beetles, and spiders). The regional diversity (γ) was partitioned into species richness per site (α-diversity), diversity among sites within one class (β_within-diversity), and diversity between the two classes (β_between-diversity). The β-diversity generally accounted for the largest share of the γ-diversity, with patterns of diversity components being highly taxon- and class-specific. Carnivorous carabids had a higher α-diversity at high-AP sites. Ants, springtails, and cursorial spiders had a higher β_within-diversity in low-AP grasslands. Low-AP sites also harboured many more species that occurred exclusively in one grassland class. We conclude that grasslands that may be unfavourable for agricultural production contributed more to regional diversity of epigeic arthropods than favourable grasslands. We therefore suggest that future agricultural schemes should promote arthropod biodiversity by specifically targeting agri-environment schemes or other wildlife-friendly farming approaches to areas of low agronomic potential, since this bears the greatest potential to preserve a comparatively high species turnover (β-diversity) and in consequence high regional diversity.     

Cross-scale analysis of the region effect on vascular plant species diversity in southern and northern European mountain ranges

Background

The divergent glacial histories of southern and northern Europe affect present-day species diversity at coarse-grained scales in these two regions, but do these effects also penetrate to the more fine-grained scales of local communities?

Methodology/Principal Findings

We carried out a cross-scale analysis to address this question for vascular plants in two mountain regions, the Alps in southern Europe and the Scandes in northern Europe, using environmentally paired vegetation plots in the two regions (n = 403 in each region) to quantify four diversity components: (i) total number of species occurring in a region (total γ-diversity), (ii) number of species that could occur in a target plot after environmental filtering (habitat-specific γ-diversity), (iii) pair-wise species compositional turnover between plots (plot-to-plot β-diversity) and (iv) number of species present per plot (plot α-diversity). We found strong region effects on total γ-diversity, habitat-specific γ-diversity and plot-to-plot β-diversity, with a greater diversity in the Alps even towards distances smaller than 50 m between plots. In contrast, there was a slightly greater plot α-diversity in the Scandes, but with a tendency towards contrasting region effects on high and low soil-acidity plots.

Conclusions/Significance

We conclude that there are strong regional differences between coarse-grained (landscape- to regional-scale) diversity components of the flora in the Alps and the Scandes mountain ranges, but that these differences do not necessarily penetrate to the finest-grained (plot-scale) diversity component, at least not on acidic soils. Our findings are consistent with the contrasting regional Quaternary histories, but we also consider alternative explanatory models. Notably, ecological sorting and habitat connectivity may play a role in the unexpected limited or reversed region effect on plot α-diversity, and may also affect the larger-scale diversity components. For instance, plot connectivity and/or selection for high dispersal ability may increase plot α-diversity and compensate for low total γ-diversity.     

Intensive agriculture erodes β-diversity at large scales

Biodiversity is declining from unprecedented land conversions that replace diverse, low-intensity agriculture with vast expanses under homogeneous, intensive production. Despite documented losses of species richness, consequences for β-diversity, changes in community composition between sites, are largely unknown, especially in the tropics. Using a 10-year data set on Costa Rican birds, we find that low-intensity agriculture sustained β-diversity across large scales on a par with forest. In high-intensity agriculture, low local (α) diversity inflated β-diversity as a statistical artefact. Therefore, at small spatial scales, intensive agriculture appeared to retain β-diversity. Unlike in forest or low-intensity systems, however, high-intensity agriculture also homogenised vegetation structure over large distances, thereby decoupling the fundamental ecological pattern of bird communities changing with geographical distance. This ~40% decline in species turnover indicates a significant decline in β-diversity at large spatial scales. These findings point the way towards multi-functional agricultural systems that maintain agricultural productivity while simultaneously conserving biodiversity.     

Scale-Dependence of Processes Structuring Dung Beetle Metacommunities Using Functional Diversity and Community Deconstruction Approaches

Community structure is driven by mechanisms linked to environmental, spatial and temporal processes, which have been successfully addressed using metacommunity framework. The relative importance of processes shaping community structure can be identified using several different approaches. Two approaches that are increasingly being used are functional diversity and community deconstruction. Functional diversity is measured using various indices that incorporate distinct community attributes. Community deconstruction is a way to disentangle species responses to ecological processes by grouping species with similar traits. We used these two approaches to determine whether they are improvements over traditional measures (e.g., species composition, abundance, biomass) for identification of the main processes driving dung beetle (Scarabaeinae) community structure in a fragmented mainland-island landscape in southern Brazilian Atlantic Forest. We sampled five sites in each of four large forest areas, two on the mainland and two on the island. Sampling was performed in 2012 and 2013. We collected abundance and biomass data from 100 sampling points distributed over 20 sampling sites. We studied environmental, spatial and temporal effects on dung beetle community across three spatial scales, i.e., between sites, between areas and mainland-island. The γ-diversity based on species abundance was mainly attributed to β-diversity as a consequence of the increase in mean α- and β-diversity between areas. Variation partitioning on abundance, biomass and functional diversity showed scale-dependence of processes structuring dung beetle metacommunities. We identified two major groups of responses among 17 functional groups. In general, environmental filters were important at both local and regional scales. Spatial factors were important at the intermediate scale. Our study supports the notion of scale-dependence of environmental, spatial and temporal processes in the distribution and functional organization of Scarabaeinae beetles. We conclude that functional diversity may be used as a complementary approach to traditional measures, and that community deconstruction allows sufficient disentangling of responses of different trait-based groups.     

CRCView: a web server for analyzing and visualizing microarray gene expression data using model-based clustering

CRCView is a user-friendly point-and-click web server for analyzing and visualizing microarray gene expression data using a Dirichlet process mixture model-based clustering algorithm. CRCView is designed to clustering genes based on their expression profiles. It allows flexible input data format, rich graphical illustration as well as integrated GO term based annotation/interpretation of clustering results. Availability: http://helab.bioinformatics.med.umich.edu/crcview/.     

Response of soil bacterial communities to moisture and grazing in the Tibetan alpine steppes on a small spatial scale

As the Third Pole of the world, the Tibetan Plateau provides a typical alpine grassland environment for soil bacteria with its unique frigid and arid climate. Owing to clear changes in spatial moisture and increased grazing intensity, moisture and livestock grazing have become key factors influencing the microbial communities. Accordingly, we investigated the diversity and composition of soil bacteria in a selected alpine grassland within the dual gradients of moisture and grazing using high-throughput sequencing. Our results showed that grazing changed the soil bacterial diversity and composition, whereas moisture only influenced the relative abundance of the segmental community at the small spatial scale. Species richness was found to be increased by moderate grazing compared with that by high or low-grazing intensity. The relative abundance of dominant species and β-diversity of soil bacteria both showed differences with heavy, moderate, and low grazing. Some dominant bacteria were altered with the moisture content. However, there were no significant differences according to the moisture gradient in terms of the overall bacterial β diversity and composition. These results might be taken account into the small spatial scale as well as the compensation of grazing to moisture on this scale. This work provides new insights into the soil bacterial response to moisture gradients and grazing intensity in alpine steppe habitat.     

Vegetation structure determines insect herbivore diversity in seasonally dry tropical forests

Vegetation structure can often determine insect herbivore fauna in forests, but this mechanism has been demonstrated in seasonally dry tropical forests (SDTFs) only at small spatial scales. In this study we evaluated the effects of the geographical location of SDTFs and vegetation structure on insect herbivore communities (leaf-chewing and sap-sucking guilds) in three Brazilian ecoregions (Cerrado, Cerrado/Caatinga transition, and Caatinga). We tested the following predictions: (1) insect herbivore species composition, richness, abundance and beta diversity differ among forests in different ecoregions; (2) insect richness, abundance and beta diversity are positively related to tree richness and density; (3) spatial turnover of species is the primary mechanism that generates herbivorous insect β-diversity in different ecoregions, and is positively influenced by tree richness. The composition, richness, and abundance of herbivorous insects differed over SDFs along the gradient of Cerrado and Caatinga. Both herbivore guilds responded positively to tree richness. Tree density only determined the richness and abundance of sap-sucking herbivores. Insect β-diversity was similar among Cerrado and transition areas, but lower in Caatinga itself; β-diversity was also positively affected by tree richness. Species turnover, as opposed to nestedness, was the main mechanism generating β-diversity, but itself was not related to tree richness. We demonstrate in this study the importance of landscape diversity and availability of local resources for herbivorous insect communities, and we emphasize the importance of SDTF conservation in different ecoregions as a result of species turnover.     

Elevational Gradients in β-Diversity Reflect Variation in the Strength of Local Community Assembly Mechanisms across Spatial Scales

Despite long-standing interest in elevational-diversity gradients, little is known about the processes that cause changes in the compositional variation of communities (β-diversity) across elevations. Recent studies have suggested that β-diversity gradients are driven by variation in species pools, rather than by variation in the strength of local community assembly mechanisms such as dispersal limitation, environmental filtering, or local biotic interactions. However, tests of this hypothesis have been limited to very small spatial scales that limit inferences about how the relative importance of assembly mechanisms may change across spatial scales. Here, we test the hypothesis that scale-dependent community assembly mechanisms shape biogeographic β-diversity gradients using one of the most well-characterized elevational gradients of tropical plant diversity. Using an extensive dataset on woody plant distributions along a 4,000-m elevational gradient in the Bolivian Andes, we compared observed patterns of β-diversity to null-model expectations. β-deviations (standardized differences from null values) were used to measure the relative effects of local community assembly mechanisms after removing sampling effects caused by variation in species pools. To test for scale-dependency, we compared elevational gradients at two contrasting spatial scales that differed in the size of local assemblages and regions by at least an order of magnitude. Elevational gradients in β-diversity persisted after accounting for regional variation in species pools. Moreover, the elevational gradient in β-deviations changed with spatial scale. At small scales, local assembly mechanisms were detectable, but variation in species pools accounted for most of the elevational gradient in β-diversity. At large spatial scales, in contrast, local assembly mechanisms were a dominant force driving changes in β-diversity. In contrast to the hypothesis that variation in species pools alone drives β-diversity gradients, we show that local community assembly mechanisms contribute strongly to systematic changes in β-diversity across elevations. We conclude that scale-dependent variation in community assembly mechanisms underlies these iconic gradients in global biodiversity.     

东灵山辽东栎林木本植物多样性的研究

应用α多样性和β多样性指数对东灵山地区辽东栎林在不同样地环境梯度的物种多样性进行了初步研究。结果表明:不同样地梯度的辽东栎林乔灌木物种α多样性逐步降低,但变化幅度较小,群落物种组成趋于简单。不同样地梯度内辽东栎林乔木物种的β多样性的二元属性测度与数量数据测度结果反映出乔木物种和灌木物种对整个辽东栎林多样性的影响是不同的。数量数据β多样性测度综合地考虑了物种数与物种数量对β多样性变化的影响,适于对单优群落物种多样性进行分析。在中海拔样地梯度,辽东栎林乔灌木物种各样地对之间的β多样性数值较小,表明辽东栎林内物种替代速率较低,物种组成相对稳定,总体上是比较稳定的林型。     

Euxinic freshwater hypolimnia promote bacterial endemicity in continental areas

Bacteria and archaea represent the vast majority of biodiversity on Earth. The ways that dynamic ecological and evolutionary processes interact in the microbial world are, however, poorly known. Here, we have explored community patterns of planktonic freshwater bacteria inhabiting stratified lakes with oxic/anoxic interfaces and euxinic (anoxic and sulfurous) water masses. The interface separates a well-oxygenated upper water mass (epilimnion) from a lower anoxic water compartment (hypolimnion). We assessed whether or not the vertical zonation of lakes promoted endemism in deeper layers by analyzing bacterial 16S rRNA gene sequences from the water column of worldwide distributed stratified lakes and applying a community ecology approach. Community similarity based on the phylogenetic relatedness showed that bacterial assemblages from the same water layer were more similar across lakes than to communities from different layer within lakes and that anoxic hypolimnia presented greater β-diversity than oxic epilimnia. Higher β-diversity values are attributable to low dispersal and small connectivity between community patches. In addition, surface waters had significant spatial but non-significant environmental components controlling phylogenetic β-diversity patterns, respectively. Conversely, the bottom layers were significantly correlated with environment but not with geographic distance. Thus, we observed different ecological mechanisms simultaneously acting on the same water body. Overall, bacterial endemicity is probably more common than previously thought, particularly in isolated and environmentally heterogeneous freshwater habitats. We argue for a microbial diversity conservation perspective still lacking in the global and local biodiversity preservation policies.     

Recurrent landslides affect the functional beta diversity of a megadiverse tropical forest

Background: Natural disturbance is an important factor that contributes to structuring plant communities. In tropical mountain areas, landslides are frequent and could enhance the diversity in mountain forests. However, the spatial scale in which landslide affect diversity is not known.

Aims: To investigate whether landslides affect taxonomic and functional diversity at different spatial scales. We tested if: (1) taxonomic and functional α-diversity were lower in areas with landslide history; (2) the taxonomic β-diversity was high while the functional β-diversity was low in landslide-affected areas; and (3) plants in areas with landslide history would have, on average, smaller and thicker leaves, with greater pubescence, lower specific leaf area and higher dry matter content.

Methods: At five sites in the Atlantic Forest, we sampled five 5 m × 5 m plots in areas with recent landslide history (from 2 to 39 years) and in adjacent control areas. We identified all juvenile trees (30–100 cm in height) and measured their leaf traits.

Results: Taxonomic α-diversity and functional β-diversity and the occurrence of leaves with trichomes were greater in areas affected by landslide.

Conclusion: The habitat heterogeneity in areas subject to recurrent landslides influenced the functional dispersion and the structuring of plant communities.     

Contrasting diversity patterns of soil mites and nematodes in secondary succession

Soil biodiversity has been recognized as a key feature of ecosystem functioning and stability. However, soil biodiversity is strongly impaired by agriculture and relatively little is known on how and at what spatial and temporal scales soil biodiversity is restored after the human disturbances have come to an end. Here, a multi-scale approach was used to compare diversity patterns of soil mites and nematodes at four stages (early, mid, late, reference site) along a secondary succession chronosequence from abandoned arable land to heath land. In each field four soil samples were taken during four successive seasons. We determined soil diversity within samples (α-diversity), between samples (β-diversity) and within field sites (γ-diversity). The patterns of α- and γ-diversity developed similarly along the chronosequence for oribatid mites, but not for nematodes. Nematode α-diversity was highest in mid- and late-successional sites, while γ-diversity was constant along the chronosequence. Oribatid mite β-diversity was initially high, but decreased thereafter, whereas nematode β-diversity increased when succession proceeded; indicating that patterns of within-site heterogeneity diverged for oribatid mites and nematodes. The spatio-temporal diversity patterns after land abandonment suggest that oribatid mite community development depends predominantly on colonization of new taxa, whereas nematode community development depends on shifts in dominance patterns. This would imply that at old fields diversity patterns of oribatid mites are mainly controlled by dispersal, whereas diversity patterns of nematodes are mainly controlled by changing abiotic or biotic soil conditions. Our study shows that the restoration of soil biodiversity along secondary successional gradients can be both scale- and phylum-dependent.     

A spatial model of tree α-diversity and tree density for the Amazon

Large-scale patterns of Amazonian biodiversity have until now been obscured by a sparse and scattered inventory record. Here we present the first comprehensive spatial model of tree -diversity and tree density in Amazonian rainforests, based on the largest-yet compilation of forest inventories and bolstered by a spatial interpolation technique that allows us to estimate diversity and density in areas that have never been inventoried. These data were then compared to continent-wide patterns of rainfall seasonality. We find that dry season length, while only weakly correlated with average tree -diversity, is a strong predictor of tree density and of maximum tree -diversity. The most diverse forests for any given DSL are concentrated in a narrow latitudinal band just south of the equator, while the least diverse forests for any given DSL are found in the Guayana Shield and Amazonian Bolivia. Denser forests are more diverse than sparser forests, even when we used a measure of diversity that corrects for sample size. We propose that rainfall seasonality regulates tree -diversity and tree density by affecting shade tolerance and subsequently the number of different functional types of trees that can persist in an area.