Soil and Geographic Distance as Determinants of Floristic Composition in the Azuero Peninsula (Panama)

Many studies analyzing the relative contribution of soil properties versus distance‐related processes on plant species composition have focused on lowland tropical forests. Very few have investigated two forest types simultaneously, to contrast ecological processes that assemble the communities. This study analyses—at the landscape scale—the relative contribution of soil and distance on lowland and submontane tropical forests, which co‐occur in two reserves of the Azuero peninsula (Panama). Floristic inventories and soil sampling were conducted in 81 0.1‐ha plots clustered in 27 sites, and data were analyzed using Mantel tests, variance partitioning and non‐metric multidimensional scaling. The largest differences in floristic composition occurred between reserves in both forest types. Soil variation and geographic distance were important determinants of floristic composition, but their effects were highly correlated; together they explained 7–25 percent and 46–50 percent of the variation in lowland and submontane forests, respectively. Soil variables that had the best correlations with floristic composition were iron, zinc, and silt content in lowland, and calcium, copper, iron, potassium, magnesium, phosphorus, zinc, and sand content in submontane forests. The studied forests showed a high beta diversity that seems to be related primarily with soils and, secondarily, with dispersal limitation and stochastic events. The results reveal a response of tree assemblages to environmental gradients, which are particularly conspicuous in Panama. The effects of limited dispersal seem to be more important in submontane than in lowland forests, probably as a result of higher isolation.     

Geographical and environmental controls of palm beta diversity in paleo-riverine terrace forests in Amazonian Peru

The palm (Arecaceae) community on low paleo-riverine terraces (terrace forest) in the north-western Amazon, is described, and we assessed the importance of environmental differences and geographic distance as drivers of its local (25² grain and 0–500 extent) and regional scale (500² grain and 0.3–143 km extent) beta diversity using ordination, multiple regressions on distance matrices and Indicator Species Analysis. A total of 15,869 individuals and 37 species of palm were sampled in 10 terrace forest transects, while 3758 individuals and 21 species were sampled in two adjacent floodplain forest transects for comparison. The terrace and floodplain forest were clearly different in their diversity and floristic composition. The relative importance of geographical distance and environmental difference as controls of terrace forest beta diversity was scale dependent, with environmental differences, notably in soil moisture, dominating at local scales and geographical distance dominating at regional scales. In fact, none of the environmental factors had a significant influence on regional-scale beta diversity. The geographical distance decay in floristic similarity was markedly steeper at local scale ( −0.25 km ⁻¹) than at regional scale ( −0.003 km⁻¹). Such a nonlinear decay is expected if simple dispersal limitation controls beta diversity. However, the absent flattening of the distance decay at the largest distances and the sub-Andean affinities of the westernmost palm communities suggest that large-scale biogeographical processes also contribute to the regional-scale beta diversity. Hereby our results indicate that not only local environment, but also dispersal limitation and biogeographical history can be important controls of the diversity and composition of local plant communities.     

Tree species composition and diversity gradients in white-water forests across the Amazon Basin

Aim Attention has increasingly been focused on the floristic variation within forests of the Amazon Basin. Variations in species composition and diversity are poorly understood, especially in Amazonian floodplain forests. We investigated tree species composition, richness and α diversity in the Amazonian white‐water (várzea) forest, looking particularly at: (1) the flood‐level gradient, (2) the successional stage (stand age), and (3) the geographical location of the forests. Location Eastern Amazonia, central Amazonia, equatorial western Amazonia and the southern part of western Amazonia. Methods The data originate from 16 permanent várzea forest plots in the central and western Brazilian Amazon and in the northern Bolivian Amazon. In addition, revised species lists of 28 várzea forest inventories from across the Amazon Basin were used. Most important families and species were determined using importance values. Floristic similarity between plots was calculated to detect similarity variations between forest types and over geographical distances. To check for spatial diversity gradients, α diversity (Fisher) of the plots was correlated with stand age, longitudinal and latitudinal plot location, and flood‐level gradient. Results More than 900 flood‐tolerant tree species were recorded, which indicates that Amazonian várzea forests are the most species‐rich floodplain forests worldwide. The most important plant families recorded also dominate most Neotropical upland forests, and c. 31% of the tree species listed also occur in the uplands. Species distribution and diversity varied: (1) on the flood‐level gradient, with a distinct separation between low‐várzea forests and high‐várzea forests, (2) in relation to natural forest succession, with species‐poor forests in early stages of succession and species‐rich forests in later stages, and (3) as a function of geographical distance between sites, indicating an increasing α diversity from eastern to western Amazonia, and simultaneously from the southern part of western Amazonia to equatorial western Amazonia. Main conclusions The east‐to‐west gradient of increasing species diversity in várzea forests reflects the diversity patterns also described for Amazonian terra firme. Despite the fine‐scale geomorphological heterogeneity of the floodplains, and despite high disturbance of the different forest types by sedimentation and erosion, várzea forests are dominated by a high proportion of generalistic, widely distributed tree species. In contrast to high‐várzea forests, where floristic dissimilarity increases significantly with increasing distance between the sites, low‐várzea forests can exhibit high floristic similarity over large geographical distances. The high várzea may be an important transitional zone for lateral immigration of terra firme species to the floodplains, thus contributing to comparatively high species richness. However, long‐distance dispersal of many low‐várzea trees contributes to comparatively low species richness in highly flooded low várzea.     

Geographical patterns in the beta diversity of China's woody plants: the influence of space,environment and range size

Beta diversity (i.e. species turnover rate across space) is fundamental for understanding mechanisms controlling large‐scale species richness patterns. However, the influences on beta diversity are still a matter of debate. In particular, the relative role of environmental and spatial processes (e.g. environmental niche versus dispersal limitation of species) remains elusive, and the influence of species range size has been poorly tested. Here, using distribution maps of 11 405 woody species in China (ca 9.6 × 10⁶ km²), we investigated 1) the geographical and directional patterns of beta diversity for all woody species and species with different range sizes, and 2) compared the effects of environmental and spatial processes on these patterns. Beta diversity was calculated as the decay of similarity in species composition with increasing distance. Variables representing environmental energy, water availability, climatic seasonality, habitat heterogeneity and human activities were used to evaluate the effects of environmental processes, while spatial distance was used to assess the influence of spatial processes. The results indicated significant directional patterns of beta diversity: the similarity decay along the latitudinal gradient was 1.6–2.3 times faster than that along the longitudinal gradient. Beta diversity also increased with the decrease of species range size. As compared with spatial processes, environmental processes had stronger effects on longitudinal beta diversity and on the beta diversity of widely‐ranged species. This was opposite to the larger influence of spatial processes on latitudinal beta diversity and the beta diversity of narrowly‐ranged species. These results suggest that the distributions of narrowly‐ranged woody species in China may have not reached equilibrium with their environmental niches due to dispersal limitation induced by China's topography and/or their low dispersal ability. The projected rapid climatic changes will likely endanger such species. Species dispersal processes should be taken into account in future conservation strategies in China.     

Altitudinal Patterns in Two Syntopic Species of Sturnira (Mammalia: Chiroptera: Phyllostomidae) in the Montane Rain Forests of Argentina

We evaluated altitudinal segregation in two Sturnira species as a mechanism allowing their coexistence. Tests were devised to discern between interspecific interactions and regional responses to geographic and environmental variables, using extensive capture data from 18 montane rain forest sites. No significant correlation between captures was found. Additionally and according to the hypothesis of historical occupation of highland versus lowland forests, each species has shown specificity in their response to the geographical and environmental variables. Our results indicated that abundance patterns in these bats likely result from the regional distribution of each species rather than local interactions between them, a pattern that may have ancient roots within the group.     

Beta diversity and oligarchic dominance in the tropical forests of Southern Costa Rica

Recent studies have reported a consistent pattern of strong dominance of a small subset of tree species in neotropical forests. These species have been called “hyperdominant” at large geographical scales and “oligarchs” at regional‐landscape scales when being abundant and frequent. Forest community assembly is shaped by environmental factors and stochastic processes, but so far the contribution of oligarchic species to the variation of community composition (i.e., beta diversity) remains poorly known. To that end, we established 20.1‐ha plots, that is, five sites with four forest types (ridge, slope and ravine primary forest, and secondary forest) per site, in humid lowland tropical forests of southwestern Costa Rica to (a) investigate how community composition responds to differences in topography, successional stage, and distance among plots for different groups of species (all, oligarch, common and rare/very rare species) and (b) identify oligarch species characterizing changes in community composition among forest types. From a total of 485 species of trees, lianas and palms recorded in this study only 27 species (i.e., 6%) were nominated as oligarch species. Oligarch species accounted for 37% of all recorded individuals and were present in at least half of the plots. Plant community composition significantly differed among forest types, thus contributing to beta diversity at the landscape scale. Oligarch species was the component best explained by geographical and topographic variables, allowing a confident characterization of the beta diversity among tropical lowland forest stands. Abstract in Spanish is available with online material.     

Landscape-Scale Environmental and Floristic Variation in Costa Rican Old-Growth Rain Forest Remnants

Studies of tropical rain forest beta-diversity debate environmental determinism versus dispersal limitation as principal mechanisms underlying floristic variation. We examined the relationship between soil characteristics, terrain, climate variation, and rain forest composition across a 3000 km² area in northeastern Costa Rica. Canopy tree and arboreal palm species abundance and soils were measured from 127 0.25-ha plots across Caribbean lowlands and foothills. Plot elevation, slope, temperature, and precipitation variation were taken from digital grids. Ordination of forest data yielded three floristic groups with strong affinities to foothills and differing lowland environments. Variation in floristics, soil texture, and climate conditions showed parallel patterns of significantly positive spatial autocorrelation up to 13 km and significantly negative correlation beyond 40 km. Partial Mantel tests resulted in a significant correlation between floristic distance and terrain, climate and soil textural variables controlling the effect of geographical distance. Separate comparisons for palm species showed significant correlation with Mg and Ca concentrations among other soil factors. Arboreal palm species demonstrated a stronger relationship with soil factors than did canopy trees. Correlation between floristic data and geographical distance, related to seed dispersal or unmeasured variables, was not significant after controlling for soil characteristics and elevation. Canopy trees and palms showed differing relationships to soil and other environmental factors, but lend greater support for a niche-assembly hypothesis than to a major role for dispersal limitation in determining species turnover for this landscape.     

It's a long way to the top: Plant species diversity in the transition from managed to old‐growth forests

Questions

Do vascular plant species richness and beta‐diversity differ between managed and structurally complex unmanaged stands? To what extent do species richness and beta‐diversity relate to forest structural attributes and heterogeneity?

Location

Five national parks in central and southern Italy.

Methods

We sampled vascular plant species composition and forest structural attributes in eight unmanaged temperate mesic forest stands dominated or co‐dominated by beech, and in eight comparison stands managed as high forests with similar environmental features. We compared plant species richness, composition and beta‐diversity across pairs of stands (unmanaged vs managed) using GLMM s. Beta‐diversity was quantified both at the scale of each pair of stands using plot‐to‐plot dissimilarity matrices (species turnover), and across the whole data set, considering the distance in the multivariate species space of individual plots from their centroid within the same stand (compositional heterogeneity). We modelled the relationship between species diversity (richness and beta‐diversity) and forest structural heterogeneity and individual structural variables using GLMM s and multiple regression on distance matrices.

Results

Species composition differed significantly between managed and unmanaged stands, but not richness and beta‐diversity. We found weak evidence that plant species richness increased with increasing levels of structural heterogeneity and canopy diversification. At the scale of individual stands, species turnover was explained by different variables in distinct stands, with variables related to deadwood quantity and quality being selected most often. We did not find support for the hypothesis that compositional heterogeneity varies as a function of forest structural characteristics at the scale of the whole data set.

Conclusions

Structurally complex unmanaged stands have a distinct herb layer species composition from that of mature stands in similar environmental conditions. Nevertheless, we did not find significantly higher levels of vascular plant species richness and beta‐diversity in unmanaged stands. Beta‐diversity was related to patterns of deadwood accumulation, while for species richness the evidence that it increases with increasing levels of canopy diversification was weak. These results suggest that emulating natural disturbance, and favouring deadwood accumulation and canopy diversification may benefit some, but not all, facets of plant species diversity in Apennine beech forests.

     

Distinguishing the importance between habitat specialization and dispersal limitation on species turnover

Understanding what governs community assembly and the maintenance of biodiversity is a central issue in ecology, but has been a continuing debate. A key question is the relative importance of habitat specialization (niche assembly) and dispersal limitation (dispersal assembly). In the middle of the Loess Plateau, northwestern China, we examined how species turnover in Liaodong oak (Quercus wutaishanica) forests differed between observed and randomized assemblies, and how this difference was affected by habitat specialization and dispersal limitation using variation partitioning. Results showed that expected species turnover based on individual randomization was significantly lower than the observed value (P < 0.01). The turnover deviation significantly depended on the environmental and geographical distances (P < 0.05). Environmental and spatial variables significantly explained approximately 40% of the species composition variation at all the three layers (P < 0.05). However, their contributions varied among forest layers; the herb and shrub layers were dominated by environmental factors, whereas the canopy layer was dominated by spatial factors. Our results underscore the importance of synthetic models that integrate effects of both dispersal and niche assembly for understanding the community assembly. However, habitat specialization (niche assembly) may not always be the dominant process in community assembly, even under harsh environments. Community assembly may be in a trait‐dependent manner (e.g., forest layers in this study). Thus, taking more species traits into account would strengthen our confidence in the inferred assembly mechanisms.     

A floristic analysis of the lowland dipterocarp forests of Borneo

Aim To (1) identify floristic regions in the lowland (below 500 m a.s.l.) tropical dipterocarp rain forest of Borneo based on tree genera, (2) determine the characteristic taxa of these regions, (3) study tree diversity patterns within Borneo, and (4) relate the floristic and diversity patterns to abiotic factors such as mean annual rainfall and geographical distance between plots. Location Lowland tropical dipterocarp rain forest of Borneo. Methods We used tree (diameter at breast height ≥ 9.8 cm) inventory data from 28 lowland dipterocarp rain forest locations throughout Borneo. From each location six samples of 640 individuals were drawn randomly. With these data we calculated a Sørensen and Steinhaus similarity matrix for the locations. These matrices were then used in an UPGMA clustering algorithm to determine the floristic relations between the locations (dendrogram). Principal coordinate analysis was used to ordinate the locations. Characteristic taxa for the identified floristic clusters were determined with the use of the INDVAL method of Dufrene & Legendre (1997) . Finally, Mantel analysis was applied to determine the influence of mean annual rainfall and geographical distance between plots on floristic composition. Results A total of 77 families and 363 genera were included in the analysis. On average a random sample of 640 trees from a lowland dipterocarp forest in Borneo contains 41.6 ± 3.8 families and 103.0 ± 12.7 genera. Diversity varied strongly on local scales. On a regional scale, diversity was found to be highest in south‐east Borneo and central Sarawak. The most common families were Dipterocarpaceae (21.9% of trees) and Euphorbiaceae (12.2% of trees). The most common genera were Shorea (12.3% of trees) and Syzygium (5.0% of trees). The 28 locations were clustered in geographically distinct floristic regions. This was related to the fact that floristic similarity depended strongly on the geographical distance between plots and similarity in mean annual rainfall. Conclusions We identified five main floristic regions within the lowland dipterocarp rain forests of Borneo, each of which had its own set of characteristic genera. Mean annual rainfall is an important factor in explaining differences in floristic composition between locations. The influence of geographical distance on floristic similarity between locations is probably related to the fact that abiotic factors change with distance between plots. Borneo's central mountain range generally forms an effective dispersal barrier for the lowland tree flora. Diversity patterns in Borneo are influenced by the mid‐domain effect, habitat size and the influence of past climatic changes (ice ages during the Pleistocene).     

Tree turnover in a premontane neotropical forest (1998–2009) in Costa Rica

Tropical premontane forests between 700 and 1,400 m.a.s.l. represent a particular component of the gamma diversity of neotropical ecosystems; however, the extent of information about their dynamics lags behind the more studied lowland rain forests. Data from three 1-ha permanent plots in a premontane forest in Costa Rica collected during an 11-year period (1998–2009) suggested a high tree turnover rate for this ecosystem (high mortality rate, λ = 2.4% and annual recruitment, μ = 2.6%). The floristic composition did not significantly change during the study period, but its high dynamism (2.4%) exceeded that of several reported values from highly diverse neotropical lowland rain forests. The documented decrease in abundance (8.6%) and basal area (14.3%) of trees ≥10 cm in DBH differs from the general trend of increase described for several lowland tropical rain forests in recent decades. We detected a significant population reduction (>15% of individuals from 1998 to 2009) in several relatively abundant tree species, whereas the populations of the three most dominant species remained nearly constant. The high tree turnover recorded for this premontane forest might not have affected tree diversity; but it might be promoting recruitment and growth of some tree species that may eventually become over-dominant in this ecosystem.     

Contrasting patterns and mechanisms of spatial turnover for native and exotic freshwater fish in Europe

Aim We compare the distribution patterns of native and exotic freshwater fish in Europe, and test whether the same mechanisms (environmental filtering and/or dispersal limitation) govern patterns of decrease in similarity of native and exotic species composition over geographical distance (spatial species turnover). Locations Major river basins of Europe. Methods Data related to geography, habitat diversity, regional climate and species composition of native and exotic freshwater fish were collated for 26 major European river basins. We explored the degree of nestedness in native and exotic species composition, and quantified compositional similarity between river basins according to the beta‐sim (independent of richness gradient) and Jaccard (dependent of richness gradient) indices of similarity. Multiple regression on distance matrices and variation‐partitioning approaches were used to quantify the relative roles of environmental filtering and dispersal limitation in shaping patterns of decreasing compositional similarity over geographical distance. Results Native and exotic species exhibited significant nested patterns of species composition, indicating that differences in fish species composition between river basins are primarily the result of species loss, rather than species replacement. Both native and exotic compositional similarity decreased significantly with increasing geographical distance between river basins. However, gradual changes in species composition with geographical distance were found only for exotic species. In addition, exotic species displayed a higher rate of similarity decay (higher species turnover rate) with geographical distance, compared with native species. Lastly, the majority of explained variation in exotic compositional similarity was uniquely related to geography, whereas native compositional similarity was either uniquely explained by geography or jointly explained by environment and geography. Main conclusions Our study suggests that large‐scale patterns of spatial turnover for exotic freshwater fish in Europe are generated by human‐mediated dispersal limitation, whereas patterns of spatial turnover for native fish result from both dispersal limitation relative to historical events (isolation by mountain ranges, glacial history) and environmental filtering.     

Effects of an Epiphytic Orchid on Arboreal Ant Community Structure in Panama

Epiphytes are conspicuous structural elements of tropical forest canopies. Individual tree crowns in lowland forests may support more than 30 ant species, yet we know little about the effects of epiphytes on ant diversity. We examined the composition of arboreal ant communities on Annona glabra trees and their interactions with the epiphytic orchid Caularthron bilamellatum in Panama. We surveyed the ants on 73 trees (45 with C. bilamellatum and 28 lacking epiphytes) and recorded their nest sites and behavioral dominance at baits. We found a total of 49 ant species (in 20 genera), ranging 1–9 species per tree. Trees with C. bilamellatum had higher average (±SD) ant species richness (4.2±2.28) than trees without epiphytes (2.7±1.21). Hollow pseudobulbs (PBs) of C. bilamellatum were used as nest sites by 32 ant species, but only 43 percent of suitable PBs were occupied. Ant species richness increased with PB abundance in trees, but nest sites did not appear to be a limiting resource on A. glabra. We detected no close association between ants and the orchid. We conclude that higher ant species richness in the presence of the orchid is due to bottom‐up effects, especially the year‐round supply of extrafloral nectar. The structure of ant communities on A. glabra partly reflects interference competition among behaviorally dominant species and stochastic factors, as observed in other forests.     

哀牢山亚热带中山湿性常绿阔叶林树种beta多样性格局形成的驱动力

Beta多样性通常指群落在时间和空间上物种组成的差异, 包括物种周转组分和物种丰富度差异组分。驱动beta多样性格局形成的生态过程决定了群落的时空动态, 然而关于beta多样性及其两个组分格局形成的驱动力还存在较多争议。以往研究表明, beta多样性的格局存在取样尺度的依赖性, 驱动其形成的生态过程在不同取样尺度下的相对重要性也随之改变。本研究以哀牢山亚热带中山湿性常绿阔叶林20 ha动态监测样地为研究对象, 在不同取样尺度上, 将样方间的Bray-Curtis指数分解为物种周转组分和物种丰富度差异组分, 通过典范冗余分析和方差分解的方法揭示环境过滤和扩散限制对于beta多样性及其两个组分格局形成的相对重要性及其尺度依赖性。结果表明: (1) beta多样性、物种周转组分和物种丰富度差异组分均随取样尺度的增大而减小。在不同取样尺度下, 物种周转组分对于beta多样性的贡献始终占主导地位。(2)随着取样尺度的增大, 环境过滤驱动beta多样性格局形成的相对重要性逐渐增加, 而扩散限制的相对重要性逐渐降低。本研究进一步证实了取样尺度在beta多样性格局形成及其驱动力定量评价中的重要性, 今后的研究需要进一步解析上述尺度效应的形成机制。     

Assessing spatial and environmental drivers of phylogenetic structure in Brazilian Araucaria forests

Evidence of phylogenetic conservatism in plant ecological traits has accumulated over the past few years, suggesting an interplay between the distribution of phylogenetic clades and major environmental gradients. Nonetheless, determining what environmental factors underlie the distribution of phylogenetic lineages remains a challenge because environmental factors are correlated with spatial gradients where the latter might indicate some degree of dispersal limitation in phylogenetic pools. We analyzed the phylogenetic structure of plant assemblages across the Brazilian Araucaria forests and assessed how phylogenetic structure responds to environmental and spatial gradients. We compiled data on plant occurrence in 45 plots across the Araucaria forest biome. The phylogenetic structure of the plots was characterized using phylogenetic fuzzy‐weighting followed by principal coordinates of phylogenetic structure (PCPS). We used distance‐based redundancy analysis (db‐RDA) to analyze the relationships between phylogenetic clades and environmental and spatial factors. Variation partitioning showed that the phylogenetic structure of Brazilian Araucaria forests was better explained by environment factors (altitude and annual mean temperature) than by space. Yet, spatially‐structured environmental variation explained about one‐third of total variation in the phylogenetic structure. Thus, the influence of spatial filters on the phylogenetic structure was more related to environmental gradients across the Brazilian Araucaria forest biome than to dispersal limitation of phylogenetic lineages. Furthermore, the influence of explanatory factors on the phylogenetic structure was concentrated in few nodes, the one splitting tree ferns from seed plants, and a second splitting malvids from other eurosids. Assessing the functional links between species distribution patterns and environmental gradients is not an easy task when we have to deal with large species pools. Identifying major phylogenetic gradients across an environmental and/or geographical range of interest can represent a first step towards a better understanding of general assembly processes in ecological communities.     

Biodiversity assessment in incomplete inventories: leaf litter ant communities in several types of Bornean rain forest

Biodiversity assessment of tropical taxa is hampered by their tremendous richness, which leads to large numbers of singletons and incomplete inventories in survey studies. Species estimators can be used for assessment of alpha diversity, but calculation of beta diversity is hampered by pseudo-turnover of species in undersampled plots. To assess the impact of unseen species, we investigated different methods, including an unbiased estimator of Shannon beta diversity that was compared to biased calculations. We studied alpha and beta diversity of a diverse ground ant assemblage from the Southeast Asian island of Borneo in different types of tropical forest: diperocarp forest, alluvial forest, limestone forest and heath forests. Forests varied in plant composition, geology, flooding regimes and other environmental parameters. We tested whether forest types differed in species composition and if species turnover was a function of the distance between plots at different spatial scales. As pseudo-turnover may bias beta diversity we hypothesized a large effect of unseen species reducing beta diversity. We sampled 206 ant species (25% singletons) from ten subfamilies and 55 genera. Diversity partitioning among the four forest types revealed that whereas alpha species richness and alpha Shannon diversity were significantly smaller than expected, beta-diversity for both measurements was significantly higher than expected by chance. This result was confirmed when we used the unbiased estimation of Shannon diversity: while alpha diversity was much higher, beta diversity differed only slightly from biased calculations. Beta diversity as measured with the Chao-Sørensen or Morisita-Horn Index correlated with distance between transects and between sample points, indicating a distance decay of similarity between communities. We conclude that habitat heterogeneity has a high influence on ant diversity and species turnover in tropical sites and that unseen species may have only little impact on calculation of Shannon beta diversity when sampling effort has been high.     

The role of dispersal ability, climate and spatial separation in shaping biogeographical patterns of phylogenetically distant plant groups in seasonally dry Andean forests of Bolivia

Aim To assess biogeographical patterns of Acanthaceae, Bromeliaceae, Cactaceae and Pteridophyta in Bolivian Andean seasonally dry forest islands and to explain current floristic differences between these islands by means of extrinsic (precipitation, elevation) and intrinsic (dispersal ability) factors. Location Ten isolated and disjunct seasonally dry forest areas in the Bolivian Andes and the adjacent seasonal forest areas of the Chiquitanía and Chaco regions. Methods We collated species data from recently updated and revised taxonomic treatments and herbarium collections for Acanthaceae, Bromeliaceae, Cactaceae and Pteridophyta, constructed floristic distance matrices to estimate beta diversity at the study sites and subjected them to Mantel correlation analyses. Multiple regressions on distance matrices allowed us to test the influence of geographical distance and environmental (elevation and precipitation) differences on floristic differentiation. Results Acanthaceae and Bromeliaceae, and to a lesser extent Cactaceae, showed coincident biogeographical patterns and suggested the presence of two seasonally dry forest groups in Andean Bolivia: one including all small isolated northern dry valleys and another including all southern valleys with connections to the lowland seasonal forests of the Chiquitanía and the Chaco. Most of the variation in the floristic distance matrices in these plant groups, with seed dispersal typically restricted to short distances, was explained by spatial separation between habitat islands. In contrast, pteridophytes showed a different biogeographical pattern. Their floristic differences between sites were determined by the environmental variables. The anemochorous and spore‐based dispersal system of this plant group seems to be a highly effective mechanism allowing pteridophytes to easily reach even the isolated dry valleys in inter‐Andean Bolivia. Main conclusions Current biogeographical patterns in dry Andean habitat islands can provide insights into the factors that control the processes of community assembly. We show that differences in community composition of phylogenetically distant plant groups in the understorey of seasonally dry forest islands can be explained by a combination of the habitat characteristics where the group is present (either precipitation, elevation or both) and, more interestingly, by group specific dispersal limitation (as inferred by geographical distance between island habitats).     

Phylogenetic community structure and phylogenetic turnover across space and edaphic gradients in western Amazonian tree communities

Ecological and evolutionary processes influence community assembly at both local and regional scales. Adding a phylogenetic dimension to studies of species turnover allows tests of the extent to which environmental gradients, geographic distance and the historical biogeography of lineages have influenced speciation and dispersal of species throughout a region. We compare measures of beta diversity, phylogenetic community structure and phylobetadiversity (phylogenetic distance among communities) in 34 plots of Amazonian trees across white‐sand and clay terra firme forests in a 60 000 square kilometer area in Loreto, Peru. Dominant taxa in white‐sand forests were phylogenetically clustered, consistent with environmental filtering of conserved traits. Phylobetadiversity measures found significant phylogenetic clustering between terra firme communities separated by geographic distances of <200–300 km, consistent within recent local speciation at the watershed scale in the Miocene‐aged clay‐soil forests near the foothills of the Andes. Although both distance and habitat type yielded statistically significant effects on both species and phylogenetic turnover, the patterns we observed were more consistent with an effect of habitat specialization than dispersal limitation. Our results suggest a role for both broad‐scale biogeographic and evolutionary processes, as well as habitat specialization, influencing community structure in Amazonian forests.     

Competition and Facilitation in the Capuchin–Squirrel Monkey Relationship

In Guyana, the range of the brown capuchin, Cebus apella, meets the range of its congener, the wedge‐capped capuchin, C. olivaceus, with the two species exhibiting a mutually exclusive patchy distribution. Squirrel monkeys, Saimiri sciureus, and C. apella form ubiquitous interspecific associations, but the reason remains debatable. With a large biogeographic field study, we tested the degree to which the distribution and abundance of Cebus and S. sciureus is determined by habitat type, fruit availability, and geography (i.e., determinants of the fundamental niche) relative to interspecific interactions, such as competition and facilitation (i.e., the realized niche). We used the competition between the two capuchin monkeys as a natural experiment that subjected S. sciureus to C. apella and C. olivaceus ‘treatments’. Using spatial regression models and principal components analysis, we found that S. sciureus was associated with seasonally flooded forests, and was correlated with fruit abundance and diversity (fundamental niche), but was also correlated with C. apella density even when accounting for habitat and fruit availability (realized niche). Saimiri sciureus density was unrelated to C. olivaceus density. Cebus apella was associated with a variety of forest types, but particularly included disturbed and edge habitats such as logged forests, seasonally flooded forests, and upland savanna, in addition to mature forest. Cebus apella was also positively correlated with S. sciureus density and negatively correlated with the density of C. olivaceus. In contrast, C. olivaceus avoided riparian areas and was associated with mixed‐height forests on sloped mountainous terrain. In sum, interspecific interactions such as competition between species of Cebus and facilitation between C. apella and S. sciureus were as important as habitat and fruit availability in determining the distribution and abundance of these primates.     

海南岛霸王岭热带低地雨林树木的空间格局

树木空间格局及其形成过程是物种共存及生物多样性维持机制研究的一个重要方面。该文以海南岛两个1 hm ²的典型热带低地雨林老龄林森林动态样地为基础, 通过4个点格局模型(均质Poisson过程、异质Poisson过程、均质Thomas过程和异质Thomas过程)模拟扩散限制和生境异质性作用对树木空间分布格局的影响, 并分析不同空间尺度下(< 2 m, 2-5 m, 5-10 m, 10-15 m, 15-20 m和20-25 m)不同作用的相对重要性。结果表明: 热带低地雨林的所有树木总体上呈现聚集分布的空间格局, 随着尺度的增大, 聚集强度逐渐减小。树种在模拟空间分布格局最优模型中的比例由高到低分别是: 均质Thomas过程, 均质Poisson过程、异质Thomas过程和异质Poisson过程。扩散限制作用是形成热带低地雨林树木空间分布格局最重要的生态过程, 其次是完全随机作用以及生境异质性和扩散限制的联合作用, 而生境异质性的作用最小。不同空间尺度上模拟各树种空间分布格局的最优模型比例差异显著, 扩散限制作用能够在多数空间尺度上模拟多个树种的空间分布格局, 其次为随机作用; 生境异质性和扩散限制的联合作用主要在小尺度(0-5 m)影响树种分布, 而生境异质性在较大尺度(15-25 m)上影响树种的空间分布格局。