亚热带-温带气候过渡区落叶阔叶林物种-生境关联分析

物种-生境关联分析有利于更好地理解物种共存理论和群落构建机制。根据秦岭落叶阔叶林25 hm²固定监测样地的调查数据,将树种分为幼苗、幼树和成树3个生活阶段,利用Torus-translation检验方法分析物种与不同生境类型之间的关联性。结果表明: 生境对各物种的影响不同。与高坡显著关联的物种数最多,其中95.7%为负关联;与低坡呈负相关的物种占89.5%;与山脊呈显著负关联的物种占90.9%;物种与高谷生境多存在显著正关联,呈负相关的只有1种,占0.03%。物种在幼苗、幼树和成树阶段与生境分别存在80、44和23个关联,表明幼苗阶段对生境的依赖程度更大。幼苗阶段的物种中有38个(占总物种数的90.5%)至少与一类生境存在显著的关联性;幼树阶段有25个(占总物种数的58.1%)至少与一类生境存在显著关联;成树阶段只有17个(占总物种数的39.5%)至少与一类生境存在显著关联。同一生境对不同生活史阶段物种的影响存在差异,到生活史阶段后期,生境的影响逐渐减弱。由于特定的环境需求,多数物种在不同生活史阶段表现出不同的生境偏好。     

Exploring tree-habitat associations in a Chinese subtropical forest plot using a molecular phylogeny generated from DNA barcode loci

Elucidating the ecological mechanisms underlying community assembly in subtropical forests remains a central challenge for ecologists. The assembly of species into communities can be due to interspecific differences in habitat associations, and there is increasing evidence that these associations may have an underlying phylogenetic structure in contemporary terrestrial communities. In other words, by examining the degree to which closely related species prefer similar habitats and the degree to which they co-occur, ecologists are able to infer the mechanisms underlying community assembly. Here we implement this approach in a diverse subtropical tree community in China using a long-term forest dynamics plot and a molecular phylogeny generated from three DNA barcode loci. We find that there is phylogenetic signal in plant-habitat associations (i.e. closely related species tend to prefer similar habitats) and that patterns of co-occurrence within habitats are typically non-random with respect to phylogeny. In particular, we found phylogenetic clustering in valley and low-slope habitats in this forest, indicating a filtering of lineages plays a dominant role in structuring communities in these habitats and we found evidence of phylogenetic overdispersion in high-slope, ridge-top and high-gully habitats, indicating that distantly related species tended to co-occur in these high elevation habitats and that lineage filtering is less important in structuring these communities. Thus we infer that non-neutral niche-based processes acting upon evolutionarily conserved habitat preferences explain the assembly of local scale communities in the forest studied.     

Nature and Age of Neighbours Matter: Interspecific Associations among Tree Species Exist and Vary across Life Stages in Tropical Forests

Detailed information about interspecific spatial associations among tropical tree species is scarce, and hence the ecological importance of those associations may have been underestimated. However, they can play a role in community assembly and species diversity maintenance. This study investigated the spatial dependence between pairs of species. First, the spatial associations (spatial attraction and spatial repulsion) that arose between species were examined. Second, different sizes of trees were considered in order to evaluate whether the spatial relationships between species are constant or vary during the lifetime of individuals. Third, the consistency of those spatial associations with the species-habitat associations found in previous studies was assessed. Two different tropical ecosystems were investigated: a montane cloud forest and a lowland moist forest. The results showed that spatial associations among species exist, and these vary among life stages and species. The rarity of negative spatial interactions suggested that exclusive competition was not common in the studied forests. On the other hand, positive interactions were common, and the results of this study strongly suggested that habitat associations were not the only cause of spatial attraction among species. If this is true, habitat associations and density dependence are not the only mechanisms that explain species distribution and diversity; other ecological interactions, such as facilitation among species, may also play a role. These spatial associations could be important in the assembly of tropical tree communities and forest succession, and should be taken into account in future studies.     

Strong plant-soil associations in a heterogeneous subtropical broad-leaved forest

The relative importance of deterministic and neutral processes on community assembly is currently a topic of much debate among ecologists. Analyzing species-environment associations is an effective way to assess the importance of deterministic process such as niche differentiation, but both habitat association and dispersal limitation can produce similar patterns of spatial aggregation in species. Therefore, it is crucial to control for the impact of dispersal limitation on species distributions when analyzing species-environment associations. We sampled soil with high resolutions in a 24 ha stem-mapped subtropical forest and tested plant-soil associations. We controlled for the influence of dispersal limitation by employing the homogeneous Thomas process to simulate the effect of dispersal limitation on the aggregation of tree species. After controlling for the effect of dispersal limitation, we found that the spatial heterogeneity of soil properties was associated with distributions of 88.2% (90 of 102 species) of tree species in this subtropical forest. Furthermore, not only did soil properties influence the distribution of tree species, but also tree species tended to affect properties of the soil around them. The soil factors most strongly influencing species distributions were TC, TN, TP, K, Mg, Si, soil moisture, and bulk density. We found the spatial heterogeneity of soil properties to be strongly associated with tree species distributions. Niche partitioning of soil gradients contributed substantially to species coexistence in this subtropical forest.     

Higher treefall rates on slopes and waterlogged soils result in lower stand biomass and productivity in a tropical rain forest

1.  Relationships between tropical rain forest biomass and environmental factors have been determined at regional scales, e.g. the Amazon Basin, but the reasons for the high variability in forest biomass at local scales are poorly understood. Interactions between topography, soil properties, tree growth and mortality rates, and treefalls are a likely reason for this variability.
2.  We used repeated measurements of permanent plots in lowland rain forest in French Guiana to evaluate these relationships. The plots sampled topographic gradients from hilltops to slopes to bottomlands, with accompanying variation in soil waterlogging along these gradients. Biomass was calculated for >175 tree species in the plots, along with biomass productivity and recruitment rates. Mortality was determined as standing dead and treefalls.
3.  Treefall rates were twice as high in bottomlands as on hilltops, and tree recruitment rates, radial growth rates and the abundance of light-demanding tree species were also higher.
4.  In the bottomlands, the mean wood density was 10% lower than on hilltops, the basal area 29% lower and the height:diameter ratio of trees was lower, collectively resulting in a total woody biomass that was 43% lower in bottomlands than on hilltops.
5.  Biomass productivity was 9% lower in bottomlands than on hilltops, even though soil Olsen P concentrations were higher in bottomlands.
6.   Synthesis . Along a topographic gradient from hilltops to bottomlands there were higher rates of treefall, which decreased the stand basal area and favoured lower allocation to height growth and recruitment of light-demanding species with low wood density. The resultant large variation in tree biomass along the gradient shows the importance of determining site characteristics and including these characteristics when scaling up biomass estimates from stand to local or regional scales.     

Differential effects of local habitat and landscape characteristics on bird communities in Mediterranean afforestations motivated by the EU Common Agrarian Policy

We investigated the effects of local habitat structure and surrounding landscape characteristics (proportion of land use types and connectedness) on species density and composition of bird communities inhabiting the interior of young tree plantations on former cropland in central Spain, which were motivated by the Common Agrarian Policy. Variation of species density (number of species/0.78 ha) among tree plantations showed different environmental associations across seasons: local habitat was more important than landscape characteristics during winter, whereas they were similarly important during spring. Species density increased with the development of the tree layer in winter and with the presence of urban areas around tree plantations and cover of the herbaceous layer within them in the breeding season. We identified 15 species that exhibit high relative abundance in woodland habitats within the Mesomediterranean region of Central Spain that were absent in both seasons in the studied tree plantations, which were an attractive habitat for urban exploiter species but an unfavorable habitat for the regional forest species pool except for forest generalist species. Composition of bird assemblages was more related to local habitat structure than to landscape characteristics around tree plantations and was rather similar in winter and spring seasons. The very different effects of local habitat and landscape characteristics on bird communities make difficult suggesting management practices with positive effects for all avifauna species during the entire year. We conclude that the small size and low maturity of the studied tree plantations do not contribute to enhancing the bird diversity value of current CAP aids to afforest former cropland with pines in the Mediterranean region.     

Geographical distributions in tropical trees: can geographical range predict performance and habitat association in co‐occurring tree species?

Aim A major floristic and climatic transition from aseasonal to seasonal evergreen tropical forest (the Kangar–Pattani Line; KPL) exists in the Indo‐Sundaic region of Southeast Asia. Mechanisms constraining species distribution here are at present poorly understood, but it is hypothesized that species differ in their tolerances of abiotic factors, in particular water availability. Under this hypothesis, we anticipate differences in performance or habitat preferences, or both, of species differing in distribution with respect to the KPL. The aim of this study is to test whether geographical distributions can be used to explain variation in growth, mortality and habitat preferences in co‐occurring tree species differing in their distribution in relation to the KPL. Location Pasoh Forest Reserve, Negeri Sembilan, Malaysia; south of the KPL. Methods All tree species within a 50‐ha forest dynamics plot were classified as widespread or southern based upon their distributions in relation to the KPL and as habitat specialists or generalists based on spatial association with soil‐based habitat categories. Growth and mortality rates, variation in growth and mortality with respect to soil type, and levels of habitat association were quantified for species with different geographical distributions. Results Differences existed in species performance based upon geographical distributions. Specifically, widespread species had lower growth rates than did species restricted to the aseasonal forests. Mortality rates did not differ as a function of geographical distribution. The growth responses of species to soil habitats also diverged, such that differences in performance of widespread species among soil types were more conservative than those of species restricted in their distribution to the aseasonal forests. However, the proportion of species showing positive habitat associations did not differ significantly between widespread and southern species. Main conclusions Distribution‐based differences in species performance and response to soil type support the hypothesis that species tolerant of wider climatic variation perform less well in any given environment due to limitations on plasticity. These performance differences provide quantitative evidence of the role of climatic transitions in determining tree species distributions in relation to the Kangar–Pattani Line in the Indo‐Malay region. Such differences in performance have important implications for our understanding of biodiversity gradients and responses of Indo‐Sundaic forests to climate change.     

Differential Responses of Dipterocarp Seedlings to Soil Moisture and Microtopography

Niche diversification is prominent among the mechanisms proposed to explain tropical rain forest tree diversity, with many studies focusing on trade‐offs among shade tolerance and growth. Less obvious is the impact of occasional, ephemeral and often minor disturbances on tree seedling survival. We propose that differential tolerances to soil waterlogging can contribute to the distribution of tree seedling communities along microtopographical gradients. We test this hypothesis experimentally by evaluating survival and performance of planted seedlings across microtopographical gradients in a periodically inundated tropical rain forest environment. Survival and relative growth rates were assessed for six Shorea (Dipterocarpaceae) species in Sepilok Forest Reserve (Sabah, Malaysia) over a 2‐yr period, during which seedlings were subjected to two brief flooding events. The species were selected on the basis of soil habitat affinities, with two species being primarily associated with low‐lying alluvial flats subject to inundation, two being associated with non‐flooded mudstone hills, and two species occurring in both habitats. Seedling performance was related to microtopographic elevation within and among plots and to soil moisture among plots. The faster growing species, Shorea argentifolia, Shorea leprosula and Shorea parvifolia, tended to be more vulnerable to high soil moisture in terms of mortality than the three species with lower growth rates. Within plots, soil moisture was inversely correlated with microelevation, and seedlings located at higher microelevations had an increased probability of survival. Microtopographical differences in seedling position could therefore contribute to species assembly processes through differential mortality, particularly in areas subject to minor and ephemeral flooding events.     

Inter-specific aggression generates ant mosaics in canopies of primary tropical rainforest

The ant mosaic is a concept of the non-random spatial distribution of individual ant species in trees built upon the assumption of interspecific behavioural associations. However, colony identity and environmental variance may also play a role in species distribution. Here we assess the presence of ant mosaics in a primary forest ecosystem and whether they are structured by species' aggressive behaviours or by habitat filtering. We sampled arboreal ants from vertically stratified baits exposed in 225 canopy trees in a 9-ha plot of primary lowland forest in Papua New Guinea, the largest forest area surveyed to detect ant mosaics. We performed behavioural tests on conspecific ants from adjacent trees to determine the territories of individual colonies. We explored the environmental effects on the ant communities using information on the plot vegetation structure and topography. Furthermore, we created a novel statistical method to test for the community non-random spatial structure across the plot via spatial randomisation of individual colony territories. Finally, we linked spatial segregation among the four most common species to experimentally assessed rates of interspecies aggression. The ant communities comprised 57 species of highly variable abundance and vertical stratification. Ant community composition was spatially dependent, but it was not affected by tree species composition or canopy connectivity. Only local elevation had a significant but rather small effect. Individual colony territories ranged from one tree to 0.7 ha. Species were significantly over-dispersed, with their territory overlap significantly reduced. The level of aggression between pairs of the four most common species was positively correlated with their spatial segregation. Our study demonstrates the presence of ant mosaics in tropical pristine forest, which are maintained by interspecific aggression rather than habitat filtering, with vegetation structure having a rather small and indirect effect, probably linked to microclimate variability.     

百山祖常绿阔叶林灌草层物种组成和 分布的10年动态

森林群落的动态受多方面因素的影响。林下的草本植物和木本植物幼苗幼树对于森林的更新及动态具有重要作用。为了解百山祖常绿阔叶林群落下层植物物种组成和分布的动态变化, 我们分析了2003-2013年间百山祖5 ha森林动态样地灌草层物种(包括DBH < 1 cm的木本植物和所有草本植物)在物种重要值、α多样性以及物种分布等方面的变化。结果表明: (1) 10年间, 群落灌草层植物个体数减少了28.7%, 其中草质藤本植物个体数下降比例最大(76.9%), 而乔木的幼苗和幼树下降比例最小(14.4%); (2)整个灌草层的物种数明显下降, 同时乔木的幼苗和幼树及直立灌木的均匀度均下降, 而草本植物均匀度有所上升; (3)除短尾柯(Lithocarpus brevicaudatus)、叶萼山矾(Symplocos phyllocalyx)、显脉野木瓜(Stauntonia conspicua)和福建悬钩子(Rubus fujianensis)等植物重要值逆势上扬外, 直立灌木物种重要值10年间的变化值与其在2003年时的重要值呈显著正相关, 而其余各类生活型植物都显示, 初始重要值越高的物种在10年后下降幅度越大; (4)物种分布与生境类型的相关性变化复杂, 除与山谷生境正相关的物种数量增加外, 研究期间与生境存在显著相关性的物种数都有所减少; (5) 10年来仅陡坡处物种多样性指数没有显著下降。总体来说, 百山祖常绿阔叶林灌草层群落仍未达到顶极状态, 2003-2013年间正缓慢向顶极群落演替。群落内部的种间和种内竞争应是当前群落动态的主导因素。     

Aboveground Roots in Amazonian Floodplain Trees1

Sediment‐rich rivers seasonally flood central Amazonian várzea forests, leading to periodic anoxic conditions in the rhizosphere and requiring morphological and structural adaptations, such as aboveground root systems. We investigated some possible relationships between root types and environmental factors in forest plots covering 3.1 ha of várzea in the Mamirauá Sustainable Development Reserve, Brazil. Digital elevation models of the study sites were obtained; sedimentation and soil texture were investigated to check relationship between position of trees on the flood gradient, soil conditions, and aboveground root systems. Different types of aboveground roots were closely related to flooding duration and habitat dynamics. Species subjected to higher and more prolonged floods tended to produce more aboveground roots than species subjected to lower and shorter inundations. Plank‐buttressing species increased with decreasing flood height and/or flood duration, and with increasing growth height and basal area. Habitats inundated for long periods were dominated by species with low growth heights and low basal areas, which formed stilt roots and aerial roots. Root system and sediment deposition showed a close relationship, plank buttressing being more common in sites subjected to lower sediment rates. In the disturbed sites close to the main river channel colonized by pioneer species, the occurrence of buttresses was lower than in less disturbed climax stages. No clear relationship was found between root systems and sediment grain sizes.     

Species‐habitat associations change in a subtropical forest of China

Question: Do tree and shrub species in an evergreen broadleaf forest show similar habitat associations across different life stages? Location: A 24‐ha evergreen broadleaf forest plot in a heterogeneous landscape in Gutianshan National Nature Reserve, Zhejiang Province, Eastern China. Methods: Species having positive associations with four habitat types (low valley, low ridge, upper valley, and upper ridge) at three life stages (sapling, juvenile, and mature stages) were compared for 60 tree and shrub species using torus‐translation tests. Results: A total of 117 significant positive associations with the four habitats were observed at the three life stages (43, 41, and 33 at the sapling, juvenile, and mature stages, respectively). For the 52 species significantly associated with habitats, only 16 were associated with the same habitat across all three stages. The majority of associated species at the juvenile stage (34 out of 40) were associated with the same habitat at their sapling stage, whereas half of species at the mature stage had consistent associations with the same habitat at their sapling stage. More species were associated with the upper ridge at the sapling and juvenile stages compared to the mature stage. Conversely, more species were associated with the low valley at the mature stage compared to the sapling and juvenile stages. Conclusions: Our results indicate that species ecological habitat associations can differ between developmental stages beyond 1 cm DBH, as most species habitat preferences were consistent from the sapling stage to the juvenile stage but changed at the mature stage.     

A taxonomic comparison of local habitat niches of tropical trees

The integration of ecology and evolutionary biology requires an understanding of the evolutionary lability in species’ ecological niches. For tropical trees, specialization for particular soil resource and topographic conditions is an important part of the habitat niche, influencing the distributions of individual species and overall tree community structure at the local scale. However, little is known about how these habitat niches are related to the evolutionary history of species. We assessed the relationship between taxonomic rank and tree species’ soil resource and topographic niches in eight large (24–50 ha) tropical forest dynamics plots. Niche overlap values, indicating the similarity of two species’ distributions along soil or topographic axes, were calculated for all pairwise combinations of co-occurring tree species at each study site. Congeneric species pairs often showed greater niche overlap (i.e., more similar niches) than non-congeneric pairs along both soil and topographic axes, though significant effects were found for only five sites based on Mantel tests. No evidence for taxonomic effects was found at the family level. Our results indicate that local habitat niches of trees exhibit varying degrees of phylogenetic signal at different sites, which may have important ramifications for the phylogenetic structure of these communities.     

Woody plant communities of isolated Afromontane cloud forests in Taita Hills,Kenya

In the Taita Hills in southern Kenya, remnants of the original Afromontane forest vegetation are restricted to isolated mountain peaks. To assess the level of degradation and the need for forest restoration, we examined how forest plant communities and their indicator species vary between and within remnant patches of cloud forest. We used ordinal abundance data to compare plant communities in eight forest fragments. We also analyzed data on the diversity and abundance of trees in 57 0.1 ha plots to compare tree communities within and between the largest two of these fragments, Ngangao (120 ha) and Mbololo (220 ha). The extant vegetation of the Taita Hills at landscape scale consists of secondary moist montane to intermediate montane forest. There was a high species dissimilarity between fragments (69%). Variation in species composition coincided with an abiotic gradient related to elevation. At plot level, secondary successional species and species of forest edges were most abundant and most frequent. Inferred clusters of plots almost entirely coincided with the two forest fragments. Indicator species associated with forest margins and gaps were more frequent in the smaller of the two forest fragments, while indicators for the larger fragment were more typical for less disturbed moist forest. Abiotic site variability but also different levels of disturbance determine site-specific variants of the montane forest. Conservation efforts should not only focus on maintaining forest quantity (size), but also on forest quality (species composition). Late-successional rainforest species are underrepresented in the woody plant communities of the Taita Hills and assisting restoration of viable populations of cloud forest climax tree species is urgently needed.     

Bryophyte Species Diversity in Secondary Forests Dominated by the Introduced Species Spathodea campanulata Beauv. in Puerto Rico

The introduced tree species Spathodea campanulata (Bignoniaceae) forms novel forests in Puerto Rico, these having emerged after the abandonment of fields in the mid‐20th century and resulting in forests with a new species composition. We assessed bryophyte species richness in these novel forests and sought correlations with geological substrate, past land use, forest edge and patch area, forest structure, elevation, microhabitat diversity, tree species richness, and microclimatic conditions. Transects were established (edge and forest interior) in nine moist forest patches dominated by Spathodea in north‐central Puerto Rico. These Spathodea forest patches ranged from 0.6 to 9 ha. ANOVA, Chi‐square, correlation, and cluster analyses were used in data analyses. We found 57 bryophyte species. There was a significant difference in bryophyte richness among patches. Those on karst exhibited highest bryophyte richness due to microhabitat diversity, past land use, and shorter hydroperiods. Alluvial sites scored lowest in bryophyte species richness, and forest structure was important for bryophyte communities on these sites. Significant differences in temperature, relative humidity, and light intensity were observed between edge and forest interior. These appeared important for establishing bryophyte species cover but not richness and composition. Microhabitat diversity, patch area, and forest age were more related to bryophyte species richness than elevation, exposed edge, and tree species richness, regardless of geologic substrate. Collectively, Spathodea patches were similar to mature forests on the Island with respect to bryophyte species richness and composition. Novel Spathodea forests have conservation value due to their habitat suitability for bryophyte communities.     

Developing landscape habitat models for rare amphibians with small geographic ranges: a case study of Siskiyou Mountains salamanders in the western USA

To advance the development of conservation planning for rare species with small geographic ranges, we determined habitat associations of Siskiyou Mountains salamanders (Plethodon stormi) and developed habitat suitability models at fine (10 ha), medium (40 ha), and broad (202 ha) spatial scales using available Geographic Information Systems data and logistic regression analysis with an information theoretic approach. Across spatial scales, there was very little support for models with structural habitat features, such as tree canopy cover and conifer diameter. Model-averaged 95% confidence intervals for regression coefficients and associated odds ratios indicated that the occurrence of Siskiyou Mountains salamanders was positively associated with rocky soils and Pacific madrone (Abutus menziesii) and negatively associated with elevation and white fir (Abies concolor); these associations were consistent across 3 spatial scales. The occurrence of this species also was positively associated with hardwood density at the medium spatial scale. Odds ratios projected that a 10% decrease in white fir abundance would increase the odds of salamander occurrence 3.02–4.47 times, depending on spatial scale. We selected the model with rocky soils, white fir, and Oregon white oak (Quercus garryana) as the best model across 3 spatial scales and created habitat suitability maps for Siskiyou Mountains salamanders by projecting habitat suitability scores across the landscape. Our habitat suitability models and maps are applicable to selection of priority conservation areas for Siskiyou Mountains salamanders, and our approach can be easily adapted to conservation of other rare species in any geographical location.     

Impacts of an Extreme Precipitation Event on Dipterocarp Mortality and Habitat Filtering in a Bornean Tropical Rain Forest

The frequency of extreme precipitation events is predicted to increase in some tropical regions in response to global climate change, but the impacts of this form of disturbance on the structure and dynamics of tropical tree communities across heterogeneous landscapes remain understudied. We determined the effects of an extreme precipitation event (EPE) in July 2006 on mortality of dipterocarps on a 68 ha permanent inventory plot in Sepilok Forest Reserve, Sabah. For stems ≥30 cm dbh, 12 of the 15 species of Dipterocarpaceae on this plot have significant positive and/or negative associations to habitats defined by topography and soil type. Short‐term mortality induced by the EPE was much greater for individuals growing on the alluvial floodplain (13.7%) than in the mudstone (1.4%) or sandstone (0.0%) habitats, but mortality of dipterocarps did not differ among these habitats in the subsequent 5‐yr interval. The likelihood of mortality in response to the EPE was highest for a small group of fast growing dipterocarps that possess low wood density and a strong association to the alluvial forest habitat. This group of species represents a high percentage of dipterocarp individuals but a low proportion of dipterocarp diversity in this habitat. We conclude that disturbance induced by high rainfall events contributes to the episodic nature of tropical forest dynamics, and that increases in the frequency of these events would disproportionately impact low‐lying alluvial forest environments and some of the species growing in them.     

Habitat specificity and diversity of tree species in an African wet tropical forest

Niche differentiation with respect to habitat has been hypothesized to shape patterns of diversity and species distributions in plant communities. African forests have been reported to be relatively less diverse compared to highly diversed regions of the Amazonian or Southeast Asian forests, and might be expected to have less niche differentiation. We examined patterns of structural and floristic differences among five topographically defined habitats for 494 species with stems ≥1 cm dbh in a 50-ha plot in Korup National Park, Cameroon. In addition, we tested for species–habitat associations for 272 species (with more than 50 individuals in the plot) using Torus translation randomization tests. Tree density and basal area were lowest in areas with negative convexity, which contained streams or were inundated during rainy periods and highest in moist well-drained habitats. Species composition and diversity varied along the topographical gradient from low flat to ridge top habitats. The low depression and low flat habitats were characterized by high diversity and similar species composition, relative to slopes, high gullies and ridge tops. Sixty-three percent of the species evaluated showed significant positive associations with at least one of the five habitat types. The majority of associations were with low depressions (75 species) and the fewest with ridge tops (8 species). The large number of species–habitat associations and the pronounced contrast between low (valley) and elevated (ridgetop) habitats in the Korup plot shows that niche differentiation with respect to edaphic variables (e.g., soil moisture, nutrients) contributes to local scale tree species distributions and to the maintenance of diversity in African forests.     

Seasonal and habitat differences in the abundance of primates in the Amazon (Tapajos) National Park,Brazil

Twelve species of primates occur in the Amazon (Tapajós) National Park. The abundance of these species varies with habitat type and extent of human disturbance. Seasonality of rainfall and river level significantly affect the abundance of primates in seasonally inundated forest but not in upland forest types.     

Breakdown of the species-area relationship in exotic but not in native forest patches

We studied the pattern of bird species richness in native and exotic forest patches in Hungary. We hypothesized that species-area relationship will depend on forest naturalness, and on the habitat specialization of bird species. Therefore, we expected strong species-area relationship in native forest patches and forest bird species, and weaker relationship in exotic forest patches containing generalist species. We censused breeding passerine bird communities three times in 13 forest patches with only native tree species, and 14 with only exotic trees in Eastern Hungary in 2003. Although most bird species (92%) of the total of 41 species occurred in both exotic and native forests, the species-area relationship was significant for forest specialist, but not for generalist species in the native forests. No relationship between bird species and area was found for either species group in the forest with exotic tree species. The comparison of native versus exotic forest patches of similar sizes revealed that only large (>100 ha) native forests harbor higher bird species richness than exotic forests for the forest specialist bird species. There is no difference between small and medium forest patches and in richness of generalist species. Thus, the species-area relationship may diminish in archipelago of exotic habitat patches and/or for habitat generalist species; this result supports the warning that the extension of exotic habitats have been significantly contributing to the decline of natural community patterns.