Understory spider assemblages from a cloud forest in Chiapas,Mexico, and their relationships to environmental variables

Cloud forests have high ecological complexity, but their reduced area and exploitation by human communities, make them one of the most endangered ecosystems in Mexico. The spider assemblages of a cloud forest reserve in Chiapas, Mexico, were studied to analyze influence of environmental variables (forest stand structure, temperature and relative humidity) and their temporal variation, on the distribution, abundance, species richness and assemblage structure of spiders. Ten parcels were established for the sampling of spiders and the recording of forest and climatic variables. Spider sampling took place during the dry and rainy seasons. Vegetation data were recorded at the end of the study (except canopy cover, which was registered at the end of each season). Some differences were found among parcels in forest stand structure, but only the density of seedlings showed a high correlation with spider abundance, seemingly seedlings (by its size and architecture) offered numerous supports for the understory spiders’ webs and then promote the settlement of weaver spiders. Also there were some correspondences between the similarity patterns of forest structure and spider assemblages, giving some evidence of a forest structure influence on the integration of spiders’ assemblages. Spider abundance was notoriously higher in the dry season. Other environmental variables had only weak effects on spider variables (abundance and species richness) and assemblage structure. The most abundant families were Tetragnathidae, Theridiidae and Linyphiidae, which were also among the dominant families in other tropical cloud forests, with the latter two also being among the most diverse. As complex ecosystems, tropical cloud forests seem to have complicated interactions with their inhabitant animals, not easy to elucidate.     

Spider diversity in a tropical habitat gradient in Chiapas, Mexico

This paper presents an assessment of spider diversity in a complex landscape of southern Mexico. Eighteen different habitats were identified, measured and mapped across this fragmented landscape. Habitat types were characterized by measuring various features, including number of plant forms, tree cover and litter depth. Each month from February to April (dry season) and from June to August 2002 (wet season), spiders were sampled on each habitat by using pitfall traps and direct collection. Correlations between spider diversity and habitat characteristics were carried out to explore the relative contribution of each habitat variable as related to changes in spider composition and richness. In total, 115 spider species were recorded in 18 habitat types, and the mean number and density of species per habitat were 21 (± 3, standard error of mean) and 57 (± 9), respectively. The species recorded represent 41% of the fauna recorded in the Mexican state of Chiapas and 4% of the fauna recorded in Mexico. Relatively pristine habitats (e.g. deciduous forest) contained an important proportion of spider diversity in this fragmented landscape. Epigean spider diversity was significantly correlated with tree cover and with the diversity of plant forms during the rainy season. No correlation was detected between soil spider diversity and the habitat variables measured for any season. The results of this work suggest that in highly fragmented tropical landscapes, some habitat types (e.g. coffee plantations, hedgerows) might play an important role for the persistence of spider populations. The prevalence of relatively stable conditions in some of these habitats can allow spiders species (e.g. Nephila clavipes ) to overcome adverse conditions such as a decrease in humidity and dramatic changes in temperature and wind exposure, allowing them to recolonize when favourable conditions return.     

Breeding systems in a montane tropical cloud forest in Venezuela

The breeding systems, reproductive efficacies and population densities of 75 species of trees, shrubs, perennial herbs and vines in a montane tropical cloud forest in Venezuela are investigated. 56.96% and 44.32% of the trees, versus the other life forms considered, respectively possess obligate outbreeding mechanisms. Two shrubs are non-pseudogamous apomicts. The percentage of dioecy among tree species (31%) is among the highest recorded in tropical forests. Reproductive efficacy is similar under all breeding systems in the forest interior. Obligately outbred taxa are slower recolonizers of a disturbed border as compared with non-obligate outbreeders. Explanations are advanced for the high incidence of dioecy combined with a low level of self-incompatibility among hermaphroditic species. It is concluded that the breeding system spectrum reflects an unpredictable pollination pattern, rather than insufficient pollinator servicing.     

西双版纳热带山地雨林群落乔木树种多样性研究

根据块样地资料对西双版纳热带山地雨林树种多样性特征进行了分析.结果表明,在2 500m²的样地上,随着起测胸径递增,各样地乔木个体数和树种丰富度均表现为依次递减;低海拔带上(850～1000 m)的山地雨林(1、2号样地)的各指数值无一定变化规律,较高海拔带上(1200～2000 m)的山地雨林(3～6号样地)的Shannon-Wiener指数和Simpson指数均表现为依次递减,而Pielou均匀度指数则呈依次递增的趋势.较高海拔带上的山地雨林在较小乔木起测胸径(≥2 cm、≥5 cm、≥10 cm)的树种丰富度、多样性和均匀度指数均要明显大于低海拔带上的山地雨林,而两者在较大乔木起测胸径(≥20 cm、≥30 cm、≥50 cm)的各指数值无明显差异.随着取样面积的递增,各样地树种丰富度、多样性和均匀度指数在取样面积递增到2 000m²处均已趋于平缓.     

Phyllostomid bat assemblages in different successional stages of tropical rain forest in Chiapas,Mexico

Due to their role in seed dispersal, changes in the community of phyllostomid bats have direct consequences on ecological succession. The objective of this work was to document changes in the structure of bat assemblages among secondary successional stages of tropical rain forest in Chiapas, Mexico. Bats were mist-netted at ground level during 18 months in 10 sites belonging to 3 successional stages: four sites represented early succession (2–8 years of abandonment), four intermediate succession (10–20 years of abandonment), and two late succession (mature old-growth forest).We captured 1,179 phyllostomids comprising 29 species. Phyllostomid species richness was 17 (58% of all species) in the early stage, 18 (62%) in the intermediate stage and 24 (83%) in the late stage. The late successional mature forest possessed nine species that were exclusively found there, whereas early and intermediate successional stages contained only one exclusive species. Sturnira lilium, Artibeus lituratus, Carollia perpicillata, Artibeus jamaicensis and Glossophaga soricina represented 88% of all captured phyllostomid bats. Frugivores made up more than 90% of the species captured in early and intermediate successional stages and 84% in late successional forest. The Bray–Curtis index of dissimilarity showed a replacement of species through successional stages with the largest dissimilarity between early and late stages, followed by intermediate and late, and the lowest dissimilarity between early and intermediate stages. The number of gleaning insectivore species increased during succession. The carnivorous guild was exclusively found in the late stage (three species). We conclude that the late successional mature forest was the main reservoir for the gleaning insectivore and carnivore guilds; however, early and intermediate successional stages possessed a great diversity of species including many frugivores.     

Tree species richness complementarity, disturbance and fragmentation in a Mexican tropical montane cloud forest

Tropical montane cloud forest exhibits great heterogeneity in speciescomposition and structure over short geographic distances. In central Veracruz,Mexico, the conservation priority of seven cloud forest fragments was assessedby considering differences in woody plant species richness and complementarityof species among sites, forest structure, tree mortality, and timber andfirewood extraction as indicators of anthropogenic disturbance. Densities oftrees 5 cm dbh (360–1700 trees/ha) weredifferent among the sites, but basal area (35.3–89.3m²/ha) did not differ among fragments. The number of dead trees rangedfrom 10–30 to 170–200 trees/ha. The fragments'species composition was different but complementary. The Morisita–Hornindex indicated low similarity between fragments. A non-parametric estimator ofspecies richness indicated that more sampling effort would be necessary tocomplete the inventory (15 additional trees and two understory shrub species).Unfortunately, most of the fragments are threatened with deforestation. The numberof cut trees was similar among sites (0–15 cut trees/0.1 ha).Sites with immediate need for conservation were close to settlements, with highnumbers of cut trees and no legal protection. The selected sites represent thevariety of situations that exist in the region. Given the high complementarityobserved between fragments, a regional conservation approach will be required topreserve the last repositories of part of the tremendous biodiversity of theonce continuous forest in this region.     

西双版纳热带山地常绿阔叶林蕨类植物多样性研究

基于4个50m×50m(包含400个5m×5m)样方调查,统计了蕨类植物的α多样性指数、优势度指数、相似性指数及β多样性指数。结果表明:在调查的1hm2西双版纳热带山地常绿阔叶林里,蕨类植物的物种丰富度为32种;不同样地蕨类植物丰富度指数、多样性指数、优势度指数及均匀度指数的变化趋势一致;该森林群落蕨类植物的物种多样性虽然不高,但优势种群显著;通过3个无人为干扰与1个受人为干扰样地的对比分析研究看出,该类森林遭受一定程度的人为干扰后,蕨类植物物种丰富度、多样性、优势度及相似性等均显著下降,其中物种多样性的降低尤为显著,既使群落的外貌、结构等恢复至接近原始林状态,蕨类植物丰富度及多样性也难以恢复,故此,保护原始的森林植被是保护该森林蕨类植物多样性的有效措施之一。     

Fern richness,tree species surrogacy,and fragment complementarity in a Mexican tropical montane cloud forest

We related pteridophytes versus tree species composition to identify surrogate measures of diversity, and complementarity of seven cloud forest fragments. Forest structure, and fern and tree composition were determined in 70 (2 × 50 m) transects. Fern density (10,150–25,080 individuals/ha) differed among sites. We recorded 83 fern species in the transects. Nonparametric richness estimators indicated that more sampling effort was needed to complete fern inventories (14 more species). However, ferns recorded outside of the transects increased richness to 103 species (six more species than predicted). Twenty-eight species were unique and rare due to special habitat requirements (Diplazium expansum, Hymenophyllum hirsutum, Melpomene leptostoma, Terpsichore asplenifolia), or were at a geographical distribution edge (Diplazium plantaginifolium, Lycopodium thyoides, Pecluma consimilis, Polypodium puberulum). Correlations between fern richness and tree richness and density were not significant, but were significant between fern richness and fern density, between epiphytic fern density and tree richness and density. Tree richness is not a good surrogate for fern diversity. Only three species were recorded in all fragments (Polypodium lepidotrichum, P. longepinnulatum, P. plebeium); thus fragments pteridophytes compositions are highly complementary, but more similar for ferns than for trees. A regional conservation approach which includes many small reserves needs to focus supplementarity on patterns of tree and fern species richness.     

海南五指山热带山地雨林植物物种多样性研究

王指山热带山地雨林的物种种类十分丰富,在１ｈｍ＾２样地中共出现５４个科,１００个属的乔木树种１７７种,１３３７个个体。区系地理分析表明属的分布区类型以热带分布型成分占优,为８９．０％,充分体现了五指山山地雨林的热带性质。多样性指数分析结果为：样地１Ｍａｒｇａｌｅｆ指数１７．８２２,Ｓｈａｎｎｏｎ－Ｗｉｅｎｅｒ指数５．６２１,均匀度０．８２３,Ｓｉｍｐｓｏｎ指数０．０５０,均匀度６．７７５,表明五指     

Comparing environmental vulnerability in the montane cloud forest of eastern Mexico: A vulnerability index

The montane cloud forest (MCF) is one of the most threatened ecosystems, in spite of its high strategic value for sustainable development, the role it plays in the hydrological cycle maintenance, and as reservoir of endemic biodiversity. For Mexico, this forest is considered the most threatened terrestrial ecosystem at national level because of land-use changes and the effects of global climate change. To compare and assess the environmental vulnerability in the MCF we measured two physiological traits (stomatal conductance and leaf water potential), four climate variables (air temperature, photosynthetically active radiation, vapor pressure deficit, water availability) and the potential geographic distribution of eleven tree species from this forest. We evaluated stomatal conductance responses using the envelope function method (EFM), and after analyzing these responses we developed a vulnerability index that allowed us to compare the environmental vulnerability among species. We proposed the EFM as a useful tool to assess regional environmental vulnerability by comparing species. Our results showed differential species responses to all the studied variables; however, the vulnerability index allowed us to conclude that the most vulnerable species was Liquidambar styraciflua, and the least vulnerable Persea longipes. We also found that temperatures above 34 °C, and vapor pressure deficit above 2.9 kPa with relative humidity below 30% jeopardized the stomatal conductance performance of all species. We also found leaf water potential as the most influential variable over the studied species followed by vapor pressure deficit, showing that even in the MCF water is a determinant factor for species’ development.     

Drought effects on the plasticity in vessel traits of two endemic Magnolia species in the tropical montane cloud forests of eastern Mexico

本文旨在探讨气候变化如何影响两种特有墨西哥木兰的导管性状可塑性和其每年的年轮宽度。尽管如此,很少有研究评估干旱对墨西哥东部热带山地云林导管性状的影响。通过生长年轮的数字图像,我们对所研究的墨西哥木兰树种的径向生长率、树龄和导管性状可塑性进行了评估,比较了两种墨西哥木兰树种在干旱年和非干旱年的导管密度、水力直径和传导面积百分比。本研究首次对墨西哥两个热带山地云林中的两个濒危木兰树种(Magnolia vovidesii 和M. schiedeana)的多孔木质部导管性状对长期气候变化的可塑性进行了分析。结果发现,当比较干旱和非干旱年份时,温度和降水量与年轮宽度的差异密切相关。扩散型多孔木质导管解剖结构具有很高的可塑性,这与所研究的两种木兰树种的温度和/或水的有效性有关。我们的结论是,与非干旱年份相比,对干旱年份的解剖学适应导致了导管性状的大量减少;这些可塑的适应性在植物长期环境胁迫下的水分运输以及生存的安全性方面起着重要的作用。     

Amphibian species and functional diversity as indicators of restoration success in tropical montane forest

Tropical forest restoration is increasingly seen as an activity that may counteract or reduce biodiversity loss. However, few studies monitor fauna or consider measures of functional diversity to assess restoration success. We assessed the effect of a tropical montane forest restoration program on species and functional diversity, using amphibians as the target group. We compared amphibian assemblages in three types of land use: restoration areas, tropical montane cloud forest (TMCF; reference ecosystem) and cattle pastures (degraded ecosystem) in southern Mexico. We also described microclimate, microhabitat heterogeneity, woody vegetation structure and diversity for each type of land use, and their relationship to amphibian species and functional diversity. Compared to TMCF, restoration areas had similar environmental conditions. However, amphibian species richness was similar in the three types of land use and abundance was lower in the restoration areas. In TMCF, the amphibian assemblage was dominated by forest-specialist species, the pastures by generalist species, and the restoration areas by a combination of both species types. Interestingly, functional richness, functional evenness and functional divergence did not vary with land use, though the number of functional groups in restoration areas and TMCF was slightly higher. Overall, the results suggest that after seven years, active restoration provided habitat heterogeneity and recovered woody vegetation capable of maintaining amphibian species and functional groups similar to those inhabiting TMCF. Forest fragments adjacent to restoration areas seem to facilitate fauna recolonization and this emphasizes the importance of the conservation of the reference ecosystems to achieving restoration success.     

Composition and diversity of the spider fauna in the canopy of a montane forest in Tanzania

Spiders were sampled using insecticide knockdown in an African montane forest in the Uzungwa Mountains of Tanzania. The results are used to discuss the faunal composition at the site and in comparison to other sites, and the implications of the results for estimating spider diversity in Africa are discussed. A total of 5233 adults comprising 149 species were collected from 11 samples covering a total of 906 m² of projected area. Three species contributed 45% of the sample. Previous insecticide knockdown studies of tropical lowland forest canopies have shown a dominance of Theridiidae, Salticidae and Araneidae. In the present study Linyphiidae dominated in abundance and were the second most diverse in terms of species richness. Other abundant families were Oonopidae and Pholcidae, while Theridiidae, Salticidae and Araneidae were rich in species. This supports a previous study, which indicated that the importance of linyphiids increases with altitude. Species richness was predicted using a number of estimators, which produced relatively similar results. Using the abundance-based estimator, Chao 1, the predicted richness for the total area sampled is 183 ± 15 species. This indicates that at least 20% of the area's spider community remains unsampled. A high ratio of undescribed species (approximately 80%) and a relatively high species turnover compared to a site 20 km away within the same forest complex suggests that the number of spiders in Africa could well be much higher than the current, published estimate of 20000 species.     

Photosynthetic parameters,dark respiration and leaf traits in the canopy of a Peruvian tropical montane cloud forest

Few data are available describing the photosynthetic parameters of the leaves of tropical montane cloud forests (TMCF). Here, we present a study of photosynthetic leaf traits (V _cmax and J _max), foliar dark respiration (R _d), foliar nitrogen (N) and phosphorus (P), and leaf mass per area (LMA) throughout the canopy for five different TMCF species at 3025 m a.s.l. in Andean Peru. All leaf traits showed a significant relationship with canopy height when expressed on an area basis, and V _cmax-area and J _max-area almost halved when descending through the TMCF canopy. When corrected to a common temperature, average V _cmax and J _max on a leaf area basis were similar to lowland tropical values, but lower when expressed on a mass basis, because of the higher TMCF LMA values. By contrast, R _d on an area basis was higher than found in tropical lowland forests at a common temperature, and similar to lowland forests on a mass basis. The TMCF J _max–V _cmax relationship was steeper than in other tropical biomes, and we propose that this can be explained by either the light conditions or the relatively low VPD in the studied TMCF. Furthermore, V _cmax had a significant—though relatively weak and shallow—relationship with N on an area basis, but not with P, which is consistent with the general hypothesis that TMCFs are N rather than P limited. Finally, the observed V _cmax–N relationship (i.e., maximum photosynthetic nitrogen use efficiency) was distinctly different from those in tropical and temperate regions, probably because the TMCF leaves compensate for reduced Rubisco activity in cool environments.     

西双版纳热带雨林和热带山地常绿阔叶林附生苔藓的组成与多样性格局

为探讨西双版纳热带雨林和热带山地常绿阔叶林附生苔藓的组成、多样性格局及其维持机制,该文对两种植被的树干附生苔藓植物进行了调查与分析.所选择的样地位于西双版纳勐腊县,每种植被类型选择10个20 m×20 m的样方,每个样方选择约10棵样树.结果表明:(1)本调查共记录到附生苔藓20科39属60种,其中热带雨林附生苔藓有1...     

功能多样性和谱系多样性对热带云雾林群落构建的影响

近年来, 功能多样性和谱系多样性为探究群落构建机制提供了新方法。为了更准确地了解海南岛高海拔热带云雾林群落构建机制, 该研究以海南岛霸王岭热带云雾林为对象, 测定7个环境因子和13个植物功能性状。利用主成分分析(PCA)筛选环境因子, 以霸王岭、尖峰岭和黎母山热带云雾林分布物种建立区域物种库, 结合模型, 分析Rao二次熵(RaoQ)和平均成对谱系距离(MPD)变化对植物群落构建的影响。结果表明: 林冠开阔度、土壤全磷含量和坡度是影响植物群落构建的关键环境因子。多数功能性状的系统发育信号很低且不显著, 说明热带云雾林群落的系统发育关系与功能性状随历史进程变化不一致。RaoQ和MPD的实际观测值都显著低于期望值, 且其标准效应值与土壤磷含量显著相关, 说明生境过滤是驱动热带云雾林群落构建的关键因子, 土壤磷含量是群落构建的关键环境筛。     

Restoring montane cloud forest: establishment of three Fagaceae species in the old fields of central Veracruz,Mexico

Tropical montane cloud forest is rapidly disappearing and our knowledge of how to restore this system is limited. In a cloud forest of central Veracruz, Mexico, we studied seedling survival, growth, and causes of mortality (microenvironment and herbivory) of three native tree species, Fagus grandifolia, Quercus germana, and Q. xalapensis, transplanted into abandoned pastures (<1 year old) and secondary forests (9–17 years old). Microenvironment differed between the two habitats, temperature and photosynthetically active radiation were higher, and humidity was lower in the abandoned pastures than in the secondary forests. Seedling survival was greater in secondary forests than in pastures: F. grandifolia, 94 and 64%; Q. germana, 88 and 68%; and Q. xalapensis, 61 and 57%, respectively. The cause of mortality differed between habitats, with gophers (24.2% mortality) and mice (4.8%) killing the most seedlings in pastures, and damping‐off (16%) was the most important cause in secondary forests. The relative growth rate in height and basal area was significantly higher in abandoned pastures than in secondary forests; Q. xalapensis had the highest growth rate, followed by Q. germana and F. grandifolia. The environmental conditions in this mountainous cloud forest region seem less stressful to planted seedlings than the conditions of other lowland systems, as frequent clouds favor their establishment even in open sites. We conclude that Fagaceae species can successfully establish in abandoned pastures in mesic environments. Thus, the species studied can be used to speed cloud forest regeneration in the same area at different successional stages.