Plateau Habitats Research Articles

Adaptive evidence of mitochondrial genes in Pteromalidae and Eulophidae (Hymenoptera: Chalcidoidea).

Pteromalidae and Eulophidae are predominant and abundant taxa within Chalcidoidea (Hymenoptera: Apocrita). These taxa are found in diverse ecosystems, ranging from basin deserts (200 m) to alpine grasslands (4500 m). Mitochondria, cellular powerhouses responsible for energy production via oxidative phosphorylation, are sensitive to various environmental factors such as extreme cold, hypoxia, and intense ultraviolet radiation characteristic of alpine regions. Whether the molecular evolution of mitochondrial genes in these parasitoids corresponds to changes in the energy requirements and alpine environmental adaptations remains unknown. In this study, we performed a comparative analysis of mitochondrial protein-coding genes from 11 alpine species of Pteromalidae and Eulophidae, along with 18 lowland relatives, including 16 newly sequenced species. We further examined the codon usage preferences (RSCU, ENC-GC3s, neutrality, and PR2 bias plot) in these mitochondrial protein-coding sequences and conducted positive selection analysis based on their Bayesian phylogenetic relationships, and identified positive selection sites in the ATP6, ATP8, COX1, COX3, and CYTB genes, emphasizing the crucial role of mitochondrial gene adaptive evolution in the adaptation of Pteromalidae and Eulophidae to alpine environments. The phylogenetically independent contrast (PIC) analysis results verified the ω ratio of 13 PCGs from Pteromalidae and Eulophidae increased with elevation, and results from generalized linear model confirm that ATP6, ATP8, COX3, and ND1 are closely correlated with temperature-related environmental factors. This research not only enriched the molecular data of endemic alpine species but also underscores the significance of mitochondrial genes in facilitating the adaptation of these minor parasitoids to plateau habitats.

Carbon, nitrogen, and phosphorus metabolic relationships and reaction mechanisms in SBBR processes in the plateau habitat.

In this study, two laboratory-scale SBBR reactors were established in a plateau habitat. Using high flux sequencing, the SBBR process was compared by natural sediment and autotrophic sludge to characterize the functional modules and functional genes of carbon, nitrogen, and phosphorus metabolism under different working conditions and to analyze the reaction mechanism. The results showed that all the functional modules of carbon metabolism and nitrogen metabolism were found in the SBBR process, except for methane metabolism, which occurred at 25 °C in tank 2, the functional modules related to methane metabolism are enhanced at all working conditions. Except for methane metabolism, all functional genes in tank 2 are inhibited by different working conditions, whereas tank 1 shows a slight enhancement. The different working conditions in nitrogen metabolism demonstrate inhibition of functional modules and functional genes in both tanks. Oxidative phosphorylation was missing five functional modules, except for M00153, where only two genes, K00424 and K22501, are missing, all of the required genes are missing in the other four functional modules. Overall the different conditions demonstrated some inhibition in both reaction tanks of the SBBR process. It is preferable to use self-cultivated sludge for membrane acclimation when operating the SBBR process in a plateau habitat. The findings of this study can be used to further research microbial carbon, nitrogen, and phosphorus metabolism mechanisms in SBBR processes in plateau habitats.

Taxonomy and Phylogeny of Hyphomycetous Muriform Conidial Taxa from the Tibetan Plateau, China

During the investigation of lignicolous freshwater fungi in the Tibetan Plateau habitat, fifteen collections were isolated from submerged decaying wood. Fungal characteristics are commonly found as punctiform or powdery colonies with dark pigmented and muriform conidia. Multigene phylogenetic analyses of combined ITS, LSU, SSU and TEF DNA sequences showed that they belong to three families in Pleosporales. Among them, Paramonodictys dispersa, Pleopunctum megalosporum, Pl. multicellularum and Pl. rotundatum are established as new species. Paradictyoarthrinium hydei, Pleopunctum ellipsoideum and Pl. pseudoellipsoideum are reported as new records on the freshwater habitats in Tibetan Plateau, China. The morphological descriptions and illustrations of the new collections are provided.

The study on the changing pattern of microbial community function and phenotypes in anaerobic–anoxic–oxic (A2O) process under the influence of temperatures in plateau habitats

Filling a gap in the Tibetan plateau habitat and providing a valuable scientific basis and technical support for the development of wastewater. The study was carried out in the Tibetan plateau areas.

Comparison of the effects of two municipal sewage treatment process discharge on receiving rivers in plateau habitats

Comparison of the effects of two municipal sewage treatment process discharge on receiving rivers in plateau habitats

The relationship analysis and reaction mechanism of carbon, nitrogen, and phosphorus metabolism in sewage treatment in plateau habitat.

The efficiency of pollutant removal in sewage is mainly determined by the structure and abundance of microbial flora, which is essentially represented by the type and abundance of genes and enzymes, and the reaction mechanism is the abundance and degree of reaction of metabolic pathways and metabolic modules. In order to study the mechanism of carbon, nitrogen, and phosphorus metabolism of activated sludge microflora in the A2O process at high altitudes at different temperatures, so as to improve the removal rate of pollutants and reduce the discharge concentration of pollutants. Based on the research environment of high-altitude environmental research, the author used the A2O system as the treatment process and put Illumina MiSeq high-through sequencing technology to comprehensively dissect the reaction relationship of carbon, nitrogen and phosphorus metabolic pathways, and derived the main functional genes and enzymes of carbon, nitrogen, and phosphorus metabolism. It was demonstrated that the abundance of the most metabolic modules and functional genes tended to increase and then decrease with increasing temperature. In particular, the highest abundance and activity and the best pollutant removal efficiency were observed at 20°C. This study will provide a valuable reference for the study of carbon metabolism, nitrogen metabolism, and phosphorus metabolism of microbial flora in sewage treatment under plateau habitats.

Managing climate change microrefugia for vascular plants in forested karst landscapes

Microrefugia are small areas that support favourable climate and allow species to persist during regional and global climate changes. Dolines in karst landscapes may provide such areas for many climate change-vulnerable species. Here we provide a better understanding on how plant species indicate changes in their environment (temperature, soil moisture and light availability) after a few years of partial canopy removal from dolines and their close surroundings (logged areas: >1 ha). We place our results in the context of the most widely used forest management practices within the study area (Mecsek Mts, Hungary), in addition to presenting a general framework for the maintenance of doline microrefugia in forested karst landscapes. Three types of habitats were investigated: dolines before logging, dolines after logging, and the forested plateau. Three large dolines and three sites on the plateau were selected for vegetation sampling. All dolines were sampled before logging and 5–10 years after partial canopy removal. Logging resulted in a 50–80% reduction of canopy cover in the dolines and their close surroundings. We established a transect across each doline from north to south passing through doline bottoms, and across each plateau site. We estimated the percentage cover of vascular plant species (tree saplings – up to 1 m in height, shrubs and herbs) along the transects using 1 m × 1 m vegetation plots, determined the diagnostic species of the doline and plateau habitats, and used multivariate methods and linear mixed-effects models during analyses. Plant species indicated clear gradients of the main microclimatic factors within the dolines and that significant changes took place after logging. Canopy removal caused substantial changes in the main microclimatic factors of most doline microhabitats (e.g., south-facing slopes). The vegetation of the dolines before logging indicated moister conditions than that of the plateau and cooler and shadier conditions than that of the dolines after logging. These and our previous results suggest that logging may directly and indirectly influence dolines to be microrefugia under global warming. By applying our framework to refugia conservation and management for the karst landscape in the Mecsek Mts, we can conclude that the protection of old forests and natural forest dynamics in as many large dolines as possible and the implementation of close-to-nature forestry practices may be essential to maintain regional biodiversity in the long run.

Genetic analysis of three wild Eurasian eagle-owl subspecies, B. b. kiautschensis, B. b. ussuriensis, and B. b. tibetanus, in Chinese populations

The Eurasian eagle-owl (Bubo bubo) is distributed throughout Asia and Europe and contains approximately twelve subspecies. Three subspecies, B. b. kiautschensis, B. b. ussuriensis, and B. b. tibetanus, are separately distributed in the refugia and plateau habitats of China. However, the genetics of these subspecies and populations have not been studied. Genetic differences were investigated among 32 individuals from six populations of these three B. bubo subspecies based on the mitochondrial genome. Low genetic diversity but high haplotype diversity was observed in these subspecies. The phylogenetic relationship of three B. bubo subspecies distributed in China was proven to be coordinated with geographic and environmental gradients. This study provides the first detailed insights into the mitochondrial genetic diversity of three Eurasian eagle-owl subspecies distributed in China and demonstrates the utility of the mitochondrial genome in intraspecific genetic population analyses of these eagle-owls.

Integrated Analysis of Transcriptomic and Proteomics Data Reveals the Induction Effects of Rotenoid Biosynthesis of Mirabilis himalaica Caused by UV-B Radiation.

Mirabilis himalaica (Edgew.) Heimerl is one of the most important genuine medicinal plants in Tibet, in which the special plateau habitat has been associated with its excellent medicinal quality and efficacy. However, the mechanisms by which environmental factors affect biosynthesis of secondary metabolic components remain unclear in this species. In this study, RNA sequencing and iTRAQ (isobaric Tags for Relative and Absolute Quantification) techniques were used to investigate the critical molecular “events” of rotenoid biosynthesis responding to UV-B radiation, a typical plateau ecological factor presented in native environment-grown M. himalaica plants. A total of 3641 differentially expressed genes (DEGs) and 106 differentially expressed proteins (DEPs) were identified in M. himalaica between UV-B treatment and control check (CK). Comprehensive analysis of protein and transcript data sets resulted in 14 and 7 DEGs from the plant hormone signal transduction and phosphatidylinositol signaling system pathways, respectively, being significantly enriched. The result showed that the plant hormone signal transduction and phosphatidylinositol signaling system might be the key metabolic strategy of UV-B radiation to improve the biosynthesis of rotenoid in M. himalaica. At same time, most of the DEGs were associated with auxin and calcium signaling, inferring that they might drive the downstream transmission of these signal transduction pathways. Regarding those pathways, two chalcone synthase enzymes, which play key roles in the biosynthesis of rotenoid that were thought as the representative medicinal component of M. himalaica, were significantly upregulated in UV-B radiation. This study provides a theoretical basis for further exploration of the adaptation mechanism of M. himalaica to UV-B radiation, and references for cultivation standardization.

Understory host plant and insect gall diversity changes across topographic habitats differing in nutrient and water stress in the Brazilian Amazon rainforest

ABSTRACT Topographic gradients in terra firme forests are associated with pronounced changes in soil texture, soil nutrients and distance to the water-table, thereby creating different hydric and nutritional conditions for plants and their associated herbivore community. The aim of this study was to investigate galling species and host plant richness and gall species composition across topographic habitats differing in nutrient and water stress in the Brazilian Amazon rainforest. Nineteen 250 x 3 m plots were randomly sampled in the valley, slope, plateau-slope transition, and plateau habitats in terra firme forests. All individual dicotyledonous plants 1 to 3 meters high were examined for the presence of insect galls. Galling species and host plant richness differed significantly among the studied habitats and were higher in slope habitats (drier habitats), as expected. More humid areas (valleys) showed the lowest richness of galling species, and a lower number of understory host plants. PERMANOVA and PERMDISP results demonstrated that the gall species composition differed significantly in the valley, slope, plateau-slope transition, and plateau areas. However, these structural differences in species composition could be due to unequal dispersion of variability among forest habitats. Our data suggested that spatial heterogeneity, such as a mosaic of local water status and nutrient availability resulting from the topographic conditions, can affect host plants and their associated galling insects.

Phylogenetic relationships of endemic bunting species (Aves, Passeriformes, Emberizidae, Emberiza koslowi) from the eastern Qinghai-Tibet Plateau

In this study we reconstructed the phylogenetic relationships of a narrow-range Tibetan endemic, Emberiza koslowi, to its congeners and shed some light on intraspecific lineage separation of further bunting species from Far East Asia and along the eastern margin of the Tibetan Plateau in China. The onset of the Old World bunting radiation was dated to the mid Miocene and gave rise to four major clades: i) one group comprising mainly Western Palearctic species and all high-alpine endemics of the Tibetan Plateau; ii) a clade including E. lathami, E. bruniceps and E. melanocephala; iii) one group comprising mainly Eastern Palearctic species and all insular endemics from Japan and Sakhalin; iv) an exclusively Afrotropic clade that comprised all African species except E. affinis, whose phylogenetic relationships were ambiguous and only poorly supported in all reconstructions. The Tibetan bunting, E. koslowi, turned out as an early offshoot of the Western Palearctic-Tibetan clade 1 and thus represents an ancient relic lineage that dates back to a mid Miocene colonization event of its ancestors to the alpine plateau habitats. This temporal scenario of an early Miocene origin of alpine Tibetan endemics coincides with recent results for two further species, the Tibetan ground tit, Pseudopodoces humilis, and the Tibetan rosefinch, Carpodacus roborowskii. The origin of extant intraspecific phylogeographic patterns and splits among sister species in Eastern Asia were dated back to the Pleistocene with earliest lineage splits occurring among taxa from the Japanese Archipelago including Sakhalin and their mainland counterparts. A similarly ancient split separated a southern clade of E. godlewskii yunnanensis from S Sichuan and Yunnan from a northern clade including populations from central and northeastern China, Mongolia and S Siberia. Ecological segregation among breeding habitats of southern E. g. yunnanensis at lower elevations and those of other conspecifics at high-alpine habitats might have played a key role in the spatial genetic diversification of this species.

Lateritic Plateaus in the Northern Western Ghats, India; a Review of Bauxite Mining Restoration Practices

The northern Western Ghats are characterised by plateaus and hilltop carapaces formed from ferricretes rich in aluminium ore. Ferricretes in Western Ghats are home to a high number of endemic species, many with extremely limited distribution. The heterogeneity of microhabitats on ferricretes supports a great diversity of plant and animal communities. With little overburden and a high percentage of recoverable metals they are targeted for mining which leads to removal of all soil, vegetation and microhabitats. Vegetation and faunal diversity of unmined sites from Kolhapur district were studied providing reference data used to discuss restoration efforts on two mined sites in the region. Restoration efforts have faced ecological and legal hurdles. The international literature for the restoration of bauxite mines fails to demonstrate any successful model to return the species assemblage to a pre-mining profile. Restoration practices fail to adequately replicate microhabitat heterogeneity; often restoring sites to a different ecosystem from the original. The present mining policies do not take cognizance of the special nature of plateau habitats, ecology or the ecosystem functions they provide. We suggest a moratorium on mining of the high level lateritic plateaus in Western Maharashtra is justified until the biodiversity value and ecosystem services of the sites are fully understood and can be weighed against the economic gains from mining.

Evolutionary history of passerine birds (Aves: Passeriformes) from the Qinghai–Tibetan plateau: from a pre-Quarternary perspective to an integrative biodiversity assessment

As one of the most prominent topographical features on Earth, the Qinghai–Tibetan plateau (QTP) underwent a long and complex history of the QTP uplift from the collision of the Indian and the Eurasian plates to the present. At its southern and southeastern margins, it is flanked by the most significant hotspots of organismic diversity of the northern hemisphere (including birds), the Sino-Himalayan mountain forests. In contrast, the central plateau region itself harbours species-poor communities but also a good number of endemics that presumably evolved from rather ancient (pre-Pleistocene) phylogenetic lineage splits. We discuss the evolutionary history of QTP passerines from a twofold perspective including examples from our own research. First, we provide an overview of those alpine QTP endemics that represent late Miocene and Pliocene lineage splits, i.e. early colonisations to the central alpine QTP region. As an example, true rosefinches (genus Carpodacus) presumably evolved from a forested eastern QTP centre of origin and colonised the (semi-)open plateau habitats several times independently. Second, we discuss younger speciation events corresponding to phylogeographic east–west divides along the southern QTP margin. A multidisciplinary approach combining genetic, bioacoustic and morphological markers shed new light on the phylogenetic relationships of Pnoepyga wren babblers and on the intraspecific subdivision of the Buff-barred Warbler (Phylloscopus pulcher).

Contributions of vulnerable hydrogeomorphic habitats to endemic plant diversity on the Kas Plateau, Western Ghats

BackgroundThe Western Ghats of India are known to be a major biological hotspot that supports plant diversity and endemism. On the Kas Plateau, a lateritic plateau of the northern Western Ghats, we examined mesoscale distributions of endemic, rare, or locally significant plant species in forest habitats or on the plateau and its escarpments, and assessed the edaphic and hydrological parameters of seasonal plateau microhabitats.FindingsAlmost two thirds of over 100 phytogeographically significant species occur on the plateau top; these represent 26 plant families and 43 genera. About 80% of the species are restricted to the upper plateau and its escarpments.ConclusionSince botanically critical plateau habitats are generally small, dependent on seasonal monsoon moisture, and determined by drainage-related parameters that can be altered by anthropogenic activities, they are highly vulnerable. Maintenance of appropriate microhabitats should be a key consideration for conservation of regionally significant plant biota.

Resource‐based habitat associations in a neotropical liana community

Summary1. Lianas are a conspicuous element of many tropical forests, accounting for up to 40% of woody stem density and 20% of species richness in seasonal forests. However, lianas have seldom been surveyed at sufficiently large spatial scales to allow an assessment of the importance of habitat variables in structuring liana communities.2. We compare the association patterns of 82 liana species and an equivalent sample of tree species on the 50 ha Forest Dynamics Project plot on Barro Colorado Island, Panama, with topographic habitat variables (high and low plateau, slope, swamp and streamside), and thirteen mapped soil chemical variables. In addition, we test for liana species associations with canopy disturbance using a canopy height map of the plot generated using light detection and ranging.3. For all liana species combined, densities differed among topographic habitat types in the plot, with significantly higher densities on the seasonally drier lower plateau habitat (1044 individuals ha−1) than the moister slope habitat (729 individuals ha−1). Lianas were also significantly more abundant than expected in areas with low canopy height.4. The proportion of liana species associated with one or more topographic habitat variables (44%) was significantly lower than that for trees (66%). Similarly, liana species were significantly less frequently associated with PC axes derived from soil chemical variables (21%) than trees (52%). The majority of liana species (63%) were significantly associated with areas of the plot with low canopy height reflecting an affinity for treefall gaps.5. Synthesis. The habitat associations detected here suggest that liana density is associated primarily with canopy disturbance, and to a lesser extent with topography and soil chemistry. Relative to trees, few liana species were associated with local variation in topography and soil chemistry, suggesting that nutrient availability exerts only weak effects on liana community composition compared to trees. Results from this study support the contention that increases in forest disturbance rates are a driver of recently observed increases in liana abundance and biomass in neotropical forests.

Ant (Hymenoptera: Formicidae) Communities of the Southern Cumberland Plateau

Abstract The Cumberland Plateau supports diverse plant communities that vary greatly across cove and plateau habitats. Unfortunately, little is known about how terrestrial invertebrate communities vary across cove and plateau habitats and how disturbance affects these communities. To address this deficiency, we used the Ant Leaf Litter protocol to survey ant diversity on the southern Cumberland Plateau in Tennessee. We surveyed forested habitats on top of the plateau surface and on the cove slopes, as well as sites that were logged within the past 6 yr. After surveying 14 sites we found 1) 10,130 ants representing 55 species from 21 genera and six subfamilies, including five new records for Tennessee; 2) significant differences in ant communities by habitat type; 3) that south-facing cove slope ant communities more closely resembled the ant community of plateau surface native forest sites than the ant community of north-facing cove slopes; 4) that recently logged sites hosted a distinct ant community (including hybrid imported fire ants) not found in undisturbed habitats; and 5) by resampling three sites surveyed 5 yr earlier, that the ant leaf litter protocol can be used to track ant community change over time. Ants thus proved to be an excellent system for examining invertebrate diversity across habitats on the Cumberland Plateau.

Herpetological surveys of south-western and south-eastern regions of Nigeria

The herpetofauna of part of the south-western (Lagos, Ogun and Oyo States) and south-eastern (Cross River State) regions were investigated. Specimens were located opportunistically during visual surveys. Both regions fall in the tropical zone, and the south-western region surveyed, was mostly lowland, degraded forests (mostly secondary) and savanna. The southeastern regions surveyed were of primary forests, montane, sub-montane and plateau habitats. A total of 35-38 amphibian species were recorded in south-western Nigeria and over 49 species in the south-eastern region. Higher amphibian diversity was observed in the south-eastern region due to the diversity of habitat types. The difference in species diversity was due to the presence of Werneria mertensiana, Didynamipus sjoskedti, Cardioglossa gracilis, C. leucomystax, Astylosternus batesi, A. djedematus, A. montanus, Amietophrynus superciliaris, Petropedetes johnstoni, Leptodactylodon bicolor, L. polycanthus among others, regarded as forest and montane species. A few farm-bush and savanna species were also observed and they include Haplobatrachus occipitalis, Amietophrynus maculatus, Phrynobatrachus accraensis, Arthroleptis variabilis and Silurana tropicalis which may indicate that the primary forests are being degraded, hence the emergence of these invasive species. The lower amphibian diversity observed in the south-western region is believed to have resulted from the high amount of degradation and conversion of the natural forests into the impoverished faunal region. Future intensive surveys of both regions especially the degraded areas of the southeastern region would undoubtly reveal existing species not encountered in this study or even undescribed species.Keywords: herpetofauna, amphibian diversity, south-western region, south-eastern region, invasive species.

Squat lobster assemblages on seamounts differ from some, but not all, deep‐sea habitats of comparable depth

AbstractThis study was carried out to test the hypothesis that benthic communities on seamounts are distinct from those of other deep‐sea habitats at comparable depths. Analysis of the squat lobster fauna of deep‐sea habitats in the Southwestern Pacific revealed that the species composition of assemblages on seamounts was not statistically dissimilar from assemblages on slope and plateau habitat at comparable depths. However, compositional differences were observed between seamount and rise and ridge habitat. Differences in assemblage composition between seamount and ridge habitat were statistically significant for two of the four ridge systems examined. Assemblages on seamounts that were distinct from non‐seamount ridge habitat were typically dominated by small‐bodied species with an abbreviated larval stage. Various environmental variables were correlated with the observed assemblage patterns observed; depth‐related variables may account for differences between seamount and rise assemblages, whilst differences in POC flux likely play a role in determining the assemblage compositional patterns between seamount and non‐seamount ridge habitat. Extensive pre‐analysis data treatment was required to ensure that multivariate analyses of assemblage data from seamount and non‐seamount habitats were robust. Our results confirm the findings of recent studies that found no compositional differences in assemblages from seamount and slope habitats, and support the idea that dissimilarity between seamount assemblages on different ridge systems increases with geographic distance. Further research will be required before the generality of these findings can be confirmed.

Habitat Choices of Nubian Ibex (Capra Nubiana) Evaluated with A habitat Suitability Modeling and Isodar Analysis

The value of a habitat for a forager may be affected by habitat characteristics related to food availability, energetic costs of foraging, predation costs, and the foraging opportunities available in other habitats. Nubian ibex (Capra nubiana) are stout, sure-footed social wild goats that inhabit arid landscapes with steep terrain. We investigated their habitat selection behavior using indicators to (1) develop a habitat suitability index (HSI) model that would account for the variation in the activity densities of Nubian ibex across habitat types and seasons, (2) apply the isodar technique to look for density-dependent habitat selection behavior in Nubian ibex, and (3) investigate the proximate environmental factors that correlate to relative activity densities of Nubian ibex. We determined relative densities of the ibex by recording sightings of animals along standard walking transects. We incorporated the habitat variables that had greatest influence on the densities of Nubian ibex into habitat suitability index models for both spring and summer seasons.The HSI models revealed that Nubian ibex most preferred open cliff face habitat offering safety during the spring season, but their habitat preference shifted towards an area with watered gardens ("grave area habitat") during the summer season. Significant isodars were only obtained for the summer season comparisons between grave area versus cliff face, and between grave area versus plateau habitats. The slopes of the isodars suggest that the grave area habitat is 10.5 and 7.6 times more productive than the plateau and the cliff face habitats, respectively. Our results suggest that the relative abundances and habitat preferences of Nubian ibex varied with the seasonal availability of habitat resources, extent of predation risks, and human nuisance disturbances across the landscape. We recommend that wildlife managers dealing with the conservation and protection of the endangered Nubian ibex should focus on the various ecological and anthropogenic factors governing the habitat selection and preferences.

Seasonal and spatial variation in water availability drive habitat associations in a tropical forest

Associations with topographic units or soil types that vary in water availability are widespread in plant communities and are one of the main structuring aspects for local species distribution patterns, yet the underlying mechanisms are poorly understood. We hypothesized that differential seedling performance across habitats, particularly during the dry season, leads to habitat associations in seasonal tropical forests. We expected this pattern to be most pronounced in particularly dry years, such as those associated with El Niño Southern Oscillation (ENSO) events. We assessed performance of 36 native tree and shrub species in a moist forest in central Panama across the dry and wet seasons in two topographic habitat types during a year in which dry-season precipitation was reduced due to an ENSO event. At the community level, we found lower growth and higher mortality in the dry season relative to the wet season and higher mortality in the drier plateau habitat relative to the wetter slope habitat. There was large variation in species' responses to season and habitat. Species' mortality and growth rates were significantly correlated with experimentally assessed drought sensitivity, but only during the dry season in the plateau habitat. Slope specialists had significantly higher survival, but not growth, in the slope vs. plateau habitat during the dry season. In contrast, plateau specialists showed no performance differences between habitats. The data suggest that associations with plateau habitats result from a numerical advantage of drought-tolerant species in dry habitats in which seedlings of drought-sensitive species are unable to persist. Overall, our results support the idea that seasonal and spatial variation in water availability, particularly in dry years, drive seedling dynamics, which in turn shape local species distributions. Predicted shifts in rainfall patterns caused by global and regional climate change are therefore expected to alter the dynamics, composition, and diversity of seasonal tropical forests.