Forest structure and tree species composition of the understory of two central Amazonian várzea forests of contrasting flood heights

We investigated species composition, distribution, and forest structure of understory trees (≥1 m height, <10 cm diameter at breast height) in two late-successional várzea forests subject to contrasting levels of inundation within the Mamirauá Sustainable Development Reserve, western Brazilian Amazon, and compared it with the overstory flora at the same study sites. In total, 1486 individuals and 116 woody species were recorded on an area totaling 3140 m². Individual densities and tree species richness were considerably higher in the high várzea than in the low várzea, which suggests that the heights and durations of the annual inundations are the main factor limiting species regeneration. In addition, approximately one third of the recorded species with densities ≥8 individuals showed regular or random spatial distribution patterns, which suggests that floodwaters act on dispersal strategies and species establishment.Independent of the forest type, floristic similarity between the understory and the overstory amounted to approximately 35%, and to approximately 10% when compared to other understory inventories in Amazonian várzea. Although the inventoried area of the understory amounted to only 16% of that of the overstory, species richness accounted for approximately 52-56% of that of the overstory. The results indicate that the understory flora of várzea forests is distinct and that it significantly increases local tree species richness. The understory flora of várzea forests therefore should be addressed in floristic inventories that provide the basis for regional and/or basin-wide estimations of tree diversity.     

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.     

Sapling communities in Amazonian white-water forests

Aim Structure and floristic composition of forest regeneration (trees between 1 and 10 cm diameter at breast height (d.b.h), ≥ 1 m growth height) was described in three forest types of Amazonian white‐water forests (várzea), in order to analyse whether floristic composition of saplings is related to the successional stage of the forests, whether it differs in comparision with the mature flora, and if there exists a zonation of sapling species along the gradients of flooding and irradiation. Location Mamirauá Sustainable Development Reserve, Western Brazilian Amazon. Methods The investigated forests were of the low and the high várzea type, on an annual average flooded around 4 and 1 months, respectively. The two low‐várzea forests belonged to the secondary and to the late‐successional stage, the high‐várzea forest also to the late‐successional stage. A total of 24 circular sample plots covering 1885 m² were installed. They were nested within three rectangular 1 ha permanent sample plots where individuals ≥ 10 cm d.b.h. were formerly inventoried. Average inundation and radiation [relative photosynthetically active radiation (rPAR)] at the forest floor was recorded in all inventoried plots. The Mean spatial Distribution Center (MDC; Ebdon, 1998 ) for all sapling species was calculated. Sapling species were grouped into associations with respect to their light‐demand and their location along the flood‐level gradient. Results Average flood height and average rPAR at the forest floor was highest in the secondary stage of the low várzea and lowest in the high‐várzea forest. Overall average density and basal area of the saplings averaged 2250 individuals and 2.3 m² ha^?1 in the secondary stage, 2330 individuals and 2.6 m² ha^?1 in the late‐successional stage of the low várzea and 5000 individuals and 4.8 m² ha^?1 in the high várzea. In all forest types, species richness of saplings was lower than species richness of trees ≥ 10 cm d.b.h., and amounted to 25 species in the secondary stage, to 35 species in the late‐successional stage of the low várzea and to 88 species in the high‐várzea forest. The amount of ‘immigrants’ ( Bazzaz, 1991 ) at the sapling level increased with proceeding forest succession and amounted to 24 and 29% in the low várzea and to 31% in the high várzea. Sapling species distribution, species richness and individual density was linked to both, the gradient of flooding and the gradient of irradiation. Species richness and individual density was highest in the high várzea and decreased with increasing influence of flooding. The high várzea was predominated by pronounced shade‐tolerant sapling species, whereas in the low várzea occured both, light demanding and shade‐tolerant species groups. Main conclusions Influence of flooding seems to be the main factor triggering species composition and structure of sapling communities in várzea forests. Proceeding forest succession reduces the impact of flooding because of the biogenical induced silting up of the forested sites. However, forest succession also alters forest architecture of the overstory and such the light conditions at the sapling level. Therefore, radiation is an important factor influencing species composition of sapling communities in várzea forests.     

Wattled Curassows in Bolivia: abundance,habitat use,and conservation status

ABSTRACT The Wattled Curassow (Crax globulosa) is a globally threatened species restricted to humid várzea forest (seasonally flooded forest along white‐water rivers) in low‐lying regions of Amazonia. The Wattled Curassow were thought to have been extirpated from the Beni area of Bolivia, but were rediscovered near the Río Negro River in 2001. Our objectives were to determine the size of this population, examine habitat use, and based on our results, assess the conservation status of the Wattled Curassow. During July and August 2006, we used distance sampling to estimate the population density in our study area. We estimated the density of Wattled Curassows at 3.4 (95% CI: 1.4–8.1) individuals/km² and all were observed within 300 m of the river. Based on the availability of suitable habitat (18 km² of riparian várzea habitat within 300 m of the river), we estimated that the breeding population of Wattled Curassows in our study area consisted of 61 individuals. The specialized habitat requirements of the Wattled Curassow has important conservation implications because previous population estimates were based on the availability of várzea forest rather than the availability of water edge habitat within várzea forest. As a result, the current global population estimate (2500–9999) is higher than our estimate (500–2500) that takes the specialized habitat requirements of the Wattled Curassow into account. Given this low estimated population, along with the severely fragmented state of the few remaining populations and their dependence on a specialized and vulnerable habitat, we recommend that the status of the Wattled Curassow be upgraded from Vulnerable to Endangered.     

Angiosperm flora and biogeography of the páramo region of Colombia,Northern Andes

Páramo is the neotropical high elevation ecosystem in the northern Andes and Central America consisting of multiple dissected open areas above 3000 m a.s.l. Complex evolutionary processes that occurred within these ecosystems gave rise to a unique tropical Andean flora. Previous phytogeographical classifications for Colombian páramos have been based on subjective assessments of species distributions. However, a detailed floristic analysis highlighting affinities between páramo regions in Colombia has not yet been proposed. The aim of this study is to provide an analytical scenario for the patterns of regional plant diversity in a hierarchical framework based on the biogeographical history of the páramos, based on 30 localities of the Colombian páramos. Parsimony analysis of endemicity (PAE) and Jaccard similarity indices were applied to a presence/absence data matrix of páramo angiosperm species. Altitudinal distribution of species was used to determine the percentage of the páramo flora endemic to this ecosystem. Genera are shared among páramos, whereas species composition is highly endemic. 86% of the páramo angiosperm plant species is endemic to this ecosystem. The Colombian Páramo areas can be grouped using PAE into five biogeographical units, based on angiosperm species composition. These are: (1) Páramos de la Cordillera Oriental; (2) Páramos de la Cordillera Central and Macizo Colombiano; (3) Páramos de Antioquia; (4) Páramos del Norte; (5) Páramos de la Cordillera Occidental.     

Diurnal distribution and behavioral responses of fishes to extreme hypoxia in an Amazon floodplain lake

Synopsis Because of the need for surface access for aquatic surface respiration (ASR), fish density increases were demonstrated for the open water of a floodplain lake during severe hypoxia. This indicates an O₂-induced diurnal pattern of horizontal migrations between the zone of macrophyte cover and open water. Supplemental experimental investigations seem to suggest that species such as characoids,Colossoma macropomum andSchizodon fasciatum, deviate from this pattern. During long periods of oxygen depletion, they return to the region of macrophyte growth and survive there without displaying the usual kind of ASR. Mortality studies in net cages exposed in natural water bodies confirmed that only these two species are able to survive severe hypoxia beneath macrophyte cover. The possibility of an O₂-input through the root system of plants is discussed. The O₂-concentration has a significant influence on the locomotory behavior and the frequency of opercular movement in characoids. There is significantly less locomotory activity beneath the macrophytes during periods of oxygen depletion among those species not forced to migrate than among those in the open water regions, where normal ASR behavior is possible.     

Vertebrate responses to fruit production in Amazonian flooded and unflooded forests

We document patterns of fruit and vertebrate abundance within an extensive, virtually undisturbed mosaic of seasonally flooded (várzea and igapó) and unflooded (terra firme) forests of central Amazonia. Using phenological surveys and a standardised series of line-transect censuses we investigate the spatial and temporal patterns of immature and mature fruit availability and how this may affect patterns of habitat use by vertebrates in the landscape. All habitats showed marked peaks in fruiting activity, and vertebrate detection rates varied over time for most species both within and between forest types. Many arboreal and terrestrial vertebrates used both types of flooded forest on a seasonal basis, and fluctuations in the abundance of terrestrial species in várzea forest were correlated with fruit availability. Similarly, the abundance of arboreal seed predators such as buffy saki monkeys (Pithecia albicans) and macaws (Ara spp.) were closely linked with immature fruit availability in terra firme forest. We conclude that highly heterogeneous landscapes consisting of terra firme, várzea and igapó forest appear to play an important role in the dynamics of many vertebrate species in lowland Amazonia, but the extent to which different forest types are used is highly variable in both space and time.     

Biological diversity in the Tehuacán-Cuicatlán Valley, Mexico

A general overview of the biological knowledge of the floristic province of the Tehuacán-Cuicatlán Valley in central-southern Mexico is presented. Floristic and faunistic richness and endemism, as well as uses of the flora are analyzed and discussed for this area, recently declared a biosphere reserve. The analysis shows that, in approximately 10 000 km² the Tehuacán-Cuicatlán Valley contains between 10 and 11.4% of the Mexican flora. In addition, the valley possesses 365 endemic species that represent 13.9% of its flora. With respect to the fauna diversity, the available information is less comprehensive than for plants. Nevertheless, the study shows that the 11 species of amphibians, 48 species of reptiles, and 91 species of birds recorded for the valley surpasses the diversity found in other dry-lands of the world. In relationship to the mammals of the region, the available data are poor for most of the groups except for bats, for which 24 species have been reported. Regarding the use of the flora, the analysis revealed that 815 species are utilized by the people in the valley. A discussion related to future research activities is also included.     

Riparian flooded forests of the Orinoco and Amazon basins: a comparative review

This paper compares the non-deltaic, riparian-flooded forests of the Orinoco and Amazon River basins. Ecological relationships between these forests and their environments that can be useful in establishing schemes for biodiversity conservation are identified. Adaptations of species to flow seasonality, flooding intensity, sedimentation pattern and nutrient depletion are described. The variability and diversity of riparian-flooded forests is related to (i) landscape evolution (regional-scale, long-term), (ii) water quality (basin scale, long-term) and (iii) hydrology and geomorphology (sector-scale, medium-term). The floristic analysis has produced a preliminary list of 242 tree species common to the riparian-flooded forests of both basins. This relatively high number of species is related to connectivity between the riparian corridors of both basins and the effective operation of dispersal mechanisms. Highly oligotrophic environments add uniqueness at the regional scale through the evolution of endemic species presenting adaptations not only to flooding but also to nutrient depletion. The process of genetic diversification and the evolution of genotypes adapted to flooding are suggested to explain longitudinal gradients at tributary junctions and floodplain-upland ecotones where current fluvial dynamics are unpredictable over ecological time scales. The paper presents information that may be used to devise appropriate measures to evaluate sites for riparian biodiversity conservation and management.     

Physiological adaptation to hypoxia of a neotropical characoid fish Colossoma macropomum,Serrasalmidae

Synopsis Investigations of seasonal changes in the hematological parameters of Colossoma macropomum revealed that during times of the year when they are exposed to low oxygen concentrations (< 0.5 mg 1^–1), there is an increase in the hemoglobin content of the blood and the erythrocyte count. Experiments to determine the influence of oxygen content on the routine oxygen consumption showed that the critical concentration is 2 mg 1^–1 at 30°C. At concentrations below 0.5 mg O₂ 1^–1, surface water is used for aquatic respiration. Above the critical concentration, short-term fluctuations in oxygen availability are compensated for by adjustment in the ventilation rate. Gas exchange is facilitated by the unusually large gill surface area (349 mm²g^–1 for a 200 g fish).     

Considerations on structure and function of the “Central-Amazonian inundation forest ecosystem” with particular emphasis on selected soil animals

Summary Studies were carried out in Central-Amazonian inundation forests having seasonal inundations during the emersion phase (e.p.) and the submersion phase (s.p.). Two várzea forests (white water areas), one in the Amazon valley on Ilha de Curarí and one at Lago Janauarí, and an igapó (black water area) situated in the Rio Negro valley at Rio Tarumã Mirím were investigated. A community analysis consisting of the species diversity and species similarity of the aquatic and terrestrial soil fauna was executed in these forests. Each forest is differentiated into an inner, middle, and outer part. The annual development of the soil invertebrates is dictated by the periodic changes in water level. Data on species diversity indicate an alternate occurrence of the soil- and trunk-dwelling carabids and staphylinids (Coleoptera). Low species diversity is obtained for the aquatic soil fauna during the high water period. This is correlated with both oxygen concentration and relative abundance of a few specialized species.A function model approach was tried. Investigations showed that both the phytophages and the saprophages consumed about 9.4% and 13% respectively of the yearly litter fall. Litter decomposition is retarded during the inundation period (170 g·m^-2·s.p.^-1 is decomposed) but is accelerated during the emersion phase (420 g·m^-2·e.p.^-1 is decomposed). Nearly 14% of the yearly litter fall is presumed to be exported by the current from the inundation forest during the inundation phase, probably into the surrounding rivers and lakes. A rough estimation of a nutrient budget containing some selected elements was given. The estimation allowed us to suppose, that in the igapó the loss of some elements cannot be compensated for by the input from the river water and the precipitation. Unlike the igapó, the várzea forest may compensate for this loss of litter through input of nutrients from the inflowing white water. The igapó may thus be considered as a source of nutrients while the várzea forest is a nutrient sink.     

Local and regional rarity in a diverse tropical fish assemblage

Because most species in an ecological assemblage are rare, much of the species richness we value is due to taxa with few individuals or a restricted distribution. It has been apparent since the time of ecological pioneers such as Bates and Darwin that tropical systems have disproportionately large numbers of rare species, yet the distribution and abundance patterns of these species remain largely unknown. Here, we examine the diversity of freshwater fish in a series of lakes in the Amazonian várzea, and relate relative abundance, both as numbers of individuals and as biomass, to the occurrence of species in space and time. We find a bimodal relationship of occurrence that distinguishes temporally and spatially persistent species from those that are infrequent in both space and time. Logistic regression reveals that information on occurrence helps distinguish those species that are rare in this locality but abundant elsewhere, from those that are rare throughout the region. These results form a link between different approaches used to evaluate commonness and rarity. In doing so, they provide a tool for identifying species of high conservation priority in poorly documented but species rich localities.     

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.     

Above-ground biomass structure of a Chusquea tessellata bamboo páramo,Chingaza National Park,Cordillera Oriental,Colombia

The present study was carried out in the bamboo (Chusquea tessellata) páramo of Parque Natural Nacional de Chingaza, Eastern Cordillera, Colombia from December 1987 to April 1988. Above-ground biomass structure of bamboo páramo was quantified in 16 plots. These data are compared with previous results on above-ground biomass structure of bunch-grass (Calamagrostis spp.) páramos.The total (non-living and living) above-ground biomass of a Chusquea tessellata bamboo páramo was low (2,625 g DW · m^–2) compared to bunch-grass páramo. Nevertheless, higher values of standing living biomass and litter are found in the bamboo páramo due to the leaf shed of the bamboo. The thick litter layer may inhibit germination and growth of nearby plants.Maximum biomass is found near the ground surface. Cumulative LAI (In transformed) and height in the bamboo vegetation are related parabolically for Chusquea tessellata and linearly for bunch-grass due to differences in leaf distribution. The mean bifacial LAI of living Chusquea tessellata leaves is 2.2 m² · m^–2, whereas it is 2.5 m² · m^-2 for all Poaceae.     

Stem tilting,pseudocephalium orientation,and stem allometry in <Emphasis Type="Italic">Cephalocereus columna-trajani</Emphasis> along a short latitudinal gradient

Cephalocereus columna-trajani is a giant columnar cactus endemic of the Tehuacán-Cuicatlán Valley in Central Mexico. Stem tilting and northward pseudocephalium azimuth in C.␣columna-trajani have functional advantages in terms of interception of direct solar radiation at the northernmost portions of its range. Since the success of both characters strongly depends on the apparent position of the sun during the growing season, in this paper we test the hypothesis that the occurrence of such columnar morphology is restricted geographically and imposes mechanical restrictions that limit column height. Following a latitudinal gradient along the Tehuacán-Cuicatlán Valley, we selected five populations, recorded tilting angle and pseudocephalium azimuth, and carried out allometric and biomechanical analyses of height–diameter relationships. Northern populations showed higher tilting angles. Pseudocephalium azimuth significantly differed among populations, and pseudocephalium orientation was consistently North-Northwestern. Stem allometry showed that the stems of the southern populations increased in height at a far greater rate with respect to diameter than the northern populations. The southernmost population showed the lowest safety factor. These results support the hypothesis that stem tilting in C.␣columna-trajani is functionally advantageous in a restricted geographical range, and imposes mechanical restrictions to column height.     

High Complexity Food Webs in Low-diversity Eastern Pacific Reef–Coral Communities

Community-wide feeding interrelationships in a low-diversity coral reef off the Pacific coast of Panamá (Uva Island reef) demonstrate complex pathways involving herbivore, strong corallivore, and carnivore interactions. Four trophic levels with 31 interguild links are identified in a generalized food web, and documented feeding interrelationships with 287+ species links are portrayed in a coral–corallivore subweb. The importance of trophic groups changes greatly with time, from unknown causes over annual to decadal-scale periods, and during very strong El Niño–Southern Oscillation events such that intermittent intense herbivory by echinoids (Diadema) and corallivory by gastropod mollusks, the crown-of-thorns sea star Acanthaster, hermit crabs, and fishes result in high levels of coral mortality and bioerosion of reef substratum. Intraregional differences in species composition and abundances affecting food-web interactions are briefly described for nonupwelling (Uva Island) and upwelling areas (Pearl Islands) in Panamá. Seasonal upwelling in the Pearl Islands results in high plankton productivity, which likely augments production in invertebrates, fishes, marine mammals, and seabirds, but these pathways still remain largely unquantified. The corallivore Acanthaster is absent from upwelling centers in Panamá and from upwelling and nonupwelling areas in the southern and central Galápagos Islands, and the highly destructive, facultative corallivore Eucidaris galapagensis occurs only in the latter offshore islands and at Cocos Island. Relatively recent declines in the abundances of manta rays, sharks, and spiny lobsters are correlated with, but not necessarily causally linked to, increasing fishing activities in the late 1970s to early 1980s. The extent to which the complex yet highly unstable Uva Island food web is representative of other eastern Pacific coral reef ecosystems remains to be investigated.     

Germinative behaviour of ten tree species in white-water floodplain forests in central Amazonia

Amazonian floodplain forests (known as várzea) are classified into high or low várzea depending on the spatial position on the plains. This topographic feature exposes the terrain over different time periods of inundation, causing a major limiting factor for tree seedling establishment. We hypothesize that, strategically, most of the seeds produced by trees in low várzea forests germinate faster and in synchrony (temporally concentrated germination), and that their seedlings tend to have cotyledons without reserve or foliaceous cotyledons (PEF). By contrast, seeds produced by high-várzea specialist trees exhibit slower and temporally scattered germination, and their seedlings tend to have reserve storage cotyledons (CHR). Generalist species may show no clear pattern or may be related to high-várzea species. To test this hypothesis, diaspores of 10 tree species were collected: five of low-várzea specialist trees, three of high-várzea specialist trees and two of generalist species. Seedling emergence and morphology were monitored daily in a nursery for a period of 150 days of being subjected to non-flooded (sown directly in várzea soil) and flooded conditions (15 days in water before sowing in the same soil). The seedling emergence of low-várzea species showed an increase of 37% in germinability whereas high-várzea and generalist species exhibited a decrease of 38% and 35% of germinability, respectively. Foliaceous cotyledons were preferentially found in seedlings of low-várzea species, and storage cotyledons were more common in those of high-várzea species, indicating how cotyledon morphology may determine the amount and use of resources available to a seedling during the first stages of establishment and growth. Conservation plans aiming for the maintenance of ecosystem services must consider these strategies.     

Classification of central amazon lakes on the basis of their microbiological and physico-chemical characteristics

Twenty-four Central Amazonian Várzea and Ria lakes, lateral to the Rio Negro and the Rio Solimões, were studied for a year and are classified here in terms of physical, chemical and microbiological characteristics. White water (W), mixed water (M) and black water (B) lakes are ranked according to bacterial densities, electrical conductivity, pH, DO, POC, Fe, Si0₂ and PO₄ consumption in the following order W > M > B. The range of V_max decreased as net primary production increased. Further differentiation among the three lake types is made on the basis of dominant algal species and species diversity.     

Primate assemblage structure in Amazonian flooded and unflooded forests

There is considerable variation in primate species richness across neotropical forest sites, and the richest assemblages are found in western Amazonia. Forest type is an important determinant of the patterns of platyrrhine primate diversity, abundance, and biomass. Here we present data on the assemblage structure of primates in adjacent unflooded (terra firme) and seasonally inundated (várzea and igapó) forests in the lower Purús region of central-western Brazilian Amazonia. A line-transect census of 2,026 km in terra firme, 2,309 km in várzea, and 277 km in igapó was conducted. Twelve primate species were recorded from 2,059 primate group sightings. Although terra firme was found to be consistently more species-rich than várzea, the aggregate primate density in terra firme forest was considerably lower than that in the species-poor várzea. Consequently, the total biomass estimate was much higher in várzea compared to either terra firme or igapó forest. Brown capuchin monkeys (Cebus apella) were the most abundant species in terra firme, but were outnumbered by squirrel monkeys (Saimiri cf. ustus) in the várzea. The results suggest that floodplain forest is a crucial complement to terra firme in terms of primate conservation in Amazonian forests.     

Ordination and classification of vegetation along an altitudinal gradient in the Venezuelan páramos

By means of ordination and classification techniques, the relationships between climate, soils, human activities and vegetation along an altitudinal gradient of the Venezuelan páramos are analyzed and interpreted. The altitudinal gradient chosen is characterized by decrease of temperature, precipitation, soil fertility, soil water-holding capacity, and plant cover as altitude increases. The ordination results suggest vegetation changes to be primarily related to environmental changes occurring with altitude, and secondly to disturbances caused mainly by grazing. Some results point toward a disjunction in the vegetational gradient occurring at ca. 3 500 m.a.s.l. and separating low and high páramo. This disjunction might have been caused by the glacial history of the páramos and the occurrence of frequent night-frosts.The soil samples were kindly analyzed by the Laboratorio de Edafologia, Centro Nacional de Investigaciones Agropecuarias. Help in plant identification was generously obtained from the specialists of Instituto Botánico, Instituto Nacional de Parques, Caracas.Nomenclature follows Vareschi (1970).Acknowledgements: This work was supported by the Decanato de Investigaciones, Universidad Simón Bolivar. I wish to thank A. Pacheco for help in the field sampling. Dr O. Arenas help was invaluable in the mathematical treatment of the data. Drs A. Vivas and J. M. B. Smith provided useful criticism to an earlier version of this work.