The composition of anuran assemblages was studied in 16 streams at the Serra do Cipó, south-eastern Brazil, in which 26 anuran species were found. Volume and isolation level of stream sections of 150 m were estimated; tadpoles, adult anurans, and potential tadpole predators were searched for over 16 consecutive months. Stream size, isolation, richness and diversity of tadpole predators, and some additional physical and biotic variables were measured and related to anuran species richness. Smaller streams tended to shelter more anuran species than larger ones, but neither stream size nor stream isolation explained variations in anuran species richness. Anuran species richness tended to increase with tadpole predator diversity. Tadpole species richness was influenced by predator species richness, and was highest when there were seven types of tadpole predators present. The distribution of few anuran species could be clearly related to particular physical and biotic variables. The behavioural flexibility of anurans and the similarity among streams may have contributed to this pattern.

Effects of the elephant gut and elephant dung on seed germination and early seedling establishment/growth were investigated in Banyang-Mbo Wildlife Sanctuary using undestroyed seeds of 14 plant species sorted from fresh elephant dung between 1 June 1994 and 31 May 1995 and similar seeds extracted from fresh ripe fruits fallen on the forest floor within the same period both sown in fresh elephant dung and forest soil. Parameters measured were final germination success, germination time and seedling growth rate. Results indicated that two species, Panda oleosa and Poga oleosa, did not germinate at all after 365 d irrespective of their sources and media of planting. Germination success observed in ingested seeds was significantly different from that observed in seeds from fresh fruits. Germination success observed in elephant dung was not significantly different from that in forest soil. Mean germination time varied widely between species and treatments but was generally shorter in seeds that passed through the elephant gut than those collected from fresh ripe fruits and these differences in mean germination time were significant in 92% of the species that germinated. Growth rates of seedlings from ingested seeds were higher than those from fresh ripe fruits especially in elephant dung. Growth medium was highly significant to growth in 10 of 12 species (83%) and source was important only to two species (16%) while their combined interacting effects were significant to three of the 12 species (25%). It is concluded that ingestion of seeds by the elephant is important in the germination of some rain-forest species and the elephant dung that contains the seeds dispersed is very important in the rapid growth of the seedlings. On the basis of germination success plant species that are absolutely or exclusively dependent on elephants for dispersal/germination are absent in Banyang-Mbo Wildlife Sanctuary, while Omphalocarpum elatum and Strychnos aculeata would be on the basis of fruit morphology.

Current literature on the response of tropical tree seedlings to fertilization was analysed. Fertilization effects on biomass accumulation, relative growth rate and tissue nitrogen (N) and phosphorus (P) were examined for seedlings grown under relatively high light. Higher light conditions in gaps are expected as human disturbance expands in tropical landscapes. Two questions were asked: (1) Does nutrient addition enhance growth or result in nutrient accumulation in the tissues of tropical tree seedlings grown in pots under high light? (2) Are these responses conditional on their adaptations to light availability, seed mass or growth form? Most of the species (73% of light-demanding and 60% of shade-tolerant) demonstrated a positive growth response to fertilization. The magnitude of the response of light-demanding species was more than twice that of shade-tolerant species. A higher proportion of shade-tolerant species accumulated nutrients in their tissues (up to 95% for P), but over half the light-demanding species did so as well. For both types of species, a higher percentage accumulated P than N. Responses in growth and in P accumulation were negatively correlated with seed mass. Shrubs responded more than trees in biomass accumulation, but there was a trend toward greater response by trees in relative growth rate and N and P accumulation. The results suggest that variation in nutrient availability could affect the structure of tropical forests regenerating from large-scale disturbance. In fertile sites, competitive exclusion may occur within the light-demanding species, resulting in a decline in local tree diversity. Depending on the effects of human disturbance on nutrient availability, loss of tree diversity at a local scale may compound diversity loss due to habitat destruction at the landscape scale.

Changes in morphological and anatomical leaf characteristics of woody plant species along an altitudinal gradient as well as between a late-successional and mature upper montane rain forest were examined. For leaf size, the Raunkiaer-Webb classification system was applied. The mature-forest transect comprised eight plots of 0.1 ha between 2300 and 3300 m asl, the successional-forest transect, four plots between 2400 and 2750 m asl. The latter comprised structurally heterogeneous vegetation patches. For each plot the proportions of leaf size classes and of the different categories of leaf shape, margin, and apex were calculated. Leaf size and the proportion of drip-tips decreased with increasing elevation. Serrate leaf margins were more prominent at higher elevations. Stomatal density, leaf thickness and related anatomical characteristics did not show significant trends. Differences between the mature and successional forest plots were generally slight. The advanced age of the successional forest probably led to a convergent development of leaf characteristics.

Fleshy diaspores (fruits, seeds) comprise a large portion of the litter on the floor of tropical forests, and interactions involving litter-foraging ants and diaspores are common in these areas. In this study, the interactions between ants and non-myrmecochorous diaspores (i.e. not adapted to dispersal by ants) were surveyed along a 1.4-km transect in a restinga forest (sandy soil) on the coast of south-eastern Brazil. During 2 y of monthly samplings, 562 interactions involving 48 ant species and 44 species of diaspore (0.02–11.10 g) were recorded. Ant–diaspore associations involved a considerable part of the ground-dwelling ant community. Large ponerine ants individually removed the diaspores up to 13 m, whereas small ants (myrmicines) normally recruited workers and consumed the diaspore on the spot. Ant-derived benefits to diaspores of non-myrmecochorous plants included secondary dispersal (small to medium-sized diaspores), and increased germination success after seed cleaning by ants. Large ponerine ants such as Odontomachus chelifer and Pachycondyla striata were the main seed vectors. Seedlings of three species were associated with nests of O. chelifer. The results indicate that ants play an important role in fruit/seed biology in the restinga forest.

Rain forests at Los Tuxtlas are islands surrounded by anthropogenic vegetation containing invasive species. Epizoochory is an important dispersal syndrome among invasive species but ecological studies are scant. In order to evaluate the movement of epizoochore diaspores into the mature forest, we selected two abundant secondary herbs with contrasting diaspore morphology, and five dispersers with different pelage type. We used stuffed mammals as a dummy and passed them through patches of these two plant species, counting the number of adhered diaspores. For dispersal into the forest, diaspores were manually adhered to dispersers, these were pulled along 100-m forest transects, counting the number of diaspores remaining at distance intervals. We observed the highest amount of detachment in the first 20 m of the forest edge. For Desmodium incanum diaspores with sticky hairs, adhesion to dispersers showed no differences among pelage types, therefore dispersal is determined mainly by diaspore detachment. Dispersers with long pelage (Didelphis marsupialis, Nasua narica and Procyon lotor) move diaspores for shorter distances, while dispersers with short pelage (Silvilagus floridanus and Philander opossum) are more likely to move diaspores for longer distances. In Pavonia schiedeana more diaspores (seeds with spines and hooks) were attached and remained attached on dispersers with long and thick pelage. Mean distance travelled for P. schiedeana diaspores varied between 11 and 2700 m. In D. incanum the distance travelled did not exceed 500 m. Based on comparisons between dispersal patterns and on ecological data of these two plant species and their potential dispersers, P. schiedeana has a higher probability of invading the forest and finding suitable habitats for establishment than D. incanum.

One hundred and nine soil samples were collected in 69 different localities along two transects, one North-South, about 900 km in length, and the other East-West (750 km in length), across Senegal and Gambia. The first transect followed a rainfall gradient and the second a human density gradient. The relationship between carbon content, C/N ratio and soil type on the abundance and species distribution of the nematodes along the transects was studied. Results showed that short-term fallows did not influence the specific structure of the communities, when compared with the nematode communities of fields located in the immediate vicinity, where Scutellonema cavenessi and Tylenchorhynchus gladiolatus were the dominant species. The expected negative influence of human disturbance on nematode occurrence seemed to be compensated by greater crop diversity, mainly near the towns. Less-disturbed areas also maintained a high diversity, but were characterized by the presence of particular species such as Xiphinema spp. Soil type was the most important factor affecting the species composition of the nematode community. As a result, nematode communities followed a distribution in areas, corresponding to the successive soil types, but did not change in relation to the human or climatic gradients. At a large scale, the study of plant-parasitic nematodes can give both different and complementary information on the ecological trends of an area to that of free-living nematodes.

Tree characteristics were recorded from 2829 standing trees in 24 0.25-ha terra firme forest plots in central Amazonia, 3 y after a surface fire had swept through the study area. Sixteen of the plots were within forest that burnt for the first time at the end of the 1997-98 El Niño (ENSO) event, and the remaining eight plots were within unburnt primary forest. In order to investigate the morphological correlates of tree mortality, we measured tree diameter at breast height (dbh) and bark thickness, and recorded burn height, bark roughness and the presence of latex, resin and buttress roots. Leaf litter depth was also recorded at the base of all trees in the unburnt forest. Using logistic regression models, tree mortality was best explained by the burn height, although dbh and the presence of buttresses were also important. Buttressed trees were associated with deeper leaf litter accumulation at their bases and higher char heights than trees without buttresses. Moreover, trees surviving the fire had significantly thicker bark than living trees in unburnt forest plots, indicating that thin-barked trees are more prone to selective mortality induced by heat stress. Latex did not appear to have had any significant effects on mortality, though resins were less abundant amongst the live trees in the burnt forest than in the unburnt controls. Levels of fire-mediated tree mortality in this study are compared with those in other Amazonian forest regions in light of historical factors affecting tree resistance to fires.

The otolith micro-increment technique was applied to assess the growth trajectory of early stages of the neotropical catfish Megalechis thoracata in Kaw Swamp, a coastal swamp in French Guiana, and two contrasting habitats in Suriname: the coastal Lelydorp Swamp with standing water and a rain-forest creek with running water, the Maykaboeka Creek. Daily deposition of increments on the lapilli was validated for the first 35 d after hatching and the innermost increments were deposited from hatching onwards. The natural habitats of M. thoracata in French Guiana and Suriname showed considerable variation in physico-chemical characteristics of the water, density of food organisms and fish fauna. Instantaneous growth rates and size-at-age differed significantly among two vegetation types in Kaw Swamp (3.5% d-1 and 4.1% d-1), Lelydorp Swamp (3.0% d-1) and Maykaboeka Creek (2.5% d-1). Spearman's rank correlation coefficient between instantaneous growth rates and environmental parameters differed significantly from 0 only for water temperature. Hatch date analysis revealed an extended spawning season from January to June in the rain-forest creek.

Arbuscular mycorrhizal (AM) fungi colonization and response were studied in seedlings of 80 native woody species belonging to different successional groups from the Tibagi River Basin, Paraná State, south Brazil. This study includes data from 43 native woody species already published. The results with 80 species did not differ from the results of the 43 species. The experiment was carried out in a greenhouse in plastic bags filled with a mix of subsoil (85%) and sand (15%), inoculated or not with spores of native AM fungi obtained from rhizosphere soil of different native tree species in an area with natural vegetation dominated by woody pioneer species. The successional groups were represented by 16 pioneer, 20 early secondary, 29 late-secondary and 15 climax species. The AM response and colonization in the greenhouse were 5.9 and 4.2 times greater in the early successional species than in the late-successional species, respectively. Seedlings of 49 woody species were collected in the interior under the canopy of the tropical forest of the Mata dos Godoy State Park and in a cleared area dominated by woody pioneer species. The percentage of AM colonization in the field was 54.9, 40.4, 7.2 and 3.1 for the pioneer, early secondary, late-secondary and climax species, respectively. The response to AM inoculation was strongly and directly related to AM colonization in the greenhouse and field and inversely related to seed weight. The AM colonization in the greenhouse was strongly and directly related to AM colonization in field. The late-successional species showed lower AM colonization and response than early successional species. The accentuated mycotrophism of the early successional species may be involved in their establishment, growth, survival and early forest structuring on low-fertility soils.

The distribution of the arboreal ant community plus a termite species of the genus Nasutitermes was inventoried on 938 red mangrove, Rhizophora mangle L., trees in a completely flooded mangrove forest of the Sian Ka'an Biosphere Reserve, Quintana Roo, Mexico. Colonies sheltered in dry hollow branches of the trees and the pseudobulbs of the epiphytic orchid, Myrmecophila christinae. Two size classes of dry hollow tree branches were categorized in order to test differences in ant distribution. As some trees remained unoccupied by either an ant or a termite colony, we deduced that the competition for nesting sites was low. Differences in the composition of the ant community corresponded to the nature of the shelters (i.e. diameter of the hollow branches or orchid pseudobulbs). The ant fauna was richer in the large dry hollow branches of R. mangle than in the smaller ones, with certain ant species belonging to the subfamilies Ponerinae and Formicinae being significantly more frequent in the large dry hollow branches than in the small ones. Cephalotes and Pseudomyrmex were the most frequent ant genera inhabiting the dry branches of R. mangle, while Dolichoderus bispinosus was the most frequent ant species inhabiting the orchid pseudobulbs. Arboreal Nasutitermes sp. selected mostly the orchid pseudobulbs and thus indirectly interfered with ant nest-site selection. Our results highlight niche differentiation through the selection of nest sites among different types of shelter.

Large rivers have played a prominent role in biogeographic theory for their potential to act as barriers for the dispersal of terrestrial organisms,and therefore be involved in the generation of species diversity (Brown & Lomolino 1998). In this paper, we document the potential role of macrophyte rafts as a mechanism by which Amazonian rivers could act as dispersal agents rather than barriers, transferring organisms across banks and possibly across very large distances. These vectors could therefore act against speciation and towards homogenization of the local biota.

Most researchers assume litter decomposition to take place at the site where litterfall occurs, mostly by soil micro-organisms and microfauna of less than 1 mm in size. Accordingly, the litterbag method has become the standard technique for evaluating litter decomposition rates (Schlesinger 1985, Wedderburn & Carter 1999). However, there is evidence indicating that at least in tropical arid ecosystems litter can be removed from the site in substantial amounts by animals, including large vertebrates. For example, litter is removed for forage or as building material for nests by ants (particularly leaf-cutting ants) and termites (Bucher 1982, Scholes & Walker 1993). Moreover, ruminant species (including domestic cattle and goats) supplement their food intake by feeding on falling leaf litter during the dry season in African savannas (Owen-Smith & Cooper 1987) and in the Chaco savannas of Argentina (Morello & Saravia-Toledo 1959). These observations suggest that litter removal may be an important component of the decomposition process, particularly in tropical semi-arid environments where lack of soil moisture decreases microbial activity, increasing litter availability for herbivores.

Habitat fragmentation affects the ecology of tropical rain forests in many ways, such as reducing species diversity of many taxa (Laurance et al. 2002, Lovejoy et al. 1986) and increasing rates of tree mortality and canopy-gap formation near forest edges (Laurance et al. 1997, 1998, 2001). Such obvious alterations have been documented in many fragmented forests, but more subtle changes, such as those affecting plant phenology (the timing and frequency of flower, fruit and leaf production), have received far less attention. Adler & Kiepinski (2000) showed that different populations of the successional tree Spondias mombin on small man-made islands in Panama had highly synchronous flowering and fruiting. In montane forests in Colombia, Restrepo et al. (1999) demonstrated that under-storey fruit abundance was consistently increased over time near forest edges relative to forest interiors. Beyond these and a few other studies (Ackerly et al. 1990, Nason & Hamrick 1997), however, the effects of fragmentation on plant phenology have been inadequately assessed, especially in the tropics.

VOLUME 19, NUMBER 1, JANUARY 2003, PAGES 19-25