A variety of processes have been identified as playing a key role in maintenance of hyper-rich tropical forest, among which ecological sorting caused by niche partitioning challenges stochastic dispersal processes. However, demographic responses to spatio-temporal resource variation that could result in biased species distributions are still little studied. In this paper we investigate from two censuses, c. 15 y apart, of a 12-ha permanent forest sample in French Guiana, how tree recruitment and mortality rates vary among hydrological soil types known to affect species habitat preferences and among ecological guilds related to species light requirement. The results indicate that both recruitment and mortality vary significantly with respect to these factors. While the mean instantaneous mortality and recruitment rates are estimated to 0.98 and 0.81%, respectively, pioneer species, canopy trees and hydromorphic bottomland soils depart significantly from these values. In particular, the pioneers, regenerating either from the soil seed bank or from post-opening seed rain, show faster dynamics than other species. These two guilds harbour probabilities of mortality elevated by a factor of 1.9 and 3.2, respectively, and probabilities of recruitment elevated by a factor of 4.9 and 3.1, respectively. Conversely, canopy trees show slower dynamics, with probabilities of mortality and recruitment lowered by a mean factor of about 0.5 with respect to other species. We also observe that trees growing in hydromorphic bottomlands prove to have significantly higher mortality and recruitment probabilities, by a factor of about 2 with respect to those growing in terra firme.

Levels of leaf damage due to insect folivory have been investigated in forests of different latitudes all over the world, but most research has concentrated on a few common forest types. Most studies of insect herbivory were conducted in (sub)tropical rain forests (Barone 1998, Basset 1996, Coley 1983, Lowman 1985), or in temperate forests (Landsberg & Ohmart 1989, Lowman & Heatwole 1992). In contrast, little is known about insect folivory of woody plants in tropical savannas (Fowler & Duarte 1991, Marquis et al. 2001, Ribeiro 2003, Stanton 1975), and no such data are available for the West African savanna ecosystem (Andersen & Lonsdale 1990). Savannas cover about 40% of the land surface of Africa and 20% of the world (Scholes & Walker 1993), and savanna trees may host considerable numbers of insects, including many herbivores (Grant & Moran 1986, Mody et al. 2003). Therefore, insect herbivory can be considered a potentially important aspect of plant–animal interactions for vast areas of tropical ecosystems, where it has been studied remarkably rarely so far.

Dryobalanops rappa (Dipterocarpaceae), a dominant tree in wetland forests in Borneo, often produces vegetative sprouts in its juvenile stages (trees less than 25 m in height), a characteristic that is believed to be rare in tropical forest trees. We investigated the growth characteristics of this species in a tropical forest in Merimbun Heritage Park, Brunei, to verify the hypothesis that the vigorous sprouting ability enables it to grow in a wetland forest with soft soils that promote stem decumbency and to assess the adaptive significance of vegetative sprouting in the context of its regeneration. Reproductively mature trees developed buttresses and were rarely decumbent. However, if they became decumbent, they died without sprouting. Juvenile trees were frequently decumbent, and their decumbent shoots sprouted vegetatively. Therefore, vegetative sprouting acted as a countermeasure to decumbency and death on the soft wetland soil. A decumbent shoot produced only one sprout in most cases. Decumbent shoots grew little and eventually died, but new sprouts showed rapid growth. This suggests that there is translocation of resources from decumbent shoots to sprouts. If decumbency occurs, a D. rappa genet ramifies into sprouts, and helps sustain the population in the wetland environment. This vegetative life history strategy is important for regeneration in wetland forests with soft soil.

Although the dioecious palm, Mauritia flexuosa plays a pivotal role in Amazonian ecology and economy, little is known about its flowering and fruiting patterns. We investigated the role of habitat and inter-annual precipitation in the phenology of M. flexuosa. We calculated sex ratios and recorded phenology for 20 mo in four populations (N = 246) of savanna–forest ecotone (two sites) and forest (two sites) habitat in Roraima, Brazilian Amazonia. Sex ratios were significantly female-biased, and >98% of females set fruit. No significant relationship was found between habitat and sex. Flowering occurred at the wet/dry season interface (August–November), and fruit maturation occurred during the wet season (May–August). Males and females flowered synchronously, and neither the onset nor termination of flowering differed significantly between habitats. Flowering was negatively associated with present precipitation and positively correlated with prior precipitation (3 mo). Fruiting was positively associated with present precipitation and unrelated to prior precipitation (3 mo). We conclude that habitat has an insignificant effect, although short-term climatic variation may influence phenology of this species in northern Amazonia. These results highlight the need for long-term studies relating flowering and fruiting events, and inter-annual climatic variation.

Spatial distribution patterns and habitat associations of Fagaceae species in a Fagaceae-codominated hill forest in Sumatra were investigated. Ten Fagaceae species believed to be zoochorous (animal-dispersed seed) and five codominant canopy and emergent anemochorous (wind-dispersed seed) species from Anacardiaceae and Dipterocarpaceae were studied. Five Fagaceae species and all codominant anemochorous species were significantly aggregated while the other five Fagaceae species showed a random distribution pattern. The median distance of small saplings from the nearest reproductively mature tree tended to be shorter for aggregated species than spatially random species. This implied that some Fagaceae species dispersed over longer distances than anemochorous species. Relationships between four habitat variables and distribution of the target species were examined with torus-translation tests. Three Quercus and one Lithocarpus species showed positive habitat associations. Two Quercus species aggregated at the preferred habitat, but the others were randomly distributed. Thus tree species with specific habitat preference do not only aggregate at the preferred habitat. The three ridge-specialist Quercus species showed gradual changes in habitat association, which could reflect avoidance of competition among the species. Most of the Lithocarpus species showed little correlation with habitat variables. Coexistence of the three Quercus species partly reflected subtle differences in topographical preferences. Distribution of five of the six Lithocarpus species was unrelated to topography, so other mechanisms must be sought to account for the maintenance of coexistence in this species-rich genus.

Forests are being converted to grasslands and croplands across Africa and natural regeneration of forests is typically poor. In Serengeti National Park, Tanzania, the savanna tree species Acacia polyacantha established in riparian grasslands and forest trees subsequently established within these stands. We examined the conditions for establishment of: (1) A. polyacantha and (2) riparian (non-Acacia) forests. Fire was excluded from three grassland areas for 5 y allowing A. polyacantha to establish during 1999 when dry-season rainfall was high. The seedlings of forest tree species did not establish in grasslands, but were found in large A. polyacantha stands (> 0.3 ha) with reduced grass cover (< 10%), higher cover of herbs (> 80%) and thorny shrubs (> 90%). Seeding survival was high in large stands (0.87 y−1), but declined in artificial canopy gaps due to the ingrowth of grasses (0.21 y−1) and subsequent fires (0.07 y−1). Shrub removal also reduced seedling survival (0.46 y−1) due to browsing by antelope. We propose that: (1) A. polyacantha establishes in pulses perhaps as infrequently as twice per century, and (2) riparian forests in Serengeti have established via facilitation under larger stands where shade excludes grass, and therefore fires and thorny shrubs exclude browsers.

Fruit production by Acacia albida (Leguminosae: Mimosoideae) trees in Mana Pools National Park, Zimbabwe, was monitored over eight years. Timing of ripe fruit-fall varied between years, as did fruit production: production of ripe fruits by the same tree varied from 5.4 kg in 1983 to 290.1 kg in 1988. Baboons reduced fruit production by feeding on unripe fruits and the mass eaten each year was negatively correlated with rainfall. Potential fruit production (i.e. production in the absence of baboons) was high when the late wet season was wet or cool and when fruit production in the previous year was low. Late wet season rainfall and temperature probably determined the degree of defoliation by caterpillars: in 1983 and 1987, when the late wet season was hot and dry, the trees were almost completely defoliated. During the late dry season, A. albida fruits were an important component of the diets of waterbuck, eland, elephant, buffalo and kudu; they were seldom eaten by hippopotamus and were ignored by zebra and warthog.

Nocturnally foraging insects may be supplementary pollinators to chiropterophilous plant species when bats are scarce. Given that insects are much smaller than bats, they may be more effective at transferring pollen for plant species with similar stamen and pistil lengths, such as the ‘Monthong’ durian cultivar. The present study clarifies the role of insects in pollinating the ‘Monthong’ cultivar by examining the floral biology, conducting pollination treatments on 19 trees and observing floral visitors in southern Thailand. Stigmas were receptive by 17h00, and over 50% of ‘Monthong’ anthers had dehisced by 17h30. Several bee species began foraging on flowers during the late afternoon, and the giant honey bee (Apis dorsata) continued to visit throughout the night. Our results show that at 4 wk after pollination, the highest fruit set occurred from hand-crossed pollination (13.5%), followed by open pollination (5.5%), insect pollination (3.3%) and automatic autogamy (2.0%), indicating that this cultivar is highly self-incompatible. Moreover, insects appear to be important pollinators of ‘Monthong’ durian in areas where nectar bats visit infrequently. One bee species in particular, Apis dorsata, commonly foraged on flowers at dusk and appears to be the most effective insect pollinator of durian. Our findings highlight that nocturnally foraging bees are capable of securing pollination for night-blooming plant taxa, even those typically considered to be bat-pollinated.

Vast areas of tropical forests have been deforested by human activities, resulting in landscapes comprising forest fragments in matrices of deforested habitats. Soil seed banks (SSB) are essential sources for the regeneration of tropical forests after disturbance. In a fragmented montane landscape in the Bolivian Andes, we investigated SSB in three different habitat types that were associated with different degrees of disturbance, i.e. in forest interior, at forest edges and in deforested habitats. Sampling of habitats was replicated at six sites ranging in altitude from 1950 to 2450 m asl. We extracted seeds from dried soil samples by sieving, classified seeds into morphospecies and size classes, and characterized SSB in terms of density, species richness and composition. We tested effects of disturbance (i.e. habitat type) and altitude on SSB characteristics. Overall, small seeds (<1 mm) dominated SSB (81% of sampled seeds). Seed density and species richness were lowest in deforested habitats, especially in large seeds and distant from adjacent forests (≥20 m), while small-seeded species were most numerous near forest margins. Species turnover between habitats was high. Altitude altered the composition of SSB, but had no effects on seed density and species richness. We conclude that the potential of SSB for natural regeneration of deforested habitats is low and decreases with increasing distance from forest remnants and that forest edges may be eventually invaded by small-seeded species from deforested habitats.

The spatial patterns of canopy tree and seedling life stages in the African Tropical Tree Milicia excelsa were examined to test the Janzen–Connell hypothesis (escape hypothesis). The Janzen–Connell hypothesis states that the mortality of seeds and seedlings is highest near the adult tree and declines with distance away from the adult tree of the same species. This hypothesis argues that this effect is partially responsible for maintaining the high tree species diversity of tropical forests. Solar radiation and fruit dispersal were investigated as possible explanations of observed patterns in seedling distribution. Milicia excelsa trees ≥30 cm DBH were found to be randomly dispersed and occurred at a density of ≤1 ha. Milicia excelsa seedlings were located in small clumps between parent trees and up to 150 m from parents at a mean density of 65 seedlings ha−1. Fruits were in abundance (>9000 on the ground) beneath female trees. Light levels at locations of natural seedlings ranged from 2–29% of full irradiance. Planted seedlings did not suffer greater mortality closer to adult conspecifics, and survived at light levels between 2–37% of full irradiance. Phytolyma spp., gall-forming psyllids which cause high mortality in Milicia seedlings in large openings and plantations, were not observed on any natural or planted seedlings, although galls were present in the crowns of dominant trees.

To assess the effects of soil water status on the spatial variation in soil carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes, we examined these gas fluxes and environmental factors in a tropical rain forest in Peninsular Malaysia. Measurements of soil CO2, CH4 and N2O fluxes were taken ten, nine, and seven times, respectively over 30 mo at 15 or 39 sampling point within 2-ha plot. Mean (± SE) value of spatially averaged CO2 flux was 4.70 ± 0.19 μmol CO2 m−2 s−1 and observed spatial variation in CO2 flux was negatively related to the volumetric soil water content (VSWC) during the dry period. Over the wet period, extremely high CO2 emissions were positively correlated with VSWC at some locations, suggesting that no spatial structure of CO2 flux was because of such hot-spot CO2 emissions. Flux of CH4 was usually negative with little variation, with a mean value of –0.49 ± 0.15 mg CH4 m−2 d−1, resulting in the soil at our study site functioning as a CH4 sink. Spatial variation in CH4 flux was positively related to the VSWC throughout the entire study period (dry and wet). Some CH4 hot spots were observed during dry periods, probably due to the presence of termites. Mean value of spatially averaged N2O flux was 98.9 ± 40.7 μg N m−2 h−1 and N2O flux increased markedly during the wet period. Spatially, N2O flux was positively related to both the VSWC and the soil N concentration and was higher in wet and anaerobic soils. These findings suggest that denitrification is a major contributor to high soil N2O fluxes. Additionally, analysis by adjusting confounding effects of time, location and interaction between time and location in mixed models, VSWC has a negative effect on CO2 flux and positive effects on CH4 and N2O fluxes. We found that soil water status was related temporally to rainfall and controlled greenhouse gas (GHG) fluxes from the soil at the study site via several biogeochemical processes, including gas diffusion and soil redox conditions. Our results also suggest that considering the biological effects such as decomposer activities may help to explain the complex temporal and spatial patterns in CO2 and CH4 fluxes.

Community-wide seasonal fruiting and seed dispersal by the common brown lemur (Eulemur fulvus fulvus) was investigated in a tropical dry forest, north-western Madagascar. The brown lemur is the sole disperser of large seeds > 10 mm in diameter. Considering the limited assemblage of dispersers, large-seeded plants should display distinctive fruiting patterns to acquire dispersers. To compare fruiting patterns and seed dispersal by the brown lemur between small-seeded and large-seeded plants, fruiting conditions for 432 trees on a transect, feeding activity over 1212 h of observation, and the composition of 1126 dung samples were recorded for 1 y. Seeds of a total of 52 species were identified through both observations and faecal analysis. As rainfall increased, larger numbers of species and individuals of small-seeded plants fruited. Among the 52 species, the brown lemur dispersed 29 and 13 species with small and large seeds, respectively, during the rainy season. High moisture levels probably favoured seed germination and seedling establishment in various species. During the dry season, although small-seeded species rarely fruited, a few large-seeded species, particularly Vitex beraviensis, formed a long-term fruiting peak and provided essential food resources for the brown lemur. Because seeds of these large-seeded plants were frequently dispersed by the brown lemur, dry-season fruiting seemed to be favourable to avoid competition for dispersers with other plant species.

The wind dispersal of a plant propagule is likely to be improved by any structure that increases air resistance, e.g. the pappus of the achene of Asteraceae, the wings of Acer or dipterocarp fruits, or the plumose seed appendage which is characteristic of species of the subfamily Tillandsioideae in the Bromeliaceae. Not surprisingly then, promotion of airworthiness is usually assumed to be the primary function of this so-called ‘coma’ found in epiphytic Werauhia, Tillandsia, Guzmania or Catopsis species (Benzing 1980, 2000). However, the diverse structure of coma hairs with bifurcate cross-walls or hooks also assists in sticking to rough surfaces, such as tree bark and rocks, which indicates another important function: keeping seeds in place until germination and the development of roots (Benzing 2000, Palací et al. 2004). Multiple rather than singular functions of seed plumes or pappi have also been shown for soil-rooted plants in other plant families, where these structures are not only highly efficient for wind dispersal, but also for attachment to animal fur (Couvreur et al. 2004).

Dysoxylum gaudichaudianum is an important canopy tree on the Krakatau Islands, and its ecology is of significance to an understanding of successional dynamics. It is abundant on Panjang and Sertung, but only locally common on Rakata. A study was undertaken of three aspects of its seed ecology in July/August 1992. The chief dispersers of D. gaudichaudianum are suggested here to be birds, with two species of pigeon and a bulbul prominent as fruit feeders over a short observation period. Bird activity dislodges large numbers of fruits and seeds which fall to the ground where they form a resource available to other animals. It was observed that seeds of D. gaudichaudianum suffer varying levels of attrition on the forest floor, with 40% of the total sample lost over a 12-day period, compared with 23% which had germinated. When mature, opening fruits develop a fishy aroma, which is attractive to insects. They hasten the decay process and release the seeds. The soft, rotting tissues of fallen fruits support a small, short-lived successional insect community. After about five days on the forest floor only the seeds and the outer fruit coat remain. Despite the abundance of fruit of this species during the dry season and its obvious attraction tó frugivorous birds, D. gaudichaudianum has still colonized only a small fraction of the near-coastal lowlands of Rakata.

The ‘aggregation model of coexistence’ predicts that a strong and independent aggregation of species across ephemeral resource patches promotes species coexistence and maintains diversity. This study examines the role of aggregation in maintaining tropical dung beetle diversity and the effects of deforestation on aggregation patterns and diversity loss. Using clusters of pitfall traps, dung beetle aggregation was quantified in natural and disturbed habitat at nested temporal and spatial scales in central Peru. The results indicate that dung was colonized by a greater number of species, many of which were large, leading to a higher total beetle biomass in forest habitat than in deforested, farm habitat. Beetles were intraspecifically aggregated at each spatial scale examined. Habitat-type (forest/deforested) had no effect on the intensity of intra- or interspecific aggregation. Analyses of aggregation patterns revealed that dung beetle assemblages in forest habitat were generally saturated whereas in deforested habitat they were unsaturated. In general, interspecific aggregation was too weak relative to intraspecific aggregation to explain the high diversity of species in forest habitat. Other mechanisms, including resource partitioning are likely to play a greater role in maintaining the diversity of dung beetle assemblages in the region. These results also indicate that the loss of species from disturbed habitat has not been due to a breakdown in the aggregation mechanism.

Litter breakdown is an important ecological process at the bottom of food webs in streams. Previous studies have been based only on a temporal interval of a single season, thus ignoring seasonal variation in litter input and community structure. We investigated organic matter input in a Brazilian savanna stream and the influence of its associated hyphomycetes on the invertebrate community. Organic matter input was sampled monthly and the leaves submitted to decomposition experiments. There were lower breakdown rates and higher invertebrate species richness and abundance during the dry season, which reached their maximum in July due to low stream discharge. Invertebrate composition was best explained by hyphomycetes (mainly by Flagellospora curvula and Anguillospora filiformis). Hyphomycetes have the capacity to degrade complex compounds of litter and to rapidly absorb nutrients by growing branched filaments, thus making the leaves more favourable for consumption by invertebrates. Shredder abundance was negatively related to litter richness, indicating possible species-specific relationships. We observed a sequential process with increased leaf litter input promoting an increase in hyphomycetes biomass, which in turn favoured invertebrate density.

It has long been suggested that species might exhibit their highest densities at the centre of their geographic range and decline in density towards their range limits. If true, this pattern would have important implications for ecological theory and for conservation management. However, empirical support for this pattern remains equivocal. Furthermore, most research on this topic has emphasized temperate taxa, as is true of much of ecology. Therefore, we here test for a decline in population density from centre to edge of the geographic range of a tropical taxon, primates. In the literature we found data on 30 species and 27 genera from a total of 115 studies with duration of at least 3 mo. Mixed-effects linear models and Wilcoxon matched-pairs signed-rank tests indicated no centre–edge gradient in primate densities. However, densities were significantly lower in more disturbed sites, independent of position in the geographic range.

Lake Titicaca is the largest freshwater lake in South America and one of the highest and oldest of the world's large lakes, but very little of its ecology is known. We report results from a study on the spatial variation of decomposition rate of Schoenoplectus tatora in Inner Puno Bay affected by direct wastewater discharges. The aims of the research were: (1) to evaluate the effect of benthos exclusion and the influence of other environmental factors on decomposition and (2) to map the decomposition rate in order to describe the spatial heterogeneity in the water body. We carried out the study at 21 sampling points using both fine-meshed and coarse-meshed litterbags to exclude and to allow detritivore action, respectively. Decomposition was on the average faster in the former than in the latter treatment. However, the difference decreased with increasing detritivore abundance, and reversed in the most densely populated waters of the bay. Coupled spatial dependence of the decomposition rate and temperature was observed. Both variables were related with the distance from the wastewater discharges, suggesting that thermal pollution constrains the decomposition rate within the inner bay. Detritivores did not change the general trend imposed by temperature, but their presence increased the spatial heterogeneity of the process.

Using a data set from 36 studies, we evaluated variation in ungulate biomass across a rainfall gradient using polynomial models, aiming to: (1) compare neotropical and palaeotropical dry and wet forests as well as African savannas; and (2) evaluate the usefulness of polynomial models to predict ungulate biomass at neotropical sites using data from a dry forest (Chamela-Cuixmala Biosphere Reserve, CCBR) and a wet forest (Montes Azules Biosphere Reserve, MABR) in Mexico. Our results showed that an overestimation of expected ungulate biomass can be obtained for some tropical forests if data from African savannas are included in the model. This overestimation was particularly high for predicted ungulate biomass in neotropical dry forests. These ecosystems sustain different ungulate biomass values even when rainfall is similar. This was particularly true for some tropical dry forests and savannas. Rainfall predicted the expected ungulate biomass in neotropical ecosystems relative to that of palaeotropical ones under similar precipitation regimes, but did not correctly predict the observed ungulate biomass at local level if data outside the Neotropics are included in the model. This was more evident when we compared observed biomass against predicted biomass in the tropical dry forest of CCBR, while some polynomial models successfully predicted the observed biomass for the tropical wet forest of MABR. Factors such as Pleistocene extinctions and the absence of large, native grazers (i.e. Bovidae) that have kept ungulate richness and standing biomass relatively low in neotropical forests should be accounted for when comparing data sets from different regions.