Sapling mortality exceeds recruitment for many species of trees in the dry forest of 16-y-old islets in Lago Guri, Venezuela. Failure of sapling recruitment is potentially attributable to the aberrant animal communities of these islands. Predators of vertebrates are absent and densities of pollinators and seed dispersers are substantially reduced in comparison to the nearby mainland. In contrast, predators of invertebrates, rodents and generalist herbivores (leaf-cutter ants, howler monkeys, common iguanas) are present at greatly elevated densities. Given these distortions in the animal community, recruitment failure of saplings could potentially be attributable to several causes: reduced pollination or seed dispersal, excessive seed predation or seedling herbivory. Two of these hypotheses are tested herein. The seed predation hypothesis predicts greater seed removal in the presence of hyperabundant rodents, and the seedling herbivory hypothesis predicts reduced seedling survival in the presence of hyperabundant herbivores. Seed removal trials were conducted with 18 species of forest trees, using both exposed and lightly buried seeds. Seed removal was not generally higher on islands supporting hyperabundant rodents, contrary to the seed predation hypothesis. Seedlings exposed to herbivores for 4 mo suffered the highest mortality on small islands supporting hyperabundant rodents and leaf-cutter ants. Saplings survived equally well in cages open to arthropods + rodents as in cages open only to arthropods, suggesting that there was no additive effect of rodents on seedling mortality. Current evidence points to excessive seedling herbivory by arthropods, especially by leaf-cutter ants, as the principal cause of recruitment failure on predator-free Lago Guri islets.

Data on litterfall, litter layers accumulated on top of the mineral soil and layer mineralization collected for three years in a tropical rain forest at Pernambuco, Brazil, were implemented on a simulation model. Litterfall was collected biweekly using 11 collectors 1 × 1 m. Every three months, 20 litter mat samples, 0.5 × 0.5 m, were collected, divided into the L, F and H layers and the CO2 evolution from each litter layer was determined in the laboratory. Litterfall, in the three years, averaged 7.8, 8.3 and 8.2 Mg ha-1 y-1, most of it leaves. Litter mat masses varied widely from place to place (15–90 Mg ha-1) and the overall averages were 5.6, 7.6 and 26.1 Mg ha-1 for the L, F and H layers, with CO2 evolution averages of 2.27, 0.507 and 0.123 mgC g litter C-1 day-1. According to the model, the L layer had a high turnover rate, losing 4.7 Mg ha-1 y-1 through mineralization and 3.4 Mg ha-1 y-1 transferred to the F layer. Values for the F and H layers were 1.4 and 1.2 mineralized and 2.0 and 0.8 Mg ha-1 y-1 transferred. Thus, it would take 2.1, 6.7 and 39 years for newly fallen leaves to be mostly fragments, to be transformed to humus and to be incorporated to the soil organic matter, respectively. Variations of litterfall throughout the three years would have little effect on the system which was not very sensitive to litterfall changes, except for the top layer.

All stems ≥ 1 cm dbh were measured, tagged, mapped and identified on a 1-ha plot of rain forest at Gambubal State Forest, south-east Queensland, Australia. The spatial patterns and size class distributions of 11 common tree species on the plot were assessed to search for mechanisms determining their distribution and abundance. The forest was species-poor in comparison to many lowland tropical forests and the common species are therefore present at relatively high densities. Despite this, only limited evidence was found for the operation of density-dependent processes at Gambubal. Daphnandra micrantha saplings were clumped towards randomly spaced adults, indicating a shift of distribution over time caused by differential mortality of saplings in these adult associated clumps. Ordination of the species composition in 25-m × 25-m subplots revealed vegetation gradients at that scale, which corresponded to slope across the plot. Adult basal area was dominated by a few large individuals of Sloanea woollsii but the comparative size class distributions and replacement probabilities of the 11 common species suggest that the forest will undergo a transition to a more mixed composition if current conditions persist. The current cohort of large S. woollsii individuals probably established after a large-scale disturbance event and the forest has not attained an equilibrium species composition.

Habitat fragmentation causes a sharp increase in the forested area affected by edge effects (Murcia 1995). Compared with the core of the forest, edges present higher litterfall rates, air and soil humidity reduction, higher temperature and increased wind incidence (Bierregaard et al. 1992, Didham & Lawton 1999, Laurance et al. 1998, Matlack 1993). These features of edges may increase the probability of fire occurrence, especially if the surrounding vegetation is composed of grasses (D'Antonio & Vitousek 1992, Freifelder et al. 1998). After a fire, the damaged edge will grow substantial amounts of herbaceous vegetation, extending the inflammable area into the forest, and thereby creating a positive feedback system of fire susceptibility and intensity (Cochrane & Schulze 1999, Cochrane et al. 1999). Fires may affect the structure and composition of the vegetation (Cochrane & Schulze 1999, Didham & Lawton 1999, Sanaiotti & Magnusson 1995), favouring, in the long-term, the dominance of the community by species characteristic of disturbed habitats and making the habitat unsuitable to primary forest species (Malcolm 1994, Possingham et al. 1994). Unfortunately, there are few studies on the effects of fires on neotropical small-mammal populations (Borchert & Hansen 1983, Ojeda 1989, Vieira & Marinho-Filho 1998). The objective of this study was to analyse the influence of a fire on populations of two rodent species, Akodon cursor (Winge) and Oecomys concolor (Wagner) in two fragments of Atlantic Forest in Brazil.

We investigated the links between slope variation and heterogeneity in tree growth and stand structure. The study was conducted in an undisturbed wet evergreen forest in India. We selected three plots situated on gentle slopes and three plots situated on steep slopes. Tree growth was considered as mean annual diameter increment. Stand structure was considered in relation to several characteristics: trunk diameter distributions, tree heights, and spatial distributions of stems and crowns. Except for the spatial structure, analyses were performed on samples including either all the species or only the dominant species (Vateria indica L.). Diameter growth varied according to slope intensity and to tree size: growth of large trees was clearly higher on steep slopes whereas growth of small trees proved lower or similar. Diameter distributions were different among the six plots, but the difference cannot be related to slope intensity. On the contrary, tree heights differed according to slope intensity: for a given diameter, trees were taller on gentle slopes than on steep slopes. Finally, stem spatial distributions showed strong regularity on gentle slopes whereas they were random on steep slopes. The observed changes between gentle and steep slopes suggest differences at tree level through a modification of its shape, but also differences in the major processes responsible for stand dynamics: competition, establishment and survival.

The diets of larvae and juveniles (cut-off size: 20 mm) of Limnothrissa miodon (Boulenger) were studied at 2-h intervals during four 24-h cycles (two during the rainy and two during the dry season) in the Bukavu Basin, Lake Kivu. Larvae and juveniles are both diurnal feeders, and they both feed essentially on copepods, which are the most abundant prey in littoral areas, but they show a marked preference for larger organisms (cladocerans), when available. This indicates a rather intense resource sharing, and probable competition between life stages, which is partly solved through spatial behaviour and segregation. During the dry season, when food resources are scarcer, larvae and juveniles make slightly offset inshore migrations during the day, so that they feed at different places, on copepods of different sizes. Because diel migrations are size-structured, it is suggested that cannibalistic pressure (by adults over juveniles, and by juveniles over larvae) may also be a driving factor for these migrations. Plankton samples revealed that there were few cladocerans, while copepods were abundant and their size was similar to that prior to the introduction of L. miodon in Lake Kivu, thereby suggesting that some form of dynamic equilibrium has been reached in the food web.

Seeds dispersed and deposited by wind, animals and other dispersal agents are a fundamental component of natural forest succession, plant regeneration and population maintenance, aside from increasing a population's genetic pool in tropical ecosystems (Henry & Jouard 2007, Muscarella & Fleming 2007, Wilson & Traveset 2000). Frugivorous bats and birds are ideal vectors for long-distance seed dispersal; therefore, studies of the food habits of frugivores and the specific identities of the dispersers are essential for understanding ecological patterns and processes in tropical environments. Studies related to succession processes, the frequency, number and composition of seeds dispersed by animals are essential in order to generate new data and hypotheses, consequently the method and quality of obtaining data are important.

Fruit and seed consumers can both positively and negatively affect plant recruitment through seed dispersion and seed predation, respectively. In turn, fruits influence the abundance and distribution of consumers sustained by local plant assemblages. These interactions are key processes in plant recruitment and the dynamics of tropical forests, where most plants depend on dispersal by frugivorous animals (Corlett 1998). An understanding of these interactions and the functional role of particular seed-dispersing animals is increasingly important nowadays, given that human impact on tropical forest ecosystems may negatively impact seed dispersal and forest regeneration in both natural and human-altered forests (Wright et al. 2000).

The effects of fragmentation and overstorey tree diversity on tree regeneration were assessed in tropical rain forests of the Western Ghats, India. Ninety plots were sampled for saplings (1–5 cm diameter at breast height (dbh); 5×5-m plots) and overstorey trees (>9.55 cm dbh; 20×20-m plots) within two fragments (32 ha and 18 ha) and two continuous forests. We tested the hypotheses that fragmentation and expected seed-dispersal declines (1) reduce sapling densities and species richness of all species and old-growth species, and increase recruitment of early-successional species, (2) reduce the prevalence of dispersed recruits and (3) increase influence of local overstorey on sapling densities and richness. Continuous forests and fragments had similar sapling densities and species richness overall, but density and richness of old-growth species declined by 62% and 48%, respectively, in fragments. Fragments had 39% lower densities and 24% lower richness of immigrant saplings (presumed dispersed into sites as conspecific adults were absent nearby), and immigrant densities of old-growth bird-dispersed species declined by 79%. Sapling species richness (overall and old-growth) increased with overstorey species richness in fragments, but was unrelated to overstorey richness in continuous forests. Our results show that while forest fragments retain significant sapling diversity, losses of immigrant recruits and increased overstorey influence strengthen barriers to natural regeneration of old-growth tropical rain forests.

In a 30-ha permanent plot of tropical evergreen forest at Varagalaiar, Indian Western Ghats, all trees ≥ 30 cm girth at breast height (gbh) were examined for the presence of lianas ≥ 1 cm dbh. The plot contained 13 445 trees in 152 species and 11 200 lianas in 75 species. Twenty-eight per cent of trees supported lianas and the mean number of lianas per tree was 0.38 ± 0.72. Association analysis between lianas and trees of 16 tree families and 20 abundant tree species indicated that tree susceptibility to lianas was better pronounced at species rather than at family level. Overall, at Varagalaiar site, the aggregation of lianas followed neither Poisson nor clumped distribution. Among the four dominant tree families Dipterocarpaceae and Clusiaceae fit to the negative binomial model better than Euphorbiaceae and Meliaceae. These four families differed in their susceptibility level with 34.6% , 36.7% , 24.1% and 27.7% of trees ≥ 30 cm gbh respectively supporting lianas. At the species level, the proportion of trees with lianas was positively correlated with the mean branch free bole height of trees ≥ 30-40 and ≥ 40 cm gbh classes, and the mean number of lianas per tree was also positively correlated with the mean branch bole height of trees ≥ 30 cm gbh. Of the 16 abundant families, Euphorbiaceae contributed 31% and dominated the lower canopy, but its susceptibility to lianas was lower when compared to most other families.

A pteropodid bat community was surveyed in a West African rain forest using mist-nets set for 3 mo in 2 consecutive years (1996-97). The captures were carried out in the understorey and in the canopy for a total of 5054 mist-net hours and were analysed to answer three main questions: (1) to what extent does the bat assemblage vary along the vertical axis, (2) does the observed vertical stratification depend on wingspan (with largest bats preferring canopy openings to the cluttered understorey) and (3) was the vertical stratification repeatable from one year to the next? Nine bat species were reported, among which two were captured exclusively in the canopy where the total capture rate tended to be higher. The community structure did not differ between the four canopy stations. Four species significantly favoured canopy, two significantly favoured understorey and two were opportunistic regarding vertical stratification. Wing size and canopy-preference index were not significantly correlated and except for Eidolon helvum, index values for the 2 sampling years were correlated. Important inter-annual and seasonal variations of species richness and capture rate were observed and these are discussed in relation to rainfall patterns and migratory behaviour of the species concerned.

The orchids Dendrobium infundibulum and Cymbidium insigne are pollinated by the bumblebee Bombus eximius, which also pollinates the ericaceous shrub Rhododendron lyi, A study of the three plants and the bumblebee in maquis-like mountainous vegetation in northern Thailand suggests that they form a floral mimicry system with two mimics (the orchids) to one model (R. lyi). The flowers of the two orchid species offer no food reward to pollinators. Flowers of the three species show definite morphological and visual resemblance, and the species overlap to a great extent in flowering phenology and habitat Mimic flowers were much less numerous than model flowers, which occurred abundantly in the area. The rate of pollinaria removal was very low in both orchid species, resulting in a relatively small percentage of fruit set, especially in D. infundibulum. Infrequency of pollinator visits was, however, somewhat counterbalanced by long-lasting flowers. The pollinaria of the two orchid species are differently positioned on the bee, hence interference between the different reproductive systems is minimized. This is the first report which indicates floral mimicry from tropical Asia.

The pattern of coarse-root distribution was analysed in the woody plant community along a 200-m edaphic gradient on a Kalahari sand woodland catena in Zimbabwe. The root systems of 45 trees and shrubs were excavated, mapped, and digitized to analyse rooting depth and architecture. Patterns of change in the above-ground community were also identified along this transect. Rooting depth increased, and the centre of mass of the root profile shifted towards the maximum rooting depth as a function of distance up the catena. The data also suggest that interspecific variation in rooting depth may increase up the catena. The below-ground pattern was accompanied by above-ground changes: species richness and basal area also increased up the catena. It is hypothesized that increasing soil depth allows greater coexistence of alternative water-use strategies, resulting in the observed increase in species richness up the catena.

Over recent decades, studies on post-dispersal seed predation have revealed some general patterns despite dealing with a highly variable phenomenon (reviews in Crawley 1993, Hulme 1998). Most of these studies, however, were carried out with plant species whose population density range from low to moderately high (Hulme 1998). Only rarely has seed predation been studied in very dense stands of a given plant species (Schupp 1988a, b, 1992). In such a situation, seed predators might respond to the local availability of seeds in a manner that differs from their response under conditions of low seed density. For instance, a high density of seeds beneath a fruiting plant may attract seed predators, causing a positive correlation between predation and seed density (Janzen 1970). Schupp (1992), however, noted that at a population scale, a high density of seeds could satiate predators, resulting in a negative correlation between predation and seed density (see also Burkey 1994).

Most of the land surface of Melville Island, Australia's second largest island, is covered in Eucalyptus savanna. One exception is an area at Yapilika where a large tract of savanna is dominated by Acacia shrubs. An ordination analysis of 122 quadrats revealed that the boundary of Eucalyptus dominance did not correspond to a major change in floristic composition. Detailed transect studies at one site on the boundary showed that Eucalyptus trees were abruptly replaced by a band of Grevillea trees which gradually gave way to Acacia shrub dominance. There was a gradual change in the floristic composition of the savanna across the boundary. The distributional limit of Eucalyptus was found to be independent of any hydrological discontinuity. There was a slight decrease (<2.5 m) in altitude from Eucalyptus to Acacia savanna. The Acacia savanna soils were sandier and their surface soil had significantly lower concentrations of Ca and Mg and significantly greater concentration of Al compared with the Eucalyptus savanna soils. Eucalyptus seedlings planted in the three savanna communities were not found to be under drought stress (pre-dawn leaf xylem potentials of > – 0.9 MPa) during the dry season. Over a 12 month period Eucalyptus tetrodonta and E. miniata seedling growth was not significantly different on the Acacia or Eucalyptus savanna, although this result may be due to the counteracting effects of greater soil fertility and tree competition in the Eucalyptus savanna and lower soil fertility in the treeless, and hence competition-free, Acacia savanna. This hypothesis is supported by the significantly greater growth of Eucalyptus seedlings on fertilized Acacia savanna soils. The limited production, dispersal and establishment of Eucalyptus seeds and the greater frequency of fires in the Acacia savanna probably explains the abrupt limit to Eucalyptus dominance along the edaphic gradient.

Although resource specialization occurs along a continuum, species are often defined as either specialists or generalists. In general, specialists are more prone to extinction than generalists and, thus, are often the first species to be lost when habitats are modified. The two-toed sloth (Choloepus hoffmanni) and the three-toed sloth (Bradypus variegatus) are arboreal herbivores distributed across the Neotropics. The two-toed sloth is considered a generalist while the three-toed sloth is more specialized. Both species inhabit shade-grown agro-ecosystems but, at least at one study site, only the two-toed sloth was viable. To quantify specialization in sloth species and explore how it influences population viability, we characterized the resource use for 68 adult and 12 subadult sloths across 3 y. The two-toed sloth used 14 tree species relatively uniformly across habitats, while the three-toed sloth largely depended on only two species of tree regardless of habitat type. Both species selected for patches of intact tropical forest, strongly avoided monocultures regardless of spatial scale and generally used cocoa similarly in proportion to availability. However, the sloth species differed in their use of cattle pastures, with the two-toed sloth selecting for pastures and the three-toed sloth avoiding them. Overall, the two-toed sloth exhibited greater plasticity in tree and habitat use, which is likely contributing to its enhanced resilience within this modified agro-ecosystem.

Secondary forests occupy a growing portion of the tropical landscape mosaic due to regeneration on abandoned pastures and other disturbed sites (Asner et al. 2009). Tropical secondary forests and degraded old-growth forests now account for more than half of the world's tropical forests (Chazdon 2003), and provide critical ecosystem services (Brown & Lugo 1990, Guariguata & Ostertag 2001).

This study determined variation in liana diversity, composition and community structure in different topographic habitats, as well as the environmental factors associated with them in the Atewa Range Forest Reserve, Ghana. The above-mentioned liana assemblage attributes were examined in thirty 40 × 40-m plots, randomly demarcated within three topographic habitats at different average altitudes (hill bottom: 85.6 m asl, hill slope: 343 m asl, plateau: 641 m asl). Soil properties, altitude and slope angle were determined for the plots. Using multiple stepwise regression, non-metric multidimensional scaling analysis, and analysis of similarity, environmental factors that influenced the above-mentioned attributes of liana assemblages were determined. The findings revealed significant variation in liana diversity, composition and community structure among the topographic habitats. Liana species composition related with soil P, Mg and moisture, and altitude. Soil Mg and P associated positively with species composition in the hill-bottom habitat while altitude and soil moisture related negatively with it. A reverse trend occurred in the other habitats. Five environmental factors related significantly with liana diversity and community structure as follows – species richness: soil Ca and Mg, altitude; Shannon diversity: soil Ca, altitude; abundance: soil moisture and P, altitude; basal area: soil moisture, P.

We evaluated effects of corridors between forest fragments surrounded by pastures in tropical Mexico. We used experimental translocations and capture–recapture data to measure the proportion of birds returning and time to return after translocation between connected and unconnected patches (five replicates for each treatment). Depending on each species’ degree of forest dependence (forest-restricted and forest-unrestricted species), we assigned birds to two groups to evaluate influence of species characteristics on effects of corridors on movement. Birds translocated between connected patches (n = 75) were seven times more likely to be recaptured in their original capture site when compared with birds translocated between unconnected patches (n = 109). Effects differed among the two species groups. In the presence of corridors, 46% of forest-unrestricted birds returned to the capture site while only 5% returned between unconnected patches. Forest-restricted birds showed similar results, but were only twice as likely to return to a connected capture site. Birds translocated between unconnected patches took longer to return than birds translocated between connected patches. The strong positive effect of corridors on movement, even for forest-unrestricted species, suggests that forested corridors facilitate bird movement and help maintain connectivity even in this highly fragmented landscape.