Seed dispersal is a pivotal ecological process but remains poorly understood on Madagascar, where lemurs are key dispersers. The black-and-white ruffed lemur (Varecia variegata) possesses many behavioural and ecological attributes potentially conducive to effective seed dispersal, but no studies have investigated dispersal patterns in this species. This 3-mo study quantified aspects of the primary seed dispersal patterns generated by two Varecia variegata groups (7 individuals). Feeding and ranging behaviour was quantified using behavioural observation (345.6 h), dispersal quantity and seed identity was determined by faecal analysis, and 10-wk germination trials tested effects of gut passage on germination of four species. Individual lemurs dispersed an estimated 104 seeds d−1, of 40 species. Most seeds were large (>10 mm); the largest was 42 mm long. Gut passage was rapid (mean 4.4 h) and generally increased germination speed and success. Mean and maximum inferred dispersal distances were 180 and 506 m respectively; low compared with many anthropoids, but possibly typical of lemurs. Though limited by a short study period, results suggest that the ruffed lemur is an effective disperser of seeds and possibly a critical disperser of large-seeded species which other frugivores cannot swallow. Loss of large-bodied seed dispersers such as Varecia variegata may have far-reaching ecological consequences including impacts on forest structure and dynamics.

We used regression models and information-theoretic model selection to assess the relative importance of environment, local dispersal and historical contingency as controls of the distributions of 26 common plant species in tropical forest on Barro Colorado Island (BCI), Panama. We censused eighty-eight 0.09-ha plots scattered across the landscape. Environmental control, local dispersal and historical contingency were represented by environmental variables (soil moisture, slope, soil type, distance to shore, old-forest presence), a spatial autoregressive parameter (ρ), and four spatial trend variables, respectively. We built regression models, representing all combinations of the three hypotheses, for each species. The probability that the best model included the environmental variables, spatial trend variables and ρ averaged 33%, 64% and 50% across the study species, respectively. The environmental variables, spatial trend variables, ρ, and a simple intercept model received the strongest support for 4, 15, 5 and 2 species, respectively. Comparing the model results to information on species traits showed that species with strong spatial trends produced few and heavy diaspores, while species with strong soil moisture relationships were particularly drought-sensitive. In conclusion, history and local dispersal appeared to be the dominant controls of the distributions of common plant species on BCI.

Disruption of ecosystems is one of the biggest threats posed by invasive species (Mack et al. 2000). Thus, one of the most important challenges is to understand the impact of exotic species on native species and habitats (e.g. Jones 2008). The probability that entire ‘invasive communities’ will develop increases as more species establish in new areas (Bourgeois et al. 2005). For example, introduced species may act in concert, facilitating one another's invasion, and increasing the likelihood of successful establishment, spread and impact. Simberloff & Von Holle (1999) introduced the term ‘invasional meltdown’ for this process, which has received widespread attention since (e.g. O'Dowd 2003, Richardson et al. 2000, Simberloff 2006). Positive interactions among introduced species are relatively common, but few have been studied in detail (Traveset & Richardson 2006). Examples include introduced insects and birds that pollinate and disperse exotic plants, thereby facilitating the spread of these species into non-invaded habitats (Goulson 2003, Mandon-Dalger et al. 2004, Simberloff & Von Holle 1999). From a more general ecological perspective, the study of interactions involving introduced and invasive species can contribute to our knowledge of ecological processes – for example, community assembly and indirect interactions.

The effects of defoliation on leaf and propagule production, and leaf chemistry of the mangrove Kandelia candel (L.) Druce were evaluated in a manipulative experiment in Hong Kong. Artificial defoliation of leaf lamina at 50% of the length of midrib resulted in significant reduction in leaf, twig and propagule production, and size of the latter. Through the negative effects on propagule number and size, severe herbivory may influence fitness of the mangrove, and, thus, community structure. In contrast, no apparent adverse effects on growth and production were observable at 25% defoliation. Defoliation also significantly affected leaf chemistry of the trees, particularly those suffering 50% defoliation. Concentrations of soluble tannins and carbohydrates in leaves were significantly lower at 50% defoliation compared with the control. Total nitrogen also decreased significantly with increased per cent defoliation. Plants surviving in stressful habitats, such as mangroves, are probably more affected by loss of leaf biomass than those surviving in favourable environments.

In tropical climates, nest movements by mature ant colonies are probably widespread but the phenomenon of nest relocation is poorly described (McGlynn 2007, McGlynn et al. 2004, Smallwood 1982a). For species that nest in soil, the costs and risks associated with excavating and establishing new nests are consequential, and it is assumed that relocation occurs when the costs are offset by a more advantageous nest location (Avargues-Weber & Monnin 2009, Banschbach & Herbers 1999). Nest movements may occur to areas with greater availability of food resources or to a more favourable microclimate. Here we provide the first report of nest relocation in one of the most widespread and well described ant species in the Neotropics, Ectatomma ruidum (Roger), and we perform a manipulative experiment to test whether food availability or light environment influence nest movement.

The fruits of Melastomataceae are consumed by many Neotropical frugivorous birds. Several studies have reported segregated fruiting seasons of melastomes, but this pattern is not widespread. The segregated fruiting phenologies of congeneric sympatric species may be an evolutionary response to reduce competition for seed dispersers. Alternatively, aggregated fruiting phenologies may be favoured if local fruit abundance attracts more frugivores, thus enhancing seed dispersal. We monitored melastome fruiting in transects over a 2-y period at a cloud-forest site in the Colombian Andes. Fruiting periods of nine melastome species were aggregated and fruiting peaks coincided with rainy seasons. In a separate 6-mo study, observations at focal plants revealed that 47 of 61 bird species fed on 10 species of melastome, representing 37.4% of feeding events observed. Melastomes were consumed by birds in a higher proportion than expected from their availability and peak melastome fruit abundance coincided with the breeding season of the frugivore community, when melastomes constituted 54% of feeding records. Melastomes interact with a large number of bird species throughout their annual cycles, and seem to constitute pivotal elements that sustain the frugivore community in montane forests.

Trends in structural and chemical leaf traits along a chronosequence of semi-evergreen tropical forest and their correlation with litter production and decomposition and associated carbon (C) and nitrogen (N) fluxes were assessed. Leaves of 15 dominant species in each plot were collected to measure leaf area, specific leaf area (SLA), C and N concentration and C:N ratio. Litterfall was measured and litter decomposition experiments were set up in 16 experimental plots in a chronosequence of secondary and mature forest. All five leaf traits combined discriminated the secondary forests from mature forest. SLA, N and C:N were significantly correlated to litter decomposition rates. Litter decomposition was significantly slower in mature forest compared with secondary forests. The N concentration of litter was lowest during the dry season, when litterfall was highest. N concentration in fresh leaves was higher than in litter, indicating that N is re-absorbed before leaf abscission. Leaf dynamics and associated nutrient cycling differ significantly between secondary forests and mature forest. Ecosystem-level leaf structural and chemical traits are good predictors of the stage of the forest and explain well the differences in decomposition rates between secondary and primary forests.

Drip tips are thought to resist the growth of epiphyllous fungi, lichens, bryophytes and algae on leaf surfaces by promoting the drainage of water following rain. This hypothesis was tested by altering the tip of one leaf in each of 50 pairs of opposite leaves on plants of each of two woody species in the understorey of Barro Colorado Island, Panama. After 11 mo in situ, there were no statistical differences between the mean epiphyll cover on leaves with and leaves without drip tips. Epiphyll cover was, however, strongly correlated between the opposite leaves at a node, even though one had a drip tip and the other had the tip removed. This correlation could be due to small-scale heterogeneity of insolation, temperature and humidity in the crowns of plants. A relationship between epiphyll cover and growth of the branch containing the leaves provides qualitative support for this interpretation. It seems clear that drip tips do not have a large, consistent, easily detectable effect on epiphyll cover. However, because of the tiny cost of drip tips, reductions in epiphyll growth that are small and transitory and occur in only a portion of a plant's leaves may provide sufficient advantage to explain the evolution of drip tips. No experiment to date has been capable of detecting such effects.

To explain very low fruit production in the tropical tree Ipomoea wolcottiana (Convolvulaceae), experiments and observations are presented regarding hypotheses that fecundity is limited by foliar herbivory, low soil phosphorus, inadequate cross-pollination, low rates of pollinator visitors, and parasitism of flower buds. A 2 × 2 factorial experiment was undertaken in two consecutive years which included control of herbivores with contact and systemic insecticides and addition of phosphorus. Phosphorus application in the second year increased the number of inflorescences and flowers by 200%, and the initiation of fruits by 400%. No response was observed for the number of mature fruits. Herbivore control and the addition of phosphorus increased seed weight by 22% in the first year, but could not be measured in the second year. Hand-pollination experiments increased the fruit set by 58% in the first year and by 75% in the second. Observations on visits to the flowers showed a six-fold difference between years in rates of pollinator visits. Parasitism of flower buds was 18% in the first year and 33% in the second. Several of the differences between years probably resulted from lesser and desynchronized flowering, due to heavy unseasonal rains in the second year. The differences in floral visitation and predation of floral buds were reflected in open fruit production: 16% in the first year and 6% in the second. All the factors investigated have important effects on the fecundity of I. wolcottiana. From the evolutionary point of view, the results suggest a complex interaction among selective forces which interact with the reproductive system. The theories of sexual selection and bet-hedging are the most plausible alternatives for explaining high levels of floral abortion in this species.

Understanding the determinants of the amount of biomass in various forests is presently a global imperative because forests may (e.g. Phillips et al. 2002) or may not be carbon sinks (Clark 2002). Presently, the assumption for modelling and empirical studies is that forest biomass and net primary production (NPP) are in equilibrium. For example, Beerling & Woodward (2001) modelled world-wide plant biomass on the basis of how net primary productivity (NPP) and annual transpiration rates affect tree size. They predicted that the largest stands of organic carbon are in the wet tropics. Similarly, in a recent textbook, Chapin et al. (2002) indicate that amongst forests, tropical forests have the greatest biomass and greatest NPP. In contrast, Midgley (2001) drew attention to the negative correlation between basal area and disturbance rates in some tropical forests. Also, Enquist & Niklas (2001) demonstrated that biomass is not correlated with latitude. Indeed, many indigenous forests with exceptionally large total basal areas and thus total standing stem biomass occur in the cool-temperate areas. For example, the Pacific Northwest redwood and Tasmanian mountain-ash forests have a total basal area of 300+ m2 ha−1, which exceeds the mean of many tropical forests (i.e. 35 m2 ha−1) (see Midgley 2001 and references therein).

Seed dispersal and predation by spiny rats (Proechimys semispinosus) and red-tailed squirrels (Sciurus granatensis) were studied in five forest gaps and adjacent forest understorey on Barro Colorado Island, Panama, during June and July 2003 and January 2004. Live trapping on grids was used to estimate the abundances of rats in both habitats and was conducted during 10 nights at the beginning of each field season. We captured 70 individual spiny rats (53 in forest gaps and 17 in understorey). To address the removal and dispersal of seeds, semi-permeable wire-mesh exclosures were set at randomly selected stations within the trapping grids. These exclosures allowed the entry of spiny rats, squirrels, and other small rodents but excluded larger granivorous mammals. Seeds were marked with pieces of string that were dusted with fluorescent powder and tracked at night with an ultraviolet light. A total of 304 seeds was removed (159 in forest gaps and 145 in understorey). Spiny rats removed more seeds from gaps, and squirrels removed more seeds from understorey. Both species dispersed more seeds during the rainy season than during the dry season. Squirrels dispersed seeds farther than did spiny rats. Due to their foraging behaviour and association with gaps, spiny rats may disperse seeds from forest understorey into gaps.

The canopy disturbance regime and the influence of gap methods on the interpretation of forest structure and dynamics were evaluated in a tropical semi-deciduous forest in south-eastern Brazil. We encountered a gap density of 11.2 gaps ha−1 and an average size which varied from 121 to 333 m2 depending on the gap delimitation method considered (minimum gap size was 10 m2). Although average size was slightly higher, the median value obtained (78 m2) was comparable to other tropical forest sites and the gap size-class distribution found supported the pattern described for such forest sites. Among 297 gap makers, snapping and uprooting were the most common modes of disturbance. The number and basal area of gap makers were good predictors of gap size. Almost 25% of all gaps suffered from repeated disturbance events that brought about larger gap sizes. Such processes, along with delimitation methods, strongly influenced the estimation of turnover rate and therefore the interpretation of forest dynamics. These results demonstrated the importance of further studies on repeated disturbances, which is often neglected in forest studies.

Six rhizotrons in an Eucalyptus tetrodonta savanna revealed seasonal changes in the abundance of fine roots (≤ 5 mm diameter). Fine roots were almost completely absent from the upper 1 m of soil during the dry season, but proliferated after the onset of wet-season rains. At peak abundance of 3.9 kg m−2 soil surface, fine roots were distributed relatively uniformly throughout 1 m depth, in contrast with many tropical savannas and tropical dry forests in which fine roots are most abundant near the soil surface. After 98% of cumulative annual rainfall had been received, fine roots began to disappear rapidly, such that 76 d later, less than 5.8% of peak abundance remained. The scarcity of fine roots in the upper 1 m of soil early in the dry season suggests that evergreen trees may be able to extract water from below 1 m throughout the dry season. Persistent deep roots together with abundant fine roots in the upper 1 m of soil during the wet season constitute a ‘dual’ root system. Deep roots might buffer atmospheric CO2 against increase by sequestering carbon at depth in the soil.

We studied the resource allocation process of a large-seeded species, Dryobalanops lanceolata, during germination and early stages of seedling growth in Sarawak, East Malaysia. The seeds contained high contents of starch (74.3% of the total 1.57 g mean dry weight of the cotyledon) and lipid (15.0%). All of these reserves were exhausted by the time the first two pairs of leaves had developed (about 40 d after planting), but relatively little had been reserved in leaf or root by that time. This suggests that the large amount of seed reserve of D. lanceolata is necessary just to form a certain size of stem and the necessary number of leaves to set the plant up for photosynthesis. After seed reserves were exhausted, shoot elongation and new leaf production stopped, and most photosynthate was allocated to the expansion of the root system and to storage in the root as starch. The storage reserves in the root are thought to be used for the next growing stage, not to act as insurance for sprouting in case of shoot damage.

For sustainable logging to be achieved in tropical forests, there must be successful gap-phase regeneration to restock the logged-over area. This study examined three aspects of gap-phase regeneration in selectively logged lowland swamp forest of northeast Costa Rica. First, logging gaps were censused immediately after extraction to determine the density of advanced regeneration. Stem density and basal area of residual trees ≥ 10 cm dbh in logging gaps was >85% lower than undisturbed forest, and all trees in gaps had sustained structural damage. The common canopy species Pentaclethra macroloba (Fabaceae) was the most abundant species in gaps whereas the timber tree Carapa nicaraguensis (Meliaceae) was absent from all censused gaps. This suggests that canopy replacement, particularly by Carapa, will depend on trees <10 cm dbh or by seed input into logging gaps. Second, the diversity of the understorey was compared with 6-y old single-tree and multiple-tree logging gaps. Multiple-tree logging gaps were the most diverse, but dominated by two ruderal species; however many shade-tolerant species were present in those gaps. This indicates that controlled selective logging can result in a localized shift in species composition, but that logging gaps should return to pre-logging composition with time under a carefully implemented, controlled harvesting regime. Finally, this study found a significant effect of a fringing Carapa tree on logging gap seedling density. Thus, seed arrival into gaps is a barrier to logging gap regeneration, particularly for a large-seeded tree species. Gap-phase regeneration by a large-seeded tree species in managed forest would benefit from seed broadcasting into gaps.

Euglossine bees (Hymenoptera: Apidae: Euglossini) are considered keystone species in the neotropics because of their role as pollinators of several plant species, particularly orchids (Dodson et al.1969, Roubik 1992). Pollination by male euglossine bees occurs when they visit flowers to collect fragrances, which may be used for courtship (Eltz et al. 1999) or attraction of other males and females (Peruquetti 2000). Synthetic products that mimic those fragrances have been used frequently in studies of euglossine bee ecology and population structure (Armbruster & McCormick 1990, Powell & Powell 1987, Roubik & Ackerman 1987). The ability of euglossine bees to disperse and find isolated flowers and distant baits (Dressler 1968, Janzen 1971) has led Janzen (1981) and Janzen et al. (1982) to suggest that bees attracted to fragrances come from a wide area that may include different habitats. According to this hypothesis, individuals collected at baiting stations are part of the same pool of bees. However, Armbruster (1993) found significant variation in the number of bees collected at nearby baiting stations, and he considered these differences as demonstration of within-habitat heterogeneity of the euglossine bee community. In Armbruster's model, results of bait collections are strongly affected by the concentration of resources in ‘hot spots’, therefore a sampling station would not necessarily represent the habitat, but only particular microhabitats.

This paper presents a method for estimating monkey numbers in a large area of forest where there is a gradient of monkey densities. The method is illustrated using data collected in the northeastern forests of Gabon during an earlier project. These forests are sparsely populated and there are few roads. The density of Cercopithecus nictitans increases with distance from the nearest road. A geographic information system (GIS) divided the forest into bands of increasing distance from the nearest road. The number of monkeys in each band is the product of the monkey density in that band and the area of the band. Summing across bands gives the population estimate; the standard error can be estimated by bootstrapping. The optimum sample size can be estimated by simulation. Combining estimates of the density gradient with a GIS is a cost-effective method of censusing primates in extensive forests.

Drip-tips are a common phenomenon in tropical rain forests, often believed to facilitate drainage of water from the leaf surface and, in that way, reduce epiphyll growth. Some authors suggest a function in reducing splash soil erosion, leaching of substances from the leaf, and light reflectance, while other studies did not find any such correlations. We used an experimental approach to test for the effect of drip-tips on the development of epiphyllous lichen communities. Artificial leaves with and without pronounced drip-tips were exposed in a tropical lowland rain forest at La Selva Biological Station (Costa Rica) for a period of 38 mo, and the physical behaviour of rainwater was tested. On leaves with drip-tips, the water ran off in small, frequent drops 8–30 mm3 in size. On leaves without drip-tips, the water accumulated in the apex region and dripped off periodically in large drops 50–150 mm3 in size. Nevertheless, there was no significant difference in the development of epiphyllous lichen communities on leaves with and without drip-tips, in terms of area covered, species richness and composition. However, leaves without drip-tips had more debris accumulated in the apex region and, at the same time, fewer lichen species present in this region. Thus, while drip-tips do have an influence on how water is channelled off the leaf surface, they do not impair the development of epiphyllous lichen communities, except for the apex region where the presence of drip-tips does in fact enhance, not reduce, the establishment of lichens, by preventing the accumulation of debris. We conclude that, while drip-tips may have an ecological function, this function is unrelated to the development of epiphyllous lichen communities.

A survey of small mammals was made in a tree plantation in Sabah, East Malaysia. Transects within pure plantings of Eucalyptus deglupta, Gmelina arborea, Albizia falcataria, and A. falcataria/Theobroma cacao were compared with a similar transect laid through seven-year-old logged forest near the plantation. A total of 16 small mammal species were trapped, with 11 found in the logged forest area, and 15 in the plantation. Values for the Shannon-Wiener Diversity Index (H') and for biomass were highest in logged forest, which also showed a low (<45%) Percent Similarity when compared with any of the plantation areas. Highest diversity and biomass values within the plantation were found in Albizia falcataria plantings, while the lowest were found in A. falcataria underplanted with Theobroma cacao. All plantation areas were dominated by Maxomys whiteheads, whereas A. falcataria plantings had the highest numbers of Tupaia glis and Tupaia tana.

The study shows that although tropical plantations of exotic tree species can support a large number of species of scansorial small mammals, overall diversity and species biomass per hectare is much lower than that found in logged forest.