Mbau forest covers much of the Congo, and shifts in its composition could have a large impact on the African tropics. The Ituri forest in east Congo is near a boundary between the monodominant mbau type and non-mbau mixed forest, and two 20-ha censuses of trees ≥ 1 cm diameter were carried out over 12 y to monitor forest change. Based on published diameter allometry, mbau forest had 535 Mg ha−1 biomass above ground and gained 1.1 Mg ha−1 y−1. Mixed forest had 399 Mg ha−1 and gained 3 Mg ha−1 y−1. The mbau tree (Gilbertiodendron dewevrei) increased its share of biomass from 4.1% to 4.4% in mixed forest; other common species also increased. Sapling density declined at both sites, likely because increased biomass meant shadier understorey, but the mbau tree increased in sapling density, suggesting it will become more important in the future. Tree mortality and growth rates were low relative to other tropical forests, especially in the mbau plots. Shifting toward G. dewevrei would represent a large gain in carbon in the mixed forest, but mbau is presently more important as a high-carbon stock: biomass lost during forest harvest could not recuperate for centuries due to slow community dynamics.

Food webs of streams draining tropical rain forests on Costa Rica's Pacific and Caribbean coasts were examined in the 1980s via dietary analyses, and the same streams were surveyed again in 2004 to compare trophic structure based on analysis of stable isotope ratios of fish, macro-invertebrate and plant tissues. Estimates of species’ trophic positions (TP) were calculated from stomach-contents data (51 species; 5420 specimens) and compared with TP estimates derived from analysis of nitrogen isotope ratios (82 taxa; 240 samples). Coefficients of determination for TP based on dietary versus isotopic analysis ranged from 0.18 (Quebrada Camaronal, Corcovado) to 0.73 (Quebrada Estacion, Tortuguero). Consumer taxa within all four streams spanned a broad range of carbon isotope values, indicating assimilation of variable proportions of carbon from periphyton and terrestrial vegetation that in all but one of the streams had similar δ13C values. Approximately half the consumers in all four streams had carbon ratios heavier than any of the in situ production sources examined. This pattern could be explained by consumption of other production sources that were not sampled, including periphyton taxa with variable carbon isotope signatures, or migration of prey and/or consumers between these freshwater and coastal marine habitats.

Vegetation and environment change mutually during secondary succession, yet the idiosyncrasies of the vegetation effect on the understorey environment are poorly understood. To test whether the successional understorey environment changes predictably and is shaped by the structure and seasonality of tropical dry forests, we estimated basal area and vegetation cover, and measured understorey temperature, light and moisture conditions, in 17 plots forming a 60-y chronosequence and a mature forest. Light and air and soil temperature decreased with time (75−15% of open-sky radiation, 31.7−29.3 °C, and +2.5 °C to −0.5 °C relative to ambient, respectively), whereas relative humidity increased (67−74%). Soil water availability increased with early-successional development (−45 to −1 kPa) but decreased afterwards (to −18 kPa). The first axis of a PCA of the rainy-season environment explained 60% of the variation and was strongly related to air temperature and relative humidity. During tropical dry-forest succession, such factors may be more important than light, the reduction in which is not extreme compared with taller and more vertically stratified wet forests. Seasonality significantly affected the successional environmental gradients, which were marked mainly during the wet season. Environmental heterogeneity was higher in the wet than in the dry season, and larger for resources (light and water) than for conditions (temperature and humidity). The wet-season increase in environmental heterogeneity potentially creates differential growing scenarios; the environmental harshness of the dry season would mostly challenge seedling survival.

Island biotas often have lower species diversity and less intense competition has been hypothesized as a result. This should result in lower habitat specificity compared with mainland habitats due to larger realized niches. We investigate microhabitat associations of canopy trees with regard to differences in topography on an oceanic island (Viti Levu, Fiji) using twenty 10 × 60-m plots. We find high tree-species diversity (112 species with dbh ≥ 10 cm in a total of 1.08 ha) and high endemism (c. 60%), compared with other islands in Western Polynesia. Our sample plots aggregate into three distinct groups that are mostly defined by micro-topography: (1) ridges and steep slopes (well-drained sites), (2) moderate slopes and ridge flats (moderate drainage), and (3) flats (poor drainage). Associations with microhabitat are found for more than 50% of the 41 most common species but only one species is apparently restricted to a single habitat. These findings are similar to other rain forests and demonstrate considerable niche differentiation among island rain-forest tree species.

The relationship between herbivore diet quality, and diet composition (the range of food plants consumed) and body mass on resource partitioning of herbivores remains the subject of an ongoing scientific debate. In this study we investigated the importance of diet composition and diet quality on resource partitioning among eight species of savanna herbivore in north Cameroon, with different body mass. Dung samples of four to seven wild herbivore and one domesticated species were collected in the field during the dry and wet period. Diet composition was based on microhistological examination of herbivore droppings, epidermis fragments were identified to genus or family level. In addition, the quality of the faecal droppings was determined in terms of phosphorus, nitrogen and fibre concentrations. The results showed that there was no significant correlation between body mass and (differences in) diet composition for wet and dry season. When all species are considered, only significant relationships are found by the Spearman rank correlation analyses during the wet season between body mass and phosphorus and nitrogen, but this relationship did not exist during the dry season. When the analyses focuses on ruminants only (thus leaving out hippo), none of the relationships between body mass and diet quality was significant in either season. During the dry season the proportion of graminoids ranged between 10% (small unidentified herbivore species) to 90% (hippopotamus), during the wet season this proportion ranged from 60% (zebu) to 90% (hippopotamus). All species but zebu had more graminoids in their dung during wet season compared with dry season. However all species but hartebeest had more graminoids old stems in their dung during the dry season, compared with the wet season. The niche breadth for food categories consumed by kob (0.300), hippo (0.090), hartebeest (0.350), roan (0.510) and zebu (0.300) was much greater in the dry season than in the wet season for kob (0.120), hippo (0.020), hartebeest (0.190), roan (0.090) and zebu (0.200). When looking at grass taxa consumed, the niche breadth of kob (0.220), hartebeest (0.140), and roan (0.250) was also greater in the dry season when compared with the wet season for kob (0.050), hartebeest (0.120) and roan (0.120). The opposite was found for zebu and hippo. Comparison of the species’ diet compositions with randomized data showed that dietary overlap between different herbivore species was much higher than what would be expected on the basis of chance, demonstrating surprisingly limited niche separation between species. This offers potential for competition, but it is more likely that the high niche overlap indicates absence of competition, due to low herbivore densities and abundant food resources, permitting species to share non-limiting resources. With increasing herbivore densities and subsequent increasing scarcity of resources, the relationship between diet quality and body mass in combination with increased niche separation is expected to become more visible.

The tropical montane conifer tree Widdringtonia whytei is found in small fragments on Mulanje Mountain in Malawi. A study was conducted with the objectives of determining the effect of population size, tree stem diameter and crown position on the proportion of viable seeds per cone produced by W. whytei at three sites (Sombani, Chambe and Lichenya) on Mulanje Mountain. Three population sizes, namely small (fragments with ≤10 cone-bearing trees), medium (fragments with 11–20 cone-bearing trees) and large (fragments with >20 cone-bearing trees) and isolated trees were sampled at each study site. In each fragment, four cone-bearing trees were randomly located, 20 mature cones were collected from each tree and the viability of seeds was tested. Only 23% of the seeds per cone were viable but seed viability per cone was highly variable among fragments. Large fragment populations produced the highest proportion of viable seeds per cone (30%), followed by similar proportions in small fragments (28.3%) and isolated trees (26.1%), with the lowest proportions in medium-sized fragments (18.7%), indicating a non-linear relationship between viable seed output per cone and population size. Tree stem diameter and crown position had no effect on the proportion of viable seeds per cone. Further studies are needed to identify the factors that lead to the low viable seed output per cone, and how this influences whole-tree seed production in W. whytei.

Pollinator visits to flowers of self-incompatible tropical trees are critical for plant fecundity. However, few studies have examined how much of the variance in tropical tree fecundity is explained by individual attributes of trees (e.g. number of flowers), and how much is due to contextual variables such as distances to nearest flowering neighbours. Using multiple regressions we examined the relative contributions of these factors to the pollination and fecundity of Goetzea elegans, a mainly self-incompatible tree endemic to Puerto Rico. We studied the largest wild population of the species during the peak flowering and collected data on the frequency of pollinator visits (N = 25 trees), and the fecundity of the whole population (N = 105), including the visitation rate of two pollinators (the honey bee Apis mellifera and the bananaquit Coereba flaveola), the total number of flowers produced by each tree, and the total fruit set and seed viability per tree. We also recorded the distance to flowering conspecifics and heterospecifics, and the height for each tree. Flower number had a strong positive effect on pollinator visitation, but distance to nearest neighbours was equally or more important than flower number in influencing fecundity. Also, competition for limited pollinators between G. elegans and other species has a stronger effect than the facilitation that conspecifics may provide. Our results suggest that pollinator visits and aspects of fecundity of G. elegans depend both on the attributes of individual plants, and on those of the community of other nearby plants.

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.

Many plant species in tropical dry forests partly base their ability to persist after disturbance on resprouting. Yet little is known if this ability can be affected by the intensity and seasonality of disturbance and whether the amount of resources (starch, N, P) stored in the taproot may constrain this response. We investigated resprouting after experimental clipping or burning, applied before or after the dry season and repeatedly in Acacia pennatula individuals in wooded rangelands of North-West Nicaragua. Each treatment was applied to 12 trees and replicated in six plots. One year after the onset of the experiment, survival and biomass recovery were significantly lower in burned than in clipped individuals (78% ± 4% and 75.3 ± 8.0 g vs. 94% ± 2% and 79.1 ± 6.8 g; mean ± SE). Whatever the disturbance applied, trees disturbed after the dry season significantly showed the lowest survival, growth and concentration of N and P. These results suggest that resprouting in dry tropical species may be constrained by intense disturbances (e.g. burning) but especially if they occur towards the end of the dry season. This phenological constraint could be due to the reduced availability of N and P as this dry season progresses.

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.

In South America, the invasive feral pig (Sus scrofa Linnaeus) has become established in Argentina, Uruguay, Paraguay and in a wide range within Brazil, along the southern half of the Atlantic Forest, in the cerrado (savanna) and in the Pantanal wetland. The geographical ranges of the two most common South American native peccary (Tayassu pecari Link and Pecari tajacu Linnaeus) overlap almost entirely, and the feral pig now co-occurs with them in several areas. Because feral pig, white-lipped and collared peccary are considered ecological equivalents, there has been much speculation about possible competitive interactions among them (Desbiez et al. 2009, Sicuro & Oliveira 2002).