An on-going controversy in community ecology involves the debate about the many factors that affect the assembly and composition of a given species assemblage. Theory suggests that community composition is influenced by environmental gradients or biotic processes. This study examines patterns of community composition in two tropical tree frog assemblages of primary and exploited lowland rain-forest sites in the Guiana Shield area of central Guyana, South America and the Upper Guinean rain-forest block of south-western Côte d'Ivoire, West Africa. We tested community composition and species abundance data of two adult tree frog communities collected on 21 standardized transects during a period of 5 y for evidence of spatial correlation in community composition. We applied simple and partial Mantel tests to separate the effects of environmental variables, spatial distance and spatial autocorrelation on community composition. Whenever environmental effects were accounted for, we found significant positive spatial correlation of community composition. All assemblages appeared to be spatially structured, i.e. sites in close proximity had similar species assemblages. However, spatially structured environmental variation (autocorrelation) did not account for the spatial structure of species incidence. Environmental factors did not prove to be significant predictors of species incidence in any of the assemblages analysed, even if we controlled for spatial effects. Observed correlation patterns of species composition were consistent within respective realms and disturbance regimes. Moreover, general correlation patterns were consistent between geographic regions. These results are in contrast to previously published results from a study on leaf-litter anurans and indicate that group-specific differences must not be neglected when analysing patterns of species composition in anurans as they may drastically alter the outcome of the analysis.

The relationship between leaf longevity and other leaf traits was compared among different life-form categories (trees, herbs, climbers and epiphytes) of 101 plant species in a tropical montane forest on Mt. Halimun, West Java, Indonesia. We applied the Cox proportional hazards regression to estimate the leaf longevity of each species from 30 mo of census data. We examined whether estimated longevity was explained by either species life-form categories, taxonomic groupings (eudicots, monocots, magnoliids and chloranthales, and ferns) or such leaf traits as leaf area, leaf mass per area (LMA), mass-based leaf nitrogen, penetrometer reading, condensed-tannin-free total phenolics and condensed tannin. There was a wide-ranged interspecific variation in leaf longevity, mostly 10–50 mo, similarly across life-form categories. LMA showed a strong positive influence on leaf longevity. We found that relationships between leaf longevity and some leaf traits were different among various life forms. Trees tended to have high LMA, while climbers tended to have low LMA at the same leaf longevity. We hypothesize that such difference among life forms reflects shoot architecture characteristics. Multi-shoot trees with branching architecture need to have self-supporting leaves, whereas semi-epiphytic climbers can maintain relatively low biomass investment to leaves hanging or relying upon the mechanical support from host plants.

Habitat degradation affects mixed-species bird flocks (flock hereafter) through two mechanisms – changes in the bird community from which flocks are drawn and changes in the propensities of species to flock. We determined the relative influence of these two mechanisms by examining variation in flocks across nine rain-forest fragments (range 11–2600 ha) in a plantation landscape in the Western Ghats, India. We found differences between fragments in average number of species (range 10.8–15.2) and individuals (range 19.0–37.6) per flock, number of species that participated in flocks (range 34–59), encounter rates (range 0.5–2.4 flocks h−1) and flock composition. Multiple regression and randomization tests revealed that different mechanisms contributed to this variation. Three flock variables (open-forest individuals per flock, total open-forest species that participated in flocks in a fragment, flock composition) mainly reflected changes in the bird communities of fragments. Habitat structure strongly influenced three flock variables (open-forest species per flock, total and rain-forest individuals per flock) and flock composition to a lesser extent. Finally, flock encounter rate was strongly related to fragment area, but not to abundance of flock participants indicating habitat degradation-induced changes in propensities of species to flock.

Decomposition was studied in a reciprocal litter transplant experiment to examine the effects of forest type, litter quality and their interaction on leaf decomposition in four tropical forests in south-east Brazil. Litterbags were used to measure decomposition of leaves of one tree species from each forest type: Calophyllum brasiliense from restinga forest; Guapira opposita from Atlantic forest; Esenbeckia leiocarpa from semi-deciduous forest; and Copaifera langsdorffii from cerradão. Decomposition rates in rain forests (Atlantic and restinga) were twice as fast as those in seasonal forests (semi-deciduous and cerradão), suggesting that intensity and distribution of precipitation are important predictors of decomposition rates at regional scales. Decomposition rates varied by species, in the following order: E. leiocarpa > C. langsdorffii > G. opposita > C. brasiliense. However, there was no correlation between decomposition rates and chemical litter quality parameters: C:N, C:P, lignin concentration and lignin:N. The interaction between forest type and litter quality was positive mainly because C. langsdorffii decomposed faster than expected in its native forest. This is a potential indication of a decomposer's adaptation to specific substrates in a tropical forest. These findings suggest that besides climate, interactions between decomposers and plants might play an essential role in decomposition processes and it must be better understood.

The decomposition of litter of two tree species Graffenrieda emarginata (Melastomataceae), Purdiaea nutans (Cyrillaceae) and the mixture of both was investigated in a tropical montane rain forest in southern Ecuador at two different altitudes (1850 and 2280 m). The two litter types differed strongly in nitrogen concentration, suggesting that G. emarginata (1.21% N) decomposes faster than P. nutans (0.73% N). To study the effect of soil micro-arthropods on the decomposition process, litterbags with mesh-size of 48 μm, excluding soil micro-arthropods, and 1 mm, allowing colonization by soil micro-arthropods, were used. Litter mass loss was measured after 2, 6 and 12 mo exposure in the field; further, microbial biomass and micro-arthropod colonization of the litter were investigated after 2 and 12 mo. Generally, litter decomposed faster at 1850 m than at 2280 m (60% and 76% dry mass remaining after 12 mo, respectively); G. emarginata and mixed litter decomposed faster than P. nutans litter. After 12 mo mixed litter decomposed faster (65% of dry mass remaining) than both individual litter species (70% and 71% of dry mass of G. emarginata and P. nutans litter remaining, respectively) indicating that non-additive effects contributed to litter decomposition. Microbial biomass increased during the experiment and was higher at 1850 m than at 2280 m. The most abundant micro-arthropods in both litter types were oribatid mites followed by Collembola, Gamasina, Uropodina and Prostigmata + Astigmata. Micro-arthropods were generally more abundant at 1850 m suggesting higher biotic activity at lower altitudes. Soil micro-arthropods contributed little to decomposition processes indicating that litter decomposition is mainly due to micro-organisms.

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.

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.

As top predators, wild cats play a key ecological role in tropical forests, but little is known about the factors that regulate their abundance. This study looked for correlates of ocelot (Leopardus pardalis) abundance at two spatial scales. First, camera-trap surveys conducted in the Atlantic Forest of Misiones, Argentina, were used to test the hypothesis that selective logging and poaching affect the local abundance of this cat. Second, published density estimates (N = 21) were used to test the hypothesis that rainfall and latitude are correlated with the abundance of ocelots across their continental range. In Misiones, ocelot densities ranged from 4.96 ± 1.33 individuals per 100 km2 in the intensely logged and hunted areas to 17.6 ± 2.25 individuals per 100 km2 in areas with low human impact. The frequency of records, number of individuals recorded per station, and density estimates were 2–3 times higher in areas with relatively low levels of logging and poaching. At a continental scale, ocelot densities decrease with latitude and increase with rainfall. Primary productivity seems to determine the abundance of wild cats across their range, but at a local scale their abundance may be affected by logging and poaching or by competition with other species.

We examined the seasonal and inter-annual variation of leaf-level photosynthetic characteristics of three C4 perennial species, Cyperus articulatus, Panicum repens and Imperata cylindrica, and their response to environmental variables, to determine comparative physiological responses of plants representing particular microhabitats within a seasonal tropical floodplain in the Okavango River Delta, Botswana. Five measurement campaigns were carried out over a period of 2 y which covered two early rainy seasons, two late rainy seasons and one dry season. For all three species, light-saturated net photosynthetic rates (Asat) and stomatal conductance (gsat) decreased with decreasing soil water content with a seasonal range for Asat of approximately 5–45 μmol m−2 s−1, and for gsat of 0.03–0.35 mol m−2 s−1. The species representing the wettest microhabitat (Cyperus) had the highest gsat at low leaf-to-air vapour pressure deficits (Dl), the highest ratio of intercellular to ambient CO2 concentration (Ci/Ca), as well as the highest degree of variation in Ci/Ca from season to season. We interpret this as being indicative of its adaptation to a moist growth environment allowing for non-conservative water use strategies as soil moisture is usually abundant. For all three species there was significant variation in photosynthetic fluxes from one year to another that was related to variation in leaf nitrogen and phosphorus. This study shows that when assessing the role of savanna stands in large-scale carbon balance models, the remarkable inter-annual variation in leaf photosynthesis reported in this study should be taken into account.

Santalum austrocaledonicum Vieill. (Santalaceae) is a small tree endemic to New Caledonia and Vanuatu, well-known for the highly priced aromatic oil of its heartwood (Nasi & Ehrhart 1996). In New Caledonia, sandalwood grows on Loyalty Islands, the Isle of Pines and Grande-Terre (Bottin et al. 2006). The tree produces single-seeded fleshy drupes, which turn dark-red at maturity. Sandalwood seeds are dormant because of their hard coat and germinate only on physical scarification, or after removing the coat (Chauvin & Ehrhart 1998). In natural habitats, such seeds need further processing to relieve dormancy and promote germination, within a period where there is a good chance of successful seedling establishment (Murdoch & Ellis 2000).

The yellow-throated marten, Martes flavigula, is the only living species of the genus Martes found in subtropical and tropical forests (Harrison et al. 2004). It is distributed throughout central and southern Asia in a wide variety of habitats. Despite its extensive geographical range, the ecology and behaviour of this species has so far received little attention, aside from a study of habitat use (Grassman et al. 2005). Studies on other martens have shown that fruits are an important food resource (e.g. M. martes, Bermejo & Guitian 2000; M. foina, Pandolfi et al. 1996). Thus, they are considered to be important potential seed dispersers (Corlett 1998, Herrera 1989, Willson 1993), as confirmed by recent studies (M. melampus, Otani 2002; M. americana, Hickey et al. 1999; M. foina and M. martes, Schaumann & Heinken 2002). Although no systematic study of the diet of M. flavigula has been conducted (Harrison et al. 2004), it is known to be omnivorous and to consume fruit (Gao & Wang 1987). To date, however, there has been no comprehensive study of frugivory and seed dispersal by M. flavigula (but see Corlett 1998).

Bats and birds carry out most of the seed dispersal in the Neotropics (Galindo-Gonzáles et al. 2000), and are crucial for the dynamics and regeneration of tropical forests (Whittaker & Jones 1994). However, only a few details are known about the interactions in particular bat–fruit systems. Most frugivorous bats are highly mobile (Bernard & Fenton 2003), and do not harm seeds (Fleming & Sosa 1994), suggesting that they are legitimate and effective seed dispersers (sensu Fleming & Sosa 1994).

The El Niño-Southern Oscillation (ENSO) phenomenon occurs irregularly and supra-annually at intervals of 2–7 y (Hughen et al. 1999, McPhaden et al. 2006), and is the strongest source of supra-annual climate fluctuation (Hughen et al. 1999, Philander 1990). During ENSO, the interior of the South-East Asian tropics, which is characterized by constant high temperature and no distinct dry season, experiences severe drought (Walsh 1996).