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.

Forest structure and species distribution patterns were examined among eight topographically defined habitats for the 205 species with stems ≥ 1 cm dbh inhabiting a 25-ha plot in the Sinharaja rain forest, Sri Lanka. The habitats were steep spurs, less-steep spurs, steep gullies and less-steep gullies, all at either lower or upper elevations. Mean stem density was significantly greater on the upper spurs than in the lower, less-steep gullies. Stem density was also higher on spurs than in gullies within each elevation category and in each upper-elevation habitat than in its corresponding lower-elevation habitat. Basal area varied less among habitats, but followed similar trends to stem density. Species richness and Fisher's alpha were lower in the upper-elevation habitats than in the lower-elevation habitats. These differences appeared to be related to the abundances of the dominant species. Of the 125 species subjected to torus-translation tests, 99 species (abundant and less abundant and those in different strata) showed at least one positive or negative association to one or more of the habitats. Species associations were relatively more frequent with the lower-elevation gullies. These and the previous findings on seedling ecophysiology, morphology and anatomy of some of the habitat specialists suggest that edaphic and hydrological variation related to topography, accompanied by canopy disturbances of varying intensity, type and extent along the catenal landscape, plays a major role in habitat partitioning in this forest.

This study examined the foraging behaviour of a resident bird species, the rufous-capped warbler (RCWA, Basileuterus rufifrons), in a shaded-coffee farm in Chiapas, Mexico. Unlike many resident species that use shaded-coffee agroecosystems seasonally, RCWAs do not move to other habitats when migrants are present. RCWA foraging was compared when migrant birds were present (dry season) and absent (wet season). It was hypothesized that RCWAs would exhibit a seasonal foraging niche shift because of resource competition with migrants. Observations from both the canopy and coffee understorey show that RCWAs foraged almost equally in both vegetative layers during the wet season although they were more successful foraging in the canopy. In the dry season, migrants foraged primarily in the canopy and RCWAs shifted so that 80% of RCWA foraging manoeuvres were in the understorey. At that time RCWAs foraged less successfully in both vegetative layers. Avian predation in the dry season was found to reduce densities of arthropods by 47–79% in the canopy, as opposed to 4–5% in the understorey. In the canopy, availability of large (>5 mm in length) arthropods decreased by 58% from the wet to dry season. Such resource reductions could have caused the RCWA foraging niche shift yet other alternative or additional hypotheses are discussed. Shifts in foraging niche may be a widespread mechanism for some small insectivorous residents to avoid seasonal competition with abundant migrant species.

A prediction of the hypothesis that niche processes control plant species distributions across edaphic gradients is that pairwise comparisons of related species on contrasting soils should show consistent patterns of trait divergence. This hypothesis was tested in lowland Bornean rain forest by combining measurements of leaf traits, soil nutrients and the distribution of tree species in the Dipterocarpaceae across a nutrient gradient. Nine species were studied, comprising four related pairs in Shorea (phylogenetic independent contrasts; PICs) and one habitat generalist (Dipterocarpus sublamellatus). Lamina area, specific leaf area (SLA), leaf nitrogen (N) and phosphorus (P) were measured for ∼10 saplings of each species; habitat associations were defined as a continuous function of soil nutrients and categorically in relation to substrate. Species distributions and traits varied significantly with soil nutrients. When all species were pooled, SLA and leaf P increased significantly with species' distribution across the nutrient gradient; leaf N showed the same trend. Trait shifts with habitat were stronger and more pervasive when habitat was defined categorically – in all four PICs, rich-soil specialists had larger leaves, higher SLA, leaf N and P, and lower N:P ratios. Trait shifts with habitat at least partly reflect intrinsic differences between species. Within Shorea, variation in lamina area and N:P ratio were more strongly related to phylogeny than habitat, whereas the reverse held for SLA and leaf P. Phylogeny also influenced the extent of trait divergence between related species on different soils, and patterns of trait correlation within lineages. Results support the hypothesis that niche processes influence the distribution of species and traits in lowland tropical tree communities, and highlight the value of phylogenetic information for increasing the power of comparative studies.

Ontogenetic and seasonal variation in diet was examined for 11 species of insectivorous forest-floor frogs and lizards from a lowland wet forest in north-eastern Costa Rica. Specimens were collected systematically over an entire seasonal cycle and represented individuals of all sizes. Individual prey items were removed from stomachs of preserved specimens, measured and identified. Ontogenetic shifts in prey size were pervasive. Ontogenetic shifts in prey composition were limited to four species; these were not the species with greatest range in body size, nor the species with the broadest diets. Small prey types (ants, mites, collembolans) decreased in representation and large prey types (roaches, orthopterans, millipedes) increased in importance over ontogeny; this could be because prey selection is based primarily on prey size or because of different prey preferences among age classes. There is little evidence for size-structure in this assemblage. There is no evidence that total availability of arthropod prey varies among seasons, but some evidence that preferred prey are less common in the wet season. Diet was similar between lizards and frogs. Lizards were more likely to have empty stomachs, but also greater stomach volume, than frogs; this indicates a difference in food-gathering strategies. Our study indicates strong similarity between frogs and lizards in diet despite enormous differences in physiology and behaviour.

Intraspecific synchrony in the phenology of tropical forest trees has implications for satiation of browsers and seed predators, pollination, dispersal and interpreting plant responses to environmental cues and stresses. Community phenological studies have been constrained in their consideration of these issues by the lack of concise quantitative measures of intraspecific synchrony. We propose a novel application of Colwell's predictability indices to overcome this deficiency. Its application is demonstrated by evaluating the leaf and reproductive phenologies of 8–16 individuals of each of 20 monsoon forest tree species from northern Australia monthly for 30 mo. The indices yielded substantial additional information over that provided by summaries averaged amongst conspecifics. Marked intraspecific asynchronies in leaf flush or flowering occurred in five evergreen species and two deciduous fig species, and were associated with prolonged individual commitments to these states. Five partly deciduous species exhibited marked intraspecific variation in the seasonal extent of leaf loss. We interpret the observed variation in intraspecific synchrony in terms of contrasting water-use and pollination strategies. The synchronicity indices are concise and robust to small and variable sample sizes, and may thus enhance studies of species-rich assemblages.

Secondary succession was studied in a Mexican cloud forest region along a chronosequence of 15 abandoned pastures (0.25–80 y). Our objective was to determine the effects of distance from the forest border on successional vegetation structure and woody species richness along the chronosequence. Vegetation structure similar to that of mature forests recovered over 40–50 y, both close to (0–10 m) and away from (40–50 m) the border. Total woody species richness was similar for both distances but species composition differed significantly. When primary forest species were analysed separately, basal area, height, abundance and richness were all significantly higher close to the forest border. Primary species such as Quercus spp. (barochorous-synzoochorous) and Carpinus caroliniana (anemochorous) had lower basal area, density and height away from the border than close to it. Secondary species such as Lippia myriocephala (anemochorous) and Myrsine coriacea (endozoochorous) did not differ in their rate of colonization between distances. The limitation of seed dispersal and establishment for primary woody species away from forest borders suggests that propagules need to be introduced to accelerate forest restoration.

This study investigated the nutritional ecology of forest elephants in Kibale National Park, Uganda relative to crop-raiding behaviour, and examined nutritional differences between crops and food consumed by wild elephants. An index of dietary nutrient concentration was determined by quantifying the species and parts of plants consumed along feeding trails, collecting food items, and analysing foods for energy, fibre, protein, minerals and secondary compounds. Frequency of crop raiding was quantified over 13 mo. Energy and protein concentration was within suggested levels, but concentrations of several minerals, particularly sodium, were low relative to requirements based on captive elephants and values reported for other wild populations. The very low sodium concentrations of Kibale elephant diets and low availability of alternative sodium sources, such as soil or water, suggest that sodium drive is very likely in this population. Crops consumed by Kibale elephants had higher Na concentrations and lower concentrations of fibre and secondary compounds than wild diets. The known attraction of elephants to mineral sources throughout their range and the low mineral concentration of leaves, fruits, bark, and stems consumed by forest elephant in this study suggest that mineral nutrition is likely to be an important factor driving elephant behaviour and patterns of habitat use.

According to the Janzen–Connell model, host-specific natural enemies can promote species coexistence of canopy trees in tropical forests by attacking progeny where they are most concentrated. However, empirical evidence relating negative density-dependent mortality to herbivory and, in particular, attack by specialist herbivores, remains rare. We investigated density dependence in a natural population of Swietenia macrophylla in a south-eastern Amazon forest of Brazil. Across 24 adult trees, we found that initial juvenile densities were positively correlated with basal area of adult conspecifics whereas subsequent survivorship over 1 y for these juveniles declined strongly with increasing basal area of adult conspecifics. For 18 trees with > 5 juveniles surviving for 1 y, further evidence supporting the Janzen–Connell mechanism was obtained in that leaf herbivory and attack by a specialist microlepidopteran moth (Steniscadia poliophaea) increased, and overall foliar condition decreased, with conspecific basal area. Moreover, when differences in mean juvenile size (number of extant leaves) were accounted for, juvenile survival over 1 y decreased with increased specialist leaf herbivory. Collectively, these results indicate that herbivores, in particular S. poliophaea, may contribute to density dependence among S. macrophylla juveniles. We conclude that the survival of juveniles and their probability of recruitment into the canopy is decreased where conspecific adults are largest and/or most numerous and find support for the importance of host-specific pests in driving density dependence among tropical trees.

The temporal pattern of reproduction and its consequences for age structure and density were investigated in a population of the gracile mouse opossum Gracilinanus microtarsus in south-eastern Brazil. Individuals of G. microtarsus were monitored through capture–mark–recapture methods from August 2000 to February 2003 in a remnant of cerradão, a forest-like physiognomy of the highly seasonal cerrado biome. The temporal pattern of reproduction of the population studied was highly seasonal with rearing of the offspring occurring in the first half of the warm-wet season, when the abundance of food resources – primarily insects – in the cerrado is high. Shortly after reproduction, the density of adults decreased sharply, possibly because of high post-mating mortality, leading to a gradual replacement of adults by their offspring in the following months and little overlap of generations. Our data suggest that climatic and environmental factors affect the onset of reproduction and interact with endogenous factors that decrease post-mating survival to produce the observed pattern of seasonal variation in age structure and density. It is suggested that the dynamics of populations of G. microtarsus may be driven primarily by food limitation and that long-term studies are needed to understand its feedback structure.

We used stable isotope analysis (15N/14N) to characterize the trophic relationships of consumer communities of an aquatic food web (a permanent pond) and the adjacent terrestrial food web (secondary dry dipterocarp forest) from a seasonal tropical field site in north-eastern Thailand. In general, isotopic signatures of aquatic vertebrates were higher (δ15N range = 4.51–9.90‰) than those of invertebrates (δ15N range = 1.10–6.00‰). High 15N signatures identified water snakes and swamp eels as top predators in the pond food web. In the terrestrial food web 15N signatures of saprophagous litter invertebrates (diplopods, earthworms), termites, ants and beetle larvae were lower than in those of predatory invertebrates (scolopendrids, scorpions, whip spiders). Predatory terrestrial frogs and caecilians had lower 15N signatures than snakes, indicating that snakes are among the top predators in the terrestrial web. Based on the distribution of isotopic signatures, we estimated five trophic levels for both the aquatic and terrestrial food web. The food chains of a seasonal tropical site studied were rather short, which implies similarities to the structure of temperate food webs.

Hemi-epiphytic figs (Moraceae; Ficus subgenus Urostigma) are a distinctive component of the canopy of tropical rain forests. The hemi-epiphytic habit has risen independently several times, and is recorded in over 20 plant families today, but with approximately 350 species globally figs are by far the most important (Berg & Corner 2005, Putz & Holbrook 1986). They are ubiquitously diverse in tropical lowland rain forests and are represented by independent radiations in each region (Harrison 2005, Jousselin et al. 2003). Moreover, their abundant production of fruit at all times of the year makes them functionally important as food for wildlife, especially during periods of general fruit shortage (Shanahan et al. 2001a). However, hemi-epiphytic fig populations occur at very low densities and this, combined with the difficulties of access to the canopy, has meant that study of their biology lags behind that of other rain forest plants (Harrison et al. 2003). Here, I present the first estimates of mortality and recruitment for any community of hemi-epiphytic figs.

To be able to make accurate estimates of the carbon stocks present in the world's tropical forests, there is a growing need for accurate tree biomass estimations on large spatial scales (Chave et al. 2004, Cummings et al. 2002, Nascimento & Laurance 2004). Wood-specific gravity forms an important component of these biomass estimations (Baker et al. 2004, Magcale-Macandog 2004, Nogueira et al. 2005). Even though Chave et al. (2004) found that the most important source of error in above-ground biomass estimation (AGB) is currently related to the choice of allometric model, Baker et al. (2004) show that for two estimates of AGB in Amazonian forests derived using different allometric equations, stand-level specific wood gravity still explained 45.4% and 29.7% of the total variation in AGB.

Among the hypotheses invoked to explain high species richness in tropical forests, the niche differentiation hypothesis has received observational and experimental support (Ashton 1969, Chesson 2000, Clark et al. 1999, Souza & Martins 2004, Svenning 2001, Terborgh & Mathews 1999). Habitat specialization with regard to edaphic factors and topography has been observed in several plant groups including trees, lianas, shrubs, ferns and palms (Clark et al. 1999, Ibarra-Manriquez & Martinez-Ramos 2002, Svenning 1999, Tuomisto & Ruokolainen 1993). Treefall gaps and light gradients have also been found to be important ecological factors affecting plant distribution and niche differentiation in the understory (Chazdon 1986, Poorter & Arets 2003, Terborgh & Mathews 1999). It is suggested that such habitat heterogeneity may not only maintain biodiversity but also may lead to the origin of new species through the process of parapatric speciation (Gentry 1989, Haffer 1997, Patton & Smith 1992).