The Brazilian Atlantic Forest is one of the world's ‘hot spots’ for conservation because of its high level of endemism and number of endangered species (Myers et al. 2000). After centuries of deforestation, most of the remaining Atlantic Forest is scattered as small fragments on private land (Fonseca 1985, Jorge & Garcia 1997). Pollination could be impaired in these fragments because isolation often negatively influences the dispersal of insects, the most important pollinating agents in the tropics.

‘Campos de murundus’ are a typical landscape of Central Brazil characterized by countless rounded earthmounds (the ‘murundus’), which are covered by woody ‘cerrado’ (savanna) vegetation and are found scattered over a grass-covered surface (the ‘campo’). A detailed study was carried out in the region of Cuiabá, state of Mato Grosso on a particular campo de murundus (area of 5.065 ha) lying in a sedimentary depression where the earthmounds are true islands during the annual floods, allowing the colonization both by cerrado plants and by termites. The mounds were mapped and measured for their size and shape. Mounds' diameters ranged from 0.2 to 22.0 m and heights ranged from 0.1 to 1.1m. The 445 smaller mounds (< 0.8 m diameter) were found to have a clumped distribution, occupying 0.1% of the area. They are actually small termite nests built by Armitermes euamignathus. The 80 larger mounds (> 0.8 m diameter) were uniformly distributed, occupying 6.3%, of the area. These mounds are colonized by Cornitermes snyderi and Cornitermes bequaerti which build big termite nests on the summit of the mounds. Soil analyses indicated a close similarity between the campo and the surrounding cerrado whose soils had coarser texture and were poor in nutrients. Soils of the earthmounds and termite nests showed finer texture, lower pH and higher amounts of mineral nutrients. It is suggested here that this particular type of campo de murundus is formed mainly from the localized activity of nest-building by termites, followed by nest degradation, during many generations of termite colonies.

We observed a period of famine in the lowland tropical rain forest of Sabah, Malaysia from August 1999 to September 2000. All six Malayan sun bears (Helarctos malayanus) that were captured and radio-collared were in poor physical condition, and two were later found dead. The physical condition of bearded pigs (Sus barbatus) that were captured, observed or photographed by camera traps also revealed that the pigs were in various stages of emaciation and starvation. We surmise that the famine resulted from prolonged scarcity of fruit during an intermast interval in the study area. These phenomena of emaciated animals and fruit scarcity have also been reported from other areas of Borneo. Lowland tropical rain-forest trees of Borneo display supra-annual synchronized general fruiting. We believe that the starvation we observed and the generally low density of large animals in Borneo forests is a consequence of a history of prolonged food scarcity during non-general-fruiting years, but may be accentuated by anthropogenic factors such as forest fragmentation, selective logging, and reduced density of fig trees in logged forests.

A fire-mediated recruitment bottleneck provides a possible explanation for the coexistence of trees and grasses in mesic savannas. The key element of this hypothesis is that saplings are particularly vulnerable to fire because they are small enough to be top-killed by grass fires, but unlike juveniles, they take several years to recover their original size. This limits the number of recruits into the adult size classes. Thus savanna vegetation may be maintained by a feedback whereby fire restricts the density of adult trees and allows a grass layer to develop, which provides fuel for subsequent fires. Here, we use results from a landscape-scale fire experiment in tropical Australia, to explore the possible existence of a recruitment bottleneck. This experiment compared tree recruitment and survival over 4 y under regimes of no fire, annual early and annual late dry-season fire. Stem mortality decreased with increasing stem height in the fire treatments but not in the unburnt treatment. Tree recruitment was 76–84% lower in the fire treatments than the unburnt treatment. Such fire-induced stem loss of saplings and reduced recruitment to the canopy layer in this eucalypt savanna are consistent with the predictions of the fire-mediated recruitment bottleneck hypothesis.

Palmate umbrella tents used by tent-making bats in Trinidad, West Indies, were observed in three species of Neotropical palms, Sabal mauritiiformis, Coccothrinax barbadensis and Mauritia flexuosa. Tents were most common in palm leaves that have supporting petioles angled at 50–70° above the horizontal. The shape and volume of tents is influenced mostly by leaf morphology (leaf width and leaflet length) and age of the tent. Tent-crowns varied from being heart-shaped in S. mauritiiformis, oval or round in C. barbadensis and spade-shaped in M. flexuosa. Leaves in which tents were constructed were most often beneath overhanging vegetation, and were generally free of vegetation below, allowing bats to enter and depart from tents without being impeded by the clutter of adjacent vegetation.

Singles and small apparent harem groups of two bat species, Artibeus jamaicensis and Uroderma bilobatum, were captured and observed in tents made from the leaves of S. mauritiiformis and C. barbadensis. No bats were observed in tents constructed in leaves of M. flexuosa. The apparent harem social organization in these and other tent-making bat species suggests that leaves modified into tents may provide critical and defendable resources that promote the evolution of polygyny. This hypothesis is based on the observed patchy distribution of suitable palm trees, the inappropriateness of many palm leaves as potential tents and the resultant architecture provided by palmate umbrella tents. We suggest that tent-making is an adult male behaviour.

Dual stable isotope analyses (δ13C and δ15N) of fiddler crabs from a forest-fringed, land-locked lagoon in Puerto Rico indicated the differential assimilation of material from ingested sediments. Fiddler crabs preferentially selected for nitrogen-fixing benthic microalgae (cyanobacteria) over vascular plant detritus. These results question the assumption that mangrove detritus is always the principal source of energy to estuarine consumers. Previous research from this lagoon as well as from Amazonia suggests that the magnitude of land-water ecotonal coupling may be low for these particular tropical systems where benthic algal productivity is presumably high.

Tropical montane cloud forests (TMCF) are characterized by short trees, often twisted with multiple stems, with many stems per ground area, a large stem diameter to height ratio, and small, often thick leaves. These forests exhibit high root to shoot ratio, with a moderate leaf area index, low above-ground production, low leaf nutrient concentrations and often with luxuriant epiphytic growth. These traits of TMCF are caused by climatic conditions not geological substrate, and are particularly associated with frequent or persistent fog and low cloud. There are several reasons why fog might result in these features. Firstly, the fog and clouds reduce the amount of light received per unit area of ground and as closed-canopy forests absorb most of the light that reaches them the reduction in the total amount of light reduces growth. Secondly, the rate of photosynthesis per leaf area declines in comparison with that in the lowlands, which leads to less carbon fixation. Nitrogen supply limits growth in several of the few TMCFs where it has been investigated experimentally. High root : shoot biomass and production ratios are common in TMCF, and soils are often wet which may contribute to N limitation. Further study is needed to clarify the causes of several key features of TMCF ecosystems including high tree diameter : height ratio.

Studies of mixed-species bird flocks have found that ‘nuclear’ species, those important to flock coherence, are either intraspecifically gregarious or are ‘sentinel’ species highly sensitive to predators. Both types of species are present in flocks of a Sri Lankan rain forest: orange-billed babblers (Turdoides rufescens Blyth) are highly gregarious, whereas greater racket-tailed drongos (Dicrurus paradiseus Linnaeus) are less so, but more sensitive and reliable alarm-callers. We hypothesized that flock participants would be attracted to the playback of both species more than to the clearly non-nuclear yellow-fronted barbet (Megalaima flavifrons Cuvier). Further, we hypothesized that insectivores would prefer babbler vocalizations, as babblers could facilitate their foraging in several ways. We found that the response of insectivores was three times greater during babbler or drongo playback, and eight times greater during playback of these two species together, than during barbet playback or silence. Insectivores did not show, however, any difference in their response to babbler as compared to drongo playback; omnivores and frugivores responded relatively equally to all treatments. Our results show that birds with high propensity to flock, such as insectivores, use the vocalizations of nuclear species to locate flocks and that a sentinel species may be as attractive as a highly gregarious species.

Twelve native woody species were studied to investigate the influences of soil fertility and root morphology on colonization by arbuscular mycorrhizal (AM) fungi during seedling establishment and growth. Seedlings were grown in soils of low and high natural fertility, uninoculated or inoculated with AM fungi, under greenhouse conditions. The mycorrhizal root colonization and plant responsiveness were higher among early successional species than late successional ones. Among early successional species, in both soils, mycorrhizal colonization provided significant increase in total dry mass, growth rates of shoot and root, root length, density of root tissues, root surface area and P concentration and content in the shoot. Early successional species grown with AM fungi displayed significant decreases in carbon allocation to roots, specific root length and the length and incidence of root hairs. Mycorrhizal colonization did not affect the root morphology of the late successional species in either soil. The growth of these woody species was influenced by differences in soil fertility. There was positive correlation between the degree of plant responses to AM inoculation with the percentage of root colonized by AM fungi. In both soils, plant responsiveness and mycorrhizal root colonization correlated positively to root-hair incidence and root-hair length and correlated negatively to fine-root diameter. The results suggest that during the establishment of seedlings, the large responses to the inoculation and colonization of roots by AM fungi are related to both the successional status and root morphological plasticity of the host plant, regardless of soil fertility.

Seed dispersal is a process critical to the maintenance of tropical forests, yet little is known about the interactions of most dispersers with their communities. In the Dja Reserve, Cameroon, seed dispersal by the hornbills Certaogymna atrata, C. cylindricus and C. fistulator (Aves: Bucerotidae) was evaluated with respect to the taxonomic breadth of plants dispersed, location of seed deposition and effects on seed germination. Collectively, the three hornbill species consumed fruits from 59 tree and liana species, and likely provided dispersal for 56 of them. Hornbill-dispersed tree species composed 22% of the known tree flora of the site. Hornbill visit lengths, visit frequencies, and seed passage times indicated that few seeds were deposited beneath parent trees; in five hornbill/tree species pairings studied, 69–100% of the seeds ingested were deposited away from the parent trees. Germination trials showed that hornbill gut passage is gentle on seeds. Of 24 tree species tested, 23 germinated after passage by hornbills; of 17 planted with controls taken directly from trees, only four species showed evidence of inhibition of germination rate, while seven experienced unchanged germinated rates and six experienced enhanced germination rates. Results suggested that Certaogymna hornbill rank among the most important seed dispersers found in Afrotropical forests, and they deserve increased conservation attention. Ceratogymna hornbills are likely to become increasingly important in forest regeneration as populations of larger mammalian seed dispersers (such as forest elephants and primates) diminish.

Subsamples of termite mound soil used by chimpanzees for geophagy, and topsoil never ingested by them, from the forest floor in the Mahale Mountains National Park, Tanzania, were analysed to determine the possible stimulus or stimuli for geophagy. The ingested samples have a dominant clay texture equivalent to a claystone, whereas the control samples are predominantly sandy clay loam or sandy loam, which indicates that particle size plays a significant role in soil selection for this behaviour. One potential function of the clays is to bind and adsorb toxins. Although both termite mound and control samples have similar alkaloid-binding capacities, they are in every case very high, with the majority of the samples being above 80%. The clay size material (<2 μm) contains metahalloysite and halloysite, the latter a hydrated aluminosilicate (Al2Si2O4·nH2O), present in the majority of both the termite mound soil and control soil samples.Metahalloysite, one of the principal ingredients found in the pharmaceutical Kaopectate™, is used to treat minor gastric ailments in humans. The soils commonly ingested could also function as antacids, as over half had pH values between 7.2 and 8.6. The mean concentrations of the majority of elements measured were greater in the termite mound soils than in the control soils. The termite mound soils had more filamentous bacteria, whereas the control soils contained greater numbers of unicellular bacteria and fungi.

The impact of seed size on germination and seedling growth, as affected by water stress, was studied for five tree species from tropical dry forest of India, viz. Albizia procera, Acacia nilotica, Phyllanthus emblica, Terminalia arjuna and Terminalia chebula. Germination tests were conducted under five osmotic potential levels. Seedlings from large (LS) and small (SS) seeds were grown at four soil moisture levels. Observations were made on height, leaf area, biomass and other growth traits such as relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA), and root:shoot (R:S) ratio. Seeds of pioneer species and large seeds, within species, germinated earlier, and with increasing water stress, per cent germination and germination velocity declined. RGR was inversely related with drought tolerance. R:S ratio increased, RGR and SLA declined, but NAR increased with water stress. Notwithstanding successional status, the slow-growing species registered minimum reduction in biomass due to water stress. The response of LS and SS seedlings also differed for some of the growth variables. Increase in NAR could be a compensatory response to water stress, and the marked allocational plasticity could help maximize capture of the limited resource. Seedlings from smaller seeds, particularly of fast-growing species, would be able to cope with mild drought by morphogenetic and physiological plastic response in a better way than those from large seeds. However, seedlings from large seeds had greater survival than those from smaller seeds under intense water stress.

A study of nutrient movement through rainfall, throughfall and stemflow, as well as epiphytic bryophyte (moss and liverwort) biomass and its effect on nutrient composition of stemflow, was conducted for 2 y in subtropical montane moist forest (Lithocarpus–Castanopsis association) at Xujiaba, Ailao Mountain National Nature Reserve, Yunnan, south-west China. Base cation and fluxes were increased in throughfall, while NH4+-N and NO3--N were reduced relative to precipitation. Annual throughfall inputs of N, P, Ca and S were mainly from precipitation, while most K and two-thirds of Mg throughfall input was due to canopy leaching. Input of Na in the precipitation and throughfall was low in this forest. Net flux (throughfall flux minus bulk precipitation) and deposition ratios (ratio of throughfall flux to bulk precipitation flux) were in the low part of the range reported for other tropical montane rain forests. The throughfall data for this forest reveal generally low cycling rates for mineral elements. Abundant epiphytic bryophytes on bole bark affected the chemical composition of stemflow by selective uptake or release of elements. Relative to trees without epiphytic bryophytes, the annual amounts of total N, NH4+-N, Mg, Na and SO42--S were enhanced, while NO3--N, K, P and Ca were depleted in stemflow. Contributions of N from nitrogen-fixing organisms are likely to be constrained by low temperatures.

Nests of leaf-cutting ants (Hymenoptera: Formicidae: Attini) are abundant disturbances in Neotropical rain forests, and could affect the plant community both while the nests are active and after they are abandoned. We measured the diversity and abundance of understorey plants (>1 m in height) in the area around active and abandoned nests of leaf-cutting ants (Atta cephalotes) at the La Selva Biological Station in Costa Rica. Sampel quadrats on active nests had reduced diversity (number of morphospecies) and abundance of both small (height >10 cm) and large (10 cm–1 m) understorey plants, when compared to the nearby forest floor (3 and 13 m from the nest edge). Abandoned nests had greater diversity and marginally greater abundance of small understorey plants relative to nearby forest; there was no difference in diversity or abundance of large understorey plants. Leaf-cutting ant nests create gaps in the plant understorey when active, but serve as centres of recruitment for small plants after they are abandoned. Thus, like canopy gaps, ant nests could play an important role in recruitment of new individuals and maintenance of plant species diversity in tropical forests.

Chemical baits corresponding to natural orchid fragrance chemicals were used to attract and sample male orchid bees in terra firme and flood plain forest sites on the Tambo-pata Reserve in south-eastern Perú. The study was conducted monthly for two years. A total of 38 species of bees was collected at these chemical baits, and although most species were collected from both habitats, 11 species were significantly more common in one habitat than the other. There was considerable variation in the number and types of chemicals to which each of the orchid bee species was attracted.

Two cycles of seasonal abundance occurred annually in the number of orchid bee individuals and species collected at the chemical baits. A major peak occurred a month following onset of the wet season, and a minor peak occurred during the dry season. Species body size was related to seasonal activity, but additional factors such as flowering phenology and nest parasites were also probably involved.

The number of orchid bee species found on the Tambopata Reserve was similar to the number found in forest sites of eastern and central Brazil, Costa Rica, and Panamá. This homogeneity in species richness is in marked contrast to other insect groups such as Odonata, Lepi-doptera, Asilidae (Diptera), Tabanidae (Diptera), and Cicindelidae (Coleoptera), for which the species numbers recorded on the Tambopata Reserve are the highest for any similar sized area in the world.

Early studies comparing adult and juvenile tree populations in West Africa described a contrast in flonstic composition between the two age classes. These studies have been mis-represented in more recent literature, and confusion has arisen over their interpretation.

Similar comparisons are reported here for six forest sites in Ghana. At any one site, clear differences in composition were recognized between adult and juvenile samples, but in terms of the variation in flonstic composition over the whole of the forest zone, they are slight and forest types appear to ‘breed true’.

At one site, Kade, compositional differences between size classes are fully described for all canopy species on a 0.25 ha plot. There was an abrupt change in composition at about 30 cm gbh. At this site, mortality rates for trees >30 cm gbh were greater amongst species with a high proportion of juveniles in the population. At other sites, changes in composition were sometimes abrupt, occurring at various size classes, or were more gradual.

The populations of some species included a large number of juveniles at all sample sites, but the converse, where species always have low densities of juveniles, were not seen. The possible implications of these results for future canopy composition are discussed in relation to temporal equilibrium, or lack of it, in tropical forest composition.

Due to the unbalanced distribution of their fauna and flora, which leads to the creation of a niche opportunities, it is generally accepted that island communities offer weak biotic resistance to biological invasion. In order to empirically test this statement, we compared resource use by ants in the understorey of an undisturbed New Caledonian rain forest recently invaded by the little fire ant, Wasmannia auropunctata. We tested the exploitation of: (1) food sources by placing baits on all trees with trunks greater than 5 cm in diameter; and (2) nesting sites on two tree species likely to shelter ant colonies. In non-invaded areas, the native ants occupied only 44.6% of the baits after 2 h of exposure, while in invaded areas all the baits were occupied by numerous W. auropunctata workers. Similarly, in non-invaded areas only 48.9% of Meryta coriacea (Araliaceae) trees and 64.5% of Basselinia pancheri (Arecaceae) sheltered ants, while in invaded areas W. auropunctata nested in 92.6–98.3% of these trees. Also, workers attended native Margarodidae (Hemiptera) for which they promoted the development of populations significantly larger than those attended by native ants. Thus native ants appear unable to efficiently exploit and defend several of the available food sources and nesting sites, providing a niche opportunity for an invader like W. auropunctata.

One possible mechanism underlying species losses in the tropics is an increase in predation due to habitat degradation. Relative levels of predation at three heights (ground, 1–1.5 m, > 5 m for nests and > 3 m for caterpillars) were compared across a gradient of disturbance in the Subic Bay Watershed Forest Reserve, Philippines over a 2-mo period. Four 750-m transects were established in each habitat type (closed-canopy forest, open-canopy forest, rural areas) where artificial nests and caterpillar models were placed within 10-m-radius plots and checked after a 5-d exposure period. Nests in open-canopy forest were least predated (16.7%), with predation in rural areas (58.3%) being higher than in closed-canopy forest (32.8%). Predation on nests at 1–1.5 m was significantly lower than ground nests. General linear mixed model analysis suggested that effects of habitat type on nest predation differed among heights. Attacks on caterpillars increased with disturbance (46.1–59.4%), but height was not found to have a significant effect on predation. Markings on plasticine models, camera traps and live traps were used to establish possible predators. Shifts in predator dominance among the habitats were observed. Vegetation cover, tree density and small mammal abundance were not correlated with mean predation in the transects.