Changes in density, structure and species composition of the woody component of the two predominant savanna types in Tarangire National Park, northern Tanzania, during a period of 25 y were investigated. The park is known for its large, increasing elephant numbers and high frequency of fires. In 1996 a study on woody species density, composition and age structure, which was first performed in 1971, was repeated, using the same transects and method. Access to the original data of 1971 allowed for a full comparison of the changes and an investigation whether these could be related to changes in elephant numbers and fire frequency. The total tree density declined during the 25 y, but the decline was not evenly distributed over the different height classes. Although the density of trees taller than 5 m declined significantly, the greatest decline occurred in the density of trees shorter than 1 m. The density of trees in the intermediate height class of 1–5 m did not decline. Although damage to trees by elephants increased during the 25-y period, c. 25% showed no browse damage and, except for some severely damaged trees, elephant damage was not found to reduce tree vigour. Elephants affected the size distribution of the savanna woody component much more than the density, while the data suggest no significant effect of fire on changes in tree density. The large decline in density of small trees was attributed to a severe drought in 1993. Based on large numbers of elephants during the past decades and on relatively low elephant impact on the total tree density, the present study suggests that the current elephant number of 2300 can be sustained in the park without causing detrimental effects, provided that their current range is maintained.

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.

Strangler fig density varied considerably in the evergreen forest of Karian Shola National Park, southern India, with 11 individuals ha−1 in an open trail area and 5.6 individuals ha−1 within the primary forest area. The index of light level was assessed by estimating the percentage of upper canopy cover along the longitudinal centre of ten, 500-m × 20-m plots in each of the two areas of the evergreen forest. However, the increase in strangler fig density was not correlated to light levels but was significantly correlated to the numbers of their main host species in the two areas. In Karian Shola National Park, strangler figs occurred predominantly on a few host species with 20 and 50% of strangler figs growing on Vitex altissima, Diospyros bourdilloni and Eugenia/Syzygium spp. in the primary forest and trail areas respectively. Both young and established strangler figs were recorded mainly on larger individuals of their host trees indicating that older host trees are likely to be more suitable for the germination and establishment of strangler figs. The reason for the above could be the higher incidence of humus-filled and decaying regions in the older host trees which would provide an assured supply of nutrients for the establishing strangler fig.

The emphasis of antagonistic fungus–consumer interactions to date has been on temperate taxa and predominantly zoocentric, neglecting the effects on the fungal component. These interactions are expected to be especially complex and diverse in the tropics, where both components display their greatest diversity. Variability in fungivory (apparent biomass consumed) of understorey basidiomycetes in a tropical cloud forest was investigated to test whether this could be explained (at the proximate level) by apparency-related characteristics of the aboveground structures (colour of pileus, stipe and hymenium; size and aggregation), as has been suggested for plant–herbivore relationships. Considerable interspecific variation in fungivory was detected (range 0–50%). Cluster analysis showed that neighbouring clusters had dissimilar levels of fungivory. Such clusters were similar in colour attributes of aboveground structures, but differed in aggregation size and apparent biomass. A quantitative analysis also showed that colour attributes were not strongly associated with the observed variation of consumption levels, whereas apparent biomass and aggregation size did correlate with the observed variation in fungivory. Furthermore, specific identity correlated with fungivory. It was concluded that coloration patterns may not be important for fungivory, whereas genet size and species identity (probably via characteristics unrelated to apparency, such as mycotoxins and nutritional value) seemed to be critical factors.

The morphology and allometry of the winged diaspores of 25 species in the Asian Sterculiaceae were studied. The diaspores of pioneer trees are characterized by light mass and large wings. Although their parent tree heights are low in most cases, these light diaspores are easily blown upward and widely dispersed. The diaspores of Heritiera, a genus mainly found in primary forest, can be divided into groups with large and small wings by their values of the square-root of wing loading. The frequency distribution of mature tree heights for trees with the large- and small-winged diaspores are skewed into high and low statures, respectively. Therefore, the tree size at maturity may play a vital role in determining the morphology of the diaspores. Among the large-winged diaspores, shape is almost retained, despite size change. Consequently, larger diaspores have more mass per unit of wing area, suggesting that larger diaspores fall more quickly than smaller ones. Diaspore mass is approximately proportional to the nut volume. The enlargement of the nut clearly appears to be beneficial for seedling establishment and survival under a closed canopy. However, increasing nut volume reduces the potential for wind dispersal. The fact that large-winged diaspores were always lighter than their small-winged counterparts suggests that the heavier diaspores with small wings are not dispersed, preferentially by wind. Consequently, the present study supports the hypothesis made by Suzuki & Ashton (1996): that the evolution of small wings appears to have arisen mainly due to a reduction in tree height and an increase in nut size.

Breeding systems and dispersal mechanisms of plants (≥ 2.5 cm dbh) were examined in fragments of tropical dry forest in Central America to identify life-history characteristics associated with rarity. In particular, the richness and abundance of dioecious and mammal-dispersed trees and shrubs were examined to identify potential associations with precipitation, anthropogenic disturbance, and area. Plots totalling 1000 m2 per site were established in seven nature reserves in Costa Rica (two sites) and Nicaragua (five sites). Overall, tropical dry forests of Central America have a similar proportion of dioecious species to other lowland neotropical forests and a similar proportion of wind-dispersed plants to other tropical dry forests around the world. However, the number of dioecious and mammal-dispersed species declined with decreasing forest cover within each reserve. Although dioecious species were rare in smaller forest fragments, some of these species will not be threatened with regional extinction because they are early successional plants, they have large geographic ranges, and they are not restricted to the tropical dry forest life zone. Mammal-dispersed plants were rare in small fragments, but it is not clear whether this was due to the loss of dispersal vectors or other life-history characteristics.

Hemiepiphytic plants grow for part of their life as true epiphytes, then become terrestrial through the production of aerial roots that grow from the canopy to the ground. Long-term measurement of growth, dieback and mortality of aerial roots of hemiepiphytic plants in a lower montane moist tropical forest in western Panama was used to elucidate life-history strategies of hemiepiphytes from two families. The fates of 156 aerial roots of five species of Clusiaceae and Araceae were followed for 10 mo. Some roots were cut to experimentally study the effect of injury on resprouting and survival. Aerial roots of Araceae grew more than twice as fast as those of Clusiaceae but had a much greater mortality rate. Roots of both families grew much faster during the wet than dry season. Even for the fastest growing roots, growth and survival models suggest that only 18% of Araceae roots were likely to survive long enough to reach the ground from a branch 10 m high, whereas 87% of roots of Clusiaceae were likely to do so. This suggests that only those Araceae hemiepiphytes that produce a large number of aerial roots or are located close to the ground are likely to reach the soil.

The morphology of Genipa americana seeds and post-seminal development was studied, and its germination response investigated in relation to storage in water, substrate water volume, osmotic potential and temperature and light regimes. The seeds are flattened and seedlings are phaneroepigeal with leafy cotyledons. Seeds stored in water kept viable for up to 6 mo, but germination and seedling emergence were reduced after 4 mo. Germination was not affected under water-logged conditions, but seedling emergence was reduced at the water volume corresponding to a water column two times deeper than the seeds' mean thickness (70 ml). When seeds were osmotically stressed, a reduction in the rate and germination percentage occurred at −0.2 MPa and germination was drastically inhibited at −0.6 MPa. Seeds germinated in a wide range of temperatures (15–40 °C), with optimum at continuous temperatures of 25 and 30 °C. Light was not required for germination, and no dormancy mechanisms were observed. The seed and seedling morphology and the germinative responses of the species may permit its regeneration in periodically flooded lowland forests and riparian habitats and are probably key factors in explaining the species' wide distribution.

The short-nosed fruit bat, Cynopterus sphinx, begins to visit fruit-bearing trees about 30 min after sunset. Individual bats often hover near or land on fruits or on nearby branches to remove whole or parts of fruits with their mouth. These bats seldom remain in the fruit-bearing trees to feed, but instead carry fruits to feeding roosts, repeating this behaviour several times throughout the night. Analysis of the temporal distribution of feeding behaviour has revealed two peaks of activity, one in the pre-midnight hours when bats fed mostly on ‘steady state’ fruits, and another during the post-midnight hours when bats fed on ‘big-bang’ fruits. Only solitary bats visited and fed on species with steady state fruiting phenologies, whereas groups of bats regularly visited and fed on species with big-bang fruiting phenologies. Thus, plant species which produce large numbers of fruits appear to promote group foraging during the latter hours of the night. It is suggested that the temporal use of available fruits in south India made it possible for C. sphinx to successfully exploit them, and thereby reduced interference competition with conspecifics.

Observed variation in species richness on ecological gradients and between regions has attracted several different explanations. Climatic factors, such as energy availability, precipitation and mean annual temperature, are frequently cited to explain differences in species richness (Wright et al. 1993). The relative amount of variation in these variables may be of importance as well as absolute values (Stevens 1989, 1992). Alternatively, the history of colonization and extirpation have been used to explain regional variation in diversity (Guo et al. 1998; Latham & Ricklefs 1993a, b). Area is an important factor, for example on an elevational gradient the tops of mountains are not only cooler than the bottoms, but they are also much smaller (Rahbek 1997).

Mast-fruiting is the intermittent and synchronous production of large fruits by a population of plants at long intervals (Herrera et al. 1998, Kelly 1994). Several hypotheses have been proposed concerning the adaptive advantages of mast-fruiting (Janzen 1971, 1974; Kelly 1994), and some field observations have provided evidence for these hypotheses (Norton & Kelly 1988, Shibata et al. 1998, Sork 1993). The predator-satiation hypothesis is one well-known explanation for reproductive synchrony in plants and animals (Janzen 1971, 1974; Kelly 1994). This hypothesis claims that mast fruiting at irregular intervals of several years is an effective means of satiating vertebrate fruit predators: low seed production can only support low densities of predators during the periods between mast-fruiting events, but more fruits are produced than predators can consume in masting years (Janzen 1971, Kelly 1994). Thus, it may be said that mast-fruiting is a defence strategy of plants against post-dispersal vertebrate fruit predators.