The Monteverde Cloud Forest Reserve protects a variety of primary montane forest communities on volcanic parent materials. We describe the structure and composition of the forest to provide background information for epiphyte and nutrient cycling studies and for comparison with other tropical montane forests. In a 4-ha study plot in leeward cloud forest, density of stems (2062 individuals ha−1 for stems >2 cm dbh, 555 individuals ha−1 for stems > 10cm dbh) and stem basal area (73.8 m2 ha−1 for stems >2 cm, 62.0 m2 ha−1 for stems >10 cm dbh) were high relative to other montane forests. Stems in a subset of the plot (c. 1/3 of the area) were identified and assigned to 47 families, 83 genera and 114 species, which is rich compared with other montane forests. Large stems had a higher spatial variability of structural and floristic characteristics than small stems.

The effects of irrigation and the rainy season on soil gases, water and physical properties were studied in a lowland moist forest in Panama. Two control plots experienced a normal four-month dry season and two experimental plots were irrigated during the dry season.

The forest soils were well aerated. The average soil oxygen content at 20 cm never dropped below 15%. Irrigation in the dry season resulted in treatment effects on soil oxygen and water that persisted throughout the rainy season. The late rainy season soil oxygen content at 20 cm was 18.2% in the control plots and 16.8% in the irrigated plots. The late rainy season soil water content at 0–10 cm was 0.34 m3 m-3 in the control plots and 0.36–0.37 m3 m-3 in the irrigated plots. In the control plots, in the absence of any experimental manipulation, the soil physical properties changed within a single rainy season. Specifically, soil oxygen dropped and soil water increased during the eight-month rainy season.

The observed alterations in soil physical properties probably resulted from changes in soil structure and the abundance of large pores. The rainy season or irrigation may decrease soil porosity by dispersing aggregates of soil particles, whereas soil desiccation during the dry season may enhance the formation of aggregates and large pores. As a result, the irrigated soils held more water and were less permeable to gas and water than soils experiencing a normal dry season. We conclude that the dry season may play an important role in maintaining soil structure.

Seeds of Dryobalanops aromatica and D. lanceolata (Dipterocarpaceae) were sown in gaps and understorey on a ridge and a valley in a Bornean rainforest. Germination rates were 92–100% regardless of site and species. On the ridge, the proportion of seedlings that opened primary leaves was larger in D. aromatica (19–30%) than in D. lanceolata (7–19%) due to higher root predation on D. lanceolata. In the valley, on the other hand, the proportion was larger in D. lanceolata (71–74%) than in D. aromatica (56%). After primary leaf production, seedlings of both species had higher survivorship in the gaps than in the understorey. Interactions between predators, soil conditions and light environment and their effects on seedling establishment are discussed.

Leaf and grass canopy photosynthetic rates were measured in a West African humid savanna during several stages of the early growing season. The results obtained on the dominant grass species Hyparrhenia diplandra and data published previously show that C4 savanna grasses exhibit a remarkably high leaf photosynthetic capacity despite their low nitrogen content. A variation of leaf photosynthetic capacity in relation to leaf rank on stems is observed which is interpreted by ageing and shading effects within the canopy. Seasonal variations of the canopy CO2 assimilation rate is explained in relation to variations of leaf area index and canopy nitrogen content. Despite low nitrogen content or low leaf area index, maximum canopy net photosynthesis was high (24 μmol CO2 m-3 s-1 for LAI = 1.5). The high photosynthetic nitrogen use efficiency exhibited by leaves of humid savanna grass species is a major attribute explaining high photosynthetic rates of the grass canopy in this environment. This result sustains the emerging opinion that tropical savannas could be highly productive despite the generally low nutrient status they experience.

Windthrow was assessed following a convective storm in a stand of tropical savanna in Kakadu National Park, northern Australia. Over an area of 3 ha, 79 out of 810 trees (9.8%) were damaged; 27 of them were either uprooted or snapped off at the trunk. Logistic regression showed that both species and tree height were significant determinants of the probability of wind damage. Branch loss and either uprooting or trunk snapping was highest in the canopy sub-dominant Eucalyptus porrecta. Damage was lowest in the sub-dominant trees Erythrophleum chlorostachys, a species which is relatively resistant to termite damage, and Terminalia ferdinandiana, a deciduous species which is generally shorter than the main canopy dominants. Damage was intermediate in the two most common canopy dominants, Eucalyptus tetrodonta and E. miniata. Wind damage was greatest in trees taller than 9 m and relatively minor in trees below this height. Wind disturbs savanna trees in a manner opposite to that of fire, because wind damage is greatest in taller trees, whereas fire damage is greatest in smaller trees. This, coupled with significant within-patch variability in the extent of wind damage, may act to increase small-scale environmental heterogeneity in savannas.

The habit, shade-tolerance and dispersal agent of 19 bromeliad species were studied in a rainforest community in order to relate specific traits to the spatial occurrence of the species. Highest density was found in riparian forest (RF), followed by restinga scrub (RE), rocky shore (RS) and dense canopy forest (DF). Terrestrial bromeliads occurred in open sites (RE and RS), epiphytes were absent in RS and facultative species occupied all four habitats. Bird-dispersed bromeliads occurred in the upper canopy, whereas those dispersed by mammals were low in the forest profile. Bromeliads which are dispersed by similar fauna fruit sequentially through the year. Differences in traits may allow the sharing of habitats and strata among species.

Scientific and commercial collecting have documented high levels of abundance among several species of marine snakes. Estimates of first-year mortality in populations of marine snakes range from 40 to 90%. The primary cause of this mortality is unknown. Storms, currents, sun exposure, dehydration and fire are abiotic factors that may control populations of marine and amphibious snakes. Disease, malnutrition and predation are biotic factors known to affect populations. In the literature there are isolated reports of predation by marine mammals, birds of prey, fish and invertebrates. Sharks in Australian waters are known to be predators on sea snakes. Our studies show that in the estuaries, intertidal mangrove creeks and mud flats of southeast Asia decapod crustaceans are important snake predators. Microhabitat overlap, exoskeleton armour and a respiratory advantage in an underwater standoff argue for their potential as potent predators. Field observations, a survey of crab stomach contents and encounters between snakes and crabs under laboratory conditions support this hypothesis. –

The distribution of the giraffe (Giraffa camelopardalis peralta Thomas 1898) has greatly diminished in West Africa, and now the last remaining population, reduced to less than 100 individuals, is found in Niger. These giraffes of West Africa are seriously threatened by extensive deforestation and clearing of their habitat. They live peacefully with humans and cattle and participate in an essential way in the dynamics of vegetation. Their disappearance would represent another step towards the impoverishment of the inheritance of Africa, a process already too far advanced. To save them, a fundamental rethinking of the connection between the environment and development on the one hand, and on the responsibilities of rural communities for the management of their natural resources on the other, has to be undertaken.

The relationship between Camponotus sp. ants and the carnivorous pitcher plant, Nepenthes bicalcarata, from Borneo were investigated. The ants nest in the hollow tendrils of the plant, and feed on large prey items caught by the pitchers. These are hauled from the pitcher fluid by the ants and consumed. When large prey items are absent, the ants feed upon mosquito larvae which inhabit the pitcher fluid. The accumulation of excess prey in pitchers can lead to putrefaction of the contents, and disruption of the pitcher's digestive system. Experiments on the possible benefits of the ants' behaviour to the plant showed that the accumulation of excess prey and the putrefaction of the pitcher contents were significantly reduced in the presence of the ants. The accumulation of ammonia in pitchers was unaffected by the presence of the ants when small prey were added to pitchers, but was reduced significantly in the presence of ants when large prey were added. It is suggested that Camponotus sp. and N. bicalcarata have a mutualistic association, from which the ants obtain food and nesting sites and, in return, prevent damaging accumulation of excess prey in the pitchers.

We compared reproductive characteristics of the dendrobatid frog Colostethus trinitatis at the Tamana cave in the Central Range hills and at five forest stream sites in the Northern Range hills of Trinidad. There were significant differences between sites in adult female body size, intraovarian clutch size (in absolute terms and relative to body size) and the size of tadpoles carried by male frogs. Clutch sizes ranged from 6 to 13 in the Northern Range samples and from 12 to 26 at Tamana. Adult male body size was similar at all sites. Tadpoles carried by male C. trinitatis at Tamana were significantly smaller (mean length 14.2 mm) than those carried by males at the five Northern range sites (mean length 16.4–16.7 mm). The smallest clutches and largest tadpoles were found at Mount St Benedict, where there was evidence of size-selective predation on tadpoles by fish. Tamana, where clutches were large and tadpoles small, differed from the Northern Range sites in terms of the physical environment (cave vs forest) and the abundance of invertebrates. We discuss possible ultimate and proximate causes of the differences in clutch size and tadpole size, particularly size-selective predation and availability of food.

White-eyed vireos (Vireo griseus) winter in the forests and secondary growth of the Yucatan Peninsula where Bursera simaruba (Burseraceae) is an abundant tree. Twenty-five per cent of all white-eyed vireos observed foraging visited Bursera trees. In addition, presence and abundance of territorial white-eyed vireos in small forest patches were correlated with the size of the Bursera crop. Vireos were the most reliable dispersers of Bursera seeds. These birds visited 32 of 35 trees observed for at least three hours. They accounted for approximately half of all bird visits, and two-thirds of the seeds dispersed. Most of the other species rarely visited (<5% of visits) or failed to remove seeds from the tree.

Peculiarities of phenology and fruit structure may contribute to the tendency of Bursera to be dispersed by relatively few species. The capsules of Bursera fruits do not open when the fruit ripens; birds apparently locate ripe fruit using visual cues, although these are few. In addition, only a small portion of the crop ripens daily over a 7- or 8-month period. The vireo-Bursera simaruba relationship, found regionally on the Yucatan Peninsula, may result from the prolonged fruit ripening period (October-March), the relatively depauperate frugivore community and the relatively high density of small Bursera trees in the hurricane-disturbed dry forests.

Small trees at all times, and all trees from October to February, depend upon territorial vireos for continuous, highly efficient local dispersal of a small number of fruits. In March and April residual fruits ripen rapidly and synchronously, attracting a greater variety of visitors for broad spectrum dispersal during a period of food scarcity. Thus, Bursera has an unusual two-phase phenological pattern, perhaps alternately to take advantage of both specialized and opportunistic dispersers.

Measurements of reproductive allocation, fertility and iteroparity were made on females of four species of woodlice (Isopoda: Oniscidae) from southern Africa. In three of the species between-population comparisons were made. The average body mass of reproductive females was smaller than in temperate woodlice and because of a positive scaling between body mass and fertility: brood sizes were rarely larger than 30 young and usually between 5 and 20. Reproductive allocation ranged from 16 to 27% of female pre-birth live mass and differed significantly between species. Associations between reproductive allocation and body mass were all positive although only significant in two of the populations. A small number of females produced more than one brood during the study and iteroparity appears the most likely reproductive tactic in these species.

In woodlice a restriction on body size results in lower fecundity as brood size is ultimately determined by the size of the marsupium. It is postulated that a tactic of repeated reproduction, with a relatively conservative allocation of resources to each reproductive event to enhance survival probabilities, would be favoured, particularly in an environment where juvenile mortality and the chance of complete brood failure is high.

Some savanna areas in the Orinoco Llanos region in Venezuela are characterized by the abundance of small forest groves, resulting in a parkland landscape. We hypothesized that forest groves are the result of colonization of the open savanna by forest species, facilitated by the activity of leaf-cutting ants. In this paper we present results from a field study conducted on an ecotonal belt between a deciduous gallery forest and an open savanna in the western Llanos of Venezuela. In seven transects, trees, groves and leaf-cutting ant nests were counted, size parameters evaluated and distance from grove to forest measured. Soil chemical analysis and microclimatic measurements were performed in the forest, grassland and groves. Floristic composition of the woodland component of the savanna (scattered trees) was very dissimilar from that of the forest, but the composition of the groves was essentially a mixture of both woodland and forest species. Woodland trees were present in all groves, whereas forest trees were present only in larger groves. The size structures of populations of the two types of trees differed significandy according to the size of the grove; also, woodland tree population structure differed significantly between open savanna and groves. The frequency of groves with Atta laevigata nests increased with the size of the grove, and groves with forest trees were positively associated with the presence of nests. A. laevigata nests improved the soil of groves, increasing N, Mg, Ca and organic carbon, but other soil properties were not modified. Temperatures at ground level in the dry season were ameliorated in the groves compared with the grassland, and this effect increased with the size of the grove. We concluded that a dynamic process of grove formation is facilitated by the aggregation of a few woodland trees, followed by the successful invasion of forest trees and a leaf-cutting ant nest. The results did not show any clear sequence of arrival of the ants or the forest trees, but it seems clear that these two would act synergistically, improving conditions for each other.