Diameter growth rates and age-size relationships are reported for 45 abundant tree species and one liana in tropical wet forest at La Selva, Costa Rica. Thirteen-year increments in each species were analysed using growth simulation, a stochastic technique which projects growth trajectories.

Median growth rates ranged from 0.35 mm yr-1 (Anaxagorea crassipetala) to 13.41 mm yr-1) (Stryphnodendron excelsum). Maximum ranges ranged from 0.95 mm yr-1 (Quararibea brac-teolosa) to 14.62 mm yr-1 (Hernandia didymanthera). Minimum rates ranged from zero growth (Capparis pittieri, Colubrina spinosa, Doliocarpus spp.) to 7.45 mm yr-1 (Stryphno dendron excelsum).

Projected lifespan (from 100 mm dbh to the maximum dbh for the species) varied from 52 years (Anaxagorea crassipetala, Guatteria inuncta) to 442 years (Carapa guianensis). The mean longevity among the 45 tree species studied is 190 years.

Four main patterns of growth behaviour are recognized, based upon longevity and growth rates: (1) understorey species have slow maximum growth rates and short lifespans; (2) shade-tolerant subcanopy trees live around twice as long as understorey trees and grow at approxi-mately the same maximum rates; (3) canopy and subcanopy trees that are shade-tolerant but respond opportunistically to increased light levels have long lifespans and fast maximum growth rates; (4) shade-intolerant canopy and subcanopy species are short-lived and have fast maximum growth rates. Understorey species intergrade with shade-tolerant subcanopy species in terms of growth behaviour; shade-tolerant subcanopy species with opportunistic, shade-tolerant species; and opportunistic, shade-tolerant with shade-intolerant species.

Intraspecific variation in growth rates is lower in short-lived trees (understorey species with uniformly slow growth and shade-intolerant species with uniformly rapid growth) than in the two long-lived groups. These patterns are discussed in the context of tree ecophysiology and forest light environments.

The orchids Dendrobium infundibulum and Cymbidium insigne are pollinated by the bumblebee Bombus eximius, which also pollinates the ericaceous shrub Rhododendron lyi, A study of the three plants and the bumblebee in maquis-like mountainous vegetation in northern Thailand suggests that they form a floral mimicry system with two mimics (the orchids) to one model (R. lyi). The flowers of the two orchid species offer no food reward to pollinators. Flowers of the three species show definite morphological and visual resemblance, and the species overlap to a great extent in flowering phenology and habitat Mimic flowers were much less numerous than model flowers, which occurred abundantly in the area. The rate of pollinaria removal was very low in both orchid species, resulting in a relatively small percentage of fruit set, especially in D. infundibulum. Infrequency of pollinator visits was, however, somewhat counterbalanced by long-lasting flowers. The pollinaria of the two orchid species are differently positioned on the bee, hence interference between the different reproductive systems is minimized. This is the first report which indicates floral mimicry from tropical Asia.

The altitudinal zonation of forests on Mount Kerinci, Sumatra (3800 m) is described and compared with that in the temperate region of east Asia. Nine plots were selected between 1750 m in altitude and the upper limit of vegetation at 3250 m, at intervals of about 200 m in altitude. The plots are distinguished according to their main dominants, and the population structure of the dominant species is examined. The lower forests have species showing the whole range of size classes as well as solitary giants as dominants, but the upper forests lack these giants and are floristically poorer. Between 1750 m (the start of well preserved natural vegetation) and 2950 m (the forest limit) three forest zones are distinguished, and between 2950 and 3250 m a scrub zone. Upper forest zones tend to be dominated by species of the same genus or family which form important understory components of the zone below. Based on floristic comparisons with mountains of higher latitudes (i.e. Himalayas and Japan), the two lower forest zones (up to 2400 m) represent a subtropical zone, and the upper forest zone a warm-temperate zone. Climatic conditions at the forest limit on Mount Kerinci are similar to those at the latitudinal limit of warm-temperate evergreen trees; in the Himalayas the forest limit represents the latitudinal limit of the cool-temperate, and in Japan of the subarctic Altitudinal zonation patterns change with latitude, reaching their most complex on subtropical mountains where the two floristic realms, the Boreal and Palaeotropical, meet. A scheme for the pattern of vegetation zonation in east Asia is proposed.

A method of assessing rain forest structure by ranking relative abundance of 41 habitat variables was used to describe habitat differences among six trapping sites (324 subsites). Variables included aspects of all vegetation layers but concentrated on those considered to be important to small mammal distribution. Ordination and classification methods resulted in similar analyses of the data. Differences in habitat structure were primarily related to the moisture conditions of the trapping sites and secondarily to their successional age (regenerating versus primary forest). The most important habitat variables for differentiating between sites were LITTER, CLEARING, SOILS, PIG DAMAGE, FLOODING, FAN PALM, EMERGENTS, CANOPY SURFACE and SEEDLINGS. Habitat structure also varied within sites with some suggestion of small-scale patterning.

Small mammal captures were more likely in drier sites and subsites, but there was no difference in trap success between regenerating sites and primary forest sites. Greater numbers of species were captured in sites containing a variety of habitats, a discrete layering of vegetation and an extensive understorey. Small mammal captures were positively associated with five habitat variables (EMERGENTS, LITTER, ROTTING LOGS, SEEDLINGS, ROUGH BARK) and negatively associated with five others (LAYERS, BERTAM, SEDGES, PIG DAMAGE, FLOODING). The destruction caused by pigs is thought to be a major factor since it reduces litter and food availability over wide areas. Leopoldamys sabanus was the most abundant small mammal captured (40/68 individuals) and trap success differences among sites (0.4–1.9%) reflect its preference for higher, well-drained habitats.

The study demonstrates the usefulness of a simple method of ranking habitat features according to importance/abundance thus eliminating the all but impossible task of direct measurements in this complex system. This simple method of habitat description provides a basis for studying variables influencing faunal distribution patterns.

Seedlings of Pentaclethra macroloba (Willd.) Kuntze, a dominant, shade-tolerant species of tropical moist forest in Costa Rica, were raised under three light conditions to assess their acclimatization and growth responses to irradiance. The light environments used were full sun, partial shade (25% of full sun), and full shade (1% of full sun). To test the effect of a sudden change in light level such as would occur in the event of a treefall gap, the seedlings in the above conditions were switched between environments after two months and grown for an additional 1.5 months. Plants in full sun and partial shade had similar total weight; switching between the two environments had no effect on biomass. Plants switched from full sun and partial shade to full shade had negative growth as a result of negative CO2, flux and leaf abscission. Plants transferred from full shade to full sun had lower growth rates than those switched from full shade to partial shade because of severe leaf damage in full sun. The previous environment significantly affected the response of most growth and size characteristics to the present environment. Maximum photosynthesis changed only 30% in response to light level during growth. However, large changes in other photosynthetic and structural characteristics were found. Leaves developed in full shade had lower respiration, leaf thickness, and stomatal density and higher apparent quantum yield, specific leaf area, and chlorophyll content than leaves from full sun. Osmotic potentials were similar between treatments. Despite only small changes in maximum photosynthesis, acclimatization to extreme shade or sun rendered leaves unsuitable for large changes in environment. Consequently, in the event of a large treefall gap, plants already present in the understory will require a substantial period of adjustment before they respond to the increase in light.

Estimates were made of rodent longevity, population biomass and production in a dry sub-humid grassland area in Kenya, The results were based on a live-trapping study made over a 27-month period. During this time fourteen species of rodents and four species of insectivores were recorded from the area of the trapping grid. The most numerous species were Praomys natalensis, Mus triton, Mus minutoides and Lemniscomys striatus.

Breeding took place in both wet seasons, coinciding with peaks in rodent populations. Densities ranged from 6.6 ha-1 to 52.4 ha-1, and estimates of net annual production varied from 5485 g ha-1 year-1 to 7221 g ha-1 year-1. Rodent populations appear to turn over every six to nine months.

The results are discussed in relation to studies in other tropical grassland areas of Africa.

Earth mounds are important determinants of vegetation pattern in savannas, acting as foci for establishment of woody plants. In the Kenya highlands, mounds formerly attributed to termites have recently been found to be Mima mounds produced by rhizomyid mole rats. We investigated Mima mounds on black cotton soils near Kenyatta International Airport and on brown clay soils between Nairobi and Thika. At Kenyatta Airport, mounds had loamier, more granular soils than intermounds, and contained small rocks that mole rats can move. At the site between Nairobi and Thika, mound soils were more friable, higher in pH, and lower in carbon than intermound soils. Data from this and other studies indicate that Mima mound soils are more favourable for plant growth than those of true termite mounds. Mound vegetation exhibited lower coverage of grasses and greater coverage by forbs, shrubs, and bare ground, a pattern indicative of intense grazing and soil disturbance. Acacias, absent from most mounds, were abundant in the zone bordering the mound. This pattern may reflect the favourability of mound soils, combined with the effects of high grazing pressure. Future studies of savanna vegetation should distinguish between termite mounds and Mima mounds.

The movement and spatial distribution of marked Nile rats, Arvicanthis niloticus, was traced through phases of a low density population from January to August 1981, a rapidly growing population from September to January 1982, and a high and declining post-reproductive population from February to April 1982. Apart from late in the population cycle there was considerable movement, interchange and establishment of new ranges. As the population increased individual ranges became smaller. The rats apparently preferred field edges and did not favour the fields themselves. Females frequently established themselves at certain sites where they produced their litters; some of the offspring remained with the mother in the warren. There is also evidence that ousiders of both sexes joined these warrens. Males were generally more wide-ranging than females. Agricultural practices, e.g. mowing and trampling by cattle, influenced the rats preparedness to remain within a particular location. Exploitation of all the available habitat took several months to achieve.

This study examined the ecological distribution and abundance of the small mammal fauna in the Kora National Reserve, Kenya. Over a period of eight weeks, 3300 trap-nights yielded 11 species and a total of 298 small mammals. All 11 species were trapped in the diverse nyika habitat, whereas in the riverine habitat five species were trapped and the rock outcrops had only two species. However, the catch per trap-night was the highest on the rock outcrops compared with the riverine and nyika habitats. The duration of prebaiting had a marked effect on both diversity and abundance. With one exception, males of all species were in breeding condition whereas females tended to be more erratic. The biology of small mammal species in Kora in the dry season is discussed.

The general flowering of lowland dipterocarp forests of South-east Asia is a unique phenomenon that occurs intermittently, sometimes many years apart, and may be widespread throughout the region or sporadic. During a general flowering a very large number of tree families, including the well-known Dipterocarpaceae, flower and fruit exceptionally heavily. The huge pulse of flowering is echoed by an apparent explosion in the number of pollinators, and this is further augmented by migration of pollinators from the forest fringes. The huge demand for pollinators seems to be solved among several dipterocarps through utilization of tiny, fast breeding, floral-feeding insects such as thrips and hoppers. Competition for pollinators is further reduced through development of sequential flowering among several groups of trees that share similar pollinators. The resulting massive general fruiting seems to contribute to a heightened level of faunal activity and numbers. This long-intervalled flowering and fruiting phenology which dominates these lowland dipterocarp forests may have partly contributed to the lowered animal biomass frequently alluded to when these forests are compared with neotropical forests.

Artibeus watsoni (Chiroptera: Phyllostomidae) was found in Costa Rica to alter the shape of 11 species of broad-leafed plants in the families Araceae, Cyclanthaceae, Maran-taceae, Musaceae, and Palmae to form diurnal roost sites. The plant most commonly used for tent construction was Anthurium ravenii (Araceae). Bats create a tent on A. ravenii by severing the basal 2 to 5 lateral nerves at a distance of 5 to 10 mm from the midrib; the entire margin of the leaf then collapses downward to form a pyramid-shaped tent. The number of altered leaves per plant ranges from 1 to 4 with a mean of 2.1. A. watsoni appears to be selecting leaves of medium size and low within the plant. The size, shape, and location of leaves selected is consistent with the hypothesis that tent construction provides bats with roost sites that will be available to them for a long period of time and provides protection from both predators and the elements, thus conveying a selective advantage to the bats.

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.

In the semi-deciduous forests of Santa Rosa National Park in the Pacific coastal lowlands of northwestern Costa Rica, the large and fast-growing tree Spondias mombin(Anacardiaceae) experiences greater than 95% post-dispersal seed predation by a bruchid beetle (Amblycerus spondiae) on its nuts that have been dispersed to any part of pristine or secondary successional forest. Nuts dispersed (by white-tailed deer) to abandoned pastures immediately adjacent to the forest suffer less than 20% post-dispersal seed predation but seedlings are killed by frequent grass fires. S. mombin displays significant recruitment of saplings and young trees only on forest edges free of fire for long intervals. The very high percent seed predation in the forest and the failure of many nuts to ever be dispersed away from the parent tree is attributed directly and indirectly to the absence of a herbivorous (frugivorous) megafauna that would have been part of the habitat of S. mombin through most of its evolutionary history. These large animals would have consumed large numbers of S. mombin fruits and thereby dispersed the nuts in such a manner as to have both led to more escape from bruchids and an overall reduction in the bruchid population density. By their defecation patterns, these mammals would also have defecated more nuts in sites of high quality for S. mombin sapling survival than is the case at present. In contemporary habitats, S. mombin is culturally deprived in that it can no longer interact with the habitats, animals and densities of animals whose selective pressures were a major force in the evolution of the tree's traits.

An investigation of seasonal rates of litter production in a mixed forest, Hong Kong Island, was undertaken from October 1982 to January 1984. Total annual litterfall amounted to 1218.96 g m−2 yr−1, comprising 68.6% leaves, 18.9% woody material, and 12.5% fruits, seeds and insect frass. 398.70 g m−2 of litter was recorded immediately after a severe typhoon (9 September 1983). Rates of leaf-fall and organic debris production were correlated with prevailing temperature and rainfall. Leaf-fall peaked in January 1983, March to July 1983, and in September 1983 after the typhoon, while large amounts of insect faeces were collected in May and June. Woody litter production rates were correlated with temperature and rainfall recorded in previous months. Woody litterfall exhibited no obvious periodicity but was slightly increased during March and April. The seasonal distribution of litterfall is discussed in relation to climatic factors and habitat nutrient economy.