Study of forest dynamics commonly requires measurement of canopy gap size. Hemispherical photographs can be analysed to provide various measures whereby gaps can be ranked in order of size. For ten artificial gaps in a Bornean tropical rain forest these measures were better correlated with gap microclimate than gap area measured physically on the ground. All these measures are however relative. For detailed (e.g. ecophysiological) studies the greater detail provided by absolute measures of photosynthetically active radiation (PAR) are required. Long term PAR values can be computed from hemiphots so long as measurements in the open nearby are available. Correction for cloudy weather is essential. Computed and measured PAR are compared for the test gaps. Both have inherent limits which means that below c. 15% canopy openness, differences in PAR between gaps cannot be assessed accurately.

Present theories of tropical rain forest regeneration dynamics suggest that different tree species specialize on the microclimates of different sizes of canopy gap. A detailed analysis of the microclimates of closed forest and 10 canopy gaps of different sizes was carried out in lowland dipterocarp rain forest, Sabah, Malaysian Borneo. It reveals that gaps exhibit considerable spatial and temporal variation in microclimate. As a consequence the relationship between microclimate and gap sizes is not simple. Gaps of the same size do not necessarily have the same microclimate and may favour the growth of different seedling species. Chance location and timing of gap creation play an important role in regeneration dynamics.

The ecology of the Sri Lankan elephant in the Wasgomuwa Strict Nature Reserve and its environs is reported for the first time. Seasonal changes in the availability of grazing sites influenced changes in the home range of elephants. Availability of such sites in the wet season was limited by agricultural activities. Paddylands, after the harvest of the rice crop in the late wet season, became important dry season grazing sites. In the Reserve and areas outside its southern boundary on the left bank of the Mahaweli River, (a) female herds were seen more often than solitaries (b) female herds were larger and had a higher than expected number of juveniles in the dry than in the wet season (c) about 45% of the individuals were juveniles and (d) 7.4% of adult and sub-adult females had calves. Conflict between elephants and farmers will be most intense along the southern and eastern boundaries of the Wasgomuwa National Park, established in 1984 by the addition of new areas predominantly to the northern part of the Wasgomuwa Strict Nature Reserve.

This study focused on relationships between a tropical forest grasshopper and a major group of its host plants. Microtylopteryx hebardi (Acrididae:Ommatolampinae) at La Selva Biological Station, Costa Rica, feeds on understorey palms as well as other understorey plants. We assessed leaf damage levels in populations of three geonomoid palm species (Geonoma cuneata, Geonama congcsta, Asterogyne martiana), investigated feeding response of M. hebardi to the three palms, and examined leaf characteristics presumed to be important to herbivores. In understorey and gapedge habitats, total leaf damage did not differ significantly between palm species. In the centre of small light gaps, where M. hebardi was most abundant, total leaf damage and total herbivory on G. cuneata was equal to that on the other species, but herbivory attributable to grasshoppers was significantly greater. Female M. hebardi showed strong preference for G. cuneata over the other palm species in laboratory feeding trials. Experiments to elucidate the proximate basis for this feeding preference showed that grasshoppers preferentially bit filter paper discs containing cuticular wax extract of G. cuneata. In consumption and digestibility experiments, grasshoppers consumed more fresh weight of G. cuneata and gained more weight per unit time spent feeding on this species. Leaves of G. cuneata had the highest percentage water content, highest fresh and dry mass per unit leaf area, and the lowest percentage crude lignin among the three palms studied. These factors may partially explain the preference of M. hebardi for G. cuneata, which was reflected in higher herbivory rates incurred by G. cuneata in sites where M. hebardi was locally abundant.

The floral biology, breeding system and pollination of Caryocar brasiliense were studied in the cerrado vegetation of Central Brazil. The large, yellowish-cream, brush-like flowers are pollinated mainly by glossophagine bats (Glossophaga soricina and Anoura geoffroyi). Three non-glossophagine bats (Phyllostomus discolor, Vampyrops lineatus and Carollia perspicillata) and two short probosisced hawk moths (Erinyis ello and Pseudosphinx tetrio) may also act as occasional pollinators. Caryocar brasiliense is self-compatible although it sets significantly more fruits when crossed than when selfed. The natural fruit set (fruit/flower ratio) and seed set (seed/ovule ratio) are 3.1% and 1.0% respectively. Most of the fruits and seeds are formed through the action of the flower visitors, despite the fact that about 20% of the non-visited flowers receive self pollen on at least one stigma.

Different C4 photosynthesis pathways may influence plant response to shade and/or moisture stress. In the savanna of south-eastern Botswana, seedlings of PCK C4 type grass species were frequently observed to emerge in shaded habitats. The species Digitaria eriantha subsp. pentzii, which shows the NADP-ME pathway, was also found to be associated with the tree canopy. Species emerging in habitats exposed to full sun often showed the NAD-ME C4 pathway. Seedlings or Aristida congesla, Eragrostis rigidior and Tragus berteronianus which normally emerge in full light, showed higher relative growth rates and/or unit leaf rates compared with seedlings of Panicum maximum and Urochloa panicoides which are associated with shaded habitats. Seedlings of the latter species, however, survived low light conditions. Relative growth rate of the seedlings appeared to be negatively related to caryopsis weight. Light response analysis of leaves of Digitaria eriantha subsp. pentzii, grown under low light intensities, showed similar trends in light saturation to those reported for the PCK type in Panicum maximum. Mesophyll rather than stomatal limitations appeared to induce light saturation at higher light intensities in leaves grown under shade conditions.

Orchid diversity, distribution and host specificity were examined in a tropical watershed in the Luquillo Experimental Forest of Puerto Rico. Eleven orchid species occur in the area. The low diversity is attributed to island isolation and large-scale hurricane disturbances. Pleurothallis ruscifolia and Maxillaria coccinea were by far the most abundant species in the area and occurred on the largest number of host species and host zones. None of the orchids were host specific or host zone specialists although preferences for hosts and vertical host zones were encountered.

Only 8.2% of the 426 trees and shrubs and 24.4% of the 45 species surveyed were orchid phorophytes (= hosts). Examination of host distribution by diameter at breast height (DBH) showed that 80.5% were greater than 16 cm DBH. Orchid species in the area tend to occur on rough bark hosts, but their preferences are not statistically significant. Guarea guidonia (Meliaceae) and Dacryodes excelsa (Burseraceae) are the two most important orchid hosts in our study site comprising 62.9% of all host trees. Careful management of these two tree species is suggested, since these species may be crucial to the maintenance of orchid abundance and diversity in the area.