Dew deposition was calculated for leaves of the epiphytic bromeliads Tillandsia brachycaulos and T. elongata in a tropical dry deciduous forest in Yucatán, Mexico, over one year. Plant characteristics and water relations were also measured. Estimations were made by using energy balance analysis and the Penman–Monteith equation. Dew accumulation was also quantified using a cloth-plate method and by change in mass of whole plants. Tissue water content and total leaf area were similar in the two species, but maximum tank water content was three-fold greater for T. elongata than for T. brachycaulos, which had a lower degree of tissue desiccation tolerance than T. elongata. Succulence for T. brachycaulos changed little during most of the year, decreasing significantly only during one month in the dry season. Leaf water potential and osmotic pressure did not change significantly after a dew-deposition event. Theoretical dew per night on leaves was greatest during the early dry season (about 0.72 mm) compared with 0.34 mm in the rainy season and 0.008 mm in the late dry season. Dew amounts alone are not adequate to support growth but may maintain a favourable water balance for epiphytic bromeliads during the driest months of the year.

In the first 3 mo of 1998, an aseasonal tropical rain forest at Lambir Hills National Park on the north-west coast of Borneo suffered an unusually severe drought. Extreme climatic events such as this one are expected to influence tree population structure and community dynamics through differential effects on growth and mortality. The demographics of seedlings of seven shade-tolerant tree species, including two dipterocarps, during this severe drought were contrasted with baseline demographic data from two earlier census intervals, one of which included a slight drought, and one of which included no drought. Hemispherical photographs were used to document an opening of the canopy that resulted from the dieback and mortality of large trees during the severe 1998 drought. Seedlings that experienced an increase in canopy openness were less likely to die than other seedlings. Rates of mortality and height loss were significantly increased in association with drought. The overall mortality rates during the severe drought and slight drought census intervals were 8.2% y-1 and 7.3% y-1 respectively, compared with 4.9% y-1 for the non-drought census interval. The incidence of height loss during the severe drought census interval was 27.5%, compared with rates of 11.7% and 20.1% for earlier census intervals. Dipterocarp species were less affected than some non-dipterocarp species, and the smallest seedlings suffered the greatest impact. If droughts in this region continue to increase in intensity and severity, they may ultimately cause a change in the species population densities and stand structure of the understorey seedling community of this rain forest.

Patterns of vertical stratification and canopy utilization by rodents and marsupials were analysed in two contiguous Atlantic forests at different altitudes (100 m and 900 m asl). Twenty-two species were captured using live traps placed at ground level, in the understorey (1.5–2.0 m), and in the canopy (6–15 m) over 2 y; seven species (32%) were mainly or exclusively arboreal. Community composition and relative abundance of species in the different vertical strata were not similar, with a general reduction in the number of species, and in abundance in the upper layers. The following species were captured mainly or exclusively in the canopy: Micoureus demerarae and Gracilinanus microtarsus (Didelphimorphia, Didelphidae); Wilfredomys pictipes, Oecomys aff. concolor, and Rhipidomys aff. macrurus (Rodentia, Muridae); and Nelomys nigrispinus (Rodentia, Echimyidae). Our results indicated that altitudinal changes in Atlantic forest areas may alter the community composition of different forest layers but they do not seem to alter greatly specific patterns of vertical habitat utilization. Similar-sized species tended to differ in their patterns of vertical utilization of habitat with the exception of terrestrial akodontine rodents (genera Akodon, Thaptomys, Oxymycterus and Brucepattersonius). Rodents (mainly Oryzomys russatus) dominated captures at ground level at both sites but Akodontinii were numerous only at the highest site. Unlike other neotropical forests, marsupials did not dominate canopy captures.

Patterns of species composition in a neotropical termite assemblage were studied in relation to early effects of forest fragmentation as well as other sources of environmental and spatial heterogeneity. Termite diversity surveys were carried out at three mainland forest sites, and 10 islands of varying size, in an area of lowland tropical forest that had been flooded 4 y earlier, during the creation of the Petit Saut hydroelectric project in French Guiana. The ‘ghost forest’ of dead emergent trees in the flooded zone was also studied for its influence on island termite assemblages. Results suggested that the effects of forest fragmentation upon the total assemblage, and upon soil-feeders in particular, were subordinate to the influence of forest understorey palm density, and the closely associated gradients of soil humus depth and soil pH. Moreover, gradients for these three variables were uncorrelated with forest fragmentation and probably reflected spatial environmental heterogeneity pre-dating inundation events. Nevertheless, factors associated with forest fragmentation appeared to have had a significant effect on changes in termite species composition across the study site, primarily in structuring the wood- and leaf-litter-feeder assemblage. Effects upon the latter were not apparently a result of influx of species from the ghost forest. Purely spatial variation also influenced β-diversity changes in species composition across the site. In conclusion, the effects of forest fragmentation upon termites appear to have been relatively mild compared with other faunal groups, 4 y after flooding. Nevertheless, we predict that the effects of fragmentation on termite assemblages will ultimately be negative. This study also points to the importance of Amazonian understorey palms in structuring a tropical forest termite assemblage.

Leaf quality (nutrient concentration) and herbivory were studied in a set of dominant tree species in regenerating, secondary tropical dry forests growing on limestone in the Yucatán Peninsula. The study's objective was to assess how variation in nutrient availability affects leaf nitrogen and phosphorus concentrations and herbivory. Our study included an area of young forest (10 y old), with phosphorus-poor soils, and an area of old forest (∼60 y old), in which soil P was comparatively less limiting. The foliage of representative species of each site was studied, including Acacia gaumeri, Leucaena leucocephala and Lysiloma latisiliquum at the young forest site, and A. gaumeri, Bursera simaruba and Pithecellobium dulce at the old forest. Four independent plots (12 × 12 m) at each forest were either left intact (controls) or fertilized with N, with P, or with N plus P for three consecutive years. Relaxation of nutrient limitations at the young forest resulted in an increase in leaf phosphorus and herbivory in all species. In contrast, N and P fertilization at the old forest site did not consistently affect leaf nutrient concentration and leaf damage. In this site the main response to fertilization was an increase in leaf nitrogen only in B. simaruba and an increase in herbivory in A. gaumeri; leaf phosphorus was unaffected by soil fertilization. Overall, we observed that, subsequent to nutrient addition, leaf phosphorus concentration and herbivory in the leguminous species increased at the young site; leaf nitrogen concentration in the non-leguminous species increased at the old site while herbivory only increased in A. gaumeri, following a pattern similar to that observed in the young site. We conclude that the regulatory mechanisms of leaf quality and damage by herbivores will vary, depending on the details of the site's nutrient limitations and the identity of species.

We investigated the spatial distribution of fruiting in Dryobalanops aromatica (Dipterocarpaceae), a mast-seeding emergent tree that is found in the tropical rain forests of Borneo. Of 393 adults (diameter at breast height (dbh) > 30 cm) in a 52-ha area, 143 (36.4%) individuals fruited. A second-order spatial analysis, based on Ripley's K-function, revealed that fruiting trees were significantly (P < 0.05) aggregated with respect to the total population over distances of 15–115 m. Thus, the spatial distribution of fruiting trees was more aggregated than expected from the adult tree distribution, which itself was aggregated within the study plot. Logistic regression analysis showed that fruiting trees had a significantly greater dbh and were surrounded by more conspecific adults per ha than non-fruiting individuals. Moreover, fruiting trees were found at higher elevations, on steeper slopes, and on sandy rather than clayey soils. In contrast, annual diameter growth, adult density over areas < 1 ha, and slope convexity did not significantly affect fruiting probability. The ratio of seedling (20 cm ≤ h < 60 cm) and sapling (60 cm ≤ h < 300 cm) density to adult density was higher in sites at higher elevations, on steeper slopes, and on sandy soils than that for lower elevations, flat slopes and clayey soils. This suggests that the aggregation of fruiting trees occurred not only at the time of the study, but that it had occurred repeatedly in the past, at the high-elevation, steep-sloped, sandy sites. Thus, site conditions probably affect the dynamics and spatial structure of local populations through differences in fruiting frequency among trees experiencing different site conditions.

Leafing phenology of two dry-forest sites on soils of different depth (S = shallow, D = deep) at Shipstern Reserve, Belize, were compared at the start of the rainy season (April–June 2000). Trees ≥ 2.5 cm dbh were recorded weekly for 8 wk in three 0.04-ha plots per site. Ten species were analysed individually for their phenological patterns, of which the three most common were Bursera simaruba, Metopium brownei and Jatropha gaumeri. Trees were divided into those in the canopy (> 10 cm dbh) and the subcanopy (≤ 10 cm dbh). Site S had larger trees on average than site D. The proportion of trees flushing leaves at any one time was generally higher in site S than in site D, for both canopy and subcanopy trees. Leaf flush started 2 wk earlier in site S than site D for subcanopy trees, but only 0.5 wk earlier for the canopy trees. Leaf flush duration was 1.5 wk longer in site S than site D. Large trees in the subcanopy flushed leaves earlier than small ones at both sites but in the canopy just at site D. Large trees flushed leaves earlier than small ones in three species and small trees flushed leaves more rapidly in two species. Bursera and Jatropha followed the general trends but Metopium, with larger trees in site D than site S, showed the converse with onset of flushing 1 wk earlier in site D than site S. Differences in response of the canopy and subcanopy trees on each site can be accounted for by the predominance of spring-flushing or stem-succulent species in site S and a tendency for evergreen species to occur in site D. Early flushing of relatively larger trees in site D most likely requires access to deeper soil water reserves but small and large trees utilize stored tree water in site S.

We consider whether species richness in canopy gaps in coastal scarp forest (South Africa) is constrained by competition for a limited number of available niches or is a chance effect of recruitment and dispersal limitation on species derived from the surrounding species pool. In so doing we confirm findings from relatively species-poor New Zealand Nothofagus forest. We investigate the contrasting roles of determinism and chance, and the putative assembly of woody plants in gaps, using a technique in which the species richness of small, replicate local assemblages (0.25–m2 quadrats) are sampled within regions (the surrounding gap) that vary in total species richness. The form of the regression of local species richness against regional species richness indicates the extent to which community assembly is under local-ecological control (niche limited). Species richness of local assemblages was not niche limited and increased as a constant proportion of the size of the species pool in a gap. We argue that, in general, species assembly in these forest gaps is chance-driven, and discuss the management implications this has for selective pole-harvesting in these forests.

Nutrient fluxes in stemflow and throughfall were compared among three successional stages of an upper montane rain forest and related to structural characteristics of the stands (stem density, leaf area, epiphyte abundance). An old-growth forest stand, an early successional (10-y-old) forest stand and a mid-successional (40-y-old) forest stand were studied in the Cordillera Talamanca, Costa Rica. All three sites were dominated by Quercus copeyensis with a variable admixture of other tree species. There was no difference in the average stand leaf area index between the old-growth forest and the early successional forest. A significantly higher leaf area was found in the mid-successional forest. There were large differences in litterfall from non-vascular epiphytes (mosses, liverworts and lichens) which reflected differences in epiphyte abundance, with highest values in the old-growth forest. Total nutrient transfer via stemflow and throughfall from the canopy to the soil showed only minor differences among the stands. The stands differed widely in the ratio of nutrient transport via stemflow to the total nutrient flux by water below the canopy. The K flux with stemflow accounted for 5% of the total in the old-growth forest but it accounted for 17% (early successional forest) and 26% (mid-successional forest) in the secondary forests. It is concluded that differences in canopy structure and epiphyte abundance in old-growth and secondary forests resulted in large differences in the partitioning of nutrient transport into stemflow and throughfall components although total nutrient transfers via water reaching the soil were similar.

The Hellshire Hills are an extensive area of tropical dry forest over limestone, located on the south coast of Jamaica. Despite being a protected area, they are subject to encroachment and clearance by charcoal burners, leaving a relatively pristine core within more disturbed areas of forest. Future management requires a consideration of the forest's resilience to such disturbance, and this study reports on seedling dynamics before and after different intensities of disturbance. The study was conducted within twelve 225-m2 plots comprising four blocks and three treatments. The treatments were removal of all trees (≥ 2 cm dbh), removal of 50% of stems (> 5 cm) and an uncut control plot. Seedling dynamics were monitored before and 3, 8, 13 and 20 mo after the application of treatments. The study indicates that regeneration by seed was not severely affected by this small-scale disturbance. However, the density of some species was affected by the environmental conditions created by partial and clear cutting, and seasonal effects were more pronounced after disturbance. Biomass recovery by seedlings was negligible in comparison with coppice regrowth which clearly offers considerable resilience to disturbance in this dry forest where successful regeneration by seed is highly susceptible to rainfall seasonality. This will likely affect long-term species diversity if the present rate of clearance continues.

This study demonstrates that elephant seed-dispersal is vital for Balanites wilsoniana (Zygophyllaceae), a forest canopy tree with no other effective dispersers. Non-dispersed seeds suffered high mortality (84%) and low germination (3%). Elephants were reliable at visiting fruiting trees (46%), ingesting available seeds (55%) and dispersing the fruit crop (26%). Compared with unpassed seeds, seeds passed through an elephant's gut had improved germination (54.9% vs. 2.9%) and reduced time to germination (82 vs. 132 d). Given predation rates under parent trees, elephant gut passage is expected to improve absolute germination by 66%. When this change in germination is divided by germination of unpassed seeds, elephant gut passage is expect to improve relative germination by as much as 4000%. Although post-dispersal predation occurred in dung containing B. wilsoniana seeds, dispersed seedlings were abundant. Compared with seedlings under parent trees, dispersed seedlings had greater survival and height. Dispersed seedlings survived in a diversity of environments, thrived under high-light conditions, and were negligibly affected by post-dispersal density. Although elephants are not essential for B. wilsoniana germination, their actions greatly increase seedling establishment and move a large proportion of seeds. This high degree of effectiveness, together with very low non-dispersed seed survival, provides strong evidence that B. wilsoniana is dependent on elephants for its long-term persistence.

Ranging patterns are important features of animal ecology both for evolutionary ecologists who study adaptive foraging and habitat use, and for conservationists who need information on habitat requirements and minimum resource needs. Because ranging patterns are difficult and time-consuming to measure, many researchers have sought socio-ecological variables that predict range use. For example, many studies show a correlation between daily path length (day-range length) and the number of animals in a group (Chapman et al. 1995, van Schaik et al. 1983, Waser 1977, Wrangham et al. 1993). This seems reasonable because larger groups have more mouths to feed, necessitating more travel to find adequate food supplies. Group size is far easier to measure than day range, hence the attraction of this variable. However, group size must be used cautiously as a proxy for day range because their relationship is neither strong nor straightforward.

Tropical rain forests have a high richness of plant species. However, the richness of insect species associated with the forest canopy is still poorly known. Estimates of arthropod fauna have followed several approaches from surveys on a single or few trees (Erwin 1988,1990) to regional sampling of specific insect guilds such as gall-inducing insects (Fernandes & Price 1988, Lara & Fernandes 1996, Price et al. 1998).

Fine roots are very important in ecology because of their role in nutrient and water uptake, and as a source of organic matter to the soil. In carbon-cycle models, fine roots are a significant organic matter pool (Potter 1999) with high net primary productivity (Jackson et al. 1997) and turnover (Gill & Jackson 2000). In ecosystem production studies, fine roots are usually divided between biomass and necromass.The sum of both pools is defined as root mass (Klinge & Herrera 1978) or total root biomass (Böhm 1979). In tropical forests the study of fine-root biomass is restricted because of the difficulties in distinguishing live roots. Visual methodologies are not adequate in tropical forests where high diversity is expressed through many root morphologies. On the other hand, definitions of root death are ambiguous and differ between different studies (Comas et al. 2000). Fine-root mass is easier and more accurate to measure than fine-root biomass because subjective selection criteria are avoided. However, in the measurement of below-ground production, the estimation of fine-root biomass is essential (Jackson et al. 1997). The adaptation of objective selection methods (Comas et al. 2000, Joslin & Henderson 1984) to measure live and dead root fractions is urgently needed.

Variation in local abundance of herbivores is influenced by several abiotic and biotic factors, but it may often be determined by the local availability of plant resources (Quinn et al. 1997). Leaf-cutting ants, common defoliators of plants in the Neotropics, are more abundant in early successional forests than in old-growth forest (Jaffe & Vilela 1989, Vasconcelos & Cherrett 1995). A recent study showed that the high density of mature leaf-cutting ant nests in early successional forests was mainly determined by the availability of pioneer plant species, largely preferred by the leafcutters (Farji-Brener 2001). The dominance of pioneer species in early successional forests decreases foraging costs for leaf-cutting ant colonies, and thus these habitats can support a high density of mature colonies. On the other hand, the effective defence mechanisms of shade-tolerant species, which dominate primary habitats, could explain the low density of mature leaf-cutting ant colonies in old-growth forests (palatable forage hypothesis, see Farji-Brener 2001). According to this hypothesis, it is proposed that leaf-cutting ant colonies in old-growth forests should concentrate their foraging effort in treefall gaps, in which sun and pioneer plant species (preferred by leafcutters), are readily available (Farji-Brener 2001, Nichols-Orians 1991a, b; Wetterer 1994). However, this prediction of the palatable forage hypothesis has not yet been explicitly documented.

An incomplete version of Figure 2 was published in the previous issue. The correct version is shown below. The publishers would like to apologise to the authors and their readers for this error.