Nutrient inputs into tank bromeliads were studied in relation to growth and productivity, and the abundance, diversity and biomass of their animal inhabitants, in three forest types along an elevational gradient. Concentrations of phosphorus, potassium and calcium in canopy-derived debris, and nitrogen and phosphorus in phytotelm water, declined with increasing elevation. Dwarf forest bromeliads contained the smallest amounts of debris/plant and lowest concentrations of nutrients in plant tissue. Their leaf turnover rate and productivity were highest and, because of high plant density, they comprised 12.8% of forest net primary productivity (0.47 t ha−1 y−1), and contained 3.3 t ha−1 of water. Annual nutrient budgets indicated that these microcosms were nutrient-abundant and accumulated < 5% of most nutrients passing through them. Exceptions were K and P in the dwarf forest, where accumulation was c. 25% of inputs. Animal and bromeliad biomass/plant peaked in the intermediate elevation forest, and were positively correlated with the debris content/bromeliad across all forest types. Animal species richness showed a significant mid-elevational peak, whereas abundance was independent of species richness and debris quantities, and declined with elevation as forest net primary productivity declined. The unimodal pattern of species richness was not correlated with nutrient concentrations, and relationships among faunal abundance, species richness, nutrient inputs and environment are too complex to warrant simple generalizations about nutrient resources and diversity, even in apparently simple microhabitats.

Stream water chemistry responds substantially to watershed disturbances, but hurricane effects have not been extensively investigated in tropical regions. This study presents a long-term (2.5–11 y) weekly record of stream water chemistry on eight forested watersheds (catchment basins) in the Luquillo Mountains of Puerto Rico. This includes a period before and at least 2 y after the disturbance caused by the 1989 Hurricane Hugo. Nitrate, potassium and ammonium concentrations increased after the hurricane and remained elevated for up to 2 y. Sulphate, chloride, sodium, magnesium and calcium showed smaller relative significant changes. Average stream water exports of potassium, nitrate and ammonium increased by 13.1, 3.6 and 0.54 kg ha−1 y−1 in the first post-hurricane year across all watersheds. These represent increases of 119, 182 and 102% respectively, compared to the other years of record. The increased stream outputs of potassium and nitrogen in the first 2 y post-hurricane are equivalent to 3% (potassium) and 1% (nitrogen) of the hurricane-derived plant litter. Effects of hurricanes on tropical stream water potassium and nitrogen can be greater than those caused by canopy gaps or limited forest cutting, but less than those following large-scale deforestation or fire.

The potential role of predation as a factor underlying variation in leaf-cutter ant (Atta sp.) densities was investigated on recently isolated land-bridge islands in Lago Guri, Venezuela. A survey of mature Atta colonies revealed a sharp increase in densities on small and medium islands (5.6 and 2.3 colonies ha−1 respectively) compared to large islands (0.72 colonies ha−1) and the mainland (0 nests in 5.5 ha). Incipient colonies showed the reverse trend with higher densities on larger landmasses. Cage experiments were conducted to test the impacts of predation on the survival of incipient and young Atta colonies. Protection by wire-mesh cages increased the survival of both incipient and young colonies at all sites. The survival of unprotected incipient and young colonies was significantly reduced on larger landmasses relative to small islands. These results are consistent with burrow survey data that provided indirect evidence of higher armadillo densities on larger landmasses. Findings suggest that reduced predation is a potentially important factor underlying observed variation in Atta density patterns in the Guri islands.

All individuals of Cedrela lilloi (a valuable timber species of Meliaceae) > 4 cm DBH were sampled in three rectangular plots (c. 15 000 m2 each) in northwestern Argentina subtropical montane forests between 850 and 1350 m. Regeneration dynamics of C. lilloi was characterized by testing two hypotheses: (i) C. lilloi has a gap-phase regeneration mode, which implies a negative exponential size/age distribution at forest stand scale, growth releases due to canopy openings, and juvenile trees clumped at spatial scales of treefall gaps. (ii) There is a negative spatial association between adults and juveniles of C. lilloi which could be caused by density dependent mortality. Despite differences in age structure, diameter distribution approximated a negative exponential curve at all sites. Radial growth, measured as tree-ring widths, averaged between 2 and 4 mm y−1 which is comparable to fast growing tropical species in mature forests. Aggregation of juveniles peaked at radial distances of 8 to 15 m. Size structure, growth and spatial patterns of juveniles support the first hypothesis. In support of the second hypothesis, juveniles showed a negative spatial association with conspecific mature trees at spatial scales of less than 20 m. The Janzen–Connell model of density-dependence is one potential explanation for this pattern. Although regeneration and growth patterns of C. lilloi suggest a potential for sustainable management based on small-scale gaps, spatial dynamics at stand-scale need to be considered to ensure the regeneration of mature trees.

Secondary fallow vegetation in parts of the Papua New Guinea lowlands is dominated by the shrub Piper aduncum L. that originates from South America. Here we report on its seed bank, growth rate and biomass accumulation. P. aduncum accounted for 69 % (408 m−2) of the seed bank in the forest and 53 % (1559 m−2) of the seed bank under fallow. About 90 % of the tree seed bank at the fallow site was dominated by P. aduncum whereas this was 78 % in the forest soil. Two-year-old P. aduncum had grown to 4.5 m height and had accumulated 48 Mg dry matter (DM) per ha of above ground biomass. The rate of biomass accumulation increased from 10 Mg DM ha−1 y−1 in the first year to 40 Mg DM ha−1 y−1 in the second year when 76 % of the biomass consisted of mainstems. The highest growth rate of 134 kg DM ha−1 d−1 occurred when P. aduncum was 17-mo-old. Aggressive invasion and monospecific stands of P. aduncum are explained by its dominance in the seed bank, fast growth, and high rates of biomass accumulation. P. aduncum is a major competitor to indigenous tree species and presents a threat to Papua New Guinea's rich biodiversity.

Data from a hilly forest study site at Batang Ule, Sumatra, are organized into 30 100-m × 10-m subplots lying perpendicular to the line of maximal topographic gradient, from the valley to the plateau/ridge. The following methodological question is addressed: what species diversity measures are best used in order to reveal the ecologically distinct regions in the site. The main tool used to answer this question is the α-diversity curve (Hα). Graphical examination of tree and species densities, and α-diversity curves identifies an anomalous species diversity behaviour of the ‘ridge above the slope’ subplots which may have implications on land-facet class definitions. Factor analysis of the α-diversity curves indicates that the diversity space is two-dimensional: i.e. two diversity measures are sufficient to characterize the site; the species density (H0), and the Berger-Parker index (H∞). In the

two-dimensional diversity-space three distinct species diversity groups are found which relate to the topographic gradient at the Batang Ule site. The results are compared with those for a flat homogeneous site at Pasirmayang, Sumatra. The implications of the results on land-classifications in species-diversity mapping and conservation strategy are discussed.

Termites were surveyed at an altitude of 1000 m in Maliau Basin, Sabah (Borneo), in two primary forest habitats: lower montane forest and stunted facies of upper montane forest. Soil, wood, litter, termite nests, and arboreal microhabitats up to a height of 2 m above ground were sampled using a belt transect protocol. Two transects were run in each forest type. The upper montane forest transects collected 11 and 13 species, compared with 15 and 19 in the lower montane forest transects. With the addition of species records from casual sampling (conducted with roughly equal effort in each forest type), totals of 18 species were found in the upper montane forest, and 34 species in the lower montane forest. Similar species richness and relative abundance of wood-feeding termites were found in both forest types. However, the lower montane forest had greater richness and relative abundance of species that feed on soil and extremely decayed soil-like wood. This difference is attributed mainly to (i) the well developed, organic-rich soils of the lower montane forest being more suitable for soil-dwelling and mound-building termites compared with the upper montane forest which has sandy soils with a thick covering of peat, and (ii) the low-stature and open canopy of the upper montane forest creates microclimatic conditions which are adverse for soil-feeding termites compared with the high, closed canopy in the lower montane forest. As expected, comparisons with similar studies in lowland forests in Southeast Asia confirmed that the upland forests are relatively depauperate.

Keystone plants that produce seasonally critical trophic resources comprise one of the main classes of keystone species, yet no studies have attempted to examine the ecological attributes that might help us recognize them and evaluate their importance in species-rich plant assemblages. In this paper the concept of keystone plant resources is reviewed using potential candidates proposed in the literature for neotropical forest sites. A poorly known example of a potential keystone resource—the gums produced by mature pods of two emergent tree species (Parkia nitida and P. pendula, Leguminosae: Mimosoideae)—is described for primates and other arboreal vertebrates in Amazonian forests. In particular, the fruiting phenology, tree density, patterns of vertebrate consumption, and nutritional quality of Parkia gums in Amazonian terra firme forests are considered. Putative neotropical keystone resources are then divided into four intersecting ecological attributes defining their community-wide importance to vertebrate frugivores: (1) temporal redundancy, (2) degree of consumer specificity, (3) reliability, and (4) abundance. From a vertebrate perspective, keystone plants are here defined as those producing reliable, low-redundancy resources that are consumed by a large proportion of the bird and mammal assemblage with which they coexist. Plant populations proposed to date as keystone species range widely across two of these four variables, which may disqualify most putative taxa (including Parkia spp.) from a more formal definition of keystone resources. Other importance attributes, the context-dependent role, the taxonomic refinement, and removal effects of the keystone plant resource concept as applied to tropical forests are also discussed.