We used the Hedley sequential extraction procedure to measure nine different organic and inorganic soil phosphorus fractions in forest soils of the Bragantina region of Para, Brazil. We compared the labile fractions (resin-extractable P HCO₃-extractable inorganic and organic P) in Oxisols from three secondary forests (10, 20, and 40 years old) and a primary forest. These stands were located in an area that has supported shifting agriculture for approximately a century. After agricultural use, total P and labile P in soils of young secondary forests are diminished compared to the amounts present in the primary forest soil. Within each stand, organic carbon content was a good predictor of labile organic and inorganic P, consistent with the large body of research indicating that mineralization of organic matter is important to plant nutrition in tropical ecosystems. During the reorganization of P pools during forest development, the pool of labile organic P (HCO₃-extractable) diminishes more than the other labile fractions, suggesting that it is directly or indirectly an important source of P for the regrowing forest vegetation. Across the four age classes of forest, the soil reservoir of labile P was equal to or greater than the total amount of P in the vegetation. If labile P measured by this method adequately represents P available to plants in the short term (as suggested by the current consensus), we would conclude that plant-available P is reasonably abundant, and that the effects of agriculture on available P pools are detectable but not sufficient to compromise forest regrowth in this area.

We determined rates of acetylene reduction and estimated total nitrogen fixation associated with bryophytes, lichens, and decaying wood in Hawaiian montane rain forest sites with underlying substrate ranging in age from 300 to 4.1 million years. Potential N fixation ranged from ca 0.2 kg/ha annually in the 300-year-old site to ca 1 kg/ha annually in the 150,000-year-old site. Rates of acetylene reduction were surprisingly uniform along the soil-age gradient, except for high rates in symbiotic/associative fixers at the 150,000-year-old site and in heterotrophic fixers at the 2100-year-old site. Low fixation at the youngest site, where plant production is known to be N-limited, suggests that demand for N alone does not govern N fixation. Total N fixation was highest in sites with low N:P ratios in leaves and stem wood, perhaps because epiphytic bryophytes and lichens depend on canopy leachate for mineral nutrients and because heterotrophic fixation is partly controlled by nutrient supply in the decomposing substrate; however, differences in substrate cover, rather than in fixation rates, had the largest effect on the total N input from fixation at these sites.

The goal of this study was to define differences in species richness and tree and liana species assemblages of three adjacent terra firme forests in the middle Rio Caquetá, Colombia. A vegetation survey of trees and lianas equal to or more than 10 cm diameter at breast height (DBH) was carried out along a single longitudinal transect (10 × 2160 m) passing through a low plain terrace, a high dissected terrace, and a high plain terrace. Species were classified as either locally abundant or locally rare. Abundant species were defined as “generalists” (in all environments), “intermediate” (in two environments), and “specialists” (in only one environment) using a 2 × 3 contingency table. There were 146 (39%) species classified as locally abundant and 231 (61%) as locally rare. Among the abundant species, 70 percent were generalists, 25 percent were specialists, and 5 percent were intermediate. Although there was a significant number of rare species, for those species with sufficient numbers to statistically test spatial distribution, the results suggest that many species are generalists and that beta diversity at the local scale (2.16 ha) is low. Larger data sets over larger geographical areas should be analyzed to determine the degree of species turnover in Amazonian forests.

In the tropical montane cloud forest of Veracruz, Mexico, most canopy trees are deciduous, whereas the understory is composed of small broadleaved evergreen trees and shrubs. In this study, I tested the hypotheses that (1) leafing and flowering in the understory occur when the canopy is most open; and (2) a shift in phenological patterns occurs in plants growing at the forest edge. In two microhabitats (interior and edge) at each of three study sites, foliar and reproductive phenologies were recorded in five shrub species (Eugenia xalapensis, Miconia glaberrima, Moussonia deppeana, Ocotea psychotrioides, and Palicourea padifolia), and canopy openness and photosynthetically active radiation (PAR) were measured monthly for 36 months. Canopy openness was greatest from November through February; however, PAR was highest during January–March. Leaf drop of the shrubs was continuous during the year. Leafing occurred throughout the year for Miconia, Moussonia, and Palicourea; leafing coincided with maximum PAR for Ocotea, but occurred during March–April for Eugenia. Flowering peaked from December to May, but Miconia, Moussonia, and Ocotea peaks coincided with levels of maximal PAR and were displaced by one month with respect to maximal canopy openness; the Palicourea flowering peak was negatively correlated with canopy openness. Fruiting was extended from March to October, coinciding with tree canopy fruiting. The results indicated that leafing and flowering in the understory started earlier than in the forest canopy. Leafing and flowering were synchronous in the interior and forest edge, but there was a weak trend for reduced peaks at the edge. The hypotheses were not supported: phenological patterns were temporally displaced between forest strata, but only three shrub species produced leaves and flowers during maximum PAR in the understory; there were no differences in phenological patterns between forest interior and edge.

Epiphytes perform critical functions in primary tropical forests, but their ecological roles have only rarely been studied in secondary forests or in forest plantations. We assessed the composition and distribution of epiphytic bromeliad communities in four- and eight-year-old replicated experimental monospecific tree plantations (3 species) at the La Selva Biological Station, Costa Rica. The bromeliad communities of these stands are dominated by two species, Guzmania monostachya (L.) Rusby ex. Mez and Vriesea gladioliflora (H. Wendl.) Antoine. We identified bromeliads on over 700 trees and estimated their biomass and leaf area. Mean bromeliad biomass ranged from 2 to 8 g/tree in the four-year-old plots and from 20 to 94 g/tree in the eight-year-old plots. The mean bromeliad leaf area ranged between 104 and 704 cm²/tree and from 1600 to 8500 cm²/tree in the four- and eight-year-old plots, respectively. Although bromeliads accounted for less than 2 percent of the total foliar biomass and leaf area in both four-year-old and eight-year-old plots, the biomass of bromeliads exhibited a 5- to 46-fold increase between the four-year-old and eight-year-old plots, respectively. Bromeliads showed clear patterns of host tree preference, which may be attributed to host tree characteristics that differentially favor recruitment and survivorship. Between four and eight years of growth, differences among host tree species with respect to the amount of available host tree woody biomass, host tree foliar biomass, and host tree leaf surface area were positively correlated with the abundance of epiphytic bromeliads.

We studied the occurrence of epiphytic ferns on the lower trunks of two kinds of hosts: tree ferns and angiosperms. The study was conducted in Costa Rica at the La Selva Biological Field Station (50 m elev.), Las Cruces Biological Field Station (1200 m), Monteverde Cloud Forest Reserve (1500 m), and Cuericí Biological Field Station (2600 m). At each site, 20 tree fern trunks with a root mantle were sampled for epiphytes up to a height of 3 m, and the same was done for the nearest angiosperm trunk of similar diameter at breast height (DBH). A total of 106 species of epiphytic ferns was found at all of the study sites; none occurred more frequently on angiosperm trunks, but 11 occurred more frequently on tree ferns. Seven of the 11 species were entirely restricted to tree ferns, whereas the other 4 also occurred on angiosperms. Tree ferns had a significantly higher number of epiphytic species than angiosperms, averaging (depending on the site) 3–5 species, whereas angiosperms averaged 1 or 2. Epiphytic ferns were more abundant on tree ferns than on angiosperms. No correlation existed, for tree ferns or for angiosperms, between DBH and species richness or percent cover of fern epiphytes. In conclusion, low-trunk fern epiphytes exhibited significant differences on tree fern versus angiosperm in regard to species composition, number of species per trunk, and percent cover. The differences probably were caused by the root mantles providing more favorable microhabitats for the establishment of fern prothalli and a better substrate for the attachment of fern sporophytes.

We conducted experimental manipulations and field observations to determine the role of members of a nectarivorous guild (pollinators and robbers) on nectar production and pollen deposition in Hamelia patens at the La Selva Biological Station (Costa Rica). Seven pollinators (hummingbirds) and four robbers (1 hummingbird and 3 perching birds) comprised the avian nectarivorous guild visiting H. patens during March 1997. In addition, two florivorous birds were observed visiting H. patens during the study. Pollinators accounted for 85.6 percent of the visits, robbers for 12.4 percent, and florivores for 2 percent of the visits. Visitation by pollinators and robbers was greatest when floral nectar was highest. No aggressive interactions between pollinators and robbers were observed during the study. Pollinators differed in their ability to carry and deposit pollen on the stigma. Territorial hummingbirds were the least effective pollinators but the most frequent visitors. Flowers were frequently robbed (71%) during the study. Flowers experimentally robbed did not increase nectar production compared to control flowers; therefore, robbery may not involve an extra energy investment in terms of nectar production. The number of pollen grains deposited on artificially robbed flowers was significantly less than the number found in flowers with extra nectar (nectar added) but did not differ from the number found in non-manipulated flowers, indicating that nectar robbers may not affect the foraging behavior of hummingbirds, and therefore pollen deposition.

Foliar herbivory and abundance of folivorous insects were studied on shrub species (Miconia glaberrima, Moussonia deppeana, Ocotea psychotrioides, and Palicourea padifolia) in a tropical montane cloud forest, Veracruz, Mexico. Monthly, we determined folivore damage, insect abundance on leaves, and microenvironmental variables (air and soil temperatures, relative humidity, and soil water content). Folivory per month varied between 2.04 ± 0.45 percent in April and 4.41 ± 0.86 percent in September. The highest levels of folivory occurred during the end of the wet–warm season (Palicourea), the relatively dry–cool season (Miconia and Ocotea), or during both seasons (Moussonia). Eighty-eight percent of the herbivores were caterpillars (Lepidoptera). Insect abundance was lower in the dry–warm and the beginning of wet–warm seasons (April–July) and higher during the wet–warm and dry–cool seasons. Leaf production was continuous throughout the year for Miconia, Moussonia, and Palicourea; Ocotea had a leafing peak during December–March (dry–cool). Folivory and insect abundance were negatively correlated with maximum temperature and positively correlated with soil water content. The correlations between folivory and leaf production were not significant for any of the studied species. Because leaves are produced throughout the year (except for Ocotea), insect abundance was not related to leaf flush. Also, folivory and insect abundance were not correlated (except for Palicourea). Thus, foliar phenology may not be an escape from herbivory, at least for the studied shrub species. Rather, environmental conditions may play an important role in insect abundance and indirectly affect foliar herbivory levels.

We radio-tracked five red-rumped agoutis (Dasyprocta leporina) for two to nine months each at the Estação Ecológica Ilha de Maracá in the northern Brazilian Amazon. Agoutis fed primarily on seeds and pulp but also ate cotyledons, leaves, flowers, and invertebrates. Three plant species made up 63 percent of the feeding observations. Home range size varied from 3 to 8.5 ha. High-use areas and home range boundaries shifted from the season of high fruit availability to the season of low fruit availability as different individual trees became the focus of feeding activities. Agoutis foraged preferentially within conspecific patches of preferred fruit species and concentrated their feeding and scatterhoarding activities near individual fruiting trees. These results suggest that agoutis, as extremely short-distance seed dispersers, may contribute to the aggregated dispersion pattern of large-seeded tropical forest trees.

Tropical stream food webs are thought to be based primarily on terrestrial resources (leaf litter) in small forested headwater streams and algal resources in larger, wider streams. In tropical island streams, the dominant consumers are often omnivorous freshwater shrimps that consume algae, leaf litter, insects, and other shrimps. We used stable isotope analysis to examine (1) the relative importance of terrestrial and algal-based food resources to shrimps and other consumers and determine (2) if the relative importance of these food resources changed along the stream continuum. We examined δ¹⁵N and δ¹³C signatures of leaves, algae, macrophytes, biofilm, insects, snails, fishes, and shrimps at three sites (300, 90, and 10 m elev.) along the Río Espíritu Santo, which drains the Caribbean National Forest, Puerto Rico. Isotope signatures of basal resources were distinct at all sites. Results of two-source δ¹³C mixing models suggest that shrimps relied more on algal-based carbon resources than terrestrially derived resources at all three sites along the continuum. This study supports other recent findings in tropical streams, demonstrating that algal-based resources are very important to stream consumers, even in small forested headwater streams. This study also demonstrates the importance of doing assimilation-based analysis (i.e., stable isotope or trophic basis of production) when studying food webs.

Movement of air under the canopy of a forest affects the gliding of animals such as frogs, snakes, geckos, and squirrels; the dispersal of pollen, seeds, and spores; as well as convective transport of heat and carbon dioxide. Wind speed profiles were measured under the canopy of a lowland rain forest during the morning, afternoon, and night at three sites in Costa Rica to determine the aerodynamic environment in which tree frogs maneuver while gliding. During the course of a day, average and maximum wind speeds were highest in the morning and midday, and lowest at night. Wind speeds under the canopy were highest near the top of the canopy and were lowest near the canopy floor in the morning and afternoon, and exhibited little variation with respect to height at night. Turbulence intensity (a common measure of gustiness) was constant (ca 1) for all times of day, heights in the canopy, and sites, but the absolute magnitudes of wind gust speeds were higher during the day than at night. Power spectral densities revealed that most of the variation in wind speeds occurred at frequencies that could potentially affect the gliding of tree frogs. Tree frogs (and many other gliding animals), however, glide at night and thereby avoid the higher wind speeds that occur by day. Computer simulations of the dynamic motions of frogs while gliding revealed that the night levels of wind gusts have little effect on the direction of gliding of tree frogs.

There is much interest in ways to exploit tropical timber without greatly changing forest processes and diversity. To achieve this, it is necessary to know the maximum logging intensity that can be used and how long the forest takes to recover from logging. Because little is known about the effects of selective logging on non-timber plant species, we examined the effects of logging intensity and time after logging on the diversity and abundance of flowering and fruiting understory plants in a Central Amazonian forest near Manaus, Brazil. Logging was carried out experimentally at varying intensities in eight 4 ha plots in 1987 and three plots in 1993. Logging intensity ranged between 14 and 45 m³/ha of extracted timber. Three plots were left as controls. Each month, from October 1996 to September 1998, we recorded the number of individuals and species of herbs, shrubs, small trees, and small palms that were flowering and fruiting in six transects per plot. We found 107 species flowering and 111 species fruiting. The abundance of flowering plants was affected by time after logging, but not by the intensity of logging. The abundance of fruiting plants was not related either to time after logging or logging intensity. Richness of flowering and fruiting plants was related to time after logging, but not to the intensity of logging. The results indicate that selective logging, at the intensities and scale analyzed, does not cause reductions in flower and fruit production by the understory community. Both quantity and quality of resources for animals are maintained and possibly even increased in logged areas, shortly after logging takes place. As the levels of reproduction in plots logged 11 years before remained close to those in controls, maintenance of the understory community does not seem to be problematical.

The effect of host plant inundation on survivorship of Symmeria paniculata's galling herbivores was investigated in Central Amazonian floodplain forest. The majority of submerged galls were alive (62% of morphospecies 1 and 70% of morphospecies 2). Survivorship was similar between submerged leaves and new leaves that were never submerged. Some submerged galls were eaten by fish. To the best of our knowledge, this is the first report of galling insect survivorship under severe flooding.

We offered Australian tropical stingless bees (Trigona hockingsi) artificial nectar (30% sucrose w/v) either with or without added amino acids (3.30 mM). Bees showed no preference for nectar type, suggesting that sugars, rather than amino acids, play a greater role in nectar choice by this species.

Tropical Pacific island streams have poorly understood communities that deserve scientific attention. We examined benthic macroinvertebrates and fishes of the Inem River on Kosrae, Federated States of Micronesia. Larval chironomids, lepidopterans, odonates, and freshwater shrimps dominated the benthos and drift. Diel periodicity in drift was not evident. Nine fishes, two shrimps, and one snail species were identified. Kosrae's stream fauna appears even more depauperate than other Pacific high islands, possible due to its extreme isolation.