Tropical ecosystems support a diversity of species and ecological processes that are unparalleled anywhere else on Earth. Despite their tremendous social and scientific importance, tropical ecosystems are rapidly disappearing. To help tropical ecosystems and the human communities dependent upon them better face the challenges of the 21st century, tropical biologists must provide critical knowledge in three areas: (1) the structure and functioning of tropical ecosystems; (2) the nature and magnitude of anthropogenic effects on tropical ecosystems; and (3) the socio-economic drivers of these anthropogenic effects. To develop effective strategies for conservation, restoration, and sustainable management of tropical ecosystems, scientific perspectives must be integrated with social necessities. Three principles for guiding tropical biological research are suggested: (1) broadening the set of concerns; (2) integration of biological knowledge with the social sciences and traditional knowledge; and (3) linking science to policy and action. Four broad recommendations are proposed for immediate action in tropical biology and conservation that are fundamental to all biological and social disciplines in the tropics: (1) assemble and disseminate information on life's diversity in the tropics; (2) enhance tropical field stations and build a worldwide network to link them with tropical field biologists at their field sites; (3) bring the field of tropical biology to the tropics by strengthening institutions in tropical countries through novel partnerships between tropical and temperate zone institutions and scientists; and (4) create concrete mechanisms to increase interactions between tropical biologists, social scientists, and policy makers.

Understanding why there are so many kinds of tropical trees requires learning, not only how tree species coexist, but what factors drive tree speciation and what governs a tree clade's diversification rate. Many report that hybrid sterility evolves very slowly between separated tree populations. If so, tree species rarely originate by splitting of large populations. Instead, they begin with few trees. The few studies available suggest that reproductive isolation between plant populations usually results from selection driven by lowered fitness of hybrids: speciation is usually a response to a “niche opportunity.” Using Hubbell's neutral theory of forest dynamics as a null hypothesis, we show that if new tree species begin as small populations, species that are now common must have spread more quickly than chance allows. Therefore, most tree species have some setting in which they can increase when rare. Trees face trade-offs in suitability for different microhabitats, different-sized clearings, different soils and climates, and resistance to different pests. These trade-offs underlie the mechanisms maintaining α-diversity and species turnover. Disturbance and microhabitat specialization appear insufficient to maintain α-diversity of tropical trees, although they may maintain tree diversity north of Mexico or in northern Europe. Many studies show that where trees grow readily, tree diversity is higher and temperature and rainfall are less seasonal. The few data available suggest that pest pressure is higher, maintaining higher tree diversity, where winter is absent. Tree α-diversity is also higher in regions with more tree species, which tend to be larger, free for a longer time from major shifts of climate, or in the tropics, where there are more opportunities for local coexistence.

In many forest ecosystems, green leaf deposition (greenfall) constitutes an enrichment over background levels of litterfall nutrients and may therefore influence key ecosystem processes. This study examined the litter quality and decomposition rates of green leaves compared to senescent litterfall for four dominant tree species (Dacryodes excelsa, Manilkara bidentata, Guarea guidonia, and Cecropia schreberiana) in a lower montane rain forest at El Verde Field Station, Luquillo Experimental Forest, Puerto Rico. Green leaves from the canopy and freshly senesced leaves from the forest floor were analyzed for carbon, nitrogen, and fiber and placed in litterbags in the field for up to 16 weeks. Green leaves displayed significantly higher rates of decomposition than did senescent litter among all four species. Green leaves also had significantly higher nitrogen concentrations and lower lignin to nitrogen ratios compared to senescent leaves. These results suggest that greenfall may have a major influence on decay processes and nutrient cycling in forests that experience large-scale green foliage removal.

We tested the hypothesis that growth and survival of aerial roots impose a limit on the height at which a primary hemiepiphyte can become successfully established within tree crowns and evaluate the implications for the vertical distribution of hemiepiphytes in the forest canopy. Density and spatial distribution, and growth and survival of aerial roots were studied in two common species of hemiepiphytic Araceae, Philodendron radiatum and Anthurium clavigerum, in a lowland tropical moist forest in Panama between March and October 2001. Additionally, root growth and survival were studied both in normal, unmanipulated, and experimentally cut roots to investigate the effect of damage on root resprouting and survival. Survival analysis revealed much greater survival of aerial roots of A. clavigerum than P. radiatum. In contrast, growth rates in the latter were on average about three times higher when compared to A. clavigerum. In both species, experimental cutting of the root invariably led initially to the development of dieback symptoms; however, plants responded to root damage by producing resprouts. A risk model for the two species suggests that only the fastest-growing roots of P. radiatum are likely to survive long enough to reach the soil from a host branch 6.8 m high, which equals the mean height of occurrence observed for the epiphytic stage of this species at our study site. In contrast, slow-growing appressed aerial roots of A. clavigerum may never be able to establish a connection with the soil from similar heights in the canopy before roots die. Consistent with our hypothesis, A. clavigerum is found much lower in the forest (it rarely exceeds ca 5 m).

We conducted a demographic examination of Pterocereus gaumeri, a rare and endemic columnar cactus of the Yucatan peninsula, Mexico. Growth, survival, and fecundity of individuals were recorded in two populations from 1997 to 1999. Size-based population projection matrices were constructed to document the population dynamics. Seed germination and seedling establishment experiments were conducted in the field to estimate the rate of seed and seedling survival. Our results show that P. gaumeri did not reproduce by asexual means or vegetative growth and thus relies wholly on sexual reproduction for population growth. Low reproductive success, seed predation, and low seedling survival appear to be important factors that contribute to the rarity of this species. The population growth rate (λ) varied between 0.9545 and 1.0316. According to the matrix elasticity values, population dynamics of this species depend mainly on adult survival, with low values in fecundity and survival for the lowest size categories. Our results did not indicate that the population size of P. gaumeri was decreasing; however, increasing pressure on land use transformation is one of the most important factors that may threaten the persistence of this species.

Sixteen percent of tree stems 10 cm diameter or greater recorded in seven 1 ha plots in Rabongo Forest, Uganda had stem damage attributable to elephants (Loxodonta africana). We propose four strategies that may help tree species persist under these conditions: repellence, resistance, tolerance and avoidance. We sought and found evidence for each strategy. Large, shade-tolerant Cynometra alexandri dominated basal area (often >50%) and showed severe scarring. Nearly 80 percent of stems were small pioneer species. Scarring frequency and intensity increased with stem size. Stem-size distributions declined steeply, implying a high mortality to growth rate ratio. Tree species with spiny stems or with known toxic bark defenses were unscarred. Epiphytic figs escaped damage while at small sizes. Mid-successional tree species were scarce and appeared sensitive to elephants. Savanna species were seldom scarred. Taking stem size-effects into account by using a per-stem logistic modeling approach, scarring became more probable with slower growth and with increasing species abundance, and also varied with location. Pioneer and shade-bearer guilds showed a deficit of intermediate-sized stems. Evidence that selective elephant damage is responsible for monodominant C. alexandri forests remains equivocal; however, elephants do influence tree diversity, forest structure, and the wider landscape.

The aims of this study were to investigate the diet and relative abundance of fruit bats in a lowland Malaysian rain forest and to test the hypothesis that the local assemblage structure of fruit bats varies significantly over time in relation to the availability of food. In total, 352 fruit bats of eight species were captured during 72,306 m² mist-net hours of sampling between February 1996 and September 1999. Three species of fruit bats (Balionycteris maculata, Chironax melanocephalus, and Cynopterus brachyotis) that fed on a wide range of “steady state” and “big bang” food resources were captured continuously throughout the study period, with no significant variation in capture rates over time. In contrast, five species that fed exclusively or almost exclusively on “big bang” food resources were sampled intermittently, with significant temporal variation in the capture rates of two species (Cynopterus horsfieldi and Megaerops ecaudatus). Significant variation in the capture rates of the remaining three species (Dyacopterus spadiceus, Eonycteris spelaea, and Rousettus amplexicaudatus) could not be detected due to small sample sizes. Since ephemeral “big bang” food resources were only sporadically available within the study area and were associated with large canopy trees and strangler figs, these results suggest that food abundance, or the availability of specific food items, may be important factors limiting local fruit bat species diversity in old-growth Paleotropical rain forest. Thus, only three fruit bat species were locally resident within the forest throughout the study period. Therefore, further studies on the ranging behavior and habitat requirements of Malaysian fruit bats are required to assess the adequacy of existing reserves and protected areas.

We observed ten species of psittacids, three species of columbids, and two species of cracids consuming soil from banks of the lower Tambopata River in southeastern Peru. Our study used observations and soil analyses from eight exposed riverbank sections to test the predictions of three models to determine why birds consume clay: mechanical aid to digestion (grit), adsorption of dietary toxins, and mineral supplementation. We found that preferred soils were deficient in particles large enough to aid in the mechanical breakdown of food and help digestion. Percent clay content and cation exchange capacity (CEC), both predicted to correlate with adsorption of toxins, did not differ between used and unused sites as had been found in a similar study. Instead, preferred soils were more saline and had higher concentrations of exchangeable sodium. This suggests that the choice of soils at our site was based primarily on sodium content. Birds may be using the heavy, plastic texture of soils rich in clays and high in exchangeable sodium as a proximal cue for soil selection. Our findings suggest that avian soil selection decisions depend on the range of available soil characteristics.

We studied seasonal variation in bird assemblages in a Chaco subtropical semiarid forest, Santiago del Estero Province, Argentina. We carried out seven samplings during both breeding and non breeding periods, in order to assess the resident status and the trophic guild of each species. During the last four samplings we recorded bird populations using 30 fixed-radius points, in order to estimate bird density, species density, evenness, and species diversity. We found that: (1) the bird assemblage had 96 species (67 residents, 19 summer migrants, 1 winter migrant, 5 of doubtful residency and 4 species whose resident status was unknown); (2) higher values of species density, evenness and species diversity were found during breeding periods; and (3) higher community attributes were followed by higher densities of 4 trophic guilds: nectarivores, frugivores and short and long-flight insectivores during the breeding periods. Changes in guild densities were probably associated with the arrival of summer migrants and to seasonal fluctuations in food resources, which in turn promoted seasonal changes in species density and diversity. Different from observations in other avian assemblages of the Chaco, no temporal variations were observed in the terrestrial seedeaters guild. This could be due to the fact that our study site forests are located in a landscape matrix with agricultural fields and grasslands that may offer year-round seed supply. The Chaco subtropical semiarid forest seems to be an important breeding habitat for many migrant species from both Neotropical and Nearctic regions.

Spatial ecology of Puerto Rican boas (Epicrates inornatus, Boidae) was studied with radiotelemetry in a subtropical wet forest recovering from a major hurricane (7–9 yr previous) when Hurricane Georges struck. Different boas were studied during three periods relative to Hurricane Georges: before only; before and after; and after only. Mean daily movement per month increased throughout the three periods, indicating that the boas moved more after the storm than before. Radio-tagged boas also became more visible to observers after the hurricane. Throughout the three periods, the sexes differed in movements, with males moving greater distances per move and moving more frequently than females. Males showed a bimodal peak of movement during April and June in contrast to the females' July peak. Sexes did not differ in annual home range size, which had a median value of 8.5 ha (range = 2.0–105.5 ha, N = 18) for 95 percent adaptive kernal. Females spent more time on or below ground than did males, which were mostly arboreal. Trees used by boas had larger diameters and more vines than random trees. Hurricane winds that strip leaves, vines, and branches from trees may reduce cover for boas and limit access to arboreal sites, at least for several years until succession brings about recovery with increased vine growth. Boas were especially difficult to observe; telemetrically monitored boas were detected visually at an average of only 15 percent of their fix sites, indicating that the species is more abundant than generally perceived.

Hypoxia (oxygen scarcity) is widespread in tropical freshwaters, particularly in dense swamps, and may be an important factor structuring benthic macroinvertebrate communities. Macroinvertebrates show a diversity of respiratory modes ranging from atmospheric breathing to tracheal gill breathing, and these adaptations affect their ability to use hypoxic water. The objectives of this study were to (a) describe the benthic macroinvertebrate community from ten swamp and river sites in Kibale National Park, Uganda, (b) determine the degree to which dissolved oxygen explains variation in abundance of respiratory groups (taxa with a similar respiratory mode) among sites, and (c) test for significant seasonal variation in the abundance of the numerically dominant respiratory groups. Macroinvertebrates from monthly collections over a two-year period were identified to the lowest taxonomic level necessary to place them in functional respiratory groups. Across all sites, both the relative and absolute abundance of atmospheric breathers (e.g., pulmonate snails and nepids) and mantle/ctenidia breathers (primarily fingernail clams) were negatively correlated with dissolved oxygen, while the abundance of tracheal gill breathers (e.g., anisopterans and zygopterans) was positively correlated with dissolved oxygen. We did not detect significant seasonal trends in catch per unit effort of numerically dominant respiratory groups. Dissolved oxygen concentration was a good predictor of the abundance of some respiratory groups and may be a key factor in maintaining the structure and diversity of these assemblages.

Insect defenses against avian predators often include both a primary defense that reduces the probability of being attacked and a secondary defense, typically escape behavior, employed if the primary defense fails. Escape behavior, however, can make insects potentially vulnerable to specialized flush–pursuit predators. Neotropical Redstarts of the genus Myioborus (Parulidae) exploit insect escape behavior by using their contrasting black-and-white plumage and animated foraging behavior to startle insect prey that are then pursued and captured in flight. We examined how insect primary defense strategy and natural variation in Myioborus plumage pattern influence escape behavior in six species of homopterans from Monteverde, Costa Rica. The six homopterans included two aposematic species of the family Cercopidae (Ocoaxo sp. and Sphenorhina sp.), two cryptic species of the family Cixiidae (both Bothriocera spp.), and two structurally defended species of the family Membracidae (Campylocentrus sp. and Vestistilus variabilis). We measured the distance at which models of Myioborus Redstarts elicited escape behavior in insects under field conditions. Response distances varied significantly with both homopteran primary defense and Myioborus plumage pattern. Structurally defended homopterans were the most sensitive to the models and cryptic homopterans were the least sensitive. The model simulating the plumage of endemic M. miniatus comptus of Costa Rica elicited greater responses than did models of other Myioborus taxa with either less or more white in the plumage. Our results suggest that (1) primary defense strategies can have a significant effect on insect vulnerability to flush–pursuit predators, and (2) geographic variation in the plumage pattern of Myioborus Redstarts may reflect adaptation to regional prey and habitat characteristics that maximizes flush–pursuit foraging performance.

The jumping spiders Eustiromastix nativo, Psecas sumptuosus, and Uspachus sp. n. (Salticidae) live on terrestrial bromeliads in areas with different phytophysiognomies in southeastern and northeastern Brazil. To understand these spider–plant interactions, we investigated if (1) these spiders were associated specifically with bromeliads, (2) the spiders utilized particular bromeliad species, and (3) plant size and density of bromeliads affected spider distribution. The jumping spiders were not found outside bromeliads, indicating a strict spider–plant association. Eustiromastix and Uspachus occupied bromeliads in open areas, whereas Psecas was found on forest bromeliads. Eustiromastix occurred at a higher frequency on larger bromeliads and in patches with higher bromeliad density. This is one of the few studies to demonstrate specific relationships between jumping spiders and a particular plant type.

We studied avian foraging at two shaded coffee plantations in Ciales, Puerto Rico. Both coffee plantations contained patches of second-growth forest but differed in shade types; one was a rustic plantation with a species-diverse shade including many fruiting plant species and the other was a commercial polyculture shaded almost solely by Inga vera. We quantified foraging activity of five fruit-eating bird species (Euphonia musica, Loxigilla portoricensis, Nesospingus speculiferus, Spindalis portoricensis, and Vireo altiloquous) and monthly fruit abundance in the coffee plantation and adjacent second-growth forest habitats at each site. Fruits comprised more than 50 percent of the diets for four of five focal bird species. We found a significant difference in the number of foraging records for focal bird species between coffee and forest habitats in the commercial polyculture but found few differences between these habitats in the rustic coffee farm. Overall, foraging activity was positively correlated with the abundance of fruits across study sites. Bird foraging was concentrated on plant species in the genera Cecropia, Miconia, Schefflera, Phoradendron, and Guarea, which together accounted for over 50 percent of frugivory records. Plant species in such genera fruited over prolonged time periods and provided birds with a fairly constant fruit supply. Our findings underscore the importance of fruiting plant species in making coffee plantations suitable habitat for birds and suggest that native fruiting plants be incorporated in coffee farms for avian conservation.

We studied temporal and spatial dynamics of extremely diverse moth ensembles (Lepidoptera: Pyraloidea) along a gradient of forest disturbance ranging from undisturbed primary tropical rain forest to different kinds of modified forest and open cultivated land at the margin of Mount Kinabalu National Park (Sabah, East Malaysia). We sampled moths by light trapping during two periods (March–May and August–September 1997). We collected a total of 7724 individuals representing 680 species during 78 light-trapping nights at six study sites. Species diversity (Fisher's α) of ensembles in undisturbed primary forest was distinctly higher than in disturbed or secondary forest. More pyraloid moths were attracted in undisturbed primary forest. Samples from disturbed primary or old-growth secondary forest were statistically indistinguishable from the undisturbed primary forest ensemble in regard to species composition. Thus, pyraloid ensembles from disturbed forest with tall trees remaining appeared to represent impoverished subsets of the undisturbed primary forest community. The more heavily disturbed sites had a distinct fauna and showed a stronger faunal differentiation among each other. Four species of the genus Eoophyla, in which aquatic larvae feed on algae in fast-running streams benefited prominently from forest disturbance. Temporal variation of ensembles was remarkably concordant across the disturbance gradient. Relative abundance variation of the commonest species was identical at all sites. Overall, pyraloid moths responded more sensitively to anthropogenic habitat alteration than most other moth taxa studied thus far in tropical regions and allowed for an analysis of diversity patterns at a high temporal resolution.

Species distributions of several insect groups in unlogged and adjacent logged forest were analyzed from several published data sets. The slope of the geometric series model and dominance indices proved to be unsuitable indicators of rain forest disturbance.

Nectar robbing by squirrels is reported for the first time in the striped squirrel (Tamiops swinhoei hainanus), which was found robbing nectar from ginger plants (Alpinia kwangsiensis) in tropical forests of south Yunnan, China. We describe the behavior of squirrels visiting inflorescences, and we compare the fruit set of inflorescences visited by squirrels with that of inflorescences not subject to nectar robbing by squirrels. Most of the styles of robbed flowers were damaged and the affected plants exhibited reduced fruit set.

Here, we document the invasion of equatorial Africa by the little red fire ant (Wasmannia auropunctata). Commercial logging and other forms of natural resource extraction have catapulted W. auropunctata into the interior of Gabon at a rate 60 times faster than the unassisted rate we measured over 19 years at the Lope Reserve. We also present photographic evidence suggesting that W. auropunctata is negatively affecting the country's exceptionally rich and intact large mammal fauna.

We assessed the effects of Azteca alfari presence on herbivory and growth of saplings for two Amazonian Cecropia species. For both species, rates of herbivory were low and did not differ between ant-removed and ant-maintained plants. Plant growth, measured over six months, was also similar among treatments. This is the first experiment to show that in its native mainland habitat, Cecropia may suffer low incidence of attack by insect herbivores in the absence of associated ants.