Treesearch

Two species of tropicbirds (Phaethontidae) live in the Western North Atlantic. The Whitetailed Tropicbird of the region is an endemic race, Phaethon lepturus catesbyi, with approximately 5000 pairs. This is half the estimate made less than two decades ago. The Red-billed Tropicbird, P. aethereus, has approximately 2000 pairs regionally and fewer than 8000 pairs globally. Neither species has been considered to be of conservation concern. We suggest that the Atlantic populations of Phaethon lepturus and the global population of Phaethon aethereus be considered for appropriate conservation...

Soil texture plays a key role in belowground C storage in forest ecosystems and strongly influences nutrient availability and retention, particularly in highly weathered soils. We used field data and the Century ecosystem model to explore the role of soil texture in belowground C storage, nutrient pool sizes, and N fluxes in highly weathered soils in an Amazonian forest ecosystem. Our field results showed that sandy soils stored approximately 113 Mg C ha-1 to a 1-m depth versus 101 Mg C ha-1 in clay soils. Coarse root C represented a large and significant ecosystem C pool, amounting to 62%...

Migratory freshwater shrimps represent important links between the headwaters and estuaries of many tropical rivers. These species exhibit amphidromous life cycles in which larvae are released by females in upper reaches of rivers; first stage (i.e., newly hatched) larvae drift passively to coastal environments where they develop and metamorphose into postlarvae that subsequently migrate back upstream to adult (freshwater) habitat. Recent studies in rivers draining northeastern Puerto Rico and Costa Rica’s Caribbean slope have been the first to document migratory drift of first stage...

The relationship of plant species diversity to cultural eutrophy in tropical wetlands was studied in Puerto Rico with experimental plots, a survey of 25 eutrophic sites developing from the wastes of society, and a simulation mini-model. The model is a quantitative hypothesis which contains the mechanisms to maximize empower (gross production) by reinforcing low diversity, net production overgrowth when resources are in excess, but switches to high diversity efficiency and recycle to maximize gross production when excess resources are absent. To study self-organization with eutrophy, six...

The coexistence of hurricanes, coral reefs, and rainforests in the Caribbean demonstrates that highly structured ecosystems with great diversity can flourish in spite of recurring exposure to intense destructive energy. Coral reefs develop in response to wave energy and resist hurricanes largely by virtue of their structural strength. Limited fetch also protects some reefs from fully developed hurricane waves. While storms may produce dramatic local reef damage, they appear to have little impact on the ability of coral reefs to provide food or habitat for fish and other animals. Rainforests...

How important is ecotypic differentiation along elevational gradients in the tropics? Reciprocal transplants of two shrubs, Clibadium erosum (Asteraceae) and Psychotria berteriana (Rubiaceae), and a palm, Prestoea acuminata var. montana (Palmaceae), were used to test for the effect of environment and population origin on growth and physiology in the Luquillo Experimental Forest of Puerto Rico. Two sites were used, one at Pico del Este (1000 m in cloud forest) and one at El Verde (350 m in lower montane rain forest). At the cloud forest site, plastic barriers were erected around a subset of...

Over the past 17 years, research on a rain forest population of the Pearly-eyed Thrasher (Margarops fuscatus), with additional observations on nesting Puerto Rican Parrots (Amazona vittata) within the Sierra de Luquillo, Puerto Rico, has shown that reproductive success of thrashers and parrots is often greatly reduced as a result of the additive effects of a diverse group of predators, competitors and ectoparasites, namely, other thrashers, Puerto Rican Screech-Owl (Otus nudipes), scansorial black rat (Rattus rattus); honeybee (Apis mellifera ligustica and A. m. scutellata), and a muscid...

Saplings are here defined as trees having at least 1.37 m of height and no more than 5.0 cm in diameter at breast height (DBH). Saplings may contribute less than 5 percent to nearly 100 percent of the tree biomass, depending on the successional stage of a forest. Many equations to predict the biomass for smalldiameter trees in plantations and natural stands have been published (e.g., Buech and Rugg, 1989; Chaturvedi et al., 1991; Dudley, 1992; Grundy, 1995; Kahn and Pathak, 1986; Kushalapa, 1988; Ku et al., 1981; Lo¨venstein and Berliner, 1993; Pande et al., 1988; Parrotta, 1989, 1999;...

Few topics in ecology are as intriguing or bedeviling as comparative studies of different types of mycorrhizas formed in the same plant species. Attempts to determine the relative bene®ts from each fungal type to the host plant are fraught with difficulties (Jones et al., 1998), and for this reason plants that form tripartite associations with arbuscular and ectomycorrhizal fungi make ideal experimental systems. Just such a tripartite system is explored in a report in this issue by Chen et al. (pp. 545±556)

Nitrous and nitric oxides are often studied separately by atmospheric chemists because they play such different roles in the atmosphere. N2O is a stable greenhouse gas in the lower atmosphere (the troposphere; Ramanathan et al. 1985), but it participates in photochemical reactions in the upper atmosphere (the stratosphere) that destroy ozone (Crutzen 1970). In contrast, NO participates in photochemical reactions in the troposphere that produce ozone.