Sites In Panama Research Articles

Above‐ground biomass estimation in closed canopy Neotropical forests using lidar remote sensing: factors affecting the generality of relationships

ABSTRACTAim Previous studies have developed strong, site‐specific relationships between canopy metrics from lidar (light detecting and ranging) remote sensing data and forest structural characteristics such as above‐ground biomass (AGBM), but the generality of these relationships is unknown. In this study, we examine the generality of relationships between lidar metrics and forest structural characteristics, including AGBM, from two study areas in Central America with different precipitation patterns.Location A series of tropical moist forest sites in Panama and a tropical wet forest in Costa Rica.Methods Canopy metrics (e.g. canopy height) were calculated from airborne lidar data. Basal area, mean stem diameter and AGBM were calculated from measurements taken as a part of ongoing forest dynamics studies in both areas. We examined the generality of relationship between lidar metrics and forest structure, and possible environmental effects (e.g. leaf phenology).Results We found that lidar metrics were strongly correlated (R2: 0.65–0.92) with mean stem diameter, basal area and AGBM in both regions. We also show that the relationships differed between these regions. Deciduousness of canopy trees in the tropical moist forest area accounted for the differences in predictive equations for stem diameter and basal area. The relationships between lidar metrics and AGBM, however, remained significantly different between the two study areas even after adjusting for leaf drop. We attribute this to significant differences in the underlying allometric relationships between stem diameter and AGBM in tropical wet and moist forests.Conclusions Important forest structural characteristics can be estimated reliably across a variety of conditions sampled in these closed‐canopy tropical forests. Environmental factors such as drought deciduousness have an important influence on these relationships. Future efforts should continue to examine climatic factors that may influence the generality of the relationships between lidar metrics and forest structural characteristics and assess more rigorously the generality of field‐derived allometric relationships.

Nesting bird species in sun coffee, pasture, and understory forest in southern Costa Rica

We investigated avian nest distribution and success in understoryforest, sun coffee plantations, and pasture in southern Costa Rica. Nestsearching occurred in plantations and forest in 1999 and 2000 and in pastures in2000. Nests were monitored until they failed or fledged young. Antbirds(Thamnophilidae) were the most common understory forest nesters and were notfound nesting in the plantations or pastures. Common nesting species in theplantations included Turdidae, Tyrannidae, Cardinalidae, and Thraupidae, many ofwhich are typical of forest edge/canopy or open, scrubby habitats. Two speciesassociated with forest interior, Henicorhina leucostictaand Buarremon brunneinucha, were found nesting in theplantations. Pastures supported similar types of nesting species as theplantations, with the exception of the forest-interior species. Daily mortalityrates (DMRs) for above-ground cup-nesting species in plantations and pastureswere similar to those for species nesting in forest at our site and a site inPanama. The results indicate that conversion from forest to pastures and suncoffee plantations diminishes nesting habitat for forest-interior species, whilenumerous forest edge/canopy species and open-country species are able to nest inthese agricultural land-cover types. As a group, species nesting in theplantations and pastures do not have unusually high nest mortality rates,although species-specific studies are lacking. Nesting species distributionsacross habitat types and DMRs at our study site may be influenced by the largeamount of forest in the landscape.

Not as the crow flies: a historical explanation for circuitous migration in Swainson's thrush (Catharus ustulatus).

Many migratory songbirds follow circuitous migratory routes instead of taking the shortest path between overwintering and breeding areas. Here, we study the migration patterns in Swainson's thrush (Catharus ustulatus), a neartic-neotropical migrant songbird, using molecular genetic approaches. This species is presently separated into genetically distinct coastal and continental populations that diverged during the Late Pleistocene (as indicated by molecular dating), yet appear to have retained ancestral patterns of migration. Low nucleotide diversity, a star-like haplotype phylogeny and unimodal mismatch distributions all support the hypothesis that both the coastal and the continental populations have undergone recent demographic expansions. Nearctic-neotropical banding and genetic data show nearly complete segregation of migratory routes and of overwintering locations: coastal populations migrate along the Pacific Coast to overwintering sites in Central America and Mexico, whereas continental populations migrate along an eastern route to overwintering sites in Panama and South America. Nearctic-neotropical banding data also show that continental birds north, northwest and east of this migratory divide fly thousands of miles east before turning south. We conclude that circuitous migration in the Swainson's thrush is an artefact of a Late Pleistocene range expansion.

Marked growth response of communities of two tropical tree species to elevated CO2 when soil nutrient limitation is removed

As part of an ongoing project to understand the effects of elevated atmospheric CO 2 on plants in complex, tropical communities, we studied biomass accumulation in a simplified model seedling community consisting of two species of tropical trees ( Ficus insipida , a fast growing pioneer species, and Virola surinamensis , a slow-growing, shade-tolerant late successional species). The plants were grown at ambient and elevated (about two times ambient) CO 2 concentrations using open-top chambers at a field site in Panama. Communities grew in heavily fertilized soil. Compared to a previous experiment with model communities of F. insipia and V. surinamensis grown on unfertilized soil (Winter et al., Flora [2000] 195, 289) application of soil fertilizer markedly accelerated community growth rates at ambient CO 2 , and biomass accumulation was enhanced by an additional 52% at elevated CO 2 . In contrast, elevated CO 2 had no significant effect on biomass accumulation in unfertilized communities. Communities growing on fertilized soil showed greater biomass allocation into leaves, i.e. higher leaf weight ratios (LWRs) than did communities on unfertilized soil. Higher LWRs were related to lower root: shoot ratios and together with greater specific leaf areas (area per unit leaf mass), largely a consequence of lower leaf starch contents, resulted in higher leaf area ratios (LARs). While elevated CO 2 caused the relatively low LARs in unfertilized communities to decrease further, by strongly increasing leaf starch levels and decreasing specific leaf areas, these leaf characteristics changed only slightly in fertilized communities exposed to elevated CO 2 . Thus, by maintaining relatively high LARs at elevated CO 2 , fertilized plants were able to effectively use enhanced CO 2 concentrations for increased carbon gain and growth. Leaves of plants on fertilized soil were characterized by relatively low C: N ratios which were largely unaffected by CO 2 concentration. In contrast, C: N ratios in leaves of unfertilized plants were higher than those of fertilized plants and increased in response to elevated CO 2 .

Wasp predation and wasp-induced hatching of red-eyed treefrog eggs

Eggs often suffer high levels of predation and, compared with older animals, embryos have few options available for antipredator defence. None the less, hatchlings can escape from many predators to which eggs are vulnerable. I studied early hatching as an antipredator defence of red-eyed treefrog embryos, Agalychnis callidryas, in response to egg predation by social wasps (Polybia rejecta). Red-eyed treefrogs attach their eggs to vegetation overhanging water, where they are exposed to arboreal and aerial predators. Wasps attacked half the egg clutches and killed almost a quarter of the eggs I monitored at a natural breeding site in Panama. Hatching tadpoles fall into the water, where they face aquatic predators. As predicted from improved survival of older hatchlings with aquatic predators, most undisturbed eggs hatched relatively late. However, many younger embryos directly attacked by wasps hatched immediately. Embryos attacked by wasps hatched as much as a third younger than the peak undisturbed hatching age, and most hatching embryos escaped. Thus hatching is an effective defence against wasp predation, and plasticity in hatching stage allows embryos to balance risks from stage-specific egg and larval predators. Wasp-induced hatching is behaviourally similar to the snake-induced hatching previously described in A.callidryas, but occurs in fewer eggs at a time, congruent with the scale of the risk. Individual embryos hatch in response to wasps, which take single eggs, whereas whole clutches hatch in response to snakes, which consume entire clutches. Embryos ofA.callidryas thus respond appropriately to graded variation in mortality risks.

SEASONAL, AGE, AND SEX-RELATED VARIATION IN FATTY-ACID COMPOSITION OF DEPOT FAT IN RELATION TO MIGRATION IN WESTERN SANDPIPERS

The composition of depot fat in Western Sandpipers (Calidris mauri) was dominated by C16 and C18 fatty acids (palmitate, 16:0; palmitoleate, 16:1; stearate, 18:0; oleate, 18:1), which together comprised 80 to 90% of all fatty acids analyzed. Significant seasonal variation occurred in the relative proportion of specific fatty acids and the ratio of saturated to unsaturated fatty acids in relation to the migratory cycle of the sandpipers. In adults of both sexes, the proportion of 16:0 and 18:0 fatty acids decreased from winter (December) to premigration (March) to spring migration (May), whereas the proportion of 16:1 and 18:1 fatty acids increased over these same periods. Consequently, total unsaturated fatty acids increased by 34% between the winter and premigratory phase, and by a further 22% between premigration and spring migration. Therefore, biochemical modification of adipose tissue in Western Sandpipers begins during the premigratory period in preparation for long-distance flight but continues as migration progresses, perhaps reflecting a training component of physiological modulation for migration. Juveniles showed similar changes to adults in the composition of their depot fat during the “premigratory” period, even though most juveniles do not undergo hyperphagia or rapid fattening at this wintering site. Potential prey species collected from a wintering site in Panama had a higher proportion of saturated fatty acids, less 16:1 and 18:1, and more 18:0 fatty acid compared with those from a migratory stopover site in British Columbia, paralleling the seasonal changes in depot fatty-acid composition observed in Western Sandpipers. However, the fact that Western Sandpipers show an increase in level of unsaturation and in the amounts of 16:1 and 18:1 fatty acids in their fat stores on the wintering ground prior to migration suggests that seasonal variation in fatty-acid composition is not entirely diet dependent.

Seasonal, Age, and Sex-Related Variation in Fatty-Acid Composition of Depot Fat in Relation to Migration in Western Sandpipers

AbstractThe composition of depot fat in Western Sandpipers (Calidris mauri) was dominated by C16 and C18 fatty acids (palmitate, 16:0; palmitoleate, 16:1; stearate, 18:0; oleate, 18:1), which together comprised 80 to 90% of all fatty acids analyzed. Significant seasonal variation occurred in the relative proportion of specific fatty acids and the ratio of saturated to unsaturated fatty acids in relation to the migratory cycle of the sandpipers. In adults of both sexes, the proportion of 16:0 and 18:0 fatty acids decreased from winter (December) to premigration (March) to spring migration (May), whereas the proportion of 16:1 and 18:1 fatty acids increased over these same periods. Consequently, total unsaturated fatty acids increased by 34% between the winter and premigratory phase, and by a further 22% between premigration and spring migration. Therefore, biochemical modification of adipose tissue in Western Sandpipers begins during the premigratory period in preparation for long-distance flight but continues as migration progresses, perhaps reflecting a training component of physiological modulation for migration. Juveniles showed similar changes to adults in the composition of their depot fat during the “premigratory” period, even though most juveniles do not undergo hyperphagia or rapid fattening at this wintering site. Potential prey species collected from a wintering site in Panama had a higher proportion of saturated fatty acids, less 16:1 and 18:1, and more 18:0 fatty acid compared with those from a migratory stopover site in British Columbia, paralleling the seasonal changes in depot fatty-acid composition observed in Western Sandpipers. However, the fact that Western Sandpipers show an increase in level of unsaturation and in the amounts of 16:1 and 18:1 fatty acids in their fat stores on the wintering ground prior to migration suggests that seasonal variation in fatty-acid composition is not entirely diet dependent.

Anti-termitic efficacy of the resin and rubber in fractionator overheads from a guayule extraction process

Antitermitic properties were evaluated for a mixture of resin and rubber obtained by solvent extraction of guayule. Pine ( Pinus strobus L.) sapwood was impregnated with fractionator overheads consisting of resin and low-molecular-weight rubber. The impregnated wood was exposed for 71 months at two sites in the Panama rain forest and for 67 months at a site in the Arizona desert. None of the treated wood sustained any termite damage at either site, whereas untreated baitwood was routinely destroyed. The impregnant mixture acted as a termite antifeedant rather than a repellant. Almost no loss of resin or rubber was sustained by specimens exposed in Arizona, whereas significant losses occurred at both sites in Panama. Environmental factors, including microbiological activity, may have contributed to the loss of both resin and rubber in the rain forest environment. Enough impregnant did remain in the wood to protect it from termite attack throughout the exposure period.

LETTUCE FOR PROCESSING IN LATIN AMERICA: A McGROWING PROBLEM FOR THE FAST FOOD INDUSTRIES

Latin America is targeted as one of the most rapidly growing areas for expansion for McDonald's International. For example, McDonald's opened its first store in Mexico in 1985 and now has over 50 stores in that country. McDonald's is projecting to have over 100 stores in Mexico by the year 2000. Producing vegetable crops in the same country as a store is desirable to reduce shipping problems and to enhance vegetable production within the country. Problems with lettuce in Latin America include field production (poor growth and yields) and postharvest processing and handling (short shelf life). Beginning in 1992, field studies in cooperation with McDonald's International and Asgrow Seed Company were established in three field sites in Mexico and one site in Panama to determine seasonal uses of varieties (Mexico and Panama) and sites (Mexico) in order to provide quality year round production of lettuce for processing. Results suggest that varieties acceptable for trade in fresh market may not have desirable characteristics during processing (color and cut) and storage (shelf life and odor). In addition, the introduction of new varieties may be needed for year-round production.

Comparative variation in spawning output and juvenile recruitment of some Caribbean reef fishes

It is generally accepted that the intensity of recruitment of pelagic young of temperate marine fishes is determined primarily by events that affect young as larvae, and that pelagic processes substantially increase variation in recruitment over the level expected from variation in spawning output alone. Spawning and recruitment of 6 species of Caribbean damselfishes were monitored monthly at a site in Panama for 1 to 3 yr (1983 to 1987) and 7 to 10 yr (1980 to 1989), respectively. Intermensual variation in recruitment strength exceeded corresponding variation in spawning output by average factors of at least 1.5 to 3.0 (and perhaps as much as 4 to 20) among those species. Serial changes in seasonally-adjusted monthly spawning output and 'resultant' recruitment strength were not correlated in any species. Thus, regardless of whether or not local populations are self-recruiting, pelagic processes evidently do largely control, and substantially enhance, short-term variabihty in recruitment strength in these fishes. Interannual variation in recruitment was low in all but one species. in which it also exceeded variation in spawning. Thus control of variation in recruitment strength by short-term pelagic processes had little or no net effect on interannual variation in recruitment in most cases. Interspecific differences in recruitment seasonal~ty and in levels of variation in mensual and annual recruitment strength (but not mensual and annual spawning output) ~ndicate that pelagic processes affect recruitment of some of these closely related species to different degrees and in different temporal patterns.

A comparison of several models for separating direct and diffuse components of solar irradiation

Several general, empirical separation models were tested with data from a tropical site in Panama, a desert site near the Dead Sea and a temperate site in Newfoundland. The model of Bristow et al. estimated daily diffuse irradiation from total irradiation with low accuracy. This model was superior, however, to previous versions of the Liu and Jordan model for estimating monthly average daily diffuse irradiation at all but the peculiar desert site when only total irradiation was known. Fitting site-specific parameters greatly improved the accuracy of Bristow's model, but this requires diffuse radiation measurements.

More lingual surface attrition of the maxillary anterior teeth in American Indians: prehistoric Panamanians.

Lingual surface attrition of the maxillary anterior teeth (LSA-MAT) has been found in additional prehistoric Latin American Indian skeletons. LSAMAT was first observed in crania from an Archaic Brazilian site. This second finding occurs in teeth from Venado Beach, a late prehistoric site in Panama. LSAMAT is also present in some fragmentary specimens from the Archaic Cerro Mangote site in Panama. LSAMAT at Venado Beach is present in 57% of 28 adult crania. As in the Brazilian study, LSAMAT is associated with a high caries rate (82% of 50 adults; 11.7% of 852 permanent teeth). As first suggested, eating and processing of some type of abrasive carbohydrate food, such as manioc, is the possible cause of LSAMAT. However, other possible causes relating to habitation on or near marine coasts cannot be totally ruled out.

Community composition and nearest neighbor relationships in orb-weaving spiders: the product of aggression?

Nearest-neighbor distances and species' densities were calculated for 949 individuals of 8 species of orb-weaving spiders from eight edge and meacow sites in Panama. These data were used to test the hypothesis that interspecific aggressive interactions influenced spider community structure by: (1) eliminating or decreasing the densities of sympatric, less aggressive species, or, (2) affecting nearest-neighbor relationships so that large or aggressive individuals had smaller, less aggressive or more distant neighbors. Although there was a negative relationship between the densities of two species pairs (Leucauge sp. and Mangora pia; Eriophora fuliginea and Cyclosa caroli), overall spider densities could not be predicted from indices of spider aggression obtained by introduction experiments. The spatial distribution of spiders in three dimensions was not significantly different than random. I attributed the lack of clumping to the relative vegetational homogeneity of my sites; the lack of overdispersion may reflect the fact that websites are not limiting. Relationships between nearest neighbors generally supported the aggression hypothesis, however, comparisons of the actual data with equivalent randomly-assorted data indicate that a hypothesis of randomly chosen neighborsis equally applicable. This result suggests that, unless websites differ significantly in their quality, with high quality websites in short supply, spider aggression may not affect community structure.

Use of artificial holes in studying community development in cryptic marine habitats in a tropical rocky intertidal region

Previous studies on the rocky intertidal shores of the Bay of Panama indicate that for many sessile and mobile organisms holes and crevices are important refuges from consumers. To study the dynamics of these hole-dwelling species assemblages, we devised a method allowing repetitive, non-destructive sampling and species manipulations in artificial holes. These are fiberglass sleeves with flanges at the outer edge that are inserted into receptacles made of quick-setting concrete. Predator and herbivore manipulations include: fences excluding slow-moving benthic consumers, bars across hole mouths restricting entry of large fishes and homogeneous (shelterless) surfaces created around a treatment decreasing abundance of small crabs. This design has withstood the rigors of two wet seasons in Panama. Results from two sites in Panama indicate that colonization occurs rapidly (6–7 months) in holes established in mid dry season. Encrusting fleshy algae (Ralfsia sp.) and ephemeral green algae (Cladophora spp.) colonize first and are succeeded by encrusting species of coralline algae, bryozoans and colonial tunicates and by erect fleshy red algae. Where consumers are present, encrusting corallines predominate; without consumers, bryozoans, tunicates and erect algae are more abundant. Zonation patterns develop within the holes, with the desiccation/heattolerant Ralfsia sp. dominating at the outer edges. With increasing deph, encrusting coralline algae, bryozoans and colonial tunicates reach their respective peak abundances. In contrast to the high variability observed among naturally occurring holes, replicates of each treatment tend to be similar. Between-treatment and between-site comparisons are less so. The naturally-occurring high level of small-scale patchiness is thus presumably due to variation in recruitment and in the local (microspatial) consumer regime. Substratum heterogeneity is therefore directly and indirectly important in maintaining a high local diversity in this community. As in other studies, consumers or disturbances are key factors in regulating patterns of community structure. More experiments of longer duration are necessary to ascertain the relative importances of consumers/disturbance and competition in controlling such assemblages.

Fluctuations in Abundance of Tropical Insects

Annual variability (AV), a measure for the fluctuation in abundance from year to year of insects in a given area, is defined as the variance of the distribution of log R, with R the net reproduction of a species. Some insect groups from two sites in Panama, one in a tropical forest, are compared with data from elsewhere in the world. The result is that insects from the wet tropics fluctuate about as much as their counterparts from the wet temperate zone. Hypotheses which predict greater stability (a lower AV of tropical insects) must be rejected, even for insects in a tropical forest. In areas with a relatively low and unpredictable rainfall, both tropical and temperate, AV tends to be larger. The data suggest that physical stability and predictability of the environment are important for determining the AV of the insects and that the wet but seasonal tropics are physically no more stable than the wet temperate zone. It is suggested that in nonseasonal tropics, should these exist, insect populations could be more stable.

Palm trees and Chagas' disease in Panama.

An ecological survey of triatomines in the sylvan ecosystem of the Canal Zone and selected sites in Panama disclosed for the first time a close association of Rhodnius pullescens and Triatoma dimidiata, the two most important vector species of Chagas' disease in Panama, with a single species of a widely distributed palm tree, Scheelea zonensis. This association may explain why Chagas' disease is prevalent in certain rural communities in Central Panama and rare in others. An immense focus of zoonotic Trypanosoma cruzi infection exists in the forests of the Canal Zone with presence of large populations of triatomines, associated with scheelea zonensis and other yet undescribed microhabitats, and high (50--60%) trypanosome infections in all of the major triatomine species. Common opossums, anteaters, and spiny rats seem to be the principal animal reservoirs of T. cruzi in this complex and relatively undisturbed ecosystem.

Further Data and a Date from Cerro Mangote, Panama

In the October, 1956, issue of American Antiquity (Vol. 22, No. 2) a report was made on preliminary excavations made in 1955 at Cerro Mangote, a preceramic site in Panama. During the 1956 season 6 additional weeks were spent at this site with financial assistance from the American Academy of Arts and Sciences. Briefly, the results of this more extensive work were as follows:Approximately 300 cu. m. of material were excavated, an estimated one-third of the total content of the site. A few sherds were recovered on or immediately below the surface in the same general area as those found the previous year.