Lowland Moist Forest Research Articles

Tree structure and diversity of lowland Atlantic forest fragments: comparison of disturbed and undisturbed remnants

This study describes the tree community structure of three moist lowland Atlantic Forest fragments in Rio de Janeiro State, southeastern Brazil. Two fragments were disturbed and an undisturbed one was used as reference. Our hypothesis was that disturbed fragments show distinct structural patterns in comparison with undisturbed stands due to past disturbance practices and forest fragmentation. Four 100 × 5 m sampling plots were demarcated in each fragment and all live and dead trees with DBH ≥ 5 cm were located, measured and identified. The results supported our hypothesis, due to the high values found for standing dead trees, an increase of dominance of a few pioneer species, lower values of large trees and species richness in disturbed fragments in comparison with the undisturbed one. The advanced fragmentation process in the Southern Brazilian lowland areas and the high species richness in undisturbed areas highlight these forest fragments as priority areas for conservation and management.

Higher tree transpiration due to road-associated edge effects in a tropical moist lowland forest

Newly created forest edges have significant ecophysiological effects on bordering trees. We studied edge effects on microclimate and tree transpiration rates during wet and dry seasons along a 250m transect spanning the edge of an unpaved road into an old growth tropical lowland forest in the Central Brazilian Amazon. Canopy openness decreased only minimal from the road (3.68%) towards the forest interior (1.69%). Vapor pressure deficit (measured at 2.2m height above ground) was lower in the forest interior. The edge effect on microclimate penetrated deeper into the forest (>100m) during the dry season compared to the wet season (<100m). Overall, sap flux, and therefore transpiration rate, was 54% higher in trees adjacent to the road compared to forest interior trees. Higher transpiration rates at the forest edge can be explained by higher turbulences and energy exchange of the canopy boundary layer and by a shift in species composition to high water using secondary forest species 25 years after the road construction. Similar changes might be expected for other disturbances affecting local relative humidity and in situations that favor plants with water use traits differing from those found in the forest interior.

A systematic monograph of the genus Thysananthus (Lejeuneaceae, Marchantiophyta)

A world-wide revision of the liverwort genus Thysananthus (Marchantiophyta: Lejeuneaceae) leads to the recognition of fifteen species in two sections: sect. Thysananthus (eleven species) and sect. Vittatae (four species). The genus is monophyletic with the inclusion of Dendrolejeunea fruticosa and Mastigolejeunea pancheri, and lacks synapomorpies. Morphological characters of Thysananthus are non-exclusive, and include Lejeunea-type branching, epidermal cells mostly as large as medullary cells, leaves convolute when dry, leaf cells elongate, trigones cordate, oil bodies segmented, underleaves often adnate to leaves, innovations lejeuneoid, and female involucres (incl. perianths) usually toothed. The two sections are characterized by the absence versus presence of a vitta. Species are defined by the possession of two or more independent, diagnostic morphological characters and monophyly. Based on phytochemical and molecular evidence T. gottschei, previously considered a synonym of T. convolutus, is resurrected as a distinct species. One variety, T. gottschei var. continuus, is newly described, and the new combinations T. convolutus var. laceratus and T. retusus subsp. sellingii are proposed. A key to the species of the genus Thysananthus is provided and each species is fully described and illustrated, with complete synonymy and detailed data on habitat and distribution. Thysananthus is pantropical in distribution, with four species ranging into warm temperate regions; the centre of diversity of the genus is in Southeast Asia. The species grow as epiphytes in moist lowland and montane forests, and include ecological specialists (shade epiphytes, sun epiphytes) as well as generalists.

Extraordinary Local Diversity of Disk-Winged Bats (Thyropteridae:Thyroptera) in Northeastern Peru, with the Description of a New Species and Comments on Roosting Behavior

ABSTRACT Species of Thyroptera are insectivorous foliage-roosting bats that inhabit lowland moist forests (including gallery formations in savanna landscapes) from Mexico to southeastern Brazil. Although four species are currently recognized, only one or two species were previously known to occur at most localities. Recent inventory work in northeastern Peru has documented the local cooccurrence of four species of Thyroptera, one of which is here described as new. The new species (T. wynneae), which also occurs in Brazil, can easily be recognized by a combination of diagnostic morphological traits. The latter include small size, tricolored ventral pelage, long and woolly hairs between the shoulders, a uropatagium with the proximal half densely covered by long hairs, wing tips sparsely covered by long hairs, a calcar with two lappets and five tiny skin projections between the foot disk and the proximal lappet, a rostrum considerably shorter than the braincase, third lower incisors that are subequal in heig...

Amphibians and reptiles in the swamps dominated by the palm Raphia taedigera (Arecaceae) in northeastern Costa Rica

The herpetofauna that inhabits Caribbean Costa Rica has received considerable attention in the last two decades. This assemblage includes a total of 141 species of reptiles and 95 amphibians mostly distributed in tropical wet and moist lowland forests. While most information available came from primary and secondary forest sites, little is known about the amphibians and reptiles that inhabit more open habitats, such as wetlands and swamps. For instances, swaps dominated by the yolillo palm Raphia taedigera extend through much of the northeastern Caribbean coast of Costa Rica and eastern Nicaragua, but information about the herpetological community that uses such environments remains practically unknown. This situation reflects the little research conducted in such inhospitable environments. Here, we report the results of an intensive survey conducted to assess the herpetological community that inhabit R. taedigera palm-swamps. A total of 14 species of amphibians and 17 of reptiles have been recorded from these swamps. Amphibians and reptiles that inhabit yolillo swamps have wide distributions along much of Middle America and are considered common species throughout their range. In general, yolillo swamps are poor environments for herpetofauna: richness of reptiles and amphibians is almost two times higher in the adjacent forest than in the palm dominated swamps. Furthermore, most species observed in this swamps can be considered habitat generalists that are well adapted to the extreme conditions imposed by the changes in hydroperiods, reduce understory cover, low tree diversity and simple forest architecture of these environments. Despite similarities in the herpetofauna, it is clear that not all forest species use yolillo habitat, a characteristic that is discussed in terms of physical stress driven by the prolonged hydroperiod and reduced leaflitter in the ground, as these features drive habitat structure and herpetofaunal complexity. Our list of species using yolillo swamps is not definitive, and is likely to grow as more studies are conducted in this unexplored environment.

Large trees drive forest aboveground biomass variation in moist lowland forests across the tropics

AbstractAimLarge trees (d.b.h. ≥ 70 cm) store large amounts of biomass. Several studies suggest that large trees may be vulnerable to changing climate, potentially leading to declining forest biomass storage. Here we determine the importance of large trees for tropical forest biomass storage and explore which intrinsic (species trait) and extrinsic (environment) variables are associated with the density of large trees and forest biomass at continental and pan‐tropical scales.LocationPan‐tropical.MethodsAboveground biomass (AGB) was calculated for 120 intact lowland moist forest locations. Linear regression was used to calculate variation in AGB explained by the density of large trees. Akaike information criterion weights (AICc‐wi) were used to calculate averaged correlation coefficients for all possible multiple regression models between AGB/density of large trees and environmental and species trait variables correcting for spatial autocorrelation.ResultsDensity of large trees explained c. 70% of the variation in pan‐tropical AGB and was also responsible for significantly lower AGB in Neotropical [287.8 (mean) ± 105.0 (SD) Mg ha−1] versus Palaeotropical forests (Africa 418.3 ± 91.8 Mg ha−1; Asia 393.3 ± 109.3 Mg ha−1). Pan‐tropical variation in density of large trees and AGB was associated with soil coarseness (negative), soil fertility (positive), community wood density (positive) and dominance of wind dispersed species (positive), temperature in the coldest month (negative), temperature in the warmest month (negative) and rainfall in the wettest month (positive), but results were not always consistent among continents.Main conclusionsDensity of large trees and AGB were significantly associated with climatic variables, indicating that climate change will affect tropical forest biomass storage. Species trait composition will interact with these future biomass changes as they are also affected by a warmer climate. Given the importance of large trees for variation in AGB across the tropics, and their sensitivity to climate change, we emphasize the need for in‐depth analyses of the community dynamics of large trees.

Silvicultural disturbance has little impact on tree species diversity in a Central African moist forest

Timber production is an important economic sector in most forested countries of Central Africa, where about 14 million hectares of lowland moist forests are now planned for management. This production is expected to be sustainable, but the actual impact of logging on biodiversity is still questioned.To answer this question, we used a unique long-term controlled experiment implemented more than 20years ago in an old-growth semi-deciduous moist forest of the Central African Republic (CAR). We tested whether (i) anthropogenic disturbances associated with silvicultural operations had an effect on the composition and diversity of tree communities, and (ii) there is a relationship between diversity and disturbance intensity in those forests.For this, we botanically identified all trees⩾10cm DBH in 28 1-ha plots where no treatment (controls), logging and logging+thinning operations were implemented 24years ago and created a strong gradient of disturbance. We investigated the relationships between five diversity indices and a disturbance index calculated for each 1-ha plot, for all species and separately for three regeneration guilds.We found a strong positive monotonic relationship between the intensity of disturbance and the percentage of pioneer species in the tree communities, which proved to be equally detrimental, in terms of relative abundance, to the non-pioneer light-demanding and the shade-bearing species.Overall, disturbance appeared to have a weak monotonous negative effect on diversity, irrespective to the index considered. The diversity of shade-bearers slightly decreased along the disturbance gradient without significant decrease in species density; disturbance had no effect on non-pioneer light demanders, but a clear significant negative effect on the diversity of pioneers, with a significant decrease in species density. This negative effect was associated with the massive recruitment of the early-successional, fast-growing Musanga cecropioides R. Br. (Urticaceae), which rapidly preempted space and resources in the most disturbed plots. Despite this effect, disturbance did not significantly affect the local heterogeneity in species distribution.These results suggest that the semi-deciduous moist forests of CAR are locally resilient to small-scale disturbances associated with silvicultural operations. This may be a consequence of the past anthropogenic and/or climatic disturbances, which have been stronger and more long-lasting than elsewhere within the tropical forest biome, and would have removed the most vulnerable species. Because logging intensity in these forests is usually low, we do not expect any direct major impact on tree species diversity, at least after the first felling cycle.

Notes on the distribution of Memphis montesino Pyrcz, 1995 and Memphis boliviana (Druce, 1977 (Insecta: Lepidoptera): New country records and updated geographic distribution maps

This paper provides two new distribution records from Guyana for Memphis montesino Pyrcz, 1995, extending the distribution of the species over 200 km westwards to lowland moist forests; and the first record for Memphis boliviana (Druce, 1977) from Argentina, extending its distribution over 500 km southwards.

Nutrient and Carbon Limitation on Decomposition in an Amazonian Moist Forest

Tropical forests determine global biogeochemical cycles to a large extent, but control factors for key ecosystem processes such as decomposition remain poorly understood. With a full-factorial C (cellulose), N (urea), and P (phosphate) fertilization experiment, we tested the relative importance of C and nutrient limitation on litter decomposition in a mature lowland moist forest of French Guiana. Despite the previously demonstrated litter C quality control over decomposition and the very low soil P content (0.1 mg g−1 of soil) at our study site, fertilization with C or P alone did not increase the decomposition of a wide range of litter types (N:P ratios between 20 and 80). Nitrogen fertilization alone also had no effect on decomposition. However, the combined fertilization with N and P resulted in up to 33.5% more initial litter mass lost, with an increasing effect with wider litter N:P ratios. Soil fauna strongly stimulated litter mass loss and enhanced nutrient fertilization effects. Moreover, nutrient effects on decomposition increased with additional C fertilization in the presence of fauna. Our results suggest that increased N availability is required for a positive P effect on decomposition in the studied P-poor tropical forest. Further stimulation of decomposition by C amendment through priming indicates energy limitation of decomposers that is co-determined by nutrient availability. The demonstrated intricate control of the key resources C, N, and P on decomposition calls for an intensified research effort on multiple resource limitation on key processes in tropical forests and how they change under multiple human impacts.

Stable Isotope Analysis Provides New Information on Winter Habitat Use of Declining Avian Migrants That Is Relevant to Their Conservation

Winter habitat use and the magnitude of migratory connectivity are important parameters when assessing drivers of the marked declines in avian migrants. Such information is unavailable for most species. We use a stable isotope approach to assess these factors for three declining African-Eurasian migrants whose winter ecology is poorly known: wood warbler Phylloscopus sibilatrix, house martin Delichon urbicum and common swift Apus apus. Spatially segregated breeding wood warbler populations (sampled across a 800 km transect), house martins and common swifts (sampled across a 3,500 km transect) exhibited statistically identical intra-specific carbon and nitrogen isotope ratios in winter grown feathers. Such patterns are compatible with a high degree of migratory connectivity, but could arise if species use isotopically similar resources at different locations. Wood warbler carbon isotope ratios are more depleted than typical for African-Eurasian migrants and are compatible with use of moist lowland forest. The very limited variance in these ratios indicates specialisation on isotopically restricted resources, which may drive the similarity in wood warbler populations' stable isotope ratios and increase susceptibility to environmental change within its wintering grounds. House martins were previously considered to primarily use moist montane forest during the winter, but this seems unlikely given the enriched nature of their carbon isotope ratios. House martins use a narrower isotopic range of resources than the common swift, indicative of increased specialisation or a relatively limited wintering range; both factors could increase house martins' vulnerability to environmental change. The marked variance in isotope ratios within each common swift population contributes to the lack of population specific signatures and indicates that the species is less vulnerable to environmental change in sub-Saharan Africa than our other focal species. Our findings demonstrate how stable isotope research can contribute to understanding avian migrants' winter ecology and conservation status.

Phylogeography of a species complex of lowland Neotropical rain forest trees (Carapa, Meliaceae)

AbstractAim Many tropical tree species have poorly delimited taxonomic boundaries and contain undescribed or cryptic species. We examined the genetic structure of a species complex in the tree genus Carapa in the Neotropics in order to evaluate age, geographic patterns of diversity and evolutionary relationships, and to quantify levels of introgression among currently recognized species.Location Lowland moist forests in the Guiana Shield, the Central and Western Amazon Basin, Chocó and Central America.Methods Genetic structure was analysed using seven nuclear simple sequence repeats (nuSSR), five chloroplast SSRs (cpSSR), and two chloroplast DNA (cpDNA) intergenic sequences (trnH–psbA and trnC–ycf6). Bayesian clustering analysis of the SSR data was used to infer population genetic structure and to assign 324 samples to their most likely genetic cluster. Bayesian coalescence analyses were performed on the two cpDNA markers to estimate evolutionary relationships and divergence times.Results Two genetic clusters (nu_guianensis and nu_surinamensis) were detected, which correspond to the Neotropical species C. guianensis (sensu latu) and C. surinamensis. Fourteen cpDNA haplotypes clustered into six haplogroups distributed between the two nuclear genetic clusters. Divergence between the haplogroups was initiated in the Miocene, with some haplotype structure evolving as recently as the Pleistocene. The absence of complete lineage sorting between the nuclear and chloroplast genomes and the presence of hybrid individuals suggest that interspecific reproductive barriers are incomplete. NuSSR diversity was highest in C. guianensis and, within C. guianensis, cpDNA diversity was highest in the Central and Western Amazon Basin. Regional genetic differentiation was strong but did not conform to an isolation‐by‐distance process or exhibit a phylogeographical signal.Main conclusions The biogeographical history of Neotropical Carapa appears to have been influenced by events that took place during the Neogene. Our results point to an Amazonian centre of origin and diversification of Neotropical Carapa, with subsequent migration to the Pacific coast of South America and Central America. Gene flow apparently occurs among species, and introgression events are supported by inconsistencies between chloroplast and nuclear lineage sorting. The absence of phylogeographical structure may be a result of the ineffectiveness of geographical barriers among populations and of reproductive isolation mechanisms among incipient and cryptic species in this species complex.

Plant communities, species diversity, richness, and regeneration of a traditionally managed coastal forest, Kenya

The Kenyan coastal forests make up one of the World 25 Biodiversity Hotspots. They consist of over 140 fragments (the majority with areas less than 0.5 km 2) of the once extensive Zanzibar–Inhambane lowland moist forest. The over 60 known Mijikenda sacred Kaya forests and groves scattered along the coastal hinterland form the greater part of this ecosystem. The forests are of biological and cultural significance, and this has been recognized nationally and internationally, with some now listed as World Heritage Sites. The forests are protected by councils of Kaya elders who regulate use of their resources. Increasing human population and subsequent rise in demand for forest products and land for settlement has put a strain on these relic forests. Farm encroachment and extraction of forest products in different Kaya forests have affected the vegetation ecology at varying levels. This study investigated the spatial species distribution, association and regeneration potential of commonly utilized plants in one of these traditionally managed ecosystems. A modified nested plot method was used to collect data in the field. Using TWINSPAN multivariate, and indicator species analysis, two plant communities ( Asteranthe and Bridelia) and an undifferentiated vegetation type were identified. Species association in Asteranthe consisted largely of forest dependant species, with a significant presence of woody climbers. It was comprised of two sub-communities namely Manilkara and Scorodophloeos. In contrast the second plant community, Bridelia, was dominated by light demanding species. It comprised one sub-community ( Catunaregam) and a seral stage ( Keetia). The species diversity and richness was higher in the Asteranthe community compared to Bridelia. Some of the forest species commonly utilized by the local people were observed to regenerate both in open and closed forest habitats while others had seedling recruitment confined to closed forest. Despite some coastal forests showing physiognomic similarity, detailed study shows intra-variation linked to topography, exposition, type and intensity of human perturbation both currently and in the distant past. Clearly, vegetation patterns of coastal forests of eastern Africa change at fairly short intervals. Recruitment of forest specialists is likely to decline if closed forests are opened up by farm encroachment, however their less specialized counterparts can pioneer in re-colonization of disturbed sites if conservation is strengthened. There is need to invigorate traditional management systems of forests with cultural significance by recognizing and giving increased legal mandates to the local custodians.

Soil organic phosphorus dynamics following perturbation of litter cycling in a tropical moist forest

The productivity of tropical lowland moist forests is often considered to be limited by the availability of phosphorus. Organic phosphorus is often abundant in tropical soils, but its role in forest nutrition is largely unknown. We addressed this by using a large‐scale litter manipulation experiment to investigate the stability of soil organic phosphorus in a tropical lowland forest in Central Panama. Three years of litter removal reduced the organic phosphorus concentration in the surface 2 cm of mineral soil by 23%, as determined by NaOH‐EDTA extraction and 31P‐NMR spectroscopy; this included decreases in phosphate monoesters (20%) and DNA (30%). Three years of litter addition (equivalent to adding 6 kg P ha–1 per year) increased soil organic phosphorus by 16%, which included a 31% increase in DNA. We did not detect higher‐order inositol phosphates, despite their abundance in mineral soils of temperate ecosystems. Our observed turnover rate suggests that even the 0–2‐cm layer of the mineral soil contributes a fifth of the total phosphorus needed to sustain above‐ground growth in this forest. Soil organic phosphorus is thus likely to make a more important contribution to the nutrition of semi‐evergreen forest plants than has hitherto been acknowledged.

Long‐Term Persistence of Pioneer Species in Tropical Rain Forest Soil Seed Banks

In tropical forests, pioneer tree species regenerate from seeds dispersed directly into canopy gaps and from seeds that persisted in soil seed banks before gap formation. Life-history models have suggested that selection for the long-term persistence of tree seeds in the soil should be weak because persistence potentially reduces population growth rate by extending generation time and because adult life spans may exceed the return interval of favorable recruitment sites. Here we use accelerator mass spectrometry to carbon-date seeds of three pioneer tree species extracted from undisturbed seed banks in seasonally moist lowland Neotropical forest. We show that seeds of Croton billbergianus, Trema micrantha, and Zanthoxylum ekmannii germinate successfully from surface soil microsites after 38, 31, and 18 years, respectively. Decades-long persistence may be common in large-seeded tropical pioneers and appears to be unrelated to specific regeneration requirements.

Modeling the Geographical Distribution and Fundamental Niches of Cacajao spp. and Chiropotes israelita in Northwestern Amazonia via a Maximum Entropy Algorithm

We modeled the geographical distribution of 4 pithecine primate species: brown-backed bearded sakis (Chiropotes israelita) and 3 black uakaris (Cacajao melanocephalus, C. hosomi, and C. ayresi) that inhabit remote regions of western Amazonas, Brazil. We applied a maximum entropy algorithm modeling program (MAXENT) to field data Boubli collected from 1991 to 2007. We used 23 environmental coverage variables to model the distribution of the primates. The layers were related to precipitation, temperature, topography, and ecological bioregions or Ecoregions. The predicted distribution for Cacajao hosomi was strongly associated with the Negro-Branco Moist Forest and Guianan Highlands Moist Forests Ecoregions, and the Worldclim variables Bio3 (isothermality), Bio4 (temperature seasonality) and Bio17 (precipitation of the driest quarter). Cacajao melanocephalus was strongly associated with Japura/ Solimoes-Negro Moist Forests, Caqueta Moist Forests, Purus Varzea Flooded Forests, Rio Negro Campinaranas, and Cordillera Oriental Montane Forests, Ecoregions. Cacajao ayresi was strongly associated with Negro-Branco Moist Forest and Rio Negro Campinarana Ecoregions as well as Worldclim Bio3 (isothermality). Chiropotes israelita was also strongly associated with Worldclim Bio3 (isothermality) followed by the Negro Branco Moist Forests and Guianan Piedmont and Lowland Moist Forests Ecoregion, and to the Guianan Highland moist forests. These results show a great overlap between the bearded saki and 2 black uakaris, Cacajao hosomi and C. ayresi. Given that one cannot attribute the separation between the species in the Rio Negro-Rio Branco interfluvium to the existence of geographical barriers such as rivers, we suggest that the present geographical boundaries and thus coexistence of the 3 pithecines north of the Rio Negro is maintained by competitive exclusion or stochastic events. Until more surveys are conducted, the present geographical distributions of the pithecines and the mechanism maintaining their boundaries in the Rio Negro-Rio Branco interfluvium will remain uncertain. One important contribution of our model is to identify areas of higher probability of occurrence that might be helpful in guiding future survey expeditions and choices of areas for future conservation of pithecines.

Seasonal drought and dry-season irrigation influence leaf-litter nutrients and soil enzymes in a moist lowland forest in Panama

Seasonal drought and dry-season irrigation influence leaf-litter nutrients and soil enzymes in a moist lowland forest in Panama

Differences in forest use and colonization by Neotropical tree‐hole damselflies (Odonata: Pseudostigmatidae): Implications for forest conversion

Differential habitat use in primary and secondary forests was documented for two genera of giant damselflies (Pseudostigmatidae), important predators of tree‐hole breeding mosquitoes in tropical forests. In a lowland moist forest of Panama, adults moved between old primary (>400 years old) and contiguous secondary forest (>60 years old) and reproduced seasonally in both types. However, the two Mecistogaster species were more common in secondary forest, whereas Megaloprepus caerulatus was most common in primary forest. These differences in landscape use were reflected in differential colonization of tree‐hole analogs (plastic pots) in primary forest and highly altered secondary growth (<20 years old) in a lowland wet forest in Costa Rica where reproduction of both species was aseasonal. Larvae of Mecistogaster linearis were commonly found in pots at both habitat types, whereas Megaloprepus, the majority species, rarely colonized pots in altered sites. Our results suggest that Megaloprepus is particularly susceptible to forest conversion, and call for increased focus on the dispersal ability of all pseudostigmatids. In tropical moist and wet forests that harbor water‐filled tree holes, the presence of the conspicuous Megaloprepus and similar species may serve as bio‐indicators of a healthy predator guild, the loss of which may adversely impact human health.

Seedling growth responses to water and nutrient augmentation in the understorey of a lowland moist forest, Panama

Abstract:We irrigated and fertilized (with nutrients) seedlings of Doliocarpus olivaceus (Dilleniaceae, a shade-tolerant liana), Faramea occidentalis (Rubiaceae, a shade-tolerant understorey tree) and Tetragastris panamensis (Burseraceae, a shade-tolerant canopy tree) growing in the understorey of an old-growth tropical moist forest in Panama to assess the impact of seasonal water availability and nutrient-poor soils on seedling growth rates. In control plots, height growth rates were greater in the dry season than in the wet season for Doliocarpus (21%) and for Faramea (89%), whereas Tetragastris had similar seasonal rates. For numbers of leaves, Faramea had 3.5-fold greater relative growth rates in the dry season than in the wet season, while Doliocarpus and Tetragastris lost leaves (semi-deciduous) during the same period. Irrigation and nutrient augmentation increased height growth rates for all three species (45% to 272%). For Doliocarpus, irrigation and nutrient augmentation prevented leaf fall during the dry season. For Faramea in the dry season, irrigation and nutrient augmentation when applied independently reduced the growth of new leaves by 65% to 87%, but relative growth rates for number of leaves were the same as the control rates in the combined irrigation and nutrient augmentation treatment. The growth of new leaves for Tetragastris responded to dry-season irrigation but not nutrient augmentation. Although all measurements occurred beneath the forest canopy, during the dry season, Tetragastris had a negative relationship between canopy openness and relative growth rate for number of leaves, whereas the other two species had a positive relationship. Our results show that soil resources influence growth rates even in the deep shade of the forest understorey, and demonstrate different responses to soil resources among species that might contribute to niche differentiation and species coexistence.

Seasonal variation of arthropod abundance in gaps and the understorey of a lowland moist forest in Panama

Treefalls gaps contribute to the habitat heterogeneity of tropical forest floors. Previous studies have shown that these gaps play an important role in plant and bird communities, however less is known about their role in arthropod communities. Using eight Malaise traps we investigated the difference in arthropod abundance of 19 taxonomic groups between gaps and understorey for 21 wk during the rainy season and 8 wk in the dry season on Barro Colorado Island, Panama. More (33.8%) arthropods were collected in gaps during the rainy season and 32.2% more in the understorey during the dry season. To assess the possible factors contributing to these differences we measured light, plant densities and young leaf densities, as indicators of abiotic factors and food resources for insect herbivores. Arthropod abundance was negatively correlated with light in the dry season. Thus, abiotic stress may explain the pattern of abundance in the dry season. While there was no correlation with light in the rainy season, predator abundance was positively correlated with herbivore abundance. The plant and young leaf density data suggest that there is significantly higher food availability for herbivores in gaps. Thus, less stressful abiotic conditions and more food resources may contribute to more herbivores followed by more predators in gaps during the rainy season.

Thermal Ecology Of The Neotropical Army Ant Eciton Burchellii

I explored the thermal ecology of Eciton burchellii, a New World army ant, in primary forest and forest fragments in the Atlantic lowlands of Costa Rica in 2002 and 2003. My primary objective was to determine whether high surface temperatures in pastures surrounding forest fragments posed a thermal barrier to ant colonies within those fragments; secondarily, I assessed whether thermal gradients within continuous moist forest were sufficient to elicit avoidance reactions from foraging colonies. E. burchellii colonies in forest fragments avoided entering open pasture in full sun (51.3 degrees C) on 100% of all edge interactions; however, edges were readily crossed where artificial shaded areas had previously been installed. Ant raids in primary forest avoided artificially established temperatures >43 degrees C but tolerated 45.5 degrees C in the presence of prey baits. Captive ants held at 43 degrees C survived 18.5 min; at temperatures of 51.3 degrees C survival time was only 2.8 min. Ants running on established foraging trails increased running velocity by 18% when substrate temperature was raised from 28.4 degrees to 38.0 degrees C, and they abandoned trails at temperatures >43 degrees C. The standard deviation (s) of temperatures on active raid trails in continuous forest was 2.13 degrees C, while nearby systematic sampling revealed a greater background standard deviation of 4.13 degrees C. E. burchellii colonies in this region appear to be living surprisingly near their upper limits of thermal tolerance. The heat of open pastures alone is sufficient to prevent their exiting forest fragments, or entering similarly hot areas within continuous forest. Shaded vegetative corridors are sufficient to permit mobility between isolated fragments, and their preservation should be encouraged. Despite views that tropical lowland moist forests have an essentially homogenous microclimate, army ants appear to avoid local hot spots on the forest floor, steering daily foraging trails to follow cooler routes than would be expected by chance. As deforestation remakes tropical landscapes worldwide, it is important to consider the thermal consequences of these actions and their effect on keystone organisms such as army ants. Changes in global climate patterns are likely to affect even evergreen tropical systems whose organisms may be sensitive to finer microclimatic variation than previously suspected.