Barro Colorado Nature Monument Research Articles

Acerentulus panamensis sp. nov. (Protura, Acerentomidae) from Panama

Acerentulus panamensis sp. nov. from the tropical forest of the Gigante Peninsula of Barro Colorado Nature Monument (9°06’N, 79°54’W – Panama) is described. The new species belongs to the cunhai group being characterized by a short sensillum a not reaching the base of seta γ3 and by sensillum b shorter than c. Acerentulus panamensis sp. nov. is close to A. gerezianus da Cunha, 1952, A. ladeiroi Da Cunha, 1950, A. omoi Imadaté, 1988 and A. catalanus Condé, 1951. It differs from the first species by the absence of seta Pc on sternite VII, by the chaetotaxy of tergites II–V (6/16 in the new species and 8/14 in A. gerezianus), by the longer foretarsal sensillum e and by shorter sensilla f and a’. Finally, in Acerentulus panamensis sp. nov. sensillum a’ is at the same level of t1 closer to the base of tarsus than in A. gerezianus. In A. ladeiroi, the chaetotaxy of tergites II–V is 8/14 (as in A. gerezianus). Moreover, A. ladeiroi is distinguishable from the new species by shorter foretarsal sensilla e and t2, by a longer sensillum f, and by a longer sensillum a’ placed distally to t1. The new species differs from A. omoi by the absence of seta Pc on sternite VII, by the porotaxy of sternites I–III, and by the longer foretarsal sensillum e and shorter sensillum b. Acerentulus panamensis sp. nov. differs from A. catalanus by the chaetotaxy of tergites II–V, by the shorter sensilla a, b and f, and by the number of teeth of comb VIII (11–12 vs 7–8). https://zoobank.org/urn:lsid:zoobank.org:pub:19B1F711-95B9-47DA-8157-98327ADEF104

Incomplete recovery of tree community composition and rare species after 120 years of tropical forest succession in Panama.

Determining how fully tropical forests regenerating on abandoned land recover characteristics of old-growth forests is increasingly important for understanding their role in conserving rare species and maintaining ecosystem services. Despite this, our understanding of forest structure and community composition recovery throughout succession is incomplete, as many tropical chronosequences do not extend beyond the first 50 years of succession. Here, we examined trajectories of forest recovery across eight 1-hectare plots in middle and later stages of forest succession (40-120 years) and five 1-hectare old-growth plots, in the Barro Colorado Nature Monument (BCNM), Panama. We first verified that forest age had a greater effect than edaphic or topographic variation on forest structure, diversity and composition and then corroborated results from smaller plots censused 20 years previously. Tree species diversity (but not species richness) and forest structure had fully recovered to old-growth levels by 40 and 90 years, respectively. However, rare species were missing, and old-growth specialists were in low abundance, in the mid- and late secondary forest plots, leading to incomplete recovery of species composition even by 120 years into succession. We also found evidence that dominance early in succession by a long-lived pioneer led to altered forest structure and delayed recovery of species diversity and composition well past a century after land abandonment. Our results illustrate the critical importance of old-growth and old secondary forests for biodiversity conservation, given that recovery of community composition may take several centuries, particularly when a long-lived pioneer dominates in early succession. Abstract in Spanish is available with online material.

Tropical tree height and crown allometries for the Barro Colorado Nature Monument, Panama: a comparison of alternative hierarchical models incorporating interspecific variation in relation to life history traits

Abstract. Tree allometric relationships are widely employed for estimating forest biomass and production and are basic building blocks of dynamic vegetation models. In tropical forests, allometric relationships are often modeled by fitting scale-invariant power functions to pooled data from multiple species, an approach that fails to capture changes in scaling during ontogeny and physical limits to maximum tree size and that ignores interspecific differences in allometry. Here, we analyzed allometric relationships of tree height (9884 individuals) and crown area (2425) with trunk diameter for 162 species from the Barro Colorado Nature Monument, Panama. We fit nonlinear, hierarchical models informed by species traits – wood density, mean sapling growth, or sapling mortality – and assessed the performance of three alternative functional forms: the scale-invariant power function and the saturating Weibull and generalized Michaelis–Menten (gMM) functions. The relationship of tree height with trunk diameter was best fit by a saturating gMM model in which variation in allometric parameters was related to interspecific differences in sapling growth rates, a measure of regeneration light demand. Light-demanding species attained taller heights at comparatively smaller diameters as juveniles and had shorter asymptotic heights at larger diameters as adults. The relationship of crown area with trunk diameter was best fit by a power function model incorporating a weak positive relationship between crown area and species-specific wood density. The use of saturating functional forms and the incorporation of functional traits in tree allometric models is a promising approach for improving estimates of forest biomass and productivity. Our results provide an improved basis for parameterizing tropical plant functional types in vegetation models.

Tracing the Sources of Atmospheric Phosphorus Deposition to a Tropical Rain Forest in Panama Using Stable Oxygen Isotopes.

Atmospheric dust deposition can be a significant source of phosphorus (P) in some tropical forests, so information on the origins and solubility of atmospheric P is needed to understand and predict patterns of forest productivity under future climate scenarios. We characterized atmospheric dust P across a seasonal cycle in a tropical lowland rain forest on Barro Colorado Nature Monument (BCNM), Republic of Panama. We traced P sources by combining remote sensing imagery with the first measurements of stable oxygen isotopes in soluble inorganic phosphate (δ(18)OP) in dust. In addition, we measured soluble inorganic and organic P concentrations in fine (<1 μm) and coarse (>1 μm) aerosol fractions and used this data to estimate the contribution of P inputs from dust deposition to the forest P budget. Aerosol dry mass was greater in the dry season (December to April, 5.6-15.7 μg m(-3)) than the wet season (May to November, 3.1-7.1 μg m(-3)). In contrast, soluble P concentrations in the aerosols were lower in the dry season (980-1880 μg P g(-1)) than the wet season (1170-3380 μg P g(-1)). The δ(18)OP of dry-season aerosols resembled that of nearby forest soils (∼19.5‰), suggesting a local origin. In the wet season, when the Trans-Atlantic Saharan dust belt moves north close to Panama, the δ(18)OP of aerosols was considerably lower (∼15.5‰), suggesting a significant contribution of long-distance dust P transport. Using satellite retrieved aerosol optical depth (AOD) and the P concentrations in aerosols we sampled in periods when Saharan dust was evident we estimate that the monthly P input from long distance dust transport during the period with highest Saharan dust deposition is 88 ± 31 g P ha(-1) month(-1), equivalent to between 10 and 29% of the P in monthly litter fall in nearby forests. These findings have important implications for our understanding of modern nutrient budgets and the productivity of tropical forests in the region under future climate scenarios.

Secondary forests of central Panama increase in similarity to old‐growth forest over time in shade tolerance but not species composition

AbstractQuestionDoes species and functional composition of secondary tropical forests more closely follow a deterministic or a stochastic model of succession?LocationThe Barro Colorado Nature Monument (BCNM), central Panama. The BCNM comprises Barro Colorado Island (BCI) and five adjacent mainland peninsulas and is a mosaic of tropical old‐growth (OG) and secondary forests (SF).MethodsWe studied the species and functional composition of seedling, sapling and adult tree communities in a chronosequence of SF stands ranging in age from 20 to 100 yrs since abandonment, as well as two OG stands for comparison. Functional composition was defined as the representation of species with different degrees of shade tolerance. We also examined patterns of species diversity and dominance to better understand processes driving compositional changes.ResultsSpecies diversity recovered rapidly, and, by 20 yrs, species richness for all size classes was equivalent if not higher in SF compared to OG. Species diversity tended to be lower and species dominance higher for seedlings than saplings or adults. Seedling, sapling and adult tree species composition did not clearly increase in similarity to OG with forest age. Instead, differences in species composition among stands reflected variation in dominance by particular species. Light‐demanding species became less common and shade‐tolerant species more common over stand age, with the functional composition of older secondary forests converging on that of OG. The seedling and sapling communities across the chronosequence were composed of a shade‐tolerant subset of those species found in the stands as adults.ConclusionOur results suggest that recruitment into the seedling community of SF is determined by both predictable (e.g. selection for shade‐tolerant species) and unpredictable factors (e.g. species‐specific reproduction events and dispersal limitation). Recruitment into the sapling and tree communities reflects stronger, and potentially compounded, selection for shade‐tolerant species. Therefore, changes in the species composition of regenerating forests in this area appear to be unpredictable, even though the functional composition follows a more deterministic and predictable trajectory with convergence on OG over time.

Scale-dependence of aboveground carbon accumulation in secondary forests of Panama: A test of the intermediate peak hypothesis

Accumulation of aboveground carbon is one of the most important services provided by tropical secondary forests—a land-cover type that is increasing in importance globally. Carbon accumulates rapidly for the first 20years of succession, but few studies have considered forests older than 20years, and the available data do not yield a consistent pattern. Two alternative hypotheses have been proposed: (1) an asymptotic increase, with the highest carbon stocks occurring in the oldest stands, and (2) an intermediate peak, caused by roughly synchronous tree maturity (and thus high carbon stocks) after which time treefall gaps cause carbon stocks to regress. Here we revisited a well-studied tropical moist forest chronosequence in Barro Colorado Nature Monument, Central Panama, consisting of 35, 55, 85, and 115-year-old stands, as well as old-growth stands, to determine whether past evidence for the intermediate peak hypothesis was influenced by the spatial limitations of the field plots used to assess forest structure. We used airborne LiDAR (light detection and ranging) to measure carbon stocks at the scale of the original transects (0.16ha), in surrounding forest of the same age (up to 20ha), and at a landscape scale incorporating thousands of hectares not previously measured. We also compared forest structure as measured in three dimensions by LiDAR, considering vertical and horizontal variation in canopy organization, as well as the abundance of treefall gaps. Our results suggested a strong scale-dependence of aboveground carbon accumulation, supporting the intermediate peak hypothesis at the fine scale of the 0.16-ha transects, but an asymptotic model at the landscape scale incorporating thousands of hectares. Further analyses of forest structure suggest that both the limitations of small plots and intrinsic scaling of forest structure and carbon dynamics account for the scale-dependence of aboveground carbon accumulation in this secondary forest matrix.

Tropical tree seedling growth responses to nitrogen, phosphorus and potassium addition

Summary1. Nutrients are a critical resource for plant growth, but the elements limiting growth in tropical forests have rarely been determined.2. We investigated the influence of nitrogen (N), phosphorus (P), potassium (K) and micronutrients on seedling biomass and nutrient allocation in a factorial nutrient fertilization experiment in lowland tropical forest at the Barro Colorado Nature Monument, Panama. We also measured 8 years of herbivory and growth for 1800 seedlings. We sought to determine the identity of limiting elements and possible nutrient interactions.3. The five study species were Alseis blackiana, Desmopsis panamensis, Heisteria concinna, Sorocea affinis and Tetragastris panamensis. Plants grew in deeply shaded understorey with a mean canopy openness of 4.9% (±0.7%; 1 SE).4. Tissue N concentration increased by 11% with N addition. Tissue P concentration increased by 16% with P addition. Tissue K increased by 4% with K addition. K addition reduced root‐to‐shoot biomass ratio. There was no significant effect of fertilization on specific leaf area or leaf area ratio.5. The proportion of leaves damaged and the mean level of damage by herbivory increased with P and K addition and showed a significant P × K interaction.6.7ensp;Across all species and years, relative growth rate of height increased with K addition and with N and P in combination. Relative growth rate of leaf count trended 8.5% higher with K addition (P = 0.076).7. We also added micronutrients in a parallel experiment. There was no effect of micronutrient addition on any seedling parameter.8. Synthesis. K addition affected seedlings by enhancing tissue nutrient concentration, increasing herbivory, reducing root‐to‐shoot biomass ratio and increasing height growth. Additional effects of N or P on tissue chemistry, herbivory and growth offer support for the multiple limiting resources hypothesis. Our results suggest that seedling growth is limited by nutrients, especially K, even under highly shaded conditions in this lowland tropical forest.

Habitat fragmentation and haemoparasites in the common fruit bat,Artibeus jamaicensis(Phyllostomidae) in a tropical lowland forest in Panamá

Anthropogenic influence on ecosystems, such as habitat fragmentation, impacts species diversity and interactions. There is growing evidence that degradation of habitats favours disease and hence affects ecosystem health. The prevalence of haemoparasites in the Common Fruit Bat (Artibeus jamaicensis) in a tropical lowland forest in Panamá was studied. We assessed the relation of haemoparasite to the general condition of the animals and tested for possible association of haemoparasite prevalence to habitat fragmentation, with special focus on trypanosomes. Overall, a total of 250 A. jamaicensis sampled from fragmented sites, here man-made, forested islands in Lake Gatùn, and sites in the adjacent, continuous forest in and around the Barro Colorado Nature Monument were examined. Using microscopy and DNA-sequencing 2 dominant types of haemoparasite infections, trypanosomes and Litomosoides (Nematoda) were identified. Trypanosome prevalence was significantly higher in bats from forest fragments, than in bats captured in continuous forest. We attribute this to the loss of species richness in forest fragments and specific characteristics of the fragments favouring trypanosome transmission, in particular changes in vegetation cover. Interestingly, the effect of habitat fragmentation on the prevalence of trypanosomes as multi-host parasites could not be observed in Litomosoides which probably has a higher host specificity and might be affected less by overall diversity loss.

Assemblage‐level responses of phyllostomid bats to tropical forest fragmentation: land‐bridge islands as a model system

AbstractAim Working within a system of high structural contrast between fragments and the surrounding matrix, we assessed patterns of species loss and changes in species composition of phyllostomid bats on artificial land‐bridge islands relative to mainland assemblages, and evaluated the responses of bats to forest edges. We further examined the relative influence of local‐scale characteristics (e.g. vegetation structure, island area) versus landscape attributes (e.g. forest cover, patch density) and the importance of spatial scale in determining phyllostomid species richness and composition on islands.Location Islands in Gatún Lake and adjacent mainland peninsulas in the Barro Colorado Nature Monument, Panama.Methods Bats were sampled over a 2‐year period on 11 islands as well as at forest‐edge and interior sites on adjacent mainland, resulting in &gt; 8400 captures.Results The islands harboured a less diverse and structurally simplified phyllostomid bat fauna. Islands far from the mainland were especially species‐poor. This decline in species richness was associated with compositional shifts towards assemblages strongly dominated by frugivores with good dispersal abilities. Members of other ensembles, most importantly gleaning animalivores, were much less common or absent. Although overall species composition was not significantly altered, species richness at continuous forest‐edge sites was significantly lower compared with that at interior sites. Distance from the mainland and amount of forest cover in the landscape were the best predictors of species richness and assemblage composition. Responses were scale‐dependent. At the local scale, species richness was independent of island area but was correlated positively with distance from the mainland. In contrast, area effects became more important at larger spatial scales, suggesting that many species use multiple fragments.Main conclusions Our results underline the conservation value of small habitat remnants, which, even when embedded in a hostile matrix, can support a relatively diverse bat fauna, provided that there is a low degree of patch isolation and spatial proximity to larger tracts of continuous forest. Although the results at the assemblage level were inconclusive, we demonstrate that certain bat species and ensembles, particularly gleaning animalivores, exhibit high edge‐sensitivity. Our results point to habitat loss rather than changes in landscape configuration as the main process after isolation underlying phyllostomid bat responses, suggesting that conservation efforts should focus on habitat preservation instead of trying to minimize fragmentation per se at the expense of habitat amount.

Notes on the Reproductive Morphology of the Parasitic Bee Megalopta byroni (Hymenoptera: Halictidae), and a Tentative New Host Record

W 079.72997), in nearby secondary forests near Gamboa, and in the Barro Colorado Nature Monument. Nests were collected in the field, and opened in the laboratory to collect resident adults and brood. The metasoma of each parasite was preserved in formalin and later dissected under light microscopy. The number of ovarioles per ovary was counted, as well as the number of yellow bodies. The width of the largest ovariole and the width of the Dufour’s gland were measured using an ocular micrometer. Means are given with their standard deviations. In 2005 only 2.7% of 75 nests contained an adult parasite, and in 2006 none of the 114 nests were parasitized (overall parasitism rate, ,1%). The first parasite was found in late June (beginning of the wet season) in a nest with two M. ecuadoria females and three open and empty brood cells. Thus, the new host record is tentative until it is confirmed with rearing records. The second parasite was found in a nest of M. genalis in early August. The nest was inhabited by a single M. genalis female and there were no cells in the nest, so apparently it was in an early stage of construction. Almost nothing is known on the biology of M. byroni, and we do not know if it is a cleptoparasite or a social parasite. Given the social flexibility of the host bees (i.e., some bees are solitary and some social) (Wcislo et al., 2004), this classification might not fit at all, and host-parasite relationships might depend also on the social status of particular nests. These two potential host species, M. genalis and M. ecuadoria, are sympatric in Panama, which is the only locality record for M. byroni. Both parasites had three ovarioles per ovary, which is the plesiomorphic number for Halictidae, including parasitic forms (Rozen, 2003), and the width of the largest ovariole was 0.45 mm for both parasites. By comparison, the resident M. ecuadoria had a mean ovariole width of 0.75 mm, slightly larger than the M. ecuadoria population mean of 0.37 mm 6 0.16 (N 5 54) and the M. genalis population mean of 0.41 mm 6 0.18 (N 5 59). Furthermore, the first parasite, collected in June, had 12 yellow bodies, while the second one, collected in August, had only one. In contrast, the nestmates had no yellow bodies, and the M. ecuadoria population mean was 0.32 6 0.96 (N 5 54) yellow bodies, and 1.16 6 2.65 (N 5 59) for M.

The Bushmeat Harvest Alters Seedling Banks by Favoring Lianas, Large Seeds, and Seeds Dispersed by Bats, Birds, and Wind

ABSTRACTWe evaluated predictions that hunters favor lianas, large seeds, and seeds dispersed by bats, small birds, and mechanical means for seedling banks in central Panama. We censused 3201 trees in 20 1‐ha plots and 38,250 seedlings in the central 64 m2 of each plot. We found significant differences in the species composition of the seedling bank between nine protected sites in the Barro Colorado Nature Monument and 11 hunted sites in the contiguous Parque Nacional Soberanía. Lianas, species with large seeds, and species with seeds dispersed by bats, small birds, and mechanical means were all overrepresented at hunted sites. The latter two findings could also be evaluated relative to the species composition of reproductively mature adults for canopy trees. The tree species present in the seedling bank had significantly heavier seeds than the tree species present as adults at hunted sites but not at protected sites. The representation of seed dispersal modes among the species present in the seedling bank did not reflect pre‐existing differences in the local species composition of adults. We hypothesize that hunting large seed predators favors large seeds by reducing predation and increasing survival. We also hypothesize that the harvest of large birds and mammals that disperse many seeds favors other species whose seeds are dispersed by bats, small birds, and mechanical means. This process also favors lianas because the seeds of disproportionate numbers of liana species are dispersed by wind.

Activity Pattern of the Trawling Phyllostomid Bat, Macrophyllum macrophyllum, in Panamá1

ABSTRACTWe studied activity patterns of long‐legged bats, Macrophyllum macrophyllum (Phyllostomidae), in the Barro Colorado Nature Monument, Panamá, using radio‐telemetry. Activity of four males and five females equipped with radio‐transmitters were monitored for 4–7 entire nights each between April and July 2002. Bats exhibited maximum activity around dusk and high activity during the night. Males and females foraged for equal amounts of time in continuous flight (mean: 7 min, maximum 1 h) with interspersed resting phases (mean: 15 min, maximum 3 h). Activity of M. macrophyllum was sensitive to several factors. Time of emergence and return to day roost were correlated with time of sunset and sunrise, respectively. Maximum bat activity coincided with high abundance of aerial insects. Finally, heavy rain caused bats to reduce or cease flight activity. Direct observations and field video recordings support the assumption that M. macrophyllum employs two distinct foraging modes: trawling of insects from and capture of aerial insects at low heights above water. Combination of foraging modes gives M. macrophyllum high flexibility and efficiency in prey search. Activity, foraging mode, and morphology, which are similar to trawling bats from other families, distinguish M. macrophyllum from all other phyllostomid species and grant it access to open habitat above water, a habitat no other phyllostomid bat has conquered.

Nesting ecology of a neotropical solitary wasp (Hymenoptera: Sphecidae) in Panamá

Cerceris is a very interesting genus, providing species living in all continents, in different climatic conditions, showing behaviors ranging from solitary to social. About the nesting habit of this genus, many authors described nest characteristics and prey, providing useful material for comparison. Yet, the majority of species studied so far live in temperate regions and we lack information about the tropical ones. The high number of species and their wide distribution suggest a phylogenetic adaptability that merit to be studied deeper. I investigated nest and prey of a tropical species, Cerceris binodis Spinola, on Barro Colorado Nature Monument in Panamá. The study was performed during three dry seasons, marking and excavating nests, observing individual's behavior and collecting prey. The nests, reused over the same season and in following years, are especially deep as observed only in another neotropical species, Cerceris lutzi Scullen . This result could be correlated with tropical soils depth and characteristics. In spite of the species being sexually dimorphic, the subterranean cells show no bimodality in size or content. Prey, identified from specimens carried by provisioning females, belongs to Clytrinae (Coleoptera: Chrysomelidae). Quantitative data on prey are analyzed comparing seasons and sites and differences emerged. Cerceris adaptability to ecological trait of the tropics is inferred to explain these differences as well as the ones observed in the nest structure.

HOME-RANGE SIZE AND SPACING PATTERNS OF MACROPHYLLUM MACROPHYLLUM (PHYLLOSTOMIDAE) FORAGING OVER WATER

We studied home-range size and patterns of range use of long-legged bats, Macrophyllum macrophyllum (Phyllostomidae), at Barro Colorado Nature Monument, Panama, by using radiotelemetry. Movements of 4 males and 5 females fitted with radiotransmitters were monitored for 4–7 entire nights each between April and July 2002. M. macrophyllum had an extensive range compared to other similar-sized phyllostomid bats. Median home-range size for the 9 individuals tracked was 23.9 ha (range 7.3–150.7 ha). With a median of 17.3 ha (range = 7.3–24.9 ha), home ranges of males were somewhat, but not significantly, smaller than those of females (44.4 ha, range = 16.3–150.7 ha). The bats foraged exclusively over water, whereby hunting activity was restricted to the immediate shoreline of Gatun Lake. Foraging areas ranged from 2.7 to 96.1 ha, with a median of 12.3 ha for both sexes. In general, there was high night-to-night consistency in the use of foraging areas. Most bats had multiple foraging and core areas. Core-use areas corresponded to approximately 35% of the bats' foraging areas and were larger in females (median = 5.3 ha, range = 1.1–54.1 ha) than in males (3.3 ha, range = 2.6–8.7 ha). Maximum range span varied from 0.5 to 7.5 km, whereby males in general and 1 tracked harem male in particular foraged much closer to the day roost than did females. Individual M. macrophyllum traveled an estimated 35–47 km on a nightly basis, and females moved significantly greater distances than did males. Our results do not provide support for the proposition that small bats typically have small home ranges. In contrast, we conclude that foraging strategy, diet, dispersion of food resources, and wing morphology are generally better predictors of home-range size. Furthermore, reproductive condition, as well as intraspecific competition linked to colony size or social status, also strongly affect the spacing behavior and movement patterns of these bats. Our results suggest that, although M. macrophyllum employs a gleaning foraging strategy, it closely parallels aerial insectivorous bats in terms of range size and movement distances.

Effects of Understory Foliage on Patterns of Light Attenuation near the Forest Floor1

Understory light availability is an important component of the environment for canopy tree seedlings. Understanding what generates variation in understory light availability represents one step in understanding processes regulating seedling banks, the beginning capital of regeneration in tropical forests. Near the forest floor, variation in light availability may be strongly influenced by the structure and composition of the understory. I examined abundance of understory foliage and patterns of light attenuation in five Neotropical forests (La Selva Biological Station, Costa Rica = LS; Barro Colorado Nature Monument, Panama = BCI; Cocha Cashu Biological Station, Manu National Park, Peru = CC; Kilometer 41, Manaus, Brazil = KM41; and Nouragues, French Guiana = NG). I used hemispherical canopy photos to estimate light availability at two heights (0.65 and 1.7 m) above the forest floor and counted foliage between these heights. Light availability differed significantly among sites, and site rankings depended on measurement height. At 0.65 m, NG had significantly lower mean light availability than CC, with KM41, LS, and BCI equivalent and intermediate. At 1.7 m, light availability was still lowest at NG, and highest at CC, but LS had levels similar to CC while KM41 and BCI remained intermediate. Across sites, light attenuation was positively related to foliage density. LS had the most understory foliage and the highest light attenuation between 0.65 and 1.7 m. KM41, NG and CC had intermediate amounts of foliage and intermediate light attenuation. BCI had the lowest density of understory foliage and no difference between light at the two measurement heights. My results show significant effects of understory foliage on understory light and indicate that the selective environment of canopy tree seedlings differs among sites.

Regeneration niche partitioning in neotropical pioneers: effects of gap size, seasonal drought and herbivory on growth and survival.

Adaptive trade-offs underlie the specialisation that permits habitat partitioning in species rich plant communities. We investigated the influence of the trade-offs that determine differences in growth and survival among six species of neotropical pioneer trees in gaps in semideciduous forest in Panama. Seedlings of Miconia argentea, Cecropia insignis, Luehea seemannii, Trema micrantha, Ochroma pyramidale and Croton bilbergianus were planted into artificial small (25 m(2)), medium (64 m(2)) and large (225 m(2)) gaps in secondary forest in the Barro Colorado Nature Monument. Trema and Ochroma suffered >/=50% mortality across all gap sizes, while Cecropia had high mortality only during the dry season and in the small gaps, and Miconia and Croton suffered low to zero mortality across all environments. The highest growth rates in large gaps were attained by Cecropia seedlings and in the smaller gaps by Miconia seedlings, although there were indications that Trema and Ochroma required gaps that were larger than any used in this study. Variation in growth and mortality could not be attributed to differences in foliar herbivore damage. Instead, there was strong evidence of a trade-off between maximum growth in the wet season and the ability to survive seasonal drought, particularly in small gaps. We conclude that variation in allocation in response to multiple limiting resources may be as important as allocation to growth and defence in determining the habitat preferences of neotropical pioneers.

Changes in vegetation structure and composition along a tropical forest chronosequence: implications for wildlife

Changes in tropical forest structure and species composition that occur during regeneration following land abandonment may have important consequences for wildlife populations. Many animals rely on forest resources as sites for foraging, nesting, and protection that may vary in abundance in forests of different ages. In this study, we examined aspects of forest composition and structure thought to be important to wildlife along a tropical moist forest chronosequence in the Barro Colorado Nature Monument (BCNM) of central Panama. Secondary forests of approximately 20, 40, 70, and 100 years in fallow as well as two stands of old-growth forest (>500 years) were intensively studied. All stands were located on relatively fertile soils and were in close proximity to old-growth forest. Within 70 years following cessation of active management, many structural aspects of secondary forests resembled those of old-growth stands. Large living tree (≥65 cm diameter) density and coarse-woody debris volume increased with secondary forest age and were equivalent to old-growth levels by 70 years. Snag density and basal area did not differ with stand age. Species composition and availability of food resources in secondary forests did not converge on old-growth characteristics as quickly as most structural aspects, but many resources available to generalist frugivores were common across the chronosequence. Tree, but not liana, species composition of secondary stands became more similar to old growth with increasing forest age. Understory fleshy fruit availability was highest in young secondary stands, while importance values of trees and lianas with animal-dispersed fruits remained unchanged across the chronosequence. The importance of species particularly important to some frugivores, such as Ficus and Virola, had unpredictable distributions, but palm importance value increased with stand age. We suggest that young secondary forests may provide adequate nesting, foraging, and roosting resources for many animal taxa, but some populations of animals specializing on coarse-woody debris, large trees, or particular species of trees may be limited in secondary forest less than 70 years old.

Seed germination, seedling growth and habitat partitioning in two morphotypes of the tropical pioneer tree Trema micrantha in a seasonal forest in Panama

We examined the distribution, germination, growth and photosynthetic characteristics of two co-existing morphotypes of the pioneer tree Trema micrantha at the Barro Colorado Nature Monument (BCNM), Panama. Morphotypes differed significantly in distribution and in seed characteristics. A ‘large’-seeded morphotype (endocarp mass=3.83 mg) was associated with treefall gaps in the forest interior, whereas a ‘small’-seeded morphotype (endocarp mass=1.38 mg) was found predominantly on landslides on the margins of Lake Gatun. Seeds of the small-seeded morphotype germinated faster than seeds of the large-seeded morphotype, with seedlings of the small-seeded morphotype showing both a higher Unit Leaf Rate (ULR) and a lower Specific Leaf Area (SLA). Differences in photosynthetic rates reflected differences in SLA; the small-seeded morphotype had a higher rate on a leaf area basis, while the large-seeded morphotype had a higher rate on a leaf mass basis. Although allocation patterns between morphotypes varied in a way consistent with known interspecific differences between ‘sun’ and ‘shade’ plants, relative growth rates (RGR) of the morphotypes were similar across different light conditions suggesting that factors other than light, such as water uptake efficiency, soil nutrient requirements, and perhaps seed dispersal characters may explain the habitat partitioning of morphotypes.

Seed size, growth rate and gap microsite conditions as determinants of recruitment success for pioneer species

Summary 1 We examined how seed size and seedling growth rate influence recruitment success of neotropical pioneer species. We investigated the soil seed bank, and followed seedlings from emergence and establishment to the sapling stage in artificially created gaps in secondary forest on the Barro Colorado Nature Monument, Panama. 2 To simulate microsite variation within gaps, litter addition/removal and soil disturbance treatments were applied to seedling plots in a factorial design. 3 Seedling emergence was almost three-fold higher in litter-free plots than in control plots. 4 We found a negative relationship between seed mass and seed abundance in the soil, seed mass was positively correlated with seedling emergence success from the seed bank and with seedling survival through to the end of the first dry season. 5 In the 18 months following the first dry season we observed an uncoupling of seed mass from seedling performance. Seedling mortality was now a function of maximum relative growth rate, with higher mortality of fast-growing species attributable to herbivory, notably by shoot-borers. 6 We propose that a seed size-dependent trade-off between dispersal success (selecting for large seed number), and emergence‐establishment success (selecting for large seed size) can explain the maintenance of wide variation in seed size among pioneer species. Secondarily, a trade-off between growth rate and susceptibility to herbivores acting at the post-establishment phase may contribute to observed differences in light requirements among pioneer species.

Cuticles of Vascular Epiphytes: Efficient Barriers for Water Loss after Stomatal Closure?

Water permeabilities of astomatous, isolated cuticular membranes of 15 vascular epiphyte species (families: Araceae, Orchidaceae and Piperaceae) from the moist lowland forest of Barro Colorado Nature Monument, Panama, were investigated. Permeances determined at 30°C ranged from 0.46×10−6m s−1(Aspasia principissa(Rchb. f.) R.E. Schult.) to 6.07×10−6m s−1(Polystachya foliosa(Hook.) Rchb. f.). Comparison of these data with permeances of plants from other habitats corroborates the notion that cuticular properties reflect the climatic demands of the growing sites. The studied group of vascular epiphytes, living in a very drought-prone habitat, showed the lowest cuticular permeances to water recorded to date.