Diet of the Neotropical Otter,Lontra longicaudis,in an Atlantic Forest Area,Santa Catarina State,Southern Brazil

The diet of the neotropical otter (Carnivora, Mustelidae) was studied from September 1995 to March 1997, in Volta Velha, an Atlantic Forest reserve in the coastal plain of Santa Catarina State, southern Brazil. Fecal samples were collected monthly along the rivers Saí-Mirim, Braço do Norte and Volta Velha. Additionally, from October 1996 to June 1997, a qualitative and quantitative study of fish species available in the studied rivers was performed. The analysis of 202 collected fecal samples indicated a diet based on fish (mainly Hoplias malabaricus and Geophagus brasiliensis) and crustaceans (mainly Trichodactylus fluviatilis, a river crab), characterizing the neotropical otter as piscivorous-cancrivorous in the study area. The presence of fruits, reptiles, birds and mammals in the diet is occasional and opportunistic. Probably the higher consumption of a certain fish species compared to its availability and the high percentage of occurrence of T. fluviatilis in scats of the neotropical otter reflect their higher catchability.     

Spatial and Temporal Variation of Macroinvertebrate Drift in Two Neotropical Streams1

The detection of spatial variation in macroinvertebrate drift depends on the spatial scale of investigation in streams of the La Selva Biological Station, Costa Rica. Drift samples were taken in a spatially nested design, with two streams, two reaches per stream, two riffles per reach, and four replicate samples per riffle. Drift showed little variation among streams, but varied significantly at the scales of reach and riffle, with variation among samples also high. In addition, sampling took place at two temporal scales: diel and at two different periods that differed in rainfall conditions. Drift diel periodicity was a clear pattern, while only density of individuals varied among sampling periods. This is the first study of macroinvertebrate drift at multiple spatial scales, despite the recognition that multi‐scale studies are essential for a more complete understanding of community patterns and processes.     

Species Richness,Spatial Variation,and Abundance of the Soil Seed Bank of a Secondary Tropical Rain Forest1

Despite the importance of the soil seed bank in tropical forest regeneration, little is known about spatial variability in species composition and abundance of seeds stored in the soil. To develop sampling methods for comparative studies, we examined species richness, spatial variation, and abundance of germinants from the soil seed bank in a 16 year old secondary, tropical wet forest at La Selva Biological Station, Costa Rica. Surface soil (10 cm deep, 4.7 cm diameter) was collected at the intersection points of a gridded 1 ha plot (10 × 10-m grid, 121 samples) and in a nested 100 m² subplot (2 × 2-m grid, 36 samples). The 1 ha plot had a density of 4535 seeds/m² with 34 species observed. Based on a series of 100 randomized species accumulation curves, a Michaelis-Menten fit predicted a mean species richness of 36.3 species; the number of observed species was close to the predicted asymptote. A nonparametric, first-order jackknife species richness estimator predicted a species richness of 37.0 species. Eighty-five and 95 percent of the observed species richness is contained, on average, within 41 and 74 pooled samples, respectively. Within the 100 m² nested subplot, a density of 5476 seeds/m² was observed, comprising 26 species with an estimated species richness (Michaelis-Menten fit) of 29.1 species. The jackknife species richness estimator predicted a species richness of 36.7 species. For species richness and abundance of both plots, spatial autocorrelation statistics (Moran's I) were not significantly different from zero at lag distances from 2 to 100 m, indicating a random distribution at these spatial scales. For this site, accurate estimates of species composition depend upon the number of samples collected as well as the spatial distribution of sampling effort. Many small samples distributed over a large area provide greater accuracy and precision for estimating species richness of the soil seed bank.     

Evidence for a Novel Mutualism in the Tropical Understory Shrub Piper urostachyum1

We tested the impact of a predatory species of the family Miridae (Hemiptera) on its host plant Piper urostachyum (Piperaceae) by comparing folivory in mirid‐excluded plants and controls. We also tested the effect of resident anyphaenid spiders on mirid behavior and levels of folivory. Plants without mirids suffered significantly more folivory than plants with mirids. The impact of spider removal was less clear. Together, these results support the idea that resident mirids serve in anti‐herbivore defense for P. urostachyum plants.     

Arboreal substrates influence foraging in tropical ants

1. Physically complex substrates impart significant costs on cursorial central‐place foragers in terms of time spent outside the nest and total distance travelled. Ants foraging in trees navigate varied surfaces to access patchy resources, thus providing an appropriate model system for examining interactions between foraging efficiency and substrates. 2. We expected that the speed of recruitment, body size distribution and species richness of foraging arboreal ants would differ predictably among common substrate types occurring on tropical tree trunks. We measured changes in ant abundance and species composition over time at baits placed on bare tree bark, moss‐covered bark, and vine‐like vegetation appressed to bark. We also measured average body size and body size frequency on the three substrate types. Ants discovered baits sooner and accumulated at baits relatively faster when using vine substrates as the primary foraging trail. Average body size was smaller on vine substrates than on bark. Experimental removal of vine and moss substrates nullified these differences. Contrary to our predictions, species richness and body size distributions did not differ among the three substrate types, due in part to the frequent presence of a few common ground‐nesting species at baits on bare bark. 3. Our results collectively indicate that linear substrates facilitate access of foraging ants to patchy resources. Ant use of vine‐like substrates appears to be opportunistic; vine use is not confined to certain species nor constrained by body size.     

Small Tent-Roosting Bats Promote Dispersal of Large-Seeded Plants in a Neotropical Forest

In Neotropical regions, fruit bats are among the most important components of the remaining fauna in disturbed landscapes. These relatively small-bodied bats are well-known dispersal agents for many small-seeded plant species, but are assumed to play a negligible role in the dispersal of large-seeded plants. We investigated the importance of the small tent-roosting bat Artibeus watsoni for dispersal of large seeds in the Sarapiquí Basin, Costa Rica. We registered at least 43 seed species > 8 mm beneath bat roosts, but a species accumulation curve suggests that this number would increase with further sampling. Samples collected beneath bat feeding roosts had, on average, 10 times more seeds and species than samples collected 5 m away from bat feeding roosts. This difference was generally smaller in small, disturbed forest patches. Species-specific abundance of seeds found beneath bat roosts was positively correlated with abundance of seedlings, suggesting that bat dispersal may influence seedling recruitment. Our study demonstrates a greater role of small frugivorous bats as dispersers of large seeds than previously thought, particularly in regions where populations of large-bodied seed dispersers have been reduced or extirpated by hunting.     

Ant seed removal in a non-myrmecochorous Neotropical shrub: Implications for seed dispersal

This study investigated ant seed removal of Piper sancti-felicis, an early successional Neotropical shrub. Neotropical Piper are a classic example of bat-dispersed plants, but we suggest that ants are underappreciated dispersal agents. We identified eleven ant species from the genera Aphaenogaster, Ectatomma, Paratrechina, Pheidole, Trachymyrmex, and Wasmannia recruiting to and harvesting P. sancti-felicis seeds in forest edge and secondary forest sites at La Selva, Costa Rica. We also tested for differences in ant recruitment to five states in which ants can commonly encounter seeds: unripe fruit, ripe fruit, overripe fruit, bat feces, and cleaned seeds. Overall, ants harvested more seeds from ripe and overripe fruits than other states, but this varied among species. To better understand the mechanisms behind ant preferences for ripe/overripe fruit, we also studied how alkenylphenols, secondary metabolites found in high concentrations in P. sancti-felicis fruits, affected foraging behavior in one genus of potential ant dispersers, Ectatomma. We found no effects of alkenylphenols on recruitment of Ectatomma to fruits, and thus, these compounds are unlikely to explain differences in ant recruitment among fruits of different maturity. Considering that P. sancti-felicis seeds have no apparent adaptations for ant dispersal, and few ants removed seeds that were cleaned of pulp, we hypothesize that most ants are harvesting its seeds for the nutritional rewards in the attached pulp. This study emphasizes the importance of ants as important additional dispersers of P. sancti-felicis and suggests that other non-myrmecochorous, vertebrate-dispersed plants may similarly benefit from the recruitment to fruit by ants.     

Morphological and Molecular Evidence of Arbuscular Mycorrhizal Fungal Associations in Costa Rican Epiphytic Bromeliads1

Arbuscular mycorrhizal fungi influence the growth, morphology, and fitness of a variety of plant species, but little is known of the arbuscular mycorrhizal (AM) fungal associations of plant species in forest canopies. Plant species' associations with AM fungi are most often elucidated by examining the roots for fungal structures; however, morphological data may provide a limited resolution on a plant's mycorrhizal status. We combined a traditional staining technique with a molecular marker (the 18S ribosomal gene) to determine whether or not a variety of epiphytic bromeliads form arbuscular mycorrhizal fungal associations. Using these methods we show that the epiphytic bromeliad Vriesea werkleana forms arbuscular mycorrhizal fungal associations with members of the genus Glomus. AM fungal sequences of this plant species formed three distinct clades nested within a larger Glomus clade; two of the clades did not group with any previously sequenced lineage of Glomus. Novel clades may represent novel species. Although Vriesea werkleana is associated with multiple AM fungal species, each individual plant is colonized by a single lineage. The combination of morphological and molecular methods provides a practical approach to the characterization of the mycorrhizal status of epiphytic bromeliads, and perhaps other tropical epiphytes.     

Controls Over Leaf Litter and Soil Nitrogen Fixation in Two Lowland Tropical Rain Forests

Global comparisons suggest that rates of N fixation in tropical rain forests may be among the highest on earth. However, data supporting this contention are rare, and the factors that regulate N fixation within the biome remain largely unknown. We conducted a full-factorial (N × P) fertilization experiment in two lowland tropical rain forests in Costa Rica to explore the effects of nutrient availability on rates of free-living N fixation in leaf litter and soil. P fertilization significantly increased N fixation rates in both leaf litter and soil, and the effect was dependent on sampling date. Fertilization with N did not affect rates of N fixation at any time. In addition, variation in N fixation rates measured in unfertilized plots at four sampling time points suggested seasonal variability in N fixation: leaf litter N fixation ranged from 0.36 kg/ha/yr in the dry season to 5.48 kg/ha/yr in the wet season. Soil N fixation showed similar patterns ranging from a dry season low of 0.26 kg/ha/yr to a wet season high of 2.71 kg/ha/yr. While the observed temporal variability suggests potential climatic control over free-living N fixation in these forests, data suggest that neither soil nor leaf litter moisture alone regulate N fixation rates. Instead, we hypothesize that a combination of ample C availability, low leaf litter N:P ratios, and high rainfall coincide during the latter portions of the rainy season and drive the highest free-living N fixation rates of the year.     

Retention of Inorganic Nitrogen by Epiphytic Bryophytes in a Tropical Montane Forest1

We developed and evaluated a model of the canopy of a tropical montane forest at Monteverde, Costa Rica, to estimate inorganic nitrogen (N) retention by epiphytes from atmospheric deposition. We first estimated net retention of inorganic N by samples of epiphytic bryophytes, epiphyte assemblages, vascular epiphyte foliage, and host tree foliage that we exposed to cloud water and precipitation solutions. Results were then scaled up to the ecosystem level using a multilayered model of the canopy derived from measurements of forest structure and epiphyte mass. The model was driven with hourly meteorological and event‐based atmospheric deposition data, and model predictions were evaluated against measurements of throughfall collected at the site. Model predictions were similar to field measurements for both event‐based and annual hydrologic and inorganic N fluxes in throughfall. Simulation of individual events indicated that epiphytic bryophytes and epiphyte assemblages retained 33–67 percent of the inorganic N deposited in cloud water and precipitation. On an annual basis, the model predicted that epiphytic components retained 3.4 kg N ha/yr, equivalent to 50 percent of the inorganic N in atmospheric deposition (6.8 kg N ha/yr). Our results indicate that epiphytic bryophytes play a major role in N retention and cycling in this canopy by transforming highly mobile inorganic N (ca. 50% of atmospheric deposition is NO^?₃) to less mobile (exchangeable NH⁺₄) and recalcitrant forms in biomass and remaining litter and humus.     

Variation in Seedling Density and Seed Predation Indicators for the Emergent Tree Dipteryx panamensis in Continuous and Fragmented Rain Forest1

Seedling density and the condition of stony endocarps of the tree Dipteryx panamensis were assessed in protected continuous forest and two forest fragments exposed to hunting and selective logging. Seedling density was higher in forest fragments than in continuous forest, while more whole endocarps and fewer chewed and half endocarps were found in fragments, indicating lower seed predation at fragment sites. These findings appear to contradict two earlier D. panamensis studies and we discuss methodological differences that could account for our disparate results. Hunting and fragmentation effects on mammal populations are suggested as a cause for the altered recruitment pattern in fragments.     

Studies in Neotropical paleobotany. XII. A palynoflorafrom the Pliocene Rio Banano Formation of Costa Rica and the Neogenevegetation of Mesoamerica

An assemblage of 17 identified and four unknown pollen and sporetypes is reported from the Pliocene Rio Banano Formation of southeasternCosta Rica. The most abundant are monolete fern spores, Palmae, cf.Antrophyum, Symphonia, Pelliceria,Lacmella (previously unreported in the fossil record),Alchornea, and Sabicea. These arrange into twopaleocommunities-mangroves and lowland tropical rain forest. Annual precipitation is estimated at near the present ～3500 mm, butless seasonal, and the MAT (mean annual temperature) at ～27°C. No pollen taxa representing distinctly arid or high-altitude vegetationwas being blown or washed into the coastal depositional basin, and nopollen grains were recovered of northern temperate elements that arepresent in Neogene floras to the north in Guatemala and southeasternMexico. These data are consistent with those from 12 other Miocene andPliocene palynofloras from northern Latin America, indicating the lateappearance of dry habitats and moderate paleoelevations and aprogressive southward introduction of northern temperate elements withlate Cenozoic cooling.     

Distress Calls of Birds in a Neotropical Cloud Forest1

Distress calls are loud, harsh calls given by some species of birds when they are captured by a predator or handled by humans. We recorded the frequency of distress calls and struggling behavior in 40 species of birds captured in mist nets during the dry season in a Costa Rica cloud forest. We tested the following hypotheses proposed to explain the function of distress calls: (1) calling for help from kin or reciprocal altruists; (2) warning kin; (3) eliciting mobbing behavior; (4) startling the predator; and (5) distracting the predator through attraction of additional predators. Our results did not support the calling‐for‐help, warning kin, or mobbing hypotheses. Indeed, genera that regularly occurred with kin or in flocks were not more likely to call than non‐flocking genera. There was no relationship between calling frequency and struggling behavior as predicted by the predator startle hypothesis. Genera of larger birds tended to call more than smaller birds, providing some support for both the predator distraction hypothesis and predator startle hypotheses. Calls of higher amplitude may be more effective in startling the predator. Distress calls of larger birds may also travel greater distances than those of smaller birds, supporting the predator manipulation hypothesis, but this requires further testing.     

Fallen Branches as Part of Leaf-Cutting Ant Trails: Their Role in Resource Discovery and Leaf Transport Rates in Atta cephalotes

Fallen branches, logs, and exposed roots (fallen branches hereafter) commonly form part of the trunk trail system of leaf-cutting ants that inhabit the tropical rain forest. We studied the role of fallen branches on resource discovering and on leaf transport rates in Atta cephalotes . Fallen branches were common components of the A. cephalotes trail system; they were present in all the nests, and in the majority of the trunk trails examined (13/16). A field experiment revealed that, at the beginning of their foraging activity, ants discovered food sources located at the end of fallen branches earlier than those located on the leaf litter. Additionally, laden ants walked faster along a fallen branch than along soil tracks of the trunk trails. This increment in speed was higher in slow-walking ants ( e.g. , with larger loads) than in fast-walking ants ( e.g. , with smaller loads). These results suggest that the presence of fallen branches may direct the searching effort of leaf-cutters and increase the foraging speed of laden ants when these structures are part of the trunk trail system. The advantages of using fallen branches as part of a trail system, and their potential consequences in the spatial foraging pattern of leaf-cutting ants, are discussed.     

Ecology of Foliicolous Lichens at the “Botarrama” Trail (Costa Rica), a Neotropical Rain Forest. I. Species Composition and its Ecogeographical Implications1

A total of 217 species of typically foliicolous lichens were found at the “Botarrama” trail, a premontane rain forest in the Braulio Carrillo National Park, Costa Rica. The species composition confirmed the classification of this study sice as transitional between lowland wet and montane rain forest. In terms of species tichness, the foliicolous lichen flora was dominated by the families Gomphillaceae (Calenia, Echinoplaca, Gyalideopsis, and Tricharia), Trichotheliaceae (Porina and Tricbothelium), and Pilocarpaceae (Byssoloma and Fellhanera). The most frequent species were Porina mirabilis (including its supposed anamorph Phyllophiale alba), Gyalectidium filicinum, Porina rufula, and Strigula platypoda. A large proportion of the species was rare. Frequency distributions based on area cover corresponded well to general community models by closely fitting a log-normal approximation. Half of the species had narrow ecological amplitudes while more than 70 percent exhibited a wide geographical distribution, thus making che study site representative of a Neotropical rain forest. The use of foliicolous lichens as indicators of altitudinal zonation is discussed.     

Secondary Forest Detection in a Neotropical Dry Forest Landscape Using Landsat 7 ETM+ and IKONOS Imagery1

We integrate forest structure and remotely sensed data for four successional stages (pasture, early, intermediate, and late) of a tropical dry forest area located in the Sector Santa Rosa of the Guanacaste Conservation Area in northwestern Costa Rica. We used a combination of spectral vegetation indices derived from Landsat 7 ETM+ medium resolution and IKONOS high‐resolution imagery. The indices (using the red and near‐infrared bands) simple ratio and normalized difference vegetation index separated the successional stages well. Two other indices using mid‐infrared bands did not separate successional stages as well. In a comparison of the successional stages with chronological age, there was no separability in the spectral reflectance among different age classes. Successional stages, in contrast, showed distinct groups with minimal overlap. We also applied a simple validation in another dry forest located in the Palo Verde National Park in the province of Guanacaste, Costa Rica, with reasonably good results.