Costa Rican Lowland Rain Forest Research Articles

Distribution and photosynthetic assimilation of rosulate aroid epiphytes in a Costa Rican lowland rainforest

Relatively few studies are available to characterize the distribution, abundance and ecophysiology of aroid epiphytes, distinct from aroid hemiepiphytes which are more common and abundant. The rosulate growth form is restricted to a relatively small number of aroid species. Field and experimental growth studies and ecophysiological measurements on rosulate aroids were carried out at La Selva Biological Station in the premontane rainforest of the Atlantic lowlands of Costa Rica. Rosulate aroids occur in habitats from forest understory to high canopy, and from old growth wet forest to secondary forest in Costa Rica. The distribution of rosulate and acaulescent aroid epiphytes were determined in multiple stands of old growth and secondary tropical forests at La Selva. Anthurium upalense and Philodendron wendlandii exhibited a preference for upper canopies on trees over 50 cm dbh where irradiance levels are high for much of the day. Anthurium consobrinum and A. bakeri occurred lower in the canopy in more shaded positions. To evaluate how these habitat preferences are related to plant traits, controlled shadehouse growth experiments were conducted to characterize species response to different ambient light environments. We applied conditions of high light (50% full sun), medium light (10% full sun), and low light (2% full sun) to simulate a gradient of canopy and understory light environments. Anthurium consobrinum and A. bakeri exhibited photosynthetic traits characteristic of shade-adapted understory epiphytes. In contrast, A. upalense and Ph. wendlandii, typically high canopy species, had maximum photosynthetic rates of 10.5 and 8.7 µmol m−2 s−1, respectively, higher than those previously reported for other vascular epiphytes. The variability in distribution of epiphytic aroids in Costa Rican premontane rainforest is consistent with their diversity of ecological and ecophysiological traits demonstrating adaptation to diverse canopy habitats in this aroid growth form.

Chamber measurements of high CO2 emissions from a rainforest stream receiving old C-rich regional groundwater

Carbon emissions from fluvial systems are a key component of local and regional carbon cycles. We used floating chambers to investigate the CO2 flux from stream water to air (\({\text{f}}_{{{\text{CO}}_{ 2} }}\)) in the Arboleda, a stream in the lowland rainforest of Costa Rica, fed partly by old regional groundwater high in dissolved inorganic carbon (DIC). Drifting and static chambers showed \({\text{f}}_{{{\text{CO}}_{ 2} }}\) averaging 35.5 and 72.7 μmol C m−2 s−1, respectively, bracketing the previously-published \({\text{f}}_{{{\text{CO}}_{ 2} }}\) value of 56 μmol C m−2 s−1 obtained using tracer methods in this stream. These values are much higher than most \({\text{f}}_{{{\text{CO}}_{ 2} }}\) data in the literature and reflect a large flux of deep crustal (non-biogenic) CO2 out of the Arboleda, a flux that does not represent a component of ecosystem respiration. Static chambers appeared to overestimate \({\text{f}}_{{{\text{CO}}_{ 2} }}\) by creating artificial turbulence, while drifting chambers may have underestimated \({\text{f}}_{{{\text{CO}}_{ 2} }}\) by under-sampling areas of potentially high gas exchange (e.g., riffles around coarse woody debris obstructions). Both static and drifting chambers revealed high spatial heterogeneity in \({\text{f}}_{{{\text{CO}}_{ 2} }}\) at the scale of 5–30 m reaches. Some observed temporal trends were localized, e.g., among three reaches with repeated measurements through the wet and dry seasons, (1) only the reach located between the other two showed significantly lower \({\text{f}}_{{{\text{CO}}_{ 2} }}\) during the dry season, and (2) the highest and lowest \({\text{f}}_{{{\text{CO}}_{ 2} }}\) were consistently observed in the reaches farthest upstream and downstream, respectively. Streams like the Arboleda receiving significant inputs of high-DIC regional groundwater merit additional study as hotspots for C emissions from terrestrial ecosystems.

Differences in topographic and soil habitat specialization between trees and two understorey plant groups in a Costa Rican lowland rain forest

Abstract:Two core questions in plant community ecology are to what extent the distributions of species are structured by local environmental conditions, and whether taxa differ in this regard. We compared the distributions of trees, Melastomataceae and ferns on soil and topographic gradients in a Costa Rican lowland rain forest (trees and ferns 983 plots, Melastomataceae 277 plots). To test whether these plant groups differed in the prevalence or type of habitat specialization, we calculated species’ environmental optima and tolerances on each gradient. Habitat specialization was defined as a significantly biased optimum, or a narrow tolerance, relative to values obtained under spatially restricted randomizations of species occurrences. Within plant groups, we also asked whether the dispersion of species optima differed from random expectation on each gradient. Fern optima were over-dispersed on multiple gradients, implying considerable interspecific habitat partitioning, and tree optima were over-dispersed in relation to topographic position. Habitat specialization was more prevalent in the two predominantly understorey groups than in trees (75% of Melastomataceae species, 81–87% of ferns, 57–58% of trees). Species optima of Melastomataceae and ferns also tended towards lower landscape positions than did those of trees, perhaps reflecting a higher proportion of drought-sensitive species in these two groups.

Diet and foraging behavior of a female Baird’s tapir (Tapirus bairdi) in a Costa Rican lowland rainforest

The Baird’s tapir (Tapirus bairdii) is an endangered neotropical species which has little field research to guide its conservation efforts. For this reason, the diet and foraging activity of a free ranging female was observed for 286 hrs. from June 1995 to April 1996 in Corcovado National Park, Costa Rica. She consumed 126 plant species (percents: 35.2 vines, 34.1 trees, 15.9shrubs, 14.8 herbs). Three plant genera accounted for 40% of her diet for the entire study: Monstera sp. (Areaceae), Persea sp. (Lauraceae), and Psychotria sp. (Rubiaceae). Her food consisted of 67.0% leaf matter, 18.6% fruit, 11.7% stem, 2.1% bark and 0,1% flower. More fruit and bark were consumed in the wet season and more stem in the dry season. Average time spent feeding was 29.7%, standing chewing 33.4%, moving chewing 7.6%, standing not chewing 5.7%, moving not chewing 20.1% and in social encounters 2.1%. In the wet season more time was spent feeding and chewing while moving and less time moving without chewing. Means for number of paces and bites in ten minute periods were 42,9 and 49,7 respectively. More paces and bites were recorded in the wet season. Average biomass consumed per bite (dry wt.) over a three month period was 3.32 g, for a yearly estimate of 4,307 Kg of dry mass. For an estimate of 200 tapirs in the park, total biomass consumed would be about 861,400 Kg yearly. The tapir is an important mammal in the dynamics of neotropical forests for its roles as keystone browser and potential seed disperser.

Systematics and biology of mites associated with neotropical hispine beetles in unfurled leaves of Heliconia, with descriptions of two new genera of the family Melicharidae (Acari: Mesostigmata: Gamasina: Ascoidea).

Two new genera Makarovaia and Hispiniphis are described from adults and immatures of newly described species associated with hispine beetles of the genera Chelobasis and Cephaloleia, respectively, occupying unfurled leaves of Heliconia in lowland rainforest of Costa Rica. The new genera share a suite of unique morphological attributes, but are tentatively assigned to the family Melicharidae. While all instars of the mites can be found under the elytra of their adult beetle hosts, adult mites also move freely on and off the beetles. A new form of laboulbeniaceous fungus of the genus Rickia is frequently associated with adult mites of Makarovaia as well as their beetle hosts, yet evidently rarely with mites of a species of Hispiniphis or its beetle hosts which may co-occupy the same host leaves. Limited data suggest considerable host specificity between mites and their beetle hosts. Whether the association of these mites with hispine beetles may be ancient, prior to the beetles' adaptation to living in unfurled leaves of host plants, or is a more recent invasion and partitioning of the rolled leaf beetle fauna, is discussed.

Functional constraints on the evolution of long butterfly proboscides: lessons from Neotropical skippers (Lepidoptera: Hesperiidae).

Extremely long proboscides are rare among butterflies outside of the Hesperiidae, yet representatives of several genera of skipper butterflies possess proboscides longer than 50 mm. Although extremely elongated mouthparts can be regarded as advantageous adaptations to gain access to nectar in deep-tubed flowers, the scarcity of long-proboscid butterflies is a phenomenon that has not been adequately accounted for. So far, the scarceness was explained by functional costs arising from increased flower handling times caused by decelerated nectar intake rates. However, insects can compensate for the negative influence of a long proboscis through changes in the morphological configuration of the feeding apparatus. Here, we measured nectar intake rates in 34 species representing 21 Hesperiidae genera from a Costa Rican lowland rainforest area to explore the impact of proboscis length, cross-sectional area of the food canal and body size on intake rate. Long-proboscid skippers did not suffer from reduced intake rates due to their large body size and enlarged food canals. In addition, video analyses of the flower-visiting behaviour revealed that suction times increased with proboscis length, suggesting that long-proboscid skippers drink a larger amount of nectar from deep-tubed flowers. Despite these advantages, we showed that functional costs of exaggerated mouthparts exist in terms of longer manipulation times per flower. Finally, we discuss the significance of scaling relationships on the foraging efficiency of butterflies and why some skipper taxa, in particular, have evolved extremely long proboscides.

Symbiont polyphyly, co-evolution, and necessity in pentatomid stinkbugs from Costa Rica.

Interdomain symbioses with bacteria allow insects to take advantage of underutilized niches and provide the foundation for their evolutionary success in neotropical ecosystems. The gut microbiota of 13 micro-allopatric tropical pentatomid species, from a Costa Rican lowland rainforest, was characterized and compared with insect and host plant phylogenies. Like other families within the Pentatomomorpha, these insects (within seven genera—Antiteuchus, Arvelius, Edessa, Euschistus, Loxa, Mormidea, and Sibaria) house near-monocultures of gamma-proteobacteria in midgut crypts, comprising three distinct lineages within the family Enterobacteriaceae. Identity of the dominant bacteria (78–100% of the recovered 16S rRNA genes) was partially congruent with insect phylogeny, at the level of subfamily and tribe, with bacteria closely related to Erwinia observed in six species of the subfamily Pentatominae, and bacteria in a novel clade of Enterobacteriaceae for seven species within the subfamilies Edessinae and Discocephalinae. Symbiont replacement (i.e., bacterial “contamination” from the environment) may occur during maternal transmission by smearing of bacteria onto the egg surfaces during oviposition. This transmission strategy was experimentally confirmed for Sibaria englemani, and suspected for four species from two subfamilies, based on observation of egg probing by nymphs. Symbiont-deprived S. englemani, acquired via egg surface sterilization, exhibited significantly extended second instars (9.1 days compared with 7.9 days for symbiotic nymphs; p = 0.0001, Wilcoxon's rank with Bonferroni correction), slower linearized growth rates (p = 0.005, Welch 2-sample t-test), and qualitative differences in ceca morphology, including increased translucency of crypts, elongation of extracellular cavities, and distribution of symbionts, compared to symbiotic nymphs. Combined, these results suggest a role of the symbiont in host development, the reliable transference of symbionts via egg surfaces, and a suggestion of co-evolution between symbiont and tropical pentatomid host insects.

Seasonal cycles of diversity and similarity in a Central American rainforest butterfly community

Despite the importance of understanding the effects of tropical seasonality on ecological diversity, few studies have investigated the influence of environmental factors on seasonal community composition, and even fewer use standardized sampling and robust analytical methods that are directly comparable. Our 104 months of sampling in Costa Rican lowland rainforest yielded 12 757 individuals of 106 fruit‐feeding butterfly species demonstrated biannual cycles in species diversity, but community similarity showed an annual cycle that peaked in the driest months. We found that community diversity and similarity did not decline with increasing time lag, which we attribute to lack of long‐term changes in species abundances. Our findings differ from a similar study in Ecuador, where cycles in weather and community diversity were annual. Long‐term intensive monitoring and robust statistical analysis of changes in community composition in relation to environmental factors can help to elucidate the dynamics of communities, and their response to climate change.

Mites coexistent with neotropical hispine beetles in unfurled leaves of Heliconia: a new genus and family of the Ascoidea (Acari: Mesostigmata: Gamasina)

The genus Antennocheles gen. nov. is based on adults and nymphs of two newly described species associated with hispine beetles of the genera Chelobasis and Cephaloleia occupying unfurled leaves of Heliconia in lowland rainforest of Costa Rica. Within the superfamily Ascoidea, this taxon is so distinctive morphologically and behaviourally as to justify its own family, Antennochelidae, fam. nov. These mites bear remarkably elongated cheliceral shafts, which may extend for lengths greater than the body but are fully ensheathed in repose within the body. Other unique attributes include linear arrangement of hypostomatic setae, a pore-like structure beside the corniculus, and adults with a pair of unique sternal invaginations for enlarged muscle insertions. While undergoing their life history in water films of unfurled host leaves, the mites exhibit a slow, swimming-like behaviour in quest for prey. As leaves unfurl, adult mites run quickly off and on their hispine beetle phoronts for dispersal.http://zoobank.org/urn:lsid:zoobank.org:pub:0876014C-1433-463B-B1A4-4CD6886F9D28

Habitat use in an assemblage of Central American wandering spiders

The sympatric occurrence of species is thought to be based mainly on the differences in their use of habitat and of limiting resources. Segregating parameters may be of spatial or temporal character and may include behavioral differences. We hypothesized that species of large hunting spider living sympatrically in a Costa Rican lowland rain forest should differ in their habitat and/or hunting microhabitat preferences, in daily activity pattern, and, as an adaptation to the preferred hunting microhabitat, in their specific ability to adhere to smooth surfaces. We found an assemblage of eight large species of the families Ctenidae and Trechaleidae, consisting of three subguilds: 1) two semi-aquatic species with low adhesion ability, 2) three forest-floor dwelling species with good adhesion ability, and 3) three vegetation dwelling species showing very good adhesion ability. The species were partially segregated by habitat type, with two of the vegetation dwelling species preferring the treeless area of a temporary swamp. We found no species-specific differences in daily activity patterns. The similarity in community structure between this Costa Rican and a central Amazonian assemblage suggests the existence of similar structuring mechanisms in wandering spider assemblages in climatically similar biomes.

Ants accelerate litter decomposition in a Costa Rican lowland tropical rain forest

Abstract:The decomposition of leaf litter is governed, in part, by litter invertebrates. In tropical rain forests, ants are dominant predators in the leaf litter and may alter litter decomposition through the action of a top-down control of food web structure. The role of ants in litter decomposition was investigated in a Costa Rican lowland rain forest with two experiments. In a mesocosm experiment, we manipulated ant presence in 50 ambient leaf-litter mesocosms. In a litterbag gradient experiment, Cecropia obtusifolia litter was used to measure decomposition rate constants across gradients in nutrients, ant density and richness, with 27 separate litterbag treatments for total arthropod exclusion or partial arthropod exclusion. After 2 mo, mass loss in mesocosms containing ants was 30.9%, significantly greater than the 23.5% mass loss in mesocosms without ants. In the litter bags with all arthropods excluded, decomposition was best accounted by the carbon: phosphorus content of soil (r2 = 0.41). In litter bags permitting smaller arthropods but excluding ants, decomposition was best explained by the local biomass of ants in the vicinity of the litter bags (r2 = 0.50). Once the microarthropod prey of ants are permitted to enter litterbags, the biomass of ants near the litterbags overtakes soil chemistry as the regulator of decomposition. In concert, these results support a working hypothesis that litter-dwelling ants are responsible for accelerating litter decomposition in lowland tropical rain forests.

Food resources influence spatial ecology, habitat selection, and foraging behavior in an ambush-hunting snake (Viperidae: Bothrops asper): an experimental study

Prey availability affects many aspects of predators’ life history and is considered a primary factor influencing individuals’ decisions regarding spatial ecology and behavior, but few experimental data are currently available. Snakes may represent ideal model organisms relative to other animal groups for addressing such resource dependency, due to a presumably more direct link between food resources and many aspects of behavior and natural history. We experimentally investigated the relationship between food intake and spatial behavior in a population of the snake Bothrops asper in a Costa Rican lowland rainforest. Six adult snakes were allowed to forage naturally while six were offered supplemental food in the field, with both groups monitored using radiotelemetry. Mean home range size did not differ between groups presumably due to small sample size, but supplementally fed snakes demonstrated altered patterns of macro- and microhabitat selection, shorter and less frequent movements, and increased mass acquisition. Fed snakes also devoted less time to foraging efforts, instead more frequently remaining inactive and utilizing shelter. Because snakes were always fed in situ and not at designated feeding stations, observed shifts in habitat selection are not explained by animals simply moving to areas of higher food availability. Rather, B. asper may have moved to swamps in order to feed on amphibians when necessary, but remained in preferred forest habitat when food was otherwise abundant. The strong behavioral and spatiotemporal responses of snakes in this population may have been influenced by an overall scarcity of mammalian prey during the study period.

Hematological Survey of Common Neotropical Bat Species from Costa Rica

Although bats are one of the largest groups within the class Mammalia and may carry several zoonotic diseases, basic information about their hematology is limited. In this study, hematocrit (Hct), total white blood cell counts (TWBC; leukocytes), and differential white blood cell counts (DWBC) of free-ranging Neotropical bats were quantified. Blood samples from 255 bats representing 26 species from the families of Emballonuridae (3 species; 33 individuals), Molossidae (2 species; 26 individuals), Mormoopidae (1 species; 1 individual), Phyllostomidae (18 species; 180 individuals), and Vespertilionidae (2 species; 15 individuals) were collected in a Caribbean lowland rainforest of Costa Rica. Hct was measured after centrifugation of microhematocrit capillaries, TWBCs were performed using the Unopette system and a hemocytometer, and DWBCs were performed on eosin methylene blue stained blood films. Hct of bats ranged between 51.8 +/- 0.7% for Phyllostomus discolor (n = 27) and 65.8 +/- 2.2% for Molossus sinaloae (n = 6). Bat species of the same taxonomic family had comparable TWBCs; these were lower for insectivorous emballonurid, molossid, and vespertilionid bat species than for mostly phytophagous phyllostomid bat species. However, Ectophylla alba (Phyllostomidae) exhibited exceptionally low TWBCs (836 +/- 166 /microl; n = 10); this was less than half of the TWBCs of all other bat species, which ranged from 1,714 +/- 297/microl for Molossus bondae (n = 20) to 7,339 +/- 1,503/microl for Trachops cirrhosus (n = 6). Species with higher TWBCs tended to have lower Hct values. Overall, blood cell morphology was similar to other mammalian species. A large number of polychromatophilic erythrocytes and differences in lymphocyte morphology were noted. This study provides important hematological values for Neotropical bat species and significantly expands the knowledge on basal physiological measurements of Chiroptera.

Resource landscape and spatio‐temporal activity patterns of a plant‐visiting bat in a Costa Rican lowland rainforest

We studied the home-range size and activity patterns of brown long-tongued bats Glossophaga commissarisi (Phyllostomidae) in the lowland rainforest of Costa Rica and related this to local nectar and fruit resource distribution. Home ranges were determined using radiotelemetry and food plants within were mapped. Within home ranges of 12.5 ± 6.7 ha, G. commissarisi used mainly small foraging areas of 3.0 ± 1.0 ha. Spatial use within foraging areas correlated for most bats with nectar and fruit resource density. Flight time and duration of flight phases were significantly lower for individuals feeding in a clearing with high abundance of nectar resources compared with those feeding in secondary rainforest with a lower nectar resource density. Our results indicate that G. commissarisi closely matches its flight activity to the available resource distribution.

Activity Patterns of a Neotropical Ambush Predator: Spatial Ecology of the Fer‐de‐lance (Bothrops asper, Serpentes: Viperidae) in Costa Rica

ABSTRACTPatterns of movement and space usage are important components of the ecology of any organism. Among snakes, this information is often lacking even for species that are abundant, ecologically important, and/or relevant to human health. We used radiotelemetry to examine the spatial ecology and behavior of the fer‐de‐lance (Bothrops asper), a highly venomous pit viper that is ubiquitous throughout much of Central America. Sixteen adult snakes were tracked over 2 yr in lowland rainforest of Costa Rica to determine home range, movement patterns, and foraging behavior. Consistent with previous descriptions, B. asper was found to be a highly nocturnal ambush predator, exhibiting virtually no activity during the day. Overall home range was determined using both minimum convex polygon (mean size = 5.95 ha) and 95 and 50 percent kernel density (mean size = 3.71 and 0.370 ha, respectively); home range size did not differ between males and females by any estimation method. Movement pattern was largely aseasonal and unrelated to any observed environmental conditions other than the daily low temperature. Most movements consisted of short (< 10 m) movements between daytime shelter and nocturnal ambush sites within a given area, interspersed with longer distance (> 50 m) movements to new foraging areas. Compositional analysis of habitat usage indicated an avoidance of developed areas and selection of swamp habitat. Most snakes had several activity cores (50% kernel density), the majority which were in or near swamps. These patterns suggest that space and habitat usage of fer‐de‐lance may be related to foraging strategy.

Nesting Success of Costa Rican Lowland Rain Forest Birds in Response to Edge and Isolation Effects

ABSTRACTAlthough open‐cup nesting birds generally face increased risk of nest depredation from forest edge predators and brood parasites in fragmented temperate landscapes, little information exists to assess such risks in tropical birds. We compared nesting success of real birds' nests in large and small forest fragments to a control site in Caribbean lowland wet forest of Costa Rica. Pooling across species, nesting success was significantly greater in unfragmented forest than in either small, isolated fragments or the La Selva Biological Reserve, which is at the tip of a forest ‘peninsula’ embedded in a largely deforested landscape. Nesting success in isolated fragments did not vary according to distance from edge, suggesting that predators in fragments act throughout these forest patches. The case for increased nest predation as a plausible mechanism to explain the documented decline of forest interior bird populations in this fragmented tropical landscape is enhanced by a simple demographic model that suggests nesting success is likely too low to maintain populations at La Selva and in the fragments. The fact that the large (> 1000 ha) La Selva forest reserve is experiencing nest predation rates similar to those in much smaller fragments is cause for concern. Our results make a strong case for additional studies to document the identities of nest predators in both fragmented and unfragmented forests in such tropical forest landscapes.

Nitrogen fixation by phyllosphere bacteria associated with higher plants and their colonizing epiphytes of a tropical lowland rainforest of Costa Rica

Leaf surfaces (phyllospheres) have been shown to provide appropriate conditions for colonization by microorganisms including diazotrophic bacteria that are able to fix atmospheric nitrogen (N(2)). In this study, we determined leaf-associated N(2) fixation of a range of rainforest plants in Costa Rica, under different environmental conditions, by tracing biomass N incorporation from (15)N(2). N(2)-fixing bacterial communities of the plant species Carludovica drudei, Grias cauliflora and Costus laevis were investigated in more detail by analysis of the nifH gene and leaf-associated bacteria were identified by 16S rRNA gene analysis. N(2) fixation rates varied among plant species, their growth sites (different microclimatic conditions) and light exposure. Leaf-associated diazotrophic bacterial communities detected on C. drudei and C. laevis were mainly composed of cyanobacteria (Nostoc spp.), whereas on the leaves of G. cauliflora gamma-proteobacteria were dominant in addition to cyanobacteria. The complexity of diazotrophic communities on leaves was not correlated with N(2) fixation activity. 16S rRNA gene sequence analysis suggested the presence of complex microbial communities in association with leaves, however, cyanobacteria showed only low abundance. Our findings suggest that cyanobacteria as well as gamma-proteobacteria associated with leaf-colonizing epiphytes may provide significant nitrogen input into this rainforest ecosystem.

Phenology, nectar production and visitation behaviour of bats on the flowers of the bromeliad Werauhia gladioliflora in a Costa Rican lowland rain forest

We studied the interaction between the bromeliad Werauhia gladioliflora and its flower visitors in the Caribbean lowland forest of Costa Rica, in order to quantify the mutual benefits to both partners. Over 6 y, the bromeliads flowered mainly between October and December; with an individual inflorescence flowering for an average of 34 d (n = 233 inflorescences). The bromeliad showed a flexible breeding system with autogamy occurring in addition to cross-pollination. Exclusive pollinators were small nectar-feeding bats (Phyllostomidae: Glossophaginae). The average volume of nectar produced per flower was 1.1 ml (n = 25 flowers). The main visitor was the bat Glossophaga commissarisi, which approached the flowers exclusively using hovering flight. Visitation by bats, measured by infrared light sensors, occurred throughout the night with an activity peak after midnight. Median hovering duration of the bats at the flowers was 320 ms (n = 1246 visits). Hourly mean of hovering duration was negatively correlated with hourly nectar secretion rate. The flower visitation behaviour of a bat over the night seems to be shaped by a combination of intrinsic physiological factors and by nectar availability. Size of both flowers and visitors make Werauhia gladioliflora a very accessible system for quantification of factors affecting evolution of bat–plant interactions.

Contrasting patterns of vertical stratification in two moth families in a Costa Rican lowland rain forest

Summary The vertical stratification of two species-rich moth families (Lepidoptera: Arctiidae, Geometridae) was analysed in a lowland rain forest in Costa Rica. Moths were trapped with automatic 8 W ultraviolet light traps at three sites in the understorey and canopy of a primary forest at the La Selva Biological Station (10.4° N, 84.0° W). A total of 846 arctiid moths (148 species) and 946 geometrid moths (140 species) were analysed. Species richness and diversity of arctiid moths was significantly lower in the understorey than in the canopy (Fisher's alpha: 24 vs. 49) whereas geometrid moths showed an inverse pattern (Fisher's alpha: 44 vs. 27). This resulted in an overall increase in the proportion of conspicuously coloured species towards the canopy. Moth ensembles were clearly separated in multidimensional scaling ordinations, and differed significantly in their faunal composition and dominance between the strata. The available host plant data suggest that the flight height of moths was determined by larval resource availability. Examples include understorey flyers such as the geometrid genus Eois feeding on Piper , and canopy flyers such as the arctiid moth genera Aclytia , Macrocneme and Poliopastea which feed on lianas.

The effect of water on the ground nesting habits of the giant tropical ant, Paraponera clavata

The large predatory ant, Paraponera clavata, exerts measurable top-down effects in wet and moist Neotropical forests, and therefore its distribution has potential ecological implications. To determine how water affects the presence of this important predator, the ground nesting ecology of P. clavata was examined with respect to various habitat characteristics. Four hectares of disturbed Costa Rican lowland rain forest were surveyed for ant colonies to determine nest distribution patterns in wet and dry habitat; significantly more colonies were found in dry habitat. Seventeen of 19 nests built on slopes of > 5° inclination were positioned on the downward side of the tree, possibly using the trunk as a shield against runoff during rain showers. Moisture and pH inside nests were significantly different from adjacent soil. These results suggest that water influences the ground nesting habits of P. clavata, thus ecological differences between comparatively wet and dry portions of tropical forests may arise from the relative abundance of this ant species.