Frugivorous butterflies were studied in a set of forested islands (0.1 to 1.15 ha) in a reservoir in eastern Venezuela to investigate the effects of fragmentation and the resulting isolation on their abundance, diversity and species composition. While some islands showed reduced abundance and species diversity in comparison to unfragmented (or control) sites, others did not. Isolation status affected both butterfly abundance and diversity. Islands located close to their colonizing sources (0.1–1 km) tended to support similar densities of butterflies but lower numbers of species in comparison to control sites. Far fragments (1–3 km from their colonizing sources) tended to harbour lower butterfly densities in comparison to control sites but undiminished numbers of species. Species composition varied significantly between control sites and islands and amongst control sites, near islands and far islands. Interspecific differences were observed in species' responses to fragmentation. Charaxines, medium-sized satyrines, morphines and brassolines may be vulnerable to extinction after habitat fragmentation while small-sized satyrines may be relatively resistant. Observations during the dry season indicate that butterfly species may exist as mainland-island metapopulations in Lago Guri, in which small habitat fragments require recolonization every year from source populations in large islands and mainland habitat.

A new method for investigating the age structure of the patch mosaic of a tropical forest by utilizing radiocarbon dating techniques on fallen trees is proposed. Aboveground nuclear explosions in the early 1960s, before the nuclear test ban treaty, created a spike in the 14C concentration content of the atmosphere. The amount of radiocarbon in the outer layers of wood collected from trunks of trees that had died in known years (1970–1989) on Barro Colorado Island (BCI) and Gigante Peninsula (Panama) was analysed to test the hypothesis that radiocarbon concentration was predictive of year of tree death. The date of tree death was negatively related to the level of 14C, following a trend similar to published data on tree rings from German and Amazonian trees. Combining our data with these data in a statistical analysis revealed a significant predictive effect of radiocarbon on year. Analysis of covariance showed that there was no significant difference among the slopes of the three groups of data, but there was significant heterogeneity among the intercepts. The differences suggest a need for site-specific calibration and refinement of field protocols. The technique shows promise and suggestions are made to improve its usefulness for future studies.

The spatial and temporal variation in litter disturbance by a medium-sized bird, the chowchilla (Orthonyx spaldingii Ramsay, Orthonychidae) was documented, and its potential impacts on tree seed germination and early seedling survival in an Australian tropical rain forest experimentally investigated. Chowchilla disturbances occurred on ridges, slopes and drainages in all four seasons surveyed. In some areas litter was completely turned over as frequently as every 5 wk. Tethered seeds exposed to disturbance were moved farther and experienced significantly greater variation in litter cover than those protected from disturbance. When seeds of two canopy trees were placed in litter environments simulating those created by chowchillas, the seeds of one species showed significant effects of litter treatment on germination while those of the other showed no significant effects. Seedling cohorts of four tree species were followed for 6 wk soon after germination and all showed higher survival in vertebrate exclosures. The two most abundant species suffered 68% and 35% mortality in six wks, with the majority of that unambiguously due to chowchillas. It is argued that litter-disturbing birds increase litter heterogeneity and significantly impact early seedling mortality. These effects could be important in maintaining evenness and diversity of the seedling community.

Primary tropical forests comprise a mosaic of mature, gap and building phase patches, resulting in great spatial variation in the distribution of foliage. Light may consequently penetrate into the forest interior over a wide range of angles. It thus seems possible that understorey tree species might be adapted for distinct understorey light conditions. At the Cocha Cashu Biological Station in Madre de Dios, Peru, there are two understorey treelets distinguished by contrasting crown architectures. One, Neea chlorantha (Nyctaginaceae), possesses a much-branched superstructure and displays a smoothly contoured shell of drooping elliptical leaves. The other, Rinorea viridifolia (Violaceae), displays planar arrays of horizontally-oriented obovate leaves held on whorls of stiffly radiating horizontal branches.

With the aid of hemispherical photography and the program CANOPY, the light environment at large within a 2.25-ha permanent tree plot, and above and below the crowns of Neea and Rinorea treelets, was investigated. Available light (measured as uncorrected indirect site factor (ISFU) in CANOPY) at control points showed a log-linear increase with height from 2.1 to 14.2 m. The relative amount of lateral illumination also increased with height. Photographs were taken just above and below the crowns of 50 Neea and 50 Rinorea treelets. Neea crowns were more effective at intercepting light from overhead sources, whereas Rinorea crowns were more effective at intercepting light from lateral sources. Adult Neea and Rinorea treelets occurred at locations in the forest where they were exposed to differing angular distributions of incident light, suggesting that the two species were engaged in a form of resource partitioning, a conclusion that is in conflict with the non-equilibrium model of tropical forest tree species diversity. It is suggested that tropical tree species diversity is, at least in part, a product of adaptive specialization to a spatially heterogeneous light environment.

The goal of this study was to assess territoriality and foraging home ranges for stingless bee species; and to develop methods for censusing stingless bee colonies. Colonies of two meliponine bee species, Trigona corvina Cockerell and Trigona amalthea Vachal, were censused using carrion and honey baits. Trigona corvina and Trigona amalthea are dispersed in a Costa Rican tropical wet forest (La Selva) so that foraging ranges of the colonies are non-overlapping. The nest density was c. 0.25 ha−1 for T. amalthea and 1.0 ha−1 for T. corvina. T. corvina visited carrion baits exclusively, while T. amalthea visited both carrion and honey baits. The identities of T. amalthea colonies were confirmed using a nestmate recognition assay. Partamona peckolti Friese, Plebeia frontalis Friese, and T. fulviventris Guerin also appeared at the baits. The reliability of baiting to determine colony abundance and distribution is assessed.

The consumption of arbuscular mycorrhizal fungi (AMF) by Proechimys semispinosus (Central American spiny rat) was assessed via microscopic examination of faecal material for the presence of AMF spores. Mycophagy (indicated by the presence of spores) was compared among individual spiny rats residing on eight isolated islands in Gatun Lake, Panama during January and July 1996. Spores and sporocarps of Sclerocystis coremioides and spores from at least four species of Glomus were present in 77% of the 231 faecal samples examined. The proportion of faecal samples that contained AMF spores did not differ between spiny rat sex, age classes or months of sampling or with island area. However, there was a positive relationship between the proportion of samples containing spores and rodent density in January, and a marginally significant positive trend in July. Increased consumption of AMF on islands that supported high densities of spiny rats may have resulted from increased competition for primary food resources (fruits and seeds).

In the Ciénaga Grande de Santa Marta, a brackish lagoon system on the Caribbean coast of Colombia, about 60% of the mangrove forests died from hypersalinization. The die-back was first encountered in 1964 and mass mortality started in the late 1960s. Although efforts are being made to reestablish the destroyed areas, regeneration is slow, which may be partly due to Junonia evarete caterpillars defoliating Avicennia germinans seedlings. The interaction between insects and seedlings was studied. Both J. evarete butterflies and caterpillars were abundant during the main rainy season, the time of highest fruit production in A. germinans. During the dry season the herbivore disappeared. The caterpillars fed exclusively on A. germinans propagules, seedlings, and pneumatophores. They preferred young seedlings to older plants and did not feed on trees. At some sites, 100% of the A. germinans seedlings died due to the caterpillar attack. Seedlings at open, disturbed sites were attacked more than seedlings protected by small roofs and trenches or those under a closed canopy. Only seedlings protected by insect nets or seedlings germinating at the beginning of the dry season had good chances of survival. The results suggest that in the highly disturbed areas of the Ciénaga Grande regeneration of A. germinans is strongly inhibited by the feeding behaviour of J. evarete caterpillars.

ABSTRACT: Throughout the tropics there are a few hundred ant species that nest exclusively inside myrmecophytes (i.e. ant-domatia bearing plants). For these ants, nesting space is an essential resource that must be shared among them, therefore opening the possibility for strong intraspecific and interspecific competition. Several ant–myrmecophyte systems from Central Amazonia were investigated to test the relevance and generality of the nesting space limitation hypothesis for plant-ants. Empirical patterns were drawn at four organizational levels: (a) individual level—ant species with small-bodied queens were the most frequent partners of myrmecophyte species offering small-sized domatia, while ants with large-bodied queens dominated host species with large-sized domatia, suggesting that host choice by inseminated queens and interspecific conflicts over host dominance seem to be influenced by space limitation; (b) colony level—in eight independent ant–myrmecophyte systems, ant colony size was positively correlated to the number of domatia provided by the host, and the mean occupancy level of the domatia by ants was 92%, suggesting that space can be limiting to colony growth; (c) population level—ant colony number and distribution was determined by the local availability and distribution of its plant partners; and (d) community level—across ant-myrmecophyte systems, the commonness of ant species were largely determined by the commonness of their specialized host partners. Within ant-myrmecophyte systems, rarity of ants seems to be defined by interspecific conflicts over host dominance. The ecological and evolutionary consequences of those patterns are discussed.

RESUMO. Nos trópicos existem algumas poucas centenas de espécies de formigas que nidificam exclusivamente dentro de mirmecófitas (i.e. plantas possuidoras de domácias). Para estas formigas, o espaço de nidificação é um recurso essencial que precisa ser dividido entre elas, abrindo assim a possibilidade de competição intraespecífica e interespecífica forte. Diversos sistemas formiga-plantas da Amazônia Central foram investigados para se testar a relevância e generalidade da hipótese da limitação de sítios de nidificação para formigas associadas às mirmecófitas. Padrões empíricos foram gerados a quatro níveis organizacionais: (a) nível individual—espécies de formigas com rainhas de tamanho corpóreo reduzido foram os parceiros mais frequentes de espécies de mirmecófitas que oferecem domácias pequenas, enquanto que espécies de rainhas grandes dominam espécies de hospedeiros que oferecem domácias grandes, sugerindo que a escolha de hospedeiros por rainhas inseminadas e conflitos interespecíficos pela dominância do hospedeiro parecem ser influenciados por limitações de espaço; (b) nível da colônia—em oito sistemas formiga-plantas independentes, o tamanho da colônia das formigas foi positivamente correlacionado ao número de domácias oferecido pelo hospedeiro, e o nível médio de ocupação das domácias por formigas foi 92%, sugerindo que espaço pode estar limitando o crescimento das colônias; (c) nível da população—o número e a distribuição das colônias de formigas foi determinado pela disponibilidade local e distribuição dos parceiros vegetais; e (d) nível da comunidade—entre os sistemas formiga-plantas, formigas comuns e raras correspondem a aquelas especializadas respectivamente em espécies de mirmecófitas comuns e raras. Dentro de cada sistema formiga-planta, a raridade das formigas parece ser definida por conflitos interespecíficos sobre a dominância dos hospedeiros. As conseqüências ecológicas e evolutivas destes padrões são discutidas.

Traditional shade house experiments that expose plants to relatively uniform irradiance and light quality are inadequate to characterize the morphological, allocational and physiological plasticity that seedlings show to different gap environments. Here the design of a pot experiment is described that simulates the daily time course of irradiance and light quality in idealized gaps of six different sizes. Differences in response to gap size are illustrated using data from two pioneer species, Ochroma pyramidale, which recruits exclusively in large gaps and clearings, and Luehea seemannii, which colonizes small branchfall gaps as well as large gaps. Ochroma outperformed Luehea in relative growth rate in all except the smallest simulated gap size. Ochroma's superior performance in the larger gaps could be attributed to a larger proportional investment in leaf biomass (i.e. a higher leaf area ratio, LAR), and higher photosynthetic rates both on a leaf area and leaf mass basis. In the smallest simulated gaps LAR was not significantly different between the species, but Ochroma maintained a higher net assimilation rate. These results fail to support the suggestion that gap partitioning among pioneer species arises directly from morphological and biochemical specialization to particular gap light environments. Instead, it is suggested that partitioning may result from a trade-off between seedling growth and mortality determined by species allocational patterns and mediated by interactions with herbivores and pathogens.