Distyly is a floral polymorphism that presumably evolved to facilitate cross-pollination and to prevent sexual interference. However, pollen transfer is often asymmetric, with one floral morph acting as a pollen donor and the other as a pollen recipient. We evaluated the association between floral morphology, pollinator visitation and effectiveness on patterns of pollen transfer in distylous Palicourea tetragona at La Selva Biological Station in Costa Rica. To assess floral variation we measured corolla, pistil and stamen traits from 66 plants. We quantified pollinator visitation and efficiency on 56 individuals and counted pollen loads on stigmas of flowers observed for 1 h. We determined fruit set 2 mo later and assessed between-morph variation in pollen transfer and female reproductive success. Floral variation was mostly consistent with a typical distylous system; however, there was overlap in the stigma heights of pin and thrum individuals in the study population. Primary pollinators were two species of hawkmoths that visited both morphs at a frequency of 2 visits per flower h−1. The mean number of pollen grains deposited on stigmas was 89 for pin and 153 for thrum individuals. However, loads of illegitimate pollen were higher on stigmas of thrum individuals, while loads of legitimate pollen were higher on stigmas of pin individuals. Consistently, fruit set was higher in pin (31%) than in thrum individuals (22%). High deposition of illegitimate pollen, in addition to the lower female reproductive success in the thrum morph reveal that distyly in P. tetragona does not always prevent sexual interference. We suggest that in long and narrow tubular flowers, like those of P. tetragona, stigma clogging by deposition of self- or same-morph pollen may reduce legitimate fertilization of ovules causing the observed asymmetric fruit set.

Resource depletion and associated increases in interspecific competition are likely to influence differential habitat usage amongst a guild. We tested some prominent theoretical concepts using observed differences in seasonal habitat use amongst the savanna browser guild (elephant, giraffe, impala, kudu and nyala) in Hluhluwe-iMfolozi Park, South Africa. Herbivore locations (n = 3108) were recorded over 2 y using repeated road transects and, for elephant, GPS collars (187 254 downloads). Densities were calculated using a novel GIS approach designed to be a cost-effective method for annual censuses, but also able to cope with abrupt changes in visibility. Selectivity for (Manly's α) vegetation types, and overlap (Schoener's index) in vegetation type usage were calculated. Resource depletion in the dry season resulted in all members of the guild increasing selectivity for vegetation types (sum of absolute values away from the neutral value for Manly's alpha for the guild: dry seasons 3.97, 5.16; corresponding wet seasons 3.12, 3.68), but decreasing interspecific overlap (80% of Schoener's indices lower in dry season versus wet season). These effects were more marked over the second, more severe, dry season. We found support for the niche overlap hypothesis and the niche compression hypothesis. The Jarman–Bell principle was generally supported, although unexpectedly during the severe dry season elephant showed the most selectivity for vegetation type. The greater the resource depletion, the more relevant interspecific differences in habitat usage become in relation to the differential impacts of guild members.

Abundance and physiology of three understorey tree fern species were compared in a Mexican cloud forest. We hypothesized that the distribution of species would be associated with canopy openness and leaf physiological characteristics. In gullies (1–2% full sun), Alsophila firma was abundant, Cyathea divergens was distributed in moderately open places (4–9%), and Lophosoria quadripinnata preferred more open canopy (9–30%). Although 11 leaf traits of five plants of each species growing under closed and open canopies over 1 y did not differ within species, there were significant interspecific differences. Alsophila firma had comparatively low maximum electron transport rate ETRmax (26.8 ± 1.81 μmol m−2 s−1) and ETR light saturation point (ETRLSP: 261 ± 36.1 μmol m−2 s−1), high specific leaf area (SLA), thin leaves and decreased quantum yield during a leaf desiccation experiment. Cyathea divergens had relatively high maximum quantum yield (0.84 ± 0.004), ETRmax (37.3 ± 1.8 μmol m−2 s−1) and ETRLSP (409 ± 40.0 μmol m−2 s−1). Lophosoria quadripinnata had comparatively thick leaves, low SLA, high predawn water potential, high density (606 ± 25.5 mm−2) and small length (0.026 ± 0.002 mm) stomata. The results support the hypothesis that light sensitivity shapes tree fern distribution in the cloud forest.

The contribution of vegetative recruitment by non-tree species to the regeneration of tropical forests in man-made clearings or tree-fall gaps tends to be ignored. In a series of field studies near Amacayacu, Colombian Amazonia, we tested if hemiepiphytic aroids quickly colonize such open habitats through seed dispersal, sprouting plant fragments, or lateral invasion of flagellar aroids from the closed forest nearby. A seed germination experiment applying two soil substrates and three shade levels showed that abundant light reduced the germination success of three Philodendron species. A total of 400 cuttings from five Philodendron species were placed in forest clearings and almost 12% of these sprouted within 14 wk. Monitoring more than 2000 aroid plants over 14 mo in different habitats showed that recruitment was low (0.3 plants per 10 m2) compared with initial densities (3.1 plants per 10 m2). Flagellar aroids grew about 2.5 times faster than non-flagellar aroids. In forest edges they reached a mean apical growth of 98 cm in 14 mo. However, non-flagellar aroids were five to six times more abundant than flagellar individuals everywhere. It was concluded that hemiepiphytic aroids colonize open habitats mostly through a post-disturbance survival of plants or plant fragments.

We assessed the differences and similarities in diel activities among five phytophagous bat species at two habitats over two seasons within the Sierra del Rosario Biosphere Reserve in Cuba. We characterized temporal patterns of activity and overlap of temporal activity for frugivore and nectarivore bat species (Artibeus jamaicensis, Monophyllus redmani, Phyllonycteris poeyi, Phyllops falcatus and Brachyphylla nana) that occur in tropical evergreen forest sites with distinct altitude and vegetation structure during wet and dry seasons. Capture frequencies using mist-nets of 1180 capture events were the empirical basis for analyses. For each species we compared activity patterns between habitats, between seasons, between males and females, as well as between reproductive and non-reproductive females. We also assessed temporal overlap among each possible pair of species at each habitat and used Monte Carlo simulations to evaluate assemblage-wide temporal niche overlap using a new algorithm, termed Rosario, designed specifically for temporal data. The two habitats had the same species composition and bat diel rhythms tended to be consistent across habitats, seasons and sexes for most bat species. In general bat species pairwise temporal niche overlap was high, and the ensemble-wide temporal overlap was consistently high across habitats and seasons indicating a common constraint for bat activities. Activity peaks of most bat species coincided at 4–5 h after sunset, this being in sharp contrast to other Neotropical bat assemblages at continental sites where activity peaks usually overlap within the first 2 h after sunset. This strong disparity in timing of activity peaks between continental and insular bat assemblages can provide the framework for the generation of hypotheses that explain the potential role of time as a mediator of ecological interactions in bat assemblages.

A range of species eating the same fruit suggests that niche overlap can occur, along with potential competition among them. To test if the overlap in the coterie of fruit-eating birds is larger than would be expected by chance, we performed a comparison with coteries generated from the use of null models. The study was carried out in an area of savanna woodland of 127 ha in Uberlândia city, Brazil. Four individuals of five zoochorous plant species were selected and 60 h of focal observation was performed on each species. We recorded species of birds that consumed fruits and the quantity of fruit removed. We used an index of Proportional Similarity (PS) between each pair of plant species, using the relative proportion of fruit taken by each bird species of each plant. The mean value of observed PS was compared with the mean PS generated from randomizations. Thirty-six bird species were recorded eating fruits in the selected plant species. The mean overlap observed (PS = 0.183) was significantly higher (P = 0.032) than the mean overlap generated by the null models (PS = 0.123). This pattern suggests that competition is not an important factor in the formation of the coteries and there is sharing of resources. The abundance of fruits offered, especially in the rainy season, and the relatively low number of frugivorous species may be factors explaining the low influence of interactions and therefore the overlap between coteries.

Structure and demographics in many tropical forests is changing, but the causes of these changes remain unclear. We studied 5 y (2005–2010) of species turnover, recruitment, mortality and population change data from a 20-ha subtropical forest plot in Dinghushan, China, to identify trends in forest change, and to test whether tree mortality is associated with intraspecific or interspecific competition. We found the Dinghushan forest to be more dynamic than one temperate and two tropical forests in a comparison of large, long-term forest dynamics plots. Within Dinghushan, size-class distributions were bell-shaped only for the three most dominant species and reverse J-shaped for other species. Bell-shaped population distributions can indicate a population in decline, but our data suggest that these large and long-lived species are not in decline because the pattern is driven by increasing probabilities of transition to larger size class with increasing size and fast growth in saplings. Spatially aggregated tree species distributions were common for surviving and dead individuals. Competitive associations were more frequently intraspecific than interspecific. The competition that induced tree mortality was more associated with intraspecific than interspecific interactions. Intraspecific competitive exclusion and density-dependence appear to play important roles in tree mortality in this subtropical forest.

Total ecosystem carbon storage has frequently been found to increase with woody encroachment in savannas. However the loss of grass roots associated with woody encroachment can lead to a decrease in below-ground carbon storage which is not compensated for by an increase in above-ground carbon. To investigate how the extent of total woody cover affected ecosystem carbon, soil and above-ground carbon storage along eight thicket–savanna and five forest–grassland boundaries were measured. To investigate whether changes in soil carbon concentrations were related to the percentage of C4 (grass) roots to total roots and root quantity and quality, we measured fine-root biomass, root C : N ratios, root N, and % C4 roots at three different depths across thicket patches of different ages (n = 189). Forests contained significantly more carbon than adjacent grasslands in both above-ground carbon (mean difference 12.1 kg m−2) and in the top 100 cm of the soil (mean difference 4.54 kg m−2). Thickets contained significantly more above-ground carbon than adjacent savannas (3.33 kg m−2) but no significant differences in soil carbon were evident. Total fine-root biomass appeared to be more important than root quality (root C : N) in determining soil carbon concentrations during the encroachment process (i.e. in thicket of different ages). Similarly for thickets, the % C4 roots had no significant effect on soil carbon concentrations. In conclusion, thicket invading into open savanna vegetation did not lead to significant gains in ecosystem carbon at this study site. Significant gains were only evident in mature forest, suggesting that the process may take place very slowly.

Fragmentation of tropical forests influences abiotic and biotic processes that affect the genetic structure of plant populations. In forest fragments, edge effects, i.e. changes of abiotic and biotic factors at forest edges, may be prevalent. In two forest fragments (c. 200 ha at c. 2450 m asl) of tropical montane forest in Bolivia, sympatric populations of the dioecious tree species Clusia sphaerocarpa and C. lechleri were used as case study species to compare genetic diversity and small-scale genetic structure (SGS) between edge and interior habitats. Eight microsatellite markers were employed to genotype 343 individuals including adults, juveniles and seedlings of C. sphaerocarpa and 196 of C. lechleri. Genetic differentiation was found between habitats in both species (ΦRT = 0.071 for C. sphaerocarpa and ΦRT = 0.028 for C. lechleri) and among ages in C. sphaerocarpa (ΦRT = 0.016). Overall, SGS was weak but significant with more pronounced SGS in C. lechleri (Sp = 0.0128) than in C. sphaerocarpa (Sp = 0.0073). However, positive spatial genetic autocorrelation extended only up to 10 m. For C. sphaerocarpa, SGS was stronger in seedling and juvenile stages than in adults and in the forest interior than at forest edges. Our results show that edge effects can extend to the genetic level by breaking-up local genetic structures, probably due to increased gene flow and enhanced pollination and seed-dispersal interactions at forest edges.

Spatial and temporal variation of tropical insect communities has rarely been studied, although such variation influences estimates of global species richness. Therefore, we compared spatial and temporal variation of herbivorous insect communities on Neoboutonia macrocalyx trees among seven sites over 1 y in a primary tropical rain forest in Kibale National Park, Uganda. The distance between the study sites varied from 4.8 to 31.2 km and altitudinal differences ranged from 20 to 242 m. Permutational multivariate analysis of variance (PERMANOVA) revealed significant spatial changes in community composition of the herbivorous insects and study sites differed also in insect abundance (6.9–26.2 individuals m−2 of leaf area). This is likely to be caused by differences in vegetation, altitude and microclimate among the study sites. The similarity of insect species composition was negatively correlated with geographic and altitudinal distances among sites and positively correlated with the similarity of tree community composition. Species richness varied significantly between sampling dates, ranging from 33 to 41 species. Also community compositions changed between sampling dates, which likely follows from marked seasonal changes in climate and the phenology of other host plants used by the generalist insect species also living on Neoboutonia macrocalyx. In general our study supports the idea of high variability of herbivorous insect communities in primary rain forests even at a small spatial scale. This should be considered when estimations of insect biodiversity are made.

This study investigated the effects of mistletoe infection on N cycling in a semi–arid savanna, south-west Zimbabwe. We established five plots (10 × 10 m) which each included three large canopy-dominant Acacia karroo trees infected by one of three mistletoes (Erianthemum ngamicum, Plicosepalus kalachariensis and Viscum verrucosum) and non-infected A. karroo trees. In each plot, we measured litterfall, litter quality (N, phenolics, tannins and lignin), soil nutrient concentrations and N transformations beneath tree canopies. Soil N, P and Ca were greatest beneath trees infected by P. kalachariensis than beneath non-infected trees. Litterfall and litter N returns were 1.5, 2 and 1.4 times more beneath A. karroo trees infected by E. ngamicum, P. kalachariensis and V. verrucosum, respectively. Mineral N increased with mistletoe infection but did not exceed 20%. Soil N transformations were greater beneath trees infected by E. ngamicum (> 40%), and lower beneath trees infected by P. kalachariensis (<50%) and V. verrucosum (<48%) than beneath non-infected A. karroo trees. Soil N transformations were negatively correlated with condensed tannins, lignin and lignin : N. We conclude that the improved N concentration can increase resource heterogeneity, which may alter the ecosystem structure and functioning in the semi-arid savanna.

Many landscape features represent geographic barriers to gene flow, and promote genetic discontinuity. Rivers are effective barriers. However, most studies on this subject have focused on animals and only a few have focused on plants. We studied the genetic structure and gene flow of the tropical tree Handroanthus ochraceus (Bignoniaceae) on both banks of the São Francisco River in a Brazilian seasonally dry tropical forest. The São Francisco is located in eastern Brazil and is 600 m wide at the study site. Our hypothesis was that the river is a geographic barrier to gene flow of H. ochraceus trees. We sampled two populations on the left bank and one population on the right bank. We used seven microsatellites to genotype 212 individual plants. All populations had low polymorphism and genetic diversity, but high inbreeding. There was no genetic differentiation among populations and, consequently, the estimated gene flow was high for all pairs of populations. The genetic relatedness among individuals from populations of the same margin did not differ from the relatedness among individuals from populations of opposite margins. Hence, the São Francisco River is not an effective geographic barrier to gene flow among H. ochraceus populations.

Predation ecology of large sympatric carnivores, tiger, leopard and dhole, as influenced by available wild ungulates, chital, sambar, nilgai, gaur and wild pig, were studied between January 2007 and June 2010 in a tropical deciduous forest of Central India. Both line transect and vehicle transect methods were used to estimate population structure and sex ratios of wild ungulates. The observed adult sex ratio (female:male) was found to be skewed towards females for all ungulates. A total of 123 tiger kills were recorded in the cold season and 162 in the hot season, 32 leopard kills were recorded during the cold season and 48 during the hot season and 32 dhole kills were recorded in the cold season and 55 in the hot season. The age–sex class distribution of each ungulate species in the kill data was compared with the corresponding population age–sex distribution recorded from line transects and vehicle transects. All three large carnivores preferred medium-sized prey species, e.g. chital. A significant difference was observed when comparing different health conditions of prey species predated by the three large carnivores. The observed difference in prey choice as per their body size is a strategy adopted by large carnivores to partition prey resources, thus increasing the potential to avoid intra-guild competition.

Understanding the response of biodiversity to land-use changes is an important challenge for ecologists. We assessed the effects of five landscape metrics (forest cover, number of patches, edge density, mean inter-patch isolation distance and matrix quality) and three patch metrics (patch size, shape and isolation) on the number of species and patch occupancy of medium- and large-sized terrestrial mammals in the fragmented Lacandona rain forest, Mexico. We sampled mammal assemblages in 24 forest patches and four control areas within a continuous forest. The landscape metrics were measured within a 100-ha buffer, and within a 500-ha buffer from the centre of each sampling site. A total of 21 species from 13 families was recorded. The number of species increased with shape complexity and patch size at the patch scale, and with matrix quality within 100-ha landscapes. When considering 500-ha landscapes, only the number of patches (i.e. forest fragmentation level) tended to have a negative influence at the community level. Different landscape and patch metrics predicted the occurrence of each species within the sites. Our results indicate that there is a gradient of tolerance to forest cover change, from highly sensitive species to those tolerant of, or even benefited by, forest-cover change.

Community-wide seasonal fruiting and seed dispersal by the common brown lemur (Eulemur fulvus fulvus) was investigated in a tropical dry forest, north-western Madagascar. The brown lemur is the sole disperser of large seeds > 10 mm in diameter. Considering the limited assemblage of dispersers, large-seeded plants should display distinctive fruiting patterns to acquire dispersers. To compare fruiting patterns and seed dispersal by the brown lemur between small-seeded and large-seeded plants, fruiting conditions for 432 trees on a transect, feeding activity over 1212 h of observation, and the composition of 1126 dung samples were recorded for 1 y. Seeds of a total of 52 species were identified through both observations and faecal analysis. As rainfall increased, larger numbers of species and individuals of small-seeded plants fruited. Among the 52 species, the brown lemur dispersed 29 and 13 species with small and large seeds, respectively, during the rainy season. High moisture levels probably favoured seed germination and seedling establishment in various species. During the dry season, although small-seeded species rarely fruited, a few large-seeded species, particularly Vitex beraviensis, formed a long-term fruiting peak and provided essential food resources for the brown lemur. Because seeds of these large-seeded plants were frequently dispersed by the brown lemur, dry-season fruiting seemed to be favourable to avoid competition for dispersers with other plant species.

Vast areas of tropical forests have been deforested by human activities, resulting in landscapes comprising forest fragments in matrices of deforested habitats. Soil seed banks (SSB) are essential sources for the regeneration of tropical forests after disturbance. In a fragmented montane landscape in the Bolivian Andes, we investigated SSB in three different habitat types that were associated with different degrees of disturbance, i.e. in forest interior, at forest edges and in deforested habitats. Sampling of habitats was replicated at six sites ranging in altitude from 1950 to 2450 m asl. We extracted seeds from dried soil samples by sieving, classified seeds into morphospecies and size classes, and characterized SSB in terms of density, species richness and composition. We tested effects of disturbance (i.e. habitat type) and altitude on SSB characteristics. Overall, small seeds (<1 mm) dominated SSB (81% of sampled seeds). Seed density and species richness were lowest in deforested habitats, especially in large seeds and distant from adjacent forests (≥20 m), while small-seeded species were most numerous near forest margins. Species turnover between habitats was high. Altitude altered the composition of SSB, but had no effects on seed density and species richness. We conclude that the potential of SSB for natural regeneration of deforested habitats is low and decreases with increasing distance from forest remnants and that forest edges may be eventually invaded by small-seeded species from deforested habitats.

Conversion of natural habitats to anthropogenic land uses is a primary cause of amphibian declines in species-rich tropical regions. However, agricultural lands are frequently used by a subset of forest-associated species, and the habitat value of a given land use is likely modified by the presence and characteristics of remnant trees. Here we used mark–recapture methods to examine abundances and movement probability of the poison frog, Oophaga pumilio, at individual trees in forest-fragment edges and adjacent pastures in north-eastern Costa Rica. One hundred and forty-seven trees were surveyed at three replicate sites that each included a forest fragment and adjacent pasture. Trees were sampled at distances of ≤30 m into forest and ≤150 m into pastures for Oophaga pumilio, and local environmental characteristics were measured at each tree. We also measured indices of physical condition (size and endurance) of frogs captured in forest edges and in nearby pastures. Analyses of 167 marked individuals showed no difference in per-tree abundances or sex ratios between pasture and forest edges. We found significant interactions between habitat type and leaf-litter cover, tree dbh and number of logs, indicating greater influence of local variables on abundances in pastures. Movement among trees was infrequent and not predicted by sex, size, habitat type or environmental variables. While results of endurance tests did not differ for individuals from the two habitats, frogs captured in pastures were, on average, larger than frogs captured in forest edges. These data indicate that remnant trees are important habitat features for O. pumilio in pastures and corroborate research in other systems that suggests that large relictual trees should be retained to maximize the potential for altered landscapes to provide habitat for native species.

Studying species turnover along gradients is a key topic in tropical ecology. Crucial drivers, among others, are fog deposition and soil properties. In northern Peru, a fog-dependent vegetation formation develops on mountains along the hyper-arid coast. Despite their uniqueness, these fog oases are largely uninvestigated. This study addresses the influence of environmental factors on the vegetation of these unique fog oases. Accordingly, vegetation and soil properties were recorded on 66 4 × 4-m plots along an altitudinal gradient ranging from 200 to 950 m asl. Ordination and modelling techniques were used to study altitudinal vegetation belts and floristic composition. Four vegetation belts were identified: a low-elevation Tillandsia belt, a herbaceous belt, a bromeliad belt showing highest species richness and an uppermost succulent belt. Different altitudinal levels might reflect water availability, which is highest below the temperature inversion at around 700 m asl. Altitude alone explained 96% of the floristic composition. Soil texture and salinity accounted for 88%. This is in contrast with more humid tropical ecosystems where soil nutrients appear to be more important. Concluding, this study advances the understanding of tropical gradients in fog-dependent and ENSO-affected ecosystems.

The phenology of temperate plants is vulnerable to climate change. Yet, the phenological responses of tropical plants to climate change are still unclear. In this study, temporal trends (1973–1999) of four phenological events (budburst, growing season, flowering and flowering duration) were studied among 21 plant species in Xishuangbanna Tropical Botanical Garden (south-western China). Fourteen species (67%) showed significant phenological trends during the study period. Seven species (33%) presented delaying trends in budburst (average 1.4 d y−1) and such trend was more likely to be presented in those that started budburst earlier in the dry season. Four species (19%) showed trends of extension in growing season (average of 3.5 d y−1). These vegetative events appeared to be mainly influenced by increasing temperature. Rainfall showed little effects directly, however, the effects of temperature seemed to largely depend on the moisture condition. Flowering duration of five species (24%) was shortened by average 2.1 d y−1 which was most likely to be the result of the decline in sunshine duration during the rainy season. Our results suggest that the phenology of tropical plants has changed significantly in response to the regional climate change but these reactions are somewhat different from those of temperate plants.

Patterns of social organization and mating systems have been shown to be functions of ecological factors such as resource allocation and breeding density. In some species, particularly birds, social organization and genetic mating systems differ with molecular studies providing evidence of extra-pair young frequently occurring within broods of socially monogamous species. Here we examine the social and genetic mating system of an ecologically little-known forest raptor endemic to the island of Hispaniola in the Caribbean. From 2005–2009, our field observations of over 60 breeding pairs verified a social mating system of monogamy for the species. During the same time period, we collected blood samples (n = 146 birds, 48 nests) and used microsatellite profiles from 10 loci to estimate genetic relatedness among nestlings in a brood and assign putative fathers. We found no evidence of extra-pair paternity in 41 broods. We had one instance where a social male was not assigned as the putative father, however, the confidence level of this assignment was not significant since the genotypes of the social and assigned males were very similar. Our results support our hypothesis that genetic monogamy would be exhibited by Ridgway's hawk, an island-endemic tropical raptor.