Although predation is generally seen as one of the key factors determining the abundance and composition of insect herbivore communities in tropical rain forests, quantitative estimates of predation pressure in rain-forest habitats remain rare. We compared incidence of attacks of different natural enemies on semi-concealed and exposed caterpillars (Lepidoptera) in lowland and montane tropical rain forests, using plasticine models of caterpillars. We recorded attacks on caterpillars in four habitats: primary forest, secondary forest and forest fragment in lowlands (200 m asl), and montane primary forest (1700 m asl). We used 300 exposed and 300 semi-concealed caterpillars daily, and conducted the experiment for 6 d in every habitat. Daily incidence of attacks was higher on exposed caterpillars (4.95%) than on semi-concealed (leaf-rolling) caterpillars (2.99%). Attack pressure of natural enemies differed also among habitats. In the lowlands, continuous primary and secondary forests had similar daily incidence of attacks (2.39% and 2.36%) which was however lower than that found in a primary forest fragment (4.62%). This difference was caused by higher incidence of attacks by birds, ants and wasps in the forest fragment. The most important predators were birds in montane rain forests (61.9% of identified attacks), but insect predators, mostly ants, in the lowlands (58.3% of identified attacks). These results suggest that rapid decrease in the abundance of ants with altitude may be compensated by increased importance of birds as predators in montane forests. Further, it suggests that small rain-forest fragments may suffer from disproportionately high pressure from natural enemies, with potentially serious consequences for survival of their herbivorous communities.

Insect-pollinated Laguncularia racemosa has a variable breeding system; some populations are androdioecious, with male and hermaphroditic plants, while others lack male plants. We observed the foraging behaviours of insects in three androdioecious and three hermaphrodite-only populations of L. racemosa in Florida. In each population, insect visitation rates were estimated from 30–108 timed intervals. We recorded the number of flowers visited by 144–224 insects during foraging bouts made to 15–40 male and hermaphroditic plants. Male plants in androdioecious populations had significantly more visitors than hermaphroditic plants, increasing the number of vectors carrying pollen from male plants. Further, many insects visited few flowers during foraging bouts, which should increase outcrossing frequency. According to mathematical models, male plants benefit from these combined factors. Plants in hermaphrodite-only populations had significantly more visitors than hermaphroditic plants in androdioecious populations. Proportionately more insects visited many flowers during foraging bouts in hermaphrodite-only versus androdioecious populations. The increased likelihood of geitonogamous self-pollination could help explain the lack of male plants in hermaphrodite-only populations. Differences in pollinator assemblages and the relative abundances of several species were responsible for differences in foraging behaviours: Apis mellifera, Bombus sp., Melissodes sp., Xylocopa sp., Euodynerus sp. and a calliphorid species.

Reproductive success of many plant species declines in fragmented habitat, but this effect is little studied in trees of tropical rain forest understorey. Paypayrola blanchetiana (Violaceae) is a continuous-flowering treelet endemic to the Atlantic rain forest of north-east Brazil. Plants are distributed in localized patches. Flower, fruit and seed production of a total of 86 trees was quantified in six forest fragments, each belonging to one of two categories of size (> 300 ha vs. < 50 ha) and fragmentation history (isolated for c. 25–30 y vs. at least c. 50 y). Relative fruit set (fruits/flower) and seed set (seeds/ovule) were calculated for a spatial (total fruit set of tree individuals) and a temporal analysis (combined month-by-month fruit set in patches in response to different flowering intensities). Fruit set (1%) and seed set (0.6%) were very low, but variable among trees. Plants in large fragments had significantly higher fruit set and seed set than plants in small fragments. Trees in older fragments, however, displayed similar fruit and seed set to those in recently created ones. We found no interaction effect on seed set of fragment size and isolation time. Seed set was a negative function of patch flower density. Possible drivers of the observed patterns are discussed.

Secondary forests promote an increased abundance of leaf-cutting ants (LCA) but the consequences on forest dynamics have been poorly addressed. Here we examine seedling assemblage attributes, seed germination and seedling survival across foraging zones of Atta cephalotes colonies inhabiting 15 second-growth patches (25–47 y old) of Atlantic forest. Seeds and seedlings were monitored within foraging zones and control sites over 1 y, including spots around ant nests. Overall, 1862 seedlings from 108 plant species were recorded. Seedling density decreased by 53% in foraging-zone plots (3.31 ± 0.23 seedlings m−2) when compared with control plots (7.02 ± 0.44 seedlings m−2) and a similar decrease was observed for species richness. Ant-induced alterations in the seedling assemblage were further indicated by segregation between foraging-zone and control plots (NMDS), habitat effects on species similarity (ANOSIM), and indicator tree species associated with control plots. While seed germination and seedling survivorship were uncorrelated to either nest distance or age of second-growth stands (with the exception of Tapirira guianensis), defoliation by LCAs was a significant cause of seedling mortality. Our results suggest that LCAs interfere with successional trajectories of Atlantic forest as foraging zones filter seedling establishment, supporting less-dense, impoverished and convergent seedling assemblages.

Habitat heterogeneity is an important ecological determinant of species richness. We evaluated the diversity within bird feeding guilds as related to habitat heterogeneity and land-use cover in a human-modified tropical landscape. To quantify this process, fine-scale bird census and habitat heterogeneity data were collected for a bird community in a 22.5-km2 fragmented landscape in southern Mexico. Land-use cover data derived from field surveys were used to calculate habitat heterogeneity index values and the extent of each land-use cover type in 239 grid cells of 300 × 300 m. Bird diversity values were obtained based on 1195 point-counts in these cells. Product-moment correlations and linear regression analyses were used to evaluate the relationship between bird-guild diversity values and habitat heterogeneity. A total of 109 resident bird species grouped in six feeding guilds were recorded: insectivores (42%), frugivores (21%), granivores (17%), nectarivores (9%), omnivores (8%) and carnivores (3%). Diversity values for the entire bird community were significantly positively related to habitat heterogeneity, but feeding guilds showed contrasting responses to habitat heterogeneity and the amount of land-use cover: insectivores and frugivores were more diverse and abundant in secondary forests than in any other land-cover. Our findings illustrate the importance of small landscape fragments as potential key refuges for the most diverse and specialized feeding guilds, such as granivores and insectivores.

The responses of plants to shade and foliar herbivory jointly affect growth rates and community assembly. We grew 600 seedlings of ten species of the economically important Dipterocarpaceae in experimental gradients of shading (0.3–47.0% of full sunlight) and defoliation (0, 25%, 50% or 75% of leaf area removed). We assessed stem diameters initially, after 2 and 4 mo, and calculated relative growth rates (RGR) with a linear model. Shading interacted with defoliation, reducing RGR by 21.6% in shaded conditions and 8.9% in well-lit conditions. We tested three hypotheses for interspecific trade-offs in growth responses to shading and defoliation. They could be positively related, because both reduce a plant's access to carbon, or inversely related because of trade-offs between herbivore resistance and tolerance. We observed, however, that species varied in their response to shading, but not defoliation, precluding an interspecific trade-off and suggesting that plants tolerate shade and herbivory with differing strategies. Shading most strongly reduced the growth of species with less-dense wood and larger seeds. The strong and variable growth responses to shade, contrasted with the weak and uniform responses to defoliation, suggest that variation in light availability more strongly affects the growth of tropical tree seedlings, and thus community assembly, than does variation in herbivory.

There is little understanding of how large mammalian herbivores in Asia partition habitat and forage resources, and vary their diet and habitat selection seasonally in order to coexist. We studied an assemblage of four large herbivores, chital (Axis axis), sambar (Cervus unicolor), gaur (Bos gaurus) and Asian elephant (Elephas maximus), in the seasonal tropical forests of Bandipur and Mudumalai, South India, and tested predictions regarding the species’ seasonal diet browse : graze ratios, habitat selection and habitat-niche preference and overlap. Field data collected for the study included the seasonal variation in grass quality, the seasonal variation in δ13C in the species’ faeces and the seasonal variation in the species’ habitat selection and overlap using a grid-based survey. Results of the δ13C analyses showed that the chital was more of a grazer in the wet season (−17.9‰ to −21.6‰), but that it increased the proportion of browse in its diet in the dry season (−25.6‰ to −27.7‰); the gaur was a grazer for most of the year (−15.3‰ to −18.6‰); the sambar preferred to browse throughout the year (−21.1‰ to −30.4‰); and that the elephant was a mixed feeder (−14.2‰ to −21.4‰). Elephant habitat-niche breadth was high (0.53 in wet and 0.54 in dry) and overlapped equally with that of the other species in both seasons (0.39–0.94). The gaur had the most restricted habitat-niche breadth in both seasons (0.25 in wet and 0.28 in dry), and it switched from the moist deciduous habitat in the dry season to the dry deciduous habitat in the wet season. These results offer the first insights into the seasonal variation in browse : graze diet ratios and the habitat-niche overlap amongst the common largest-bodied mammalian herbivore species found in South India.

In this study, we investigated whether landscape-scale variation of soil P accounts for 13C and 15N composition of detrital invertebrates in a lowland tropical rain forest in Costa Rica. The top 10-cm soil, leaf-litter samples and plant foliage were collected among 18 plots representing a three-fold soil P gradient during 2007–2009. Body tissue of litter invertebrates (extracted from leaf-litter samples) along with soil, leaf litter and green foliage were analysed for total C, total N, δ13C and δ15N values. Differences in δ13C and δ15N signatures across plots and relative trophic distances of detrital food webs (Δ δ15N), and their variation with soil P gradient were evaluated. We found soil P gradient had a significantly positive correlation with δ15N of Asterogyne martiana foliage, leaf litter, collembolans and oribatid mites. The δ15N of the collembolans and pseudoscorpions positively correlated to leaf-litter δ15N. Δ δ15N between the trophic levels remained consistent across the soil P gradient. Higher δ15N in the collembolans and oribatid mites might be derived from their consumption on 15N-enriched decayed debris or fungal hyphae growing on it. It suggests that fine-scale soil P variation can affect trophic dynamics of detrital arthropods via regulation of microbial community and nutrient dynamics.

The present study examined the effect of a catastrophic cyclone (Aila) on ichthyofaunal assemblages in a tidal river of the Sundarban Delta. Sampling in six stations with a gill-net of 20-m length and 1-cm mesh size resulted in the collection of 63 species in a pre-Aila survey. Among them, 16 species were not available in the year after the cyclone. However, 12 new species were added to the assemblages in the post-Aila year during which 59 species were recorded. Analysis of Similarity (ANOSIM) confirmed significant changes in fish assemblages after the cyclone with a corresponding reduction of the species diversity and variation in the seasonal pattern of abundance. Hydrological parameters also differed with a significant surge in nutrient concentrations. Tolerance to low dissolved oxygen seemed to be a determinant factor as evident from the higher abundance of certain fishes viz. Harpadon nehereus, Liza parsia, Pampus argentius, Tenualosa ilisha and Toxotes chatareus during post-Aila year. Despite the recovery of the ichthyofaunal assemblages at the later stage of the study, a strong seasonal variation was persistent. The study therefore suggests that environmental variation in terms of increasing temperature and salinity elicit greater response in an estuarine community than temporary natural disturbances even as severe as cyclones.

Ecological and morphological traits of fruiting trees, such as spatial distribution (Levey et al. 1984), crop size (Howe & vande Kerckhove 1981, Korine et al. 2000, Leighton 1993, Murray 1987), local availability of fruit (Sargent 1990), seed size or pulp/seed mass ratio (Julliot 1996a, Leighton 1993, McConkey et al. 2002, Russo 2003, Stevenson et al. 2005) and nutritional value and concentration of secondary compounds (Leighton 1993, Milton 1980, Sallabanks 1993), influence fruit preference in animals. In general, frugivores maximize energy intake by consuming ripe fruit with smaller seeds, higher pulp/seed ratio, bigger crop size, more nutritional fruits or fruits with fewer secondary compounds (Howe & vande Kerckhove 1981, Julliot 1996a, Korine et al. 2000, Leighton 1993, Milton 1980, Murray 1987, Russo 2003, Stevenson et al. 2005).

Accurate measurements of seed rain are important for understanding tree reproduction (Greene & Johnson 1994), forest regeneration (Cole et al. 2010, Cubiña & Aide 2001, Howe et al. 2010, Zahawi & Augspurger 2006), forest ecology (Muller-Landau et al. 2008, Terborgh et al. 2011) and maintenance of community diversity (Harms et al. 2000). Seed traps generally consist of a bucket or net of a fixed area suspended 0.3–1 m above the ground, and seeds are typically collected once or twice per month. An implicit assumption of all seed-rain studies is that traps do not influence seed dispersal. Should birds perch on and defecate seeds into seed traps, seed abundance will be overestimated. This behaviour could produce a directional bias if birds perch on seed traps in one habitat more than others. To our knowledge, no study has considered this potential bias.

Low germination and seedling survival probabilities are reported in various species of epiphytic bromeliad (Benzing 1978, Hietz et al. 2011, Toledo-Aceves & Wolf 2008, Winkler et al. 2005; but see Cascante-Marín et al. 2008). If germination and seedling survival are limiting factors in the life cycle, differential germination and seedling survival between species should be reflected in the relative abundance of established plants (Cascante-Marín et al. 2006, 2008) and in their presence or absence in secondary vegetation (Hietz et al. 2011), while differential germination within the tree would be expected to contribute to a heterogeneous distribution of established plants within the canopy (Hietz et al. 2011, Zotz & Vollrath 2002). Many factors influence the performance and distribution of epiphytes, including forest condition, disturbance type, distance from seed source, tree size and species, microclimate, epiphyte population dynamics and physiology (Cascante-Marín et al. 2009, Hietz et al. 2011, Valencia-Diaz et al. 2010, Zotz & Hietz 2001). In this study, we tested whether germination and seedling survival rates differ between the epiphytic bromeliads Tillandsia multicaulis Steud., T. punctulata Schldl. & Cham. and T. butzii Mez, and whether species abundance reflects the ability to germinate and survive as seedlings within the cloud-forest canopy. We also explore how morphological and physiological traits of the studied species can influence their early establishment.