Insectivorous birds and bats often protect plants through density- and trait-mediated cascades, but the degree to which insectivores reduce herbivorous arthropods and leaf damage varies among systems. Top-down interaction strength may be influenced by the biotic and abiotic context, including the presence of vegetation-disturbing animals. We tested two hypotheses: (1) insectivorous birds and bats initiate trophic cascades in tropical rain-forest understorey; and (2) the native, omnivorous collared peccary (Pecari tajacu) negates these cascades via non-trophic effects. We studied the top-down effects of birds and bats on understorey plants in north-eastern Costa Rica using 60 netted exclosures within and outside existing peccary exclosures. Excluding birds and bats increased total arthropod densities by half, both with and without peccaries. Bird/bat exclosures increased Diptera density by 28% and leaf damage by 24% without peccaries, consistent with a trophic cascade. However, bird/bat exclosures decreased Diptera density by 32% and leaf damage by 34% with peccaries, a negation of the trophic cascade. Excluding peccaries increased leaf damage by 43% on plants without birds and bats. This is the first study, to our knowledge, to demonstrate that the non-trophic activity of an omnivorous ungulate can reverse a trophic cascade.

For a total of 17 mo, we investigated the impact of a road constructed through pristine tropical lowland rain forest, on the composition and structure of the resident anuran community in the Ulu Temburong National Park (Brunei Darussalam). One year after road construction, eight new anuran species had immigrated into the impacted area. Encounter surveys were conducted and radio-transmitters attached to a total of 16 frogs to identify habitat use and distribution of the largest (>130 mm SVL) immigrant species (Limnonectes ingeri) in comparison with a similar sized resident congener. A strong preference for roadside habitat was found for the immigrant. However, several incursions of more than 500 m beyond the road into the pristine forest were also recorded. Over 200 stomach content samples as well as stable nitrogen isotope ratios of 76 individuals were used to assess the trophic ecology of the two species. Invertebrate diet composition did not differ. However, the immigrant species ate over 400% more frogs than its resident congener and had a significantly higher δ15N ratio, indicating a higher position in the food web. This suggests that L. ingeri acts as a new top frog predator in the system and indicates that it may have a significant negative impact on the local anuran community. Overall, road construction in the absence of logging has led to the immigration of new frog species with impacts far beyond the linear disturbance of the road itself.

Positive plant interactions have strong effects on plant diversity at several spatial scales, expanding species distribution under stressful conditions. We evaluated the joint effect of climate and grazing on the nurse effect of Croton wagneri, by monitoring several community attributes at two spatial scales: microhabitat and plant community. Two very close locations that only differed in grazing intensity were surveyed in an Ecuadorian dry scrub ecosystem. At each location, two 30 × 30-m plots were established at four altitudinal levels (1500, 2630, 1959 and 2100 m asl) and 40 microsites were surveyed in each plot. Croton wagneri acted as community hubs, increasing species richness and plant cover at both scales. Beneath nurses mean richness and cover values were 3.4 and 21.9%, and in open areas 2.3 and 4.5%, respectively. Magnitude of nurse effect was dependent on climate and grazing conditions. In ungrazed locations, cover increased and diversity reduced with altitude, while grazed locations showed the opposite trend. In ungrazed plots the interactions shifted from positive to negative with altitude, in grazed locations interactions remained positive. We conclude that the nurse effect is a key mechanism regulating community properties not only at microsite but also at the entire community scale.

Activity patterns of animals are generally influenced by many factors. We hypothesized that the behavioural responses (i.e. activity time-budget allocated to vigilance, feeding and moving) of mountain nyala (Tragelaphus buxtoni) should vary with habitat type, season, group-size and sex-age class. We randomly established a total of 12 permanent walking transects with the aid of a GPS device across three major habitat types used by the mountain nyala (i.e. four transects in each habitat). Following each transect, we conducted focal-animal observations to quantify the time-budget allocated to vigilance, feeding and moving. A total of 119 and 116 focal-animals were assessed in the wet and dry season respectively. Moreover, along each transect, seven habitat variables were collected in systematically laid 109 circular plots each with a 5-m radius (i.e. 31, 41 and 37 plots in the cleared vegetation, plantation and natural forest respectively) in the wet and dry season. We developed behavioural models by correlating the time-budget (i.e. proportion of time vigilance, feeding and moving) of the focal-animals in accordance with habitat variables, group-size and sex-age class. In the wet season, mountain nyala devoted most of their time to vigilance, but they allocated the largest proportion of their time to moving in the dry season. Vigilance differed among the three habitats and was highest in the cleared vegetation during the dry season. Contrary to expectations, adult males were more vigilant than both adult females and sub-adults during the dry season. The behavioural models based on time-budget help to predict how the mountain nyala perceive their environment and trade-off between food acquisition and safety in the wet and dry season. The study also improves our understanding of the adaptive behavioural ecology of the endangered mountain nyala.

At the landscape level, the four-horned antelope is confined to tropical dry deciduous forests and within these, their distribution is patchy. Various factors have been proposed as determinants for their patchy distribution within landscapes, but none provided an adequate explanation. We hypothesized that availability of a constant supply of forage influenced the species distribution. We found that the four-horned antelope mainly fed on fruits and flowers, and that a total of 60% of the tree species in Panna Tiger Reserve bore fruits at different times of the year. High tree species richness in habitat patches was considered a surrogate for constant supply of forage for the four-horned antelope. Data from 547 sighting locations between 2002 and 2006 and six spatial layers were analysed using maximum entropy to produce a probability distribution model for the four-horned antelope in Panna Tiger Reserve. Our model predicted that habitat patches summing up to only 9.5% of the 543 km2 of Panna Tiger Reserve had high probability of distribution (>0.5) of four-horned antelope. Although all variables contributed to the distribution model of the four-horned antelope, explanatory power was highest for tree species richness within habitat patches. The distribution of four-horned antelope within tropical dry deciduous forests can be treated as an indicator of high tree diversity and hence habitat quality.

We assessed seedling dynamics and understorey light before and after a hurricane in five randomly selected 5 × 5-m subplots, within 30 permanent sample plots covering a total area of 3750 m2 in a lower montane wet tropical forest, Jamaica over a period of 3 y. Understorey light increased (≈ 60%) following the passage of Hurricane Dean in 2007 but decreased in 2009. Overall, seedling density was positively related to light and survivorship was positively related to both light and density. Mortality was significantly lower and most species recorded their highest growth when the canopy was open (2007–2008). However, lower diversity during this period coincided with higher (average) mortality of uncommon species. The hurricane altered the relative importance of interactions between light, seedling density and dynamics. Consequently, interactions were significant before or 2 y after but not 1 y after the hurricane and their significance varied among the years and species. Periodic changes in the importance of these interactions and the effects of the hurricane were used to separate 12 common species along a continuum of responses, which ranged from positive (lower mortality), neutral to negative (lower growth). Our results indicate that hurricanes have positive and negative effects on seedling dynamics; therefore an increase in the intensity and frequency of hurricanes will likely alter seedling composition, and hence forest structure.

We outfitted six male Hawaiian geese, or nene (Branta sandvicensis), with 45-g solar-powered satellite transmitters and collected four location coordinates d−1 from 2010 to 2012. We used 6193 coordinates to characterize migration corridors, habitat preferences and temporal patterns of displacement for 16 migration events with Brownian bridge utilization distributions (BBUD). We used 1552 coordinates to characterize stopovers from 37 shorter-distance movement events with 25% BBUDs. Two subpopulations used a well-defined common migration corridor spanning a broad gradient of elevation. Use of native-dominated subalpine shrubland was 2.81 times more likely than the availability of this land-cover type. The nene differed from other tropical and temperate-zone migrant birds in that: (1) migration distance and the number of stopovers were unrelated (Mann–Whitney test W = 241, P < 0.006), and; (2) individual movements were not unidirectional suggesting that social interactions may be more important than refuelling en route; but like other species, nene made more direct migrations with fewer stopovers in return to breeding areas (0.58 ± 0.50) than in migration away from breeding areas (1.64 ± 0.48). Our findings, combined with the direction and timing of migration, which is opposite that of most other intratropical migrants, suggest fundamentally different drivers of altitudinal migration.

Calcium is an important nutrient for birds, especially for eggshell production and the mineralization of the skeleton of developing young. In temperate regions insects and seeds that form the bulk of the diet of breeding passerines do not contain sufficient calcium to meet the needs of breeding females and young; these birds obtain their calcium by eating snails, woodlice and millipedes. Little is known about the way tropical frugivorous passerines meet their calcium needs. The calcium contents of fruits of 34 species eaten by birds during the breeding season in mature floodplain forest in south-eastern Peru were determined. The suitability of these fruits as calcium sources for hypothetical 10-g and 25-g birds and for 26 species of frugivore that breed at the study site was evaluated based on bird body weight and on the rictal width of the bill, which influences feeding. Fruits of five species in the study area appear to be suitable sources of calcium for birds ≤25 g, although those of Ficus killipii (Moraceae) are likely optimal. The latter contain a lot of calcium (2.48% dry weight of pulp or c. 4.15 mg per pulp per fruit) and are small enough (mean diam. = 9 mm) for most birds to swallow whole, and trees produce large crops. Snails, woodlice and millipedes are common in the area and also contain sufficient calcium to meet birds’ needs. In addition, birds could likely meet their calcium needs through geophagy at natural mineral licks.

Successional state of forest and availability of pioneer plants are recognized factors affecting densities of leaf-cutting ants. However little is known about how abiotic factors can shape nest distributions. We investigated the effect of topography, soil, forest successional state and inundation risk on nest density and size of Atta cephalotes colonies along streams in a tropical wet forest in Costa Rica. In each forest type, we surveyed 12 sites, each site comprising five transects (10 × 100 m) varying in topography and proximity to streambeds. We found no difference regarding nest size or density between forest types or soil consociation. Nest density varied with topographic environment, with significantly higher nest density on slope tops (farther from streambeds) and without colonies in valley bottoms (closer to streambeds). Nests found in areas affected by the last great inundation before our study were scarcer and smaller than nests in non-flooded areas. We showed that inundation events favour an accumulation of Atta colonies towards higher sites, where they are also allowed to become larger and may survive longer. Inundation risk may be a strong force shaping the distribution of leaf-cutting ant nests in tropical floodplain forests, even concealing the relevance of successional state of forest.

Land-use change in tropical forests can affect the micro-environment for decomposition under modified canopies. In turn, decomposition may have consequences for soil fertility and ecosystem sustainability. The effects of the conversion from primary forest to pastures on leaf-litter decomposition and its recovery in secondary forests 20 y after pasture abandonment were evaluated using litterbags and a general mixed model approach. Litterbags containing leaf-litter of two contrasting qualities were placed in those three ecosystems and the mass remaining after 90 d was quantified. The mass remaining was 50% lower in high- than in low-quality leaves. The effects of the decomposition environment depended on the substrate quality. Although differences among ecosystems were not significant for low-quality leaves, high-quality leaves decomposed more slowly in pastures than in forests (mean dry mass remaining was 38% in pastures, 14% in secondary and 12% in primary forest). The decomposition of common substrates did not differ among forests. Results show that the conversion of primary forest to pasture may produce conditions for slower decomposition; however, these conditions appear be restored to a great extent in 20-y-old secondary forests.