This study addresses the pollination ecology of shrub species in an upper montane forest in Costa Rica, where the diversity of insect visitors is much below that of the well-studied tropical forests of lower elevations. Data are presented on visitation rates by the tropical bumblebee Bombus ephippiatus to flowers of three species, pollen loads on bumblebee bodies, and pollen loads on stigmas of two of the species. High visitation rates to flowers of Palicourea brenesii were found, a species which produces copious amounts of nectar. Visitation rates to nectarless Leandra subseriata and Deppea grandiflora were much lower. Conspecific pollen comprised on average 90% of the pollen load on stigmas of Leandra, while Palicourea stigmas carried only 26 to 55% conspecific pollen. With only two ovules per flower, fruit and seed set in Palicourea were not limited by a shortage of conspecific pollen. In Leandra, 20–25% of the flowers received too few conspecific pollen grains for maximum seed set among 440 ovules per flower. Individual bumblebees showed no constancy in plant choice, judging from the high number of different pollen types (6–12) on their bodies. Workers returned frequently to the same Palicourea patch without visiting nearby Palicourea plants, which suggests the use of foraging paths.

The objective of this study was to explore the leaf tissue water relations in terminal branches, as well as the relations between xylem structure and function of five sclerophyllous species coexisting on white sands within the Amazon region. In these species, which possess costly leaves and thrive in an extremely nutrient-poor habitat, the preservation of leaf survival would be of comparable importance to the preservation of xylem vessels. Three trees per species were tagged in the field for all measurements. Minimum leaf water potential (Ψ) was −1.53 ± 0.61 and −0.94 ± 0.10 MPa during rainless and rainy days, respectively. The Ψ for turgor loss averaged −1.92 ± 0.05 MPa. Therefore, minimum Ψ was maintained within a safety range above the critical value for turgor loss. Xylem (Kx) and leaf (Kl) specific conductivity averaged 1.4 ± 0.22 and 0.00033 ± 0.000045 kg m−1 s−1 MPa−1, respectively. Water supply was favoured in species with higher vessel density, and all species depended on relatively less abundant larger vessels for water transport. This would be advantageous because leaves were unable to develop very negative water potentials in order to maintain transpiration. High transpiration rates may be restricted to a few hours daily so as to prevent cavitation of widest vessels.

Many ecological relationships that are inherently reciprocal are often studied from one perspective only (Agrawal et al. 2007). One example is the interaction between tropical forests and nearctic-neotropical migratory songbirds (hereafter migrants). Several studies have determined that some migrant populations are limited by conditions at their tropical wintering grounds in Central America, South America and the Caribbean (Marra et al. 1998, Mills 2006); however, the ecological role of migrants in these tropical forests is poorly understood.

Variation in local abundance of herbivores is influenced by several abiotic and biotic factors, but it may often be determined by the local availability of plant resources (Quinn et al. 1997). Leaf-cutting ants, common defoliators of plants in the Neotropics, are more abundant in early successional forests than in old-growth forest (Jaffe & Vilela 1989, Vasconcelos & Cherrett 1995). A recent study showed that the high density of mature leaf-cutting ant nests in early successional forests was mainly determined by the availability of pioneer plant species, largely preferred by the leafcutters (Farji-Brener 2001). The dominance of pioneer species in early successional forests decreases foraging costs for leaf-cutting ant colonies, and thus these habitats can support a high density of mature colonies. On the other hand, the effective defence mechanisms of shade-tolerant species, which dominate primary habitats, could explain the low density of mature leaf-cutting ant colonies in old-growth forests (palatable forage hypothesis, see Farji-Brener 2001). According to this hypothesis, it is proposed that leaf-cutting ant colonies in old-growth forests should concentrate their foraging effort in treefall gaps, in which sun and pioneer plant species (preferred by leafcutters), are readily available (Farji-Brener 2001, Nichols-Orians 1991a, b; Wetterer 1994). However, this prediction of the palatable forage hypothesis has not yet been explicitly documented.

Conversion of forests to agricultural land may require many bird species to use resources in fragmented landscapes in order to persist. Pasture trees can make agricultural landscapes more hospitable for birds, but we do not know what factors promote bird visitation to pasture trees. Bird use of 26 focal trees of a common pasture species, Sapium glandulosum (Euphorbiaceae), was examined in three pastures in a montane landscape in Costa Rica to understand factors influencing bird visitation. Bird visits were analysed in relation to pasture tree size, distance from forest edge, degree of isolation and epiphyte load. Foraging resources (epiphyte or tree substrate) were also measured. From May–July 2012, 52 bird species from 20 families were recorded from 926 unique visits. Bird visitation was best explained by tree size, degree of isolation and epiphyte load such that larger, more isolated trees with higher epiphyte loads attracted more birds. Birds preferred food resources from focal trees (51% of visits) rather than their epiphytes (5% of visits). The results corroborate previous findings that mature pasture trees, even when isolated, may contribute more to species persistence than smaller trees.

We studied the relationships between soil nutrient availability and microbial biomass and activity of two contrasting soil conditions in a tropical deciduous forest in western Mexico. Hilltops have higher pH, water, dissolved organic C, and ammonium concentrations than hillslopes. Our main hypothesis was that soil microbial biomass, microbial activity and bacterium species richness would be higher in soils with high availability of nutrients. Fifteen soil cores, 0–5 cm depth, were taken in the dry, early rainy and rainy season, from each of the ten replicate plots in hilltop and hillslope positions located on three contiguous small watersheds. We measured moisture, C, N and P availability, potential C mineralization, net nitrification, microbial biomass and culturable heterotrophic and nitrifying bacteria in composite samples from each plot. Microbial biomass, species richness of culturable heterotrophic bacteria and C mineralization were significantly higher on hilltops than on hillslopes. Net nitrification was, in contrast, significantly higher on hillslopes than on hilltops and counts of culturable nitrifying bacteria were also significantly higher in the rainy-season samples. Hilltops and hillslopes had low similarity in composition of culturable heterotrophic bacterial species, particularly during the rainy season. The results suggested that C and N availability and seasonal changes in soil moisture are important controlling factors for some soil culturable-bacterial species, which may affect both C mineralization and nitrification in these tropical deciduous forest soils.

Timing of germination and flowering under different environmental conditions was investigated in four coexisting serotinous desert plants: Blepharis grossa (annual herb), Geigeria data, Geigeria ornativa (facultative perennial herbs) and Petalidium setosum (perennial shrub). Germination patterns were similar under varying environmental conditions in the study species, except for P. setosum, which germinated later when conditions were less favourable. B. grossa always germinated early, G. alata and G. ornativa later, which could be explained by differences in their seed dispersal mode. Thus no obvious niche separation in timing of germination was indicated in the study species. Flowering periods varied between seasons rather than between species and no niche separation in flowering times existed between the study plants. This might indicate that either interspecific competition plays a minor role in a community of desert serotinous plants or that niche separation exists in other components of the plants' niche, such as seed dispersal, seedling establishment and/or microhabitat selection.

Many plant traits might explain the different ecological and network roles of fruit-eating birds. We assessed the relationship of plant productivity, fruit traits (colour, seed size and nutritional quality) and dietary specialization, with the network roles of fruit-eating birds (number of partners, centrality and selectivity) in the Atlantic Forest, Brazil. We classified bird species according to their dietary specialization into three categories: obligate, partial and opportunistic fruit-eating birds. To test if network roles changed according to dietary specialization, fruit productivity and traits, we used a generalized linear model analysis. The selected 14 species of plant interacted with 52 bird species, which consumed 2199 fruits. The most central and generalist fruit-eating bird, Turdus albicolis, interacted with plants that produced more fruits, such as Miconia cinerascens, and had, on average, larger seeds, such as Myrcia splendens. The most selective birds interacted with fruits with a higher concentration of lipids and less intense colour, and plants that produced fewer fruits. Obligate fruit-eating birds, such as Patagioenas plumbea, were more selective than partial and opportunistic birds. Different plant traits are therefore related to the different network roles of fruit-eating birds in the Atlantic Forest, which are also dependent on bird dietary specialization.

Laboratory and growth-chamber experiments were used to evaluate whether there was evidence for nutrient retention by tropical terrestrial ecosystems being a two-stage process involving first soil adsorption and then plant absorption. Quartz sand with and without Fe and Al oxide coatings were treated with nutrient solution, then subjected to a leaching regime that simulated early wet-season conditions at a tropical location. Nutrient cations applied were rapidly lost in the initial leaches from quartz sand without oxide coatings, but showed a more gradual loss from oxide-coated sand, indicating temporary adsorption by the latter. In a second experiment, oxide-coated sand with and without seedlings of Grevillea robusta (a non-mycorrhizal tree species) were subjected to a similar treatment and leaching losses were compared. The presence of seedlings significantly reduced the losses of all nutrient cations, with the effect being minimal for Na and greatest for K, confirming that plants can gain access to temporarily adsorbed nutrients. More typical tropical soil-vegetation systems are likely to possess properties that magnify both the adsorptive and absorptive processes that have been documented in these experiments, justifying extrapolation of the experimental results to these natural systems. The existence of a two-stage process of nutrient retention provides a plausible explanation for the resistance of most tropical ecosystems to rapid loss of nutrients following events such as fires, which provide acute nutrient loading to the system.

Wild populations of a small neotropical primate, Geoffroy's tamarin (Saguinus geoffroyi), were studied through 30-s instantaneous observational sampling to identify different canopy habitats used by this tamarin. Tree and shrub canopies were sampled in randomly selected plots and in nearby plots that tamarins were observed to use in the forests of Agua Clara, Panama (28 d, 59 100-m2 plots, 32.25 h of tamarin observations, 27 tamarins in total), and in the nearby forests of Barro Colorado Island (49 d, 29 100-m2 plots, 29.6 h of tamarin observations, 14 tamarins in total). Light penetration through the canopy, ambient temperature and humidity, presence of other primates, stem diameters, plant life-forms, distribution of woody flora, abundance of fleshy fruits and arthropods typically consumed by tamarins and abundance of thorny vegetation and biting arthropods in plots used by tamarins were compared with control plots. Habitats used by tamarins had significantly shorter distances between adjacent tree canopies and between canopies and the ground. There was a random distribution of large insects and fleshy fruits that tamarins are known to eat. Habitat selection by tamarins may not be influenced by spiny vegetation, but tamarins may avoid areas with abundant hooked thorns and blood-sucking arthropods. Mobility along runways in various tiers of a rain-forest canopy may be of primary importance, with local abundance of food being a secondary consideration in habitat selection by this small primate.

High densities of palms are common in many tropical forests. In some cases, the dominance of palms has been associated with a depauperate understorey and high rates of native seedling mortality. A variety of different potential mechanisms has been suggested to explain the sustained palm dominance in the understorey and canopy of these forests. Working in a Cocos nucifera-dominated wet tropical forest at Palmyra Atoll in the central Pacific, we examine how litterfall from this pantropical, and economically important palm, impacts seedling survival. We compare rates of litterfall, and rates of litterfall-associated damage, between forest stands dominated by C. nucifera (coconut palm) and forest stands with low abundance of C. nucifera. To assess litterfall damage we survey damage to both artificial seedlings (n = 711), outplanted real seedlings of two species (with and without protection via caging; n = 204), and standing rates of litterfall damage. We find that rates of large-litterfall damage were an average of five times higher in sites with high densities of C. nucifera. Associated with these increases we observe that levels of physical damage to artificial model seedlings caused by litterfall over a 4-mo period increased from 4.9% in sites with low abundance of C. nucifera to 16.1% in sites with high abundance of C. nucifera. Extrapolated to annual rates, litterfall damage of this magnitude exceeds the average levels observed in other published studies. Living native seedlings also showed more than 300% higher levels of mortality in forest stands with high densities of C. nucifera, a difference that was greatly reduced when protected by caging from litterfall. In contrast, uncaged C. nucifera seedlings actually had slightly higher survivorship in habitats dominated by conspecifics. We suggest that litterfall damage may be an important mechanism by which this tropical palm reaches and maintains near monodominance in many coastal and insular habitats.

Seasonal variations in the breakdown and dynamics of chemical elements in Ficus fistulosa leaves in a mixed forest on Hong Kong Island were investigated between October 1982 and September 1983. Mean rate of leaf material weight loss from coarse-mesh (3 mm) bags was 1.82% day-1, about four times that inside fine-mesh (0.2 mm) bags (mean rate 0.44% day-1). Breakdown rates varied seasonally with maximum rates in spring or summer, and were significantly correlated with prevailing temperatures, the rainfall of the two previous months, and the soil moisture content of the previous month. Potassium and Mg were rapidly leached from leaf material throughout the year while the concentrations of C, N, P, Ca and Na remained relatively stable. In the absence of macrofauna (inside fine-mesh bags) decomposition rate constants (k) were positively correlated with the mean abundance of mites and Collembola, as well as with total invertebrate abundance. In the presence of macrofauna (inside coarse-mesh bags) decomposition rate constants were positively correlated with isopod and amphipod abundance. There was no significant correlation between breakdown rates of leaf material and mesofaunal abundance inside coarse-mesh bags. The importance of climate and invertebrates as rate determinants of Ficus decomposition is discussed.

The chemistry of epiphytic lichens was determined in two Venezuelan cloud forests adjacent to the Caracas Valley at Altos de Pipe and El Avila National Park. This is the second component of a two-part study examining the chemistry of fogs and their effects on sensitive biota in these forests. The widespread lichen Parmotrema madagascariaceum was chosen as an indicator of trace metal input. Background lichen collections and transplant experiments were carried out to evaluate spatial trends in atmospheric depositon of trace metals at different altitudes and exposures of the two montane locations. Elevated concentratons of metals including Pb and Zn were seen in lichen tissue and associated bark. Lead levels in lichens reached 190 μg g-1 dry wt. Lichens transplanted from relatively ‘clean’ to more polluted sites showed significant increases of metals, particularly Pb. Increases of up to 6.3 μg Pb g-1 mo-1 after 6 and 10 months were recorded relative to background and in situ lichen material. In contrast, when lichsens were reciprocally transplanted in nylon net bags from less to more exposed sites there was a significant decrease in Pb and Zn concentrations after 6 and 10 months. With long-term exposure to elevated concentrations of these trace metals epiphytic lichens, as well as other sensitive cloud forest biota, may be at risk of decline.

Several species of non-venomous snake are known to flatten their heads when disturbed, and this behaviour has been suggested to be a mimicry of vipers (Arnold & Ovenden 2002, Hailey & Davies 1986, Young et al. 1999). Using plasticine models, Guimarães & Sawaya (2011) tested the antipredatory function of a triangular head shape in snakes. Their article presents the first published empirical experiment testing the adaptive significance of vipers' triangular head shape. Guimarães & Sawaya (2011) found no support for the viper mimicry hypothesis. Accordingly, they concluded that ‘the shape of [the] head seemed not to confer advantage itself’. Although the use of plasticine models is a generally accepted method of testing predation pressure on snakes, we argue that the experiment may have failed to find the antipredatory function of triangulation due to the pooling of attacks by mammalian and avian predators. Mammals generally rely on olfactory cues during foraging. Plasticine has a strong odour which does not resemble the odour of any prey species. It is thus unlikely that mammals would treat snake replicas as true snakes.

The nilgai (Boselaphus tragocamelus) is a widespread species in India that forages in forest as well as on agricultural lands. In Tadoba-Andhari Tiger Reserve, India, it typically takes to crop-raiding at night, while it rests and forages in forest during the daytime. We studied changes in herding and vigilance behaviour during foraging in forest versus in agricultural lands and monsoon versus post-monsoon in the years 2012–2015. We recorded number of individuals (herd size), sex-age composition and number of individuals per unit area of herd's spread (compactness) for every herd under observation using instantaneous scan sampling in forest (176 herds) and farms (321 herds), while spatial trends in herd size on agricultural lands were studied using transect sampling at night. Vigilance behaviour was studied using focal-animal sampling in forest (n = 91) and farms (n = 52) by choosing a single individual per herd under 15 min of observation. Herd sizes were significantly larger in forest (monsoon, median = 3, interquartile range (IQR) = 2–6, post-monsoon, median = 5, IQR = 3–8) than on farms adjacent to forest (monsoon = 3, IQR = 1–5, post-monsoon = 4, IQR = 2–5) and further decreased non-linearly with distance from the forest edge. Herds were more compact, i.e. with smaller inter-individual distance in forests than on farms. Crop-raiding was found to be female-biased, and adult males as well as newborn calves were observed on agricultural lands significantly less frequently. The median vigilance frequency was significantly higher on farms (1.4 min−1) as compared with forests (0.205 min−1) but the median unit scan duration was significantly less in farms (6 s) compared with forest (60 s). The observed differences are likely to be due to difference in the nature of risk faced in the two habitats. In forest, detection of ambush predators such as tigers that occur at a low density, requires careful watch and larger herds increase the chances of detection. In contrast, detection of guarding farmers on agricultural lands who are present at a higher density and make their presence conspicuous to drive away crop raiders would need a glance of smaller time duration. As crop-raiding occurs at night, moonlight is likely to affect the frequency of crop-raiding but we did not find evidence for any deterrent effect of moonlight on the frequency of crop-raiding. The data suggest that the nilgai exhibits substantial behavioural plasticity in response to different nature and levels of risks faced in the two habitats.

Ecological theory predicts that interspecific interactions can affect population and community dynamics. Two experiments were conducted on Mantidactylus bicalcaratus and M. punctatus, two sympatric frog species from Madagascar that live and breed in rain-forest plants (Pandanus spp.), to test for interspecific competition. The first experiment examined larval growth rates and survivorship with and without conspecifics. While survivorship did not differ among treatments, mean growth rates for M. bicalcaratus were significantly reduced in the presence of M. punctatus larvae. The second experiment manipulated the presence and density of adults in Pandanus plants. Emigration from and immigration to experimental plants tended to be higher and lower, respectively, for M. bicalcaratus in the presence of M. punctatus, but these differences were not significant. These results demonstrate asymmetric competition (at least as larvae) and indicate that M. punctatus is the superior competitor. Field data showed that M. bicalcaratus was found significantly more frequently in the absence of M. punctatus. Also, M. bicalcaratus populations were significantly more likely to go locally extinct in the presence of M. punctatus. These data suggest that asymmetric competitive interactions are important influences on the dynamics of these populations.

East African tenebrionid beetles of the species Zophosis congesta are active on sun-exposed surfaces in dry habitats during the hottest part of the day, when most other animals have retreated to protected areas. They remain on the surface at ambient temperatures up to 65°C which is 15°C above their highest tolerated body temperature. The beetles appear to regulate their body temperature behaviourally. They frequently rest and cool in the shade, and after each cooling period they remain on the sun-exposed surface until the heat influx from the environment has caused the body temperature to rise close to the lethal level. They have relatively low rates of transpiratory water loss, and appear unable to depress their body temperature by means of evaporative heat loss. The rate of metabolic production of water amounts to only about 20% of the rate of transpiratory water loss. Thus, the beetles depend strongly on water intake from dietary sources. The advantage of this type of activity pattern is probably avoidance of predators.

Some large-seeded tree species have cotyledonary reserves that persist for months after seedling establishment. We carried out two screened growing-house experiments with seedlings of Gustavia superba (Lecythidaceae) to test hypotheses proposed to explain why cotyledons are retained. We grew seedlings from large and small seeds in sun and shade to determine if cotyledon reserves supplement photosynthetic carbon gain, and in a second experiment applied defoliation and shoot removal treatments to determine if reserves are allocated to resprout tissue. In each experiment we tracked cotyledonary resource use over time and measured the fraction of seedling biomass allocated to roots and shoots. We found no evidence that light environment, seed size or damage treatment affected the rate of cotyledon resource usage; 20% of the cotyledonary mass remained 9 wk after leaves were fully developed in both sun and shade and 25–30% of the cotyledonary mass remained 6 wk after leaf or shoot removal. Instead, cotyledon reserves appear to be slowly translocated to roots regardless of light environment or seedling damage. Once seedlings are established, lost tissue is replaced using reserves stored in roots; in high light, damaged seedlings had a lower root mass fraction (0.42) than undamaged ones (0.56) when considering the mass of tissue removed and resprout tissue combined. We conclude that cotyledon reserves are important for resprouting during early seedling emergence and establishment, but do not directly contribute to seedling growth or biomass recovery from herbivores at the post-establishment stage. Persistence of cotyledons may ultimately depend on the development of sufficient root mass for reserve reallocation.

The production of domatia is a crucial step in the evolution of myrmecophytism (Fiala – Maschwitz 1992). Current models for the evolution of domatia predict that the ancestral state is one in which domatia production occurs later in a plant's ontogeny, while more derived ant-plants produce precocial domatia (Brouat – McKey 2000). I report that the neotropical tree Cordia gerascanthus L. represents a case of the former, in which domatia appear in mature trees. Through field and herbarium investigations, I have discovered that some C. gerascanthus individuals produce swollen, hollow, stem cavities that are ant-inhabited, while other C. gerascanthus individuals produce only solid stems. I suggest that C. gerascanthus, a species that produces domatia later in ontogeny, is an ideal system in which to investigate the basis of domatia evolution.