The agouti (Dasyprocta punctata) meticulously defleshes Astrocaryum standleyanum palm seeds before scatter hoarding. On Barro Colorado Island, Panama, we experimentally tested three hypotheses on how this behaviour could reduce seed predation to the mutual benefit of the tree and the rodent. The first and established hypothesis – that defleshing reduces seed predation by bruchid beetles by intercepting larvae – was rejected. Experiments in which manually defleshed seeds or entire fruits were incubated at different times showed that defleshing reduced bruchid infestation before fruit fall but not after fruit fall. The second hypothesis – that defleshing reduces cache pilferage by making seeds less conspicuous – was supported. An experiment in which intact fruits and manually defleshed seeds were placed in mimicked agouti caches and followed showed that seeds with flesh were pilfered at higher rates than defleshed seeds. The third hypothesis – that defleshing reduces post-dispersal infestation of cached seeds – was rejected. An experiment in which intact fruits and manually defleshed seeds were placed in mammal exclosures and later collected to assess infestation showed that burial reduced seed infestation but defleshing did not. Thus, seed defleshing reduced palm seed predation, but in a different way than previously believed. We also found that (1) bruchid beetles can be pre-dispersal rather than post-dispersal seed predators, (2) seed infestation by scolytid beetles may control bruchid larvae, and (3) scolytids rather than bruchids are the main invertebrate seed predators of this palm.

Species interactions have been recently depicted as networks, in which each species is connected to one or more other species in binary interaction matrices. Forty networks of epiphytic orchid and host tree species were assessed in Brazilian gallery forests. The nestedness of the networks was estimated with the NODF index and the significance was tested with null models. The phylogenetic structure of the network was also assessed, by searching for phylogenetic signals in the number of interactions and in the similarity of interacting species. In total, 105 orchid species and 132 host tree species were sampled. A nested pattern in all orchid–host tree networks was found. However, phylogenetic signals were not observed. The results support that the host specificity of orchids is small and most of the interactions occur among generalist orchids and generalist host trees. While the concept of species-specificity can thus be rejected, the extreme alternative – that interacting orchids and host trees are not a random subset of the regional species pool – can be dismissed as well. However, factors other than phylogenetic history may structure interaction networks of epiphytic orchids and host trees.

We know surprisingly little about the fate of seeds of the Brazil nut tree (Bertholletia excelsa) under natural conditions. Here we investigate seed removal, predation and caching of Brazil nuts by scatter-hoarding rodents in the wet and dry seasons, based on an experimental approach using 900 thread-marked seeds. We tracked the fate of seeds handled by these animals to examine how seasonal food availability may influence caching rates, dispersal distances and cache longevity. Most seeds exposed to dispersal trials were removed by scatter-hoarders during the first week in both seasons and seeds were generally buried intact in single-seeded caches within 10 m of seed stations. Seeds were removed significantly faster and buried at greater distances during the dry season. The proportion of seeds buried intact was considerably higher in the wet season (74.4%) than in the dry season (38.2%). Most (99.4%) of the 881 primary caches monitored were recovered, but these had a significantly shorter lifetime in the dry season. Our results show that rodents are highly skilled at retrieving buried Brazil nuts and that caching behaviour appears to be affected by seasonal resource abundance. Reduced seed availability due to intensive harvest could potentially create a dry-season scenario where most seeds succumb to pre-dispersal predation, thereby adversely affecting the natural regeneration of Brazil nut trees.

In rain forests the fate of seeds defecated by mammals is often affected by dung beetles, but these effects can vary with mammal species. In a Colombian forest, differences in Scarabaeinae assemblages attracted to spider monkey (Ateles hybridus) and howler monkey (Alouatta seniculus) defecations were assessed. In total, 791 beetles of 35 species were captured. Mean number of individuals was similar for both dung types; mean number of species was higher for Alouatta traps. The effects of dung type (Alouatta vs. Ateles) and defecation pattern (clumped vs. scattered) on the fate of 220 Rollinia edulis (Annonaceae) seeds were determined. Burial by beetles occurred for 61% of the seeds (mean depth 2.6 cm). Seeds in Alouatta dung and in clumped defecations had higher burial rates. Horizontal movement (mean 11 cm) occurred for 80% of the seeds; no significant effects of experimental factors were detected. Survival was higher for buried vs. surface seeds. In a separate experiment, no differences were detected between dung types in the proportion of seeds buried by beetles. Changes in dung texture might have been responsible for the contrasting results. When assessing the effectiveness of an endozoochorous plant–mammal interaction, secondary dispersal by dung beetles should be addressed too.

It has been suggested that vascular epiphyte composition and abundance may be influenced by forest host composition. We studied the epiphyte species distribution among host species of a tropical dry forest in Mexico. All the epiphyte stands supported by woody plants (dbh > 3 cm) of ten forest plots (0.1 ha each) were counted. We measured the dbh of all the hosts, noted their bark characteristics (texture and peeling behaviour), and measured the bark thickness of the most abundant host species. Epiphyte distribution was biased toward a high concentration of epiphytes in three host species and a lower abundance of epiphytes on five host species. This was consistent among epiphyte taxa and host species, allowing us to classify hosts as preferred (with more epiphyte stands than expected by chance) and limiting species (with fewer epiphyte stands than expected by chance), at a community level. Host quality did not relate to mean phorophyte size (measured as basal area) or to bark characteristics (peeling behaviour, thickness and texture) between species. For some epiphyte taxa, the observed distribution indicated that the forest contained preferred and limiting host species mainly. Our data suggest that the epiphyte species in the forest studied could be host limited. We concluded that neither host size nor obvious bark characteristics can be used to predict epiphyte distribution and that further research is necessary.

In this study I document the growth rate and age of trees in an old-growth montane Hawaiian wet forest and use these results to evaluate the cyclic succession model for forest dynamics. I used two methods to estimate the age of trees – the crown-class model and radiocarbon dating. Over 6000 trees belonging to eight species were tagged and measured over 7 y on Hawaii Island. Growth rates for the dominant tree (Metrosideros polymorpha) were relatively low (mean = 1.3 mm y−1) and varied with tree size and crown class. 14C-based age estimates for 27 M. polymorpha trees loosely corroborated estimates based on the crown-class method. The oldest tree dated by 14C had a median age of 647 y BP, placing it among the oldest documented angiosperm trees in the northern hemisphere. 14C dating revealed that the upper canopy may be comprised of three distinct age groups of M. polymorpha trees of similar size, with the median age of each group separated by 200–250 y. The high density of large, very old trees in multiple groups is unusual for a tropical forest and indicates that forest development may occur through gap-phase regeneration at a fine scale and stand-level mortality at a coarser scale.

Using a data set from 36 studies, we evaluated variation in ungulate biomass across a rainfall gradient using polynomial models, aiming to: (1) compare neotropical and palaeotropical dry and wet forests as well as African savannas; and (2) evaluate the usefulness of polynomial models to predict ungulate biomass at neotropical sites using data from a dry forest (Chamela-Cuixmala Biosphere Reserve, CCBR) and a wet forest (Montes Azules Biosphere Reserve, MABR) in Mexico. Our results showed that an overestimation of expected ungulate biomass can be obtained for some tropical forests if data from African savannas are included in the model. This overestimation was particularly high for predicted ungulate biomass in neotropical dry forests. These ecosystems sustain different ungulate biomass values even when rainfall is similar. This was particularly true for some tropical dry forests and savannas. Rainfall predicted the expected ungulate biomass in neotropical ecosystems relative to that of palaeotropical ones under similar precipitation regimes, but did not correctly predict the observed ungulate biomass at local level if data outside the Neotropics are included in the model. This was more evident when we compared observed biomass against predicted biomass in the tropical dry forest of CCBR, while some polynomial models successfully predicted the observed biomass for the tropical wet forest of MABR. Factors such as Pleistocene extinctions and the absence of large, native grazers (i.e. Bovidae) that have kept ungulate richness and standing biomass relatively low in neotropical forests should be accounted for when comparing data sets from different regions.

This study examined patterns in the species richness and abundance of small non-volant mammals along a tropical altitudinal gradient in north-eastern Australia. We investigated whether a mid-altitudinal peak in diversity was apparent, and if it occurred, whether it was determined by particular environmental conditions. We sampled a small-mammal assemblage at 17 sites distributed along an altitude-environmental gradient from savanna (350 m) to rain-forest vegetation (1000 m). Over four separate occasions (5100 trap-nights) we recorded 17 species of mammal with 416 captures. A positive non-linear relationship between altitude and mammal species richness and abundance was observed, peaking at the 800–900 m range. Many species were distributed across a range of altitudes, while others were strongly associated with particular habitat conditions. There was a distinct reduction in abundance and species richness at low altitudes associated with the less complex vegetation, lower productivity and possible anthropogenic effects. Key findings were: that small-mammal richness peaked towards the summit of the gradient and not at one-half the maximum altitude predicted by the mid-domain effect; contrasting conditions and greatest vegetation juxtaposition had the greatest influence on the patterns recorded; and that local idiosyncratic influences such as habitat factors, land management and historical biogeography are significant.

The wet tropical forests in Madagascar have endemic dung beetles that have radiated for tens of millions of years using a limited range of resources produced by the species-poor mammalian fauna. Beetles were trapped in two wet-forest localities over 4 years (6407 trap nights, 18,869 individuals). More limited data for six other local communities were used to check the generality of the results. Local communities are relatively species poor (around 30 species) in comparison with wet-forest-inhabiting dung beetle communities elsewhere in the tropics (typically 50 or more species). The species belong to only two tribes, Canthonini and Helictopleurina (Oniticellini), which have evolved, exceptionally for dung beetle tribes, completely nocturnal versus diurnal diel activities, respectively. Patterns in the elevational occurrence, body size and resource use suggest that interspecific competition restricts the numbers of locally coexisting species exploiting the limited range of resources that are available. On the other hand, regional turnover in the species composition is exceptionally high due to a large number of species with small geographical ranges, yielding a very large total fauna of dung beetles in Madagascar (>250 species). Apart from exceptionally low local (alpha) diversity and high beta diversity, the Malagasy dung beetle communities are ecologically distinctive from comparable communities in other tropical regions in having high numerical dominance of the most abundant species, small average body size and low degree of resource specialization.

Nepenthes madagascariensis is a carnivorous plant which captures its prey in pitcher-like leaves. It is endemic to Madagascar where it occurs along the eastern coast. Altogether 94.3% of its prey animals belong to three taxa: Formicidae (80.2%), Diptera (9.7%) and Coleoptera (4.4%). The prey compositions of the dimorphic lower and upper pitcher types differ significantly, especially in the markedly higher proportion of ants in lower pitchers and the higher number of flying insects in upper pitchers. A comparison concerning the trap frequency of taxa with literature data from Asian Nepenthes species showed that the upper pitchers of N. madagascariensis contained much higher proportions of Coleoptera, Diptera and Lepidoptera; these differences may partly be due to seasonal reasons. No significant correlation could be established between the numbers of prey items with pitcher size. This paper is the first characterization of the prey composition of the little known N. madagascariensis.

Tree species are potential hosts for epiphytes; however in some forests epiphytes have a biased distribution among hosts. In a tropical dry forest of Mexico, previous research showed that there are trees with few epiphytes. It is possible that the bark of these hosts contain allelochemicals that influence epiphyte seed germination. The aims of this study were (1) to determine whether hosts with low epiphyte abundance (Ipomoea murucoides, I. pauciflora and Lysiloma acapulcense) would inhibit seed germination of Tillandsia recurvata through aqueous and organic bark extracts, (2) to determine whether germination of T. recurvata would differ among the hosts with low epiphyte abundance and a host with high epiphyte abundance (Bursera copallifera) and (3) to relate the chemical composition of organic bark extracts with inhibition of T. recurvata seed germination. Hexanic and dichloromethanic extracts were partially chemically characterized. Total phenolics and flavonoids concentrations of methanolic extracts were analysed. Aqueous and organic bark extracts from hosts with few epiphytes inhibited T. recurvata seed germination. Aqueous and dichloromethanic extracts of B. copallifera inhibited slightly the germination of T. recurvata. There was a positive correlation between concentration of flavonoids and inhibition of seed germination. Results suggest that a combination of compounds may be responsible for affecting the germination of T. recurvata. This study demonstrates the chemical effect of aqueous and organic bark extracts from hosts on germination of an epiphytic bromeliad.

To prevent seed losses from predation, plants have developed protective strategies. Seeds may utilize chemical or structural defences to deter predators. Mucuna holtonii (Fabaceae) has large seeds containing a toxic amino acid, L-dopa, and covered with a hard seed coat. Our study assessed the effectiveness of chemical and mechanical seed defences against vertebrate and invertebrate seed predators within Estación Biológica La Selva, Costa Rica. Pre-dispersal insect and fungus attack of M. holtonii seeds was low (95.7% of 1493 seeds were undamaged). Camera traps monitoring 90 marked M. holtonii seeds showed that the collared peccary (Pecari tajacu) consumed 98.6% of 69 removed seeds over 16 d. Field experiments involving 100 seeds with intact and 100 with opened seed coats found that only opened seeds had endosperm removed by Sericomyrmex amabilis ants (0.5–100% of endosperm removed). Shade-house experiments showed that seeds with high amounts of endosperm removed by ants resulted in low germination success and low seedling biomass production. Although M. holtonii seeds are rich in L-dopa, this compound is not an effective chemical defence against mammals that possess foregut fermentation. The seed coat of M. holtonii is an effective structural defence against invertebrate seed predators, preventing endosperm removal and enhancing seedling survival.

Forest recovery in abandoned pastures and agricultural fields is often impeded, therefore it is important to understand the factors limiting regeneration. Patterns of seed arrival and regeneration in five abandoned agricultural clearings nested within a seasonally dry tropical forest in India were examined along five transects radiating from the forest edge into the clearings. Wind-dispersed seeds dominated the seed arrival in clearings compared with vertebrate-dispersed seeds: 5563 wind-dispersed seeds and 1094 vertebrate-dispersed seeds of 14 and 13 tree species, respectively, were recorded. Numbers of the former declined steeply with increasing distance from the forest, whereas the latter showed no evident pattern with distance. Seeds of the invasive herb, Chromolaena odorata, were abundant in clearings. Although wind-dispersed seeds greatly outnumbered vertebrate-dispersed seeds, seedlings and saplings of vertebrate-dispersed species were three times more abundant than those of wind-dispersed species, indicating distinct differences in patterns of actual and effective seed dispersal. This points to recruitment limitation, and suggests that seed arrival may not be the principal barrier to regeneration in these clearings. Nonetheless, the clearings are likely to revert to forest over time.

Nectarivorous flower mites can reduce the volume of nectar available to pollinators. The effects of the flower mite Proctolaelaps sp. on nectar availability in flowers of a melittophilous bromeliad Neoregelia johannis (Bromeliaceae) was evaluated in a coastal rain forest in south-eastern Brazil. In a randomized block experiment utilizing 18 flower pairs, one per bromeliad ramet, pollinators (Bombus morio) and mites were excluded, and then nectar volume, sugar concentration and sugar mass were quantified over the anthesis period. Mites significantly reduced nectar volume early in the morning (6h00–8h00), but not later (10h00–12h00). Mites decreased total volume of nectar available up to 22%. Sugar concentration in nectar was higher earlier in the morning, and decreased between 10h00–12h00. The pronounced consumption of nectar by mites during the period of higher sugar concentration reduced the total amount of sugar available to pollinators by 31%. This is the first study showing that flower mites decrease nectar rewards in a melittophilous plant. Because nectar volume by itself incompletely describes nectar production rates and the effects of nectar removal by flower mites on the availability of sugar, our study highlights the inclusion of sugar content in future studies assessing the effects of thieves on nectar production rates.

The frequency of selection of functional groups and plant species by free-ranging cattle foraging in a diverse environment and its changes during the dry and the following prehumid seasons were investigated using direct observations and bite counting. The study was conducted at two sites in the Bolivian–Tucuman montane forests in southern Bolivia, by including datasets of a total of 16 animals. Across both study sites and the entire observation period (May to October/November), the cattle were found to select a broad spectrum of plant species from different functional groups. However, just a limited number of species made up a considerable contribution to overall plant selection. The functional group of the graminoids was selected most frequently, but their contribution to plant selection decreased significantly from 63.5% of total bites in May to 15.9% in September/October, in accordance with a decrease in availability. Selection of woody plants (shrubs and tree parts, the latter mainly in the form of leaf litter and fruits) increased with time, reaching its peak at the beginning of the prehumid season, while the herbs showed a curvilinear pattern of selection which was highest in August. Plant species belonging to the functional groups of ferns, climbers and epiphytes were also selected by the cattle, but generally at low relative proportions. Plant selection might be influenced by temporal differences in nutritional quality and availability of the preferred plant species and functional groups. Sampling behaviour seems to be the most likely reason for the inclusion of a broad range of plant species with overall low contribution to plant selection.

Precise estimation of root biomass is important for understanding carbon stocks and dynamics in tropical rain forests. However, limited information is available on individual root masses, especially large trees. We excavated 121 root systems of various species (78) and sizes (up to 116 cm in dbh), and estimated both above- and below-ground biomass in a lowland primary dipterocarp forest in the Pasoh Forest Reserve, Peninsular Malaysia. A tree census was conducted in four research plots (each 0.2 ha) and stand-level biomass was estimated. We examined relationships between tree size parameters and masses of coarse roots (roots ≥5 mm in diameter) and derived a dbh-based allometric equation. The amounts of coarse roots that were lost during excavation were corrected. Coarse-root biomass before and after correction for lost roots was estimated to be 63.8 and 82.7 Mg ha−1, indicating that significant amounts of roots (23%) were lost during the sampling. We also estimated the biomass of small root (<5 mm) by applying pipe-model theory. The estimate, 13.3 Mg ha−1, was similar to another estimate of small roots, 16.4 Mg ha−1, which was obtained directly by the soil-pit sampling method. Total below-ground (BGB) and above-ground biomass (AGB) was estimated to be 95.9 and 536 Mg ha−1, respectively. The biomass-partitioning ratio (BGB/AGB) was about 0.18. In conclusion, the dbh-based allometric equation for coarse roots developed in this study, which kept good linearity even including the data of larger trees, might be useful for evaluating below-ground carbon stocks in other stands of similar forest (old-growth dipterocarp) in South-East Asia.

Plant populations can respond to temporal environmental heterogeneity caused by natural disturbances, such as herbivory. Palm individuals of several species are preyed upon by mammals, but the effects of such herbivory events on population dynamics remain poorly known. To evaluate the effects of environmental stochasticity on a Geonoma schottiana (Arecaceae) population, we surveyed annually 40 permanent 20 × 10-m plots in a riparian tropical forest over 5 y (2000–2004) and results were analysed using matrix models. The population growth rate (λ) was in equilibrium during the study period and only one bad year was identified (2002–2003), which had a higher mortality of juvenile individuals due to herbivory. Additionally, the bad year had a higher mortality of reproductive individuals than the other periods. The stasis matrix elements of the later life stages were the vital rates with highest elasticities. The mortality of juvenile and reproductive individuals had a negative contribution to λ in the bad year. Conversely, the growth of infant and juvenile individuals and the clonal growth of juveniles were the vital rates with highest contribution to stability maintenance of λ in the bad year in a life-table response experiment. The palm population had a high individual density, high proportion of the initial life stages, clonal growth, high fertility, abundant seed bank and high seedling recruitment. Despite these traits, if stochastic herbivory events occur frequently over a long period of time, the population will have a negative growth rate and the probability of local extinction will be very high.

We determined seasonal variation in soil matric potentials (ψsoil) along a topographical gradient and with soil depth in a Bolivian tropical dry (1160 mm y−1 rain) and moist forest (1580 mm y−1). In each forest we analysed the effect of drought on predawn leaf water potentials (ψpd) and drought response (midday leaf water potential at a standardized ψpd of −0.98 MPa; ψmd) of saplings of three tree species, varying in shade-tolerance and leaf phenology. ψsoil changed during the dry season and most extreme in the dry forest. Crests were drier than slopes and valleys. Dry-forest top soil was drier than deep soil in the dry season, the inverse was found in the wet season. In the moist forest the drought-deciduous species, Sweetia fruticosa, occupied dry sites. In the dry forest the short-lived pioneer, Solanum riparium, occupied wet sites and the shade-tolerant species, Acosmium cardenasii drier sites. Moist-forest species had similar drought response. The dry-forest pioneer showed a larger drought response than the other two species. Heterogeneity in soil water availability and interspecific differences in moisture requirements and drought response suggest great potential for niche differentiation. Species may coexist at different topographical locations, by extracting water from different soil layers and/or by doing so at different moments in time.

Contrasting ecological conditions may affect the distribution, abundance and impact of parasites and predators throughout the ranges of hosts and prey. Such patterns are evident on the archipelagos of Hawaii and the Galapagos, which vary in their distribution and abundance of avian parasites within and across islands. Previous research has documented higher intensity of parasitic fly larvae (Philornis downsi) in nests of Darwin's finches on elevated islands of the Galapagos. Here we examine P. downsi intensity and predation in 71 nests of Darwin's small ground finch (Geospiza fuliginosa) on Floreana Island. We found significant differences in parasite intensity, nest predation and clutch size between the lowland (0–100 m) and highland (300–400 m) habitats. Lowland finch nests had few P. downsi parasites (mean of 8 per nest), high nest predation (44% of nests) and large clutch size (3.4). Highland finch nests showed the opposite pattern, with many P. downsi parasites (40 per nest), low nest predation (17%) and small clutch size (2.5). This study suggests that the impacts of an introduced parasite are limited by its niche requirements and resource availability within and across islands. Our findings also imply that the vulnerability of bird populations to introduced parasites and predators is linked with variation in life history strategies across habitats.

Defoliation, often caused by herbivory, is a common cause of biomass loss for plants that can affect current and future growth and reproduction. There are three models that predict contrasting compensatory growth responses of plants to herbivory and resource availability: (1) Growth rate model, (2) Compensatory continuum hypothesis and (3) Limiting resource model. The predictions of these three models were tested on the tree Brosimum alicastrum and the liana Vitis tiliifolia. Seedlings were subjected to three levels of experimental defoliation (0%, 50% and 90% leaf removal) along a light resource gradient (1%, 9% and 65% of full sun). In both species, defoliation significantly increased leaf production rate and relative growth rate of leaf area, but not of biomass. Net assimilation rate was the strongest driver of biomass growth in both species, but leaf area ratio and specific leaf area were also important in B. alicastrum. Compensatory responses of leaf area growth in B. alicastrum were significantly greater in higher than lower light availability, consistent with the compensatory continuum hypothesis predictions, but in contrast to the growth rate model predictions. The limiting resource model offered an explanation for all possible experimental outcomes by directly considering the effects of environmental differences in resource availability.