Many studies suggest that edaphic variables are major determinants of frog distributions. However, leaf-litter depth and soil characteristics are influenced by distance from streams, so the apparent relationship between edaphic characteristics and species distributions could be an artefact of the dependence of species on free water for reproduction. Therefore, we investigated the effect of edaphic variables on the mesoscale distribution of frog species not dependent on free water for reproduction. We evaluated the effects of soil texture, pH, slope, number of trees and leaf-litter volume on the distribution of nine terrestrially reproducing anuran species in the Reserva Ducke, a 100-km2 terra firme forest preserve in central Amazonia. Diurnal and nocturnal assemblages of anuran species were sampled in 72 plots systematically distributed across the reserve. We sampled the diurnal anuran assemblage by visual encounter in 250 × 1-m plots and the nocturnal assemblage in 250 × 20-m plots using both auditory and visual surveys. The majority of terrestrially breeding anuran species were influenced by topographic and/or edaphic variables, such as slope, soil clay content and pH. However, responses to environmental predictors differed among species. Most species occurred throughout all environmental gradients and relationships with soil characteristics were subtle, indicating that these species occur in the majority of habitats in Reserva Ducke. The results of this study indicate that terrestrially breeding frogs are habitat generalists that show little mesoscale beta diversity associated with habitat variation.

Parasites are ubiquitous in wild animals, with host-specific life histories considered as major determinants of prevalence and parasite assemblage patterns. It is predicted that habitat differences in logged rain forests influence population performances of small mammals and consequently may change the infection patterns of local animal populations with regard to endo- and ectoparasites. We investigated patterns of helminth species assemblages (Nematoda, Platyhelminthes) in two rat species (Leopoldamys sabanus, Niviventer cremoriventer) and two tree shrew species (Tupaia tana, T. longipes) in three logged and three unlogged rain forests in Borneo by examining 337 faecal samples with non-invasive faecal egg count (FEC). Nematode eggs prevailed in 95% of all samples with up to five (mean 1.9 ± 1.1) morphotypes. Whereas members of Strongylida were most prevalent in L. sabanus, T. tana and T. longipes, Spirurida dominated in N. cremoriventer that revealed at the same time the lowest average nematode prevalence and FEC. Cestode eggs were only found in L. sabanus and T. tana. Composition and abundance patterns of the parasitic helminth assemblages were influenced by logging. As hypothesized, species richness of nematode morphotypes and mean number of infections per host of T. longipes were larger in logged than in unlogged forest. In contrast, L. sabanus was more heavily infected with cestodes in unlogged than in logged forest and also revealed larger egg counts for strongylids and spirurids in unlogged forest. Our results suggest that forest degradation and altered environmental conditions influence helminth diversity and infection patterns of small mammals with contrasting trends among host species. The inconsistent logging-induced changes in helminth assemblages from different hosts indicate that specific sets of habitat-host-parasite interactions are uniquely influenced by the effects of logging. Consequently, predictions on changes of parasite diversity and prevalence with regard to habitat disturbance need to be based on the individual life histories of the hosts (and the parasites).

Neotropical species richness is often estimated using accumulation or rarefaction curves and extrapolations based on various methods, but the efficacy of these methods is rarely tested. We used both a time-limited trapping session and previous knowledge of the mammal fauna from a site in French Guiana to validate these different methods. Three currently used extrapolation models were tested on our data. In a 2.5-mo trapping period we caught 75 individuals representing 18 small non-volant mammal species in three different habitats. We found that for comparable trapping efforts, village edges presented a higher abundance and species richness than primary and secondary forests. Species richness extrapolations using current models demonstrated that the exponential dependence model fits the known diversity of the site better, although this model is usually applied to large geographic areas and to relatively poorly documented taxa. Both Clench equation and linear dependence models underestimate small-mammal species richness in our study. We finally emphasize the interest of sampling in such edges surrounded by either primary or secondary forest, to maximize the probability of trapping rare species.

Rapid and massive amphibian population declines have been reported throughout upland areas of the Neotropics. The abundance and species richness of Neotropical amphibian communities suggest that losses of this magnitude are likely to have strong effects at the ecosystem level. To improve understanding of the implications of their loss we used stable isotope analysis to examine trophic relationships in an ecosystem in which amphibians are dominant in a second-order forest stream at 750 m asl in Parque Nacional Omar Torrijos Herrera, Panama. We analysed δ13C, δ15N and C:N ratios of major biotic components (basal resources, invertebrates, amphibians, fish and reptiles) in the stream and of the adjacent riparian food web. Tadpoles (mean δ15N = 4.49‰) and adult amphibians (mean δ15N = 5.45‰) were intermediate links in the aquatic and terrestrial food web respectively. High δ15N signatures identified fish as top predators in the aquatic food web and snakes and the toad Bufo as top predators in the terrestrial food web. Isotopic signatures clearly distinguished between trophic groups of tadpoles: microbial feeders (Centrolenidae, δ15N range = 0.91–3.05‰), herbivores (Rana and Hyla, δ15N range = 4.74–5.15‰) and neuston feeders (Colostethus, δ15N range = 5.31–6.40‰). Dependence on autotrophic production was indicated by enriched signatures of carbon isotopes in pool dwellers versus those that reside in faster-flowing sections of the stream. High nitrogen concentrations in detrital matter (average 0.8%, C:N = 10.3) suggested that grazing tadpoles enhanced nitrogen fluxes and improved the quality of organic matter available to detritivores.

Secondary forests account for 40% of all tropical forests yet little is known regarding their suitability as habitat for diurnal large mammals and game birds. This is especially so for second-growth that develops on large areas of degraded land. We address this by investigating assemblages of large-bodied birds and mammals in extensive patches of secondary forest in the Jarí region of the north-eastern Brazilian Amazon, comparing species richness and abundance against that of adjacent undisturbed primary forests. We conducted 184 km of line-transect censuses over a period of 3 mo, and found that although primary and secondary forests held a similar abundance of large vertebrates, the species composition was very different. Secondary forests supported a high abundance of ungulate browsers (0.85 vs 0.44 indiv. per 10 km) and smaller-bodied primates (15.6 vs 4.6 indiv. per 10 km) compared with primary forests. However, large prehensile-tailed primates were absent (black spider monkey Ateles paniscus) or at very low abundance (Guyanan red howler monkey Alouatta macconelli) in secondary forest. The abundance of large frugivorous/granivorous birds was also low in secondary forests compared with primary forests (22.6 vs 37.1 individuals per 10 km, respectively). Faunal assemblages appear to reflect food resource availability. Concurrent vegetation surveys indicated that secondary forests had high levels of terrestrial and understorey browse. Fruit production was largely restricted to pioneer trees such as Bellucia and Inga spp. Although these regenerating forests were an important habitat for large mammals and birds, they were limited in terms of faunal richness, particularly dispersers of large-seeded plants.

Spatial distributions of many tropical trees are skewed to specific habitats, i.e. habitat specialization. However, habitats of specialist species must be divergent, i.e. habitat divergence, to coexist in a local community. When a pair of species specialize in the same habitat, i.e. habitat convergence, they could not coexist by way of habitat specialization. Thus, analyses of habitat divergence, in addition to habitat specialization, are necessary to discuss coexistence mechanisms of sympatric species. In this study, the habitat specialization and habitat divergence along topographic gradients of eight sympatric tree species of the Fagaceae were studied in a 15-ha study plot in a tropical lower montane forest in northern Thailand. A statistical test with torus shift randomizations for 9673 trees of Fagaceae revealed significantly biased distributions for all of the species, for at least one of the four topographic variables used: elevation, slope inclination, aspect and convexity. Slope convexity was the most critical topographic variable, along which all but one species had significantly skewed distributions. Out of 112 possible combinations of species pairs and topographic variables, 18 (16%) and two pairs (1.8%) showed significant habitat divergence and habitat convergence, respectively. The observed habitat divergence alone could not completely explain the coexistence of the eight species. There was a gradation in the habitat position of each species, with relatively large overlaps between species distributed in similar habitats, and small overlaps between species associated with contrasting habitats, respectively. The gradual changes in the habitats of the species suggested that dividing the species into a small number of distinct habitat groups, such as ridge and valley specialists, would not be straightforward.

The proliferation of climbers can have deleterious effects on tree regeneration, especially in forest canopy gaps where climbers increase in abundance. In response to the colonization by climbers, the supporting tree can suffer a reduction in growth and its allometric relationships may be modified. We evaluated the effects of three species of climber on the performance of the pioneer tree Ceiba pentandra in a moist semi-deciduous tropical forest in Ghana. In each of three gaps, four plots were set up, each with eight Ceiba seedlings paired with a single plant of one of three climber species, planted within 5–10 cm of the tree seedling, plus a control (no climber). The climber species were: Centrosema pubescens, a nitrogen-fixing woody climber; Combretum racemosum, a woody climber and Dioscorea praehensilis, an herbaceous climber. After 12 mo, Centrosema and Combretum had about four to five times more biomass than Ceiba seedlings. There was no effect of climber competition on Ceiba biomass growth, and no relationship between climber biomass and Ceiba growth rate. Individual climber species, however, had other effects: Combretum caused a significant reduction in the height and diameter growth of Ceiba, whilst competition with Centrosema was associated with significant reduction in the crown area and increase in internode length in Ceiba. The results indicate that even very different climber species appear to cause negative effects on trees during regeneration.

Treefalls gaps contribute to the habitat heterogeneity of tropical forest floors. Previous studies have shown that these gaps play an important role in plant and bird communities, however less is known about their role in arthropod communities. Using eight Malaise traps we investigated the difference in arthropod abundance of 19 taxonomic groups between gaps and understorey for 21 wk during the rainy season and 8 wk in the dry season on Barro Colorado Island, Panama. More (33.8%) arthropods were collected in gaps during the rainy season and 32.2% more in the understorey during the dry season. To assess the possible factors contributing to these differences we measured light, plant densities and young leaf densities, as indicators of abiotic factors and food resources for insect herbivores. Arthropod abundance was negatively correlated with light in the dry season. Thus, abiotic stress may explain the pattern of abundance in the dry season. While there was no correlation with light in the rainy season, predator abundance was positively correlated with herbivore abundance. The plant and young leaf density data suggest that there is significantly higher food availability for herbivores in gaps. Thus, less stressful abiotic conditions and more food resources may contribute to more herbivores followed by more predators in gaps during the rainy season.

The dynamics of early life-history stages are important for understanding regional diversity patterns in tropical trees. In this study, patterns of seed removal, seedling survival and ectomycorrhizal (ECM) colonization in monodominant and mixed tropical rain forests in Guyana were investigated during a masting event of an ECM monodominant tree, Dicymbe corymbosa. Two seed densities (1 m−2 and 6 m−2) were tested in two forest types (monodominant versus mixed) with 10 plots per treatment (40 plots total). Germination success, seed and seedling survival after 1 y were measured for the monodominant tree, and four non-dominant canopy tree species found in both forest types (Eschweilera sagotiana, Licania laxiflora, Chrysophyllum sanguinolentum and Carapa guianensis). A significant effect of forest type was detected for seed removal and seedling survival. In the mixed forest, seed removal was higher for all species, with 27% average removal compared with 7% average seed removal in the monodominant forest. Germination success was significantly lower for all but one species in the mixed forest, with average germination of 41% compared with 78% germination in the monodominant forest. Seed and seedling survival of the monodominant tree was greatest within the monodominant forest with 93% of seeds germinating and 85% of seedlings surviving after 1 y compared with 65% germination and 15% seedling survival in the mixed forest. Per cent ectomycorrhizal colonization of Dicymbe corymbosa was near 100% in the monodominant forest, but significantly lower (14%) in the mixed forest. These results suggest that seedling survival patterns, rather than seed survival, are more important for recruitment success in this system and that ectomycorrhizal inoculum may limit establishment of Dicymbe corymbosa in the mixed forest.

Spatial patterns presented by the opossums Caluromys philander, Philander frenata and Micoureus demerarae were studied, through radio-tracking, in a landscape composed of eight small (1.3–13.3 ha) forest fragments surrounded by a matrix of open vegetation in south-eastern Brazil. Sixteen individuals were fitted with radio-collar transmitters and monitored for 2–8 mo. Fixes were obtained by the ‘homing-in on the animal’ technique. Numbers of locations of each individual varied from 6 to 117. Home ranges sizes ranged from 2.5–7.0 ha for C. philander, 0.6–7.4 ha for P. frenata and 0.8–1.7 ha for M. demerarae. Fragments, both edges and interiors, were used more often than the matrix; they are the primary habitat for these marsupials in the landscape. The matrix was used for foraging by P. frenata and C. philander, and traversed in five movements between fragments by P. frenata. Ability to use fragment edges and the matrix is important in explaining how these marsupials are able to persist in the landscape.

The reciprocal importance of bromeliads and hummingbirds has been proposed for many years, even suggesting coevolution between these two groups. Nevertheless, data are lacking that allow a better test of the relationships involved. Here we investigate the relationship between bromeliads and hummingbirds in an area of secondary Atlantic rain forest in southern Brazil. The study examined the interactions among 12 species of bromeliad and 10 of hummingbird at Reserva Natural Salto Morato, Paraná state. The number of flowering species of bromeliad and the species richness and abundance of hummingbirds were quantified monthly between November 2004 and October 2005. Focal observations on each bromeliad species were made to determine the hummingbird visitors. Neither species richness nor abundance of hummingbirds were related to bromeliad phenology. Together with the monthly variation in visit frequency by a given pollinator to a given plant, these factors indicate a generalization in the use of bromeliads by hummingbirds and argue against tight coevolution. Ramphodon naevius and Thalurania glaucopis were the main pollinators in the community. Aechmea nudicaulis was the most generalist bromeliad species. The generalist species interacted with other generalists or with asymmetric specialists and there was no specialist–specialist interaction. This produced a strongly organized and nested matrix of interactions. This nestedness is similar to other plant-pollinators networks, supporting the hypothesis that the evolutionary relationship between bromeliads and hummingbirds is no stronger than that of other pollination networks.

The objective of this study was to investigate the effects of tree cover and season on soil N dynamics and microbial biomass in a semi-arid southern African savanna in Zimbabwe. We used a randomized complete block design with five blocks of 100 × 100 m, demarcated in a 10-ha pocket of Colophospermum mopane-dominated woodland protected from grazing and fire. In each block, we randomly selected three mopane trees with large canopies (8.3 m crown diameter) and another three with small canopies (2.7 m crown diameter). We determined soil organic carbon and nutrient concentrations, litterfall N and C inputs, microbial biomass and N transformations beneath large and small mopane trees as well as in the intercanopy areas. Soil organic carbon, microbial biomass, N, P and K were more than twice those beneath large trees than in the intercanopy areas. Rainy-season net mineral N accumulation rate in the surface soil (0–10 cm) ranged from 3.71 μg g−1 mo−1 in the intercanopy areas to 8.80 μg g−1 mo−1 beneath large trees; correspondingly, net nitrate accumulation rate ranged from 1.33 to 3.60 μg g−1 mo−1. Dry-season net mineral N and net nitrate accumulation rates were similar across sampling sites and did not exceed 2 and 0.4 μg g−1 mo−1, respectively. Litterfall N inputs were positively and significantly correlated with soil N availability, microbial biomass N and N transformations. At all sampling sites, microbial biomass and mineral N pools in the dry season were maximum when soil moisture (∼5%) and N transformations were minimum. In contrast, when soil moisture (9–13%) and N transformations were maximum in the rainy season, microbial biomass and mineral N pools were minimum. It is concluded that the improved soil conditions beneath isolated trees in semi-arid savannas may enhance herbaceous biomass yield especially of canopy shade-tolerant species.

Coastal wetland plant communities are strongly structured by water depth and salinity. Rising sea level will cause changes in the hydro-period, surface water salinity and salt-water intrusion in coastal areas, which will reduce the distribution of forests in these areas. We studied the dynamics of a Pterocarpus officinalis stand in Puerto Rico over a 9-y period. We observed differences in plant growth, recruitment and mortality across a salinity gradient within a 1-ha plot. In areas of high salinity, recruitment, juvenile density and growth rates of juveniles and adults were lower. The detrimental effect of salinity was also observed in a growth experiment; seedlings in 5‰ and 10‰ salinity treatments had higher mortality, slower growth and less above- and below-ground biomass than control seedlings (0‰). In addition, an increase from 0 to 1‰ in salinity resulted in approximately 50% less nodulation in seedlings. Low recruitment in high salinity areas and lack of recruitment in adjacent grasslands will further reduce the distribution of this forest type. Although some ecosystems can respond to changing conditions by migration to more favourable areas, this is not the case with P. officinalis, and thus, restoration efforts are needed to re-establish this species where it occurred historically.

Failure of reproduction is hypothesized as being a main reason for the formation of upper tree lines but there is, as yet, little supportive evidence of such. This study investigates the effects of experimental sowing, canopy cover and litter depth on seedling emergence and survival of Polylepis incana and Polylepis pauta at the upper distribution limit of the species in the Páramo de Papallacta, central Ecuador. We established 18 study plots located in the interior, at the edge and at the exterior of closed forests at the upper tree line and analysed seedling dynamics for 1 y following experimental sowing with four different litter treatments. For both species, seedling numbers were significantly higher in the forest interior than outside, and higher in the treatments with the litter layer removed. In P. pauta, sowing significantly increased seedling number, which was more pronounced within and at the edge of the forest than outside. In contrast, there was no impact of sowing on seedling emergence in P. incana. First-year seedling survival and mean growth rate per month were low in both species. Log-linear models did not reveal significant interactions between survival and canopy cover or litter removal. Our data show that seedling recruitment is limited at the upper tree line – presumably due to extreme climatic conditions – which indicates the importance of constraints in sexual regeneration for tree-line formation in central Ecuador.

Twelve native woody species were studied to investigate the influences of soil fertility and root morphology on colonization by arbuscular mycorrhizal (AM) fungi during seedling establishment and growth. Seedlings were grown in soils of low and high natural fertility, uninoculated or inoculated with AM fungi, under greenhouse conditions. The mycorrhizal root colonization and plant responsiveness were higher among early successional species than late successional ones. Among early successional species, in both soils, mycorrhizal colonization provided significant increase in total dry mass, growth rates of shoot and root, root length, density of root tissues, root surface area and P concentration and content in the shoot. Early successional species grown with AM fungi displayed significant decreases in carbon allocation to roots, specific root length and the length and incidence of root hairs. Mycorrhizal colonization did not affect the root morphology of the late successional species in either soil. The growth of these woody species was influenced by differences in soil fertility. There was positive correlation between the degree of plant responses to AM inoculation with the percentage of root colonized by AM fungi. In both soils, plant responsiveness and mycorrhizal root colonization correlated positively to root-hair incidence and root-hair length and correlated negatively to fine-root diameter. The results suggest that during the establishment of seedlings, the large responses to the inoculation and colonization of roots by AM fungi are related to both the successional status and root morphological plasticity of the host plant, regardless of soil fertility.

The Smithsonian Venezuela Project (SVP) conducted extensive surveys of mammals and ectoparasites in the 1960s. The 25 238 individuals and 130 species of bat collected by SVP hosted 36 663 streblid bat flies, representing 116 species of these ectoparasitic dipterans. Roosts of bat species differ in durability and protection, and bat flies separate from the host to pupate in the roost. We predicted higher levels of parasitism and more parasitic associates for bats roosting in more permanent structures (e.g. caves, tunnels) that would facilitate their association with hosts. We also predicted wing development of flies should correlate inversely with roost duration, restricting flightless forms to bats in permanent roosts. Ranking roosting structures by durability and protection, we sought correlations among bat species in prevalence, mean intensity and number of associated fly species. All three measures of parasitism were positively and significantly related to roosting habits: bats roosting in more permanent, enclosed structures were more likely to be infested, to carry heavier parasite loads, and to harbour more species of ectoparasitic flies. However, roosting habits were not correlated with the average wing development of bat flies. Although other factors affect parasitism rates in bats, the study provides a compelling example of both ecological and evolutionary responses of parasites to features of the host's environment.

Resource partitioning has been hypothesized to play a role in the maintenance of tree diversity in tropical forests. We looked for evidence of light and soil moisture partitioning among seedlings of four native Malagasy tree species, the pioneer, gap-adapted species Harungana madagascariensis and the three shade-tolerant species Ocotea cymosa, Stephanostegia capuronii and Uapaca ferruginea. Four hundred and eighty seedlings were transplanted in experimental plots in the Tampolo coastal forest and grown for 2 y. Growth rates increased with increasing light availability for all species, and with increasing dry-season soil moisture for H. madagascariensis. With increasing light availability, survival increased for H. madagascariensis, S. capuronii and U. ferruginea but decreased for O. cymosa. While dry-season soil moisture did not influence the growth or survival of the shade-tolerant species, it interacted with understorey light in its effect on the performance of H. madagascariensis, which performed better in wet soils at high light than in dry soils in shade. Rank reversals in species performance suggested that three of the four tree species partition resource gradients as seedlings, mostly light and secondarily dry-season soil moisture. There was only partial agreement between the performance of transplanted seedlings and the distribution of natural seedlings of the same four species with respect to light and soil moisture, suggesting that the success of tropical tree regeneration can only be partly accounted for by seedling performance across resource gradients.

Flood depth has been frequently used to explain the distribution of plant species in seasonally flooded grasslands, but its relation with vegetation production has remained ambiguous. The relationship between flooding and above-ground biomass at the end of the flooding season and during the dry season was studied to assess the impact of reflooding on the Logone floodplain, Cameroon. Above-ground biomass of a combination of all species and of the individual perennial grasses Oryza longistaminata and Echinochloa pyramidalis showed a positive linear relationship with maximum flood depth up to 1 m. The gradient of these relationships became steeper and their fit better during the 2 y following the installation of the flooding, showing the response lag to floodplain rehabilitation. Flood duration only explained the above-ground biomass of the combination of all species and not of the individual species. Above-ground biomass data from other floodplains in the three main African geographic regions showed a similar relationship with maximum flood depth less than 1 m. Dry-season regrowth, important because of its high nutrient quality during forage scarcity, was not directly related to maximum flood depth, possibly because of its dependency on the period of burning and soil moisture. Presented data indicate that a rise of water level of 1 cm corresponds to an increase in above-ground biomass of c. 150 kg DM ha−1.

It is critical to understand the responses of tropical tree species to ongoing anthropogenic disturbances. Given the longevity of large trees and the scarcity of appropriately long-term demographic data, standing size distributions are a potential tool for predicting species' responses to disturbances and resultant changes in population structure. Here we test the utility of several different measures of size distribution for predicting subsequent population changes at the intraspecific level using demographic records from two subsampled 50-ha tree plots in Malaysia (Pasoh and Lambir). Most measures of size distribution failed to successfully predict population change better than random; however, the ‘coefficient of skewness’ (a measure of the relative proportion of small vs. large stems in a population) was able to correctly predict the direction of population change for approximately three-quarters of species at both sites. At Pasoh, the magnitude of this relationship decreased with adult stature and rate of turnover, but was unrelated to sapling growth rates at either site. Finally, using data for species common at both forests, we found that size distributions were generally uninformative of subsequent differences in population change between sites (only median dbh correctly predicted the direction of change for more species than random). Based on these results we conclude that some measures of intraspecific differences in size distribution are potentially informative of population trends within forests but have limited utility across broader spatial scales.

Drip tips are thought to resist the growth of epiphyllous fungi, lichens, bryophytes and algae on leaf surfaces by promoting the drainage of water following rain. This hypothesis was tested by altering the tip of one leaf in each of 50 pairs of opposite leaves on plants of each of two woody species in the understorey of Barro Colorado Island, Panama. After 11 mo in situ, there were no statistical differences between the mean epiphyll cover on leaves with and leaves without drip tips. Epiphyll cover was, however, strongly correlated between the opposite leaves at a node, even though one had a drip tip and the other had the tip removed. This correlation could be due to small-scale heterogeneity of insolation, temperature and humidity in the crowns of plants. A relationship between epiphyll cover and growth of the branch containing the leaves provides qualitative support for this interpretation. It seems clear that drip tips do not have a large, consistent, easily detectable effect on epiphyll cover. However, because of the tiny cost of drip tips, reductions in epiphyll growth that are small and transitory and occur in only a portion of a plant's leaves may provide sufficient advantage to explain the evolution of drip tips. No experiment to date has been capable of detecting such effects.