Vertical stratification of an avian community in New Guinean tropical rainforest

Vertical stratification of avian communities has been studied in both temperate and tropical forests; however, the majority of studies used ground-based methods. In this study we used ground-to-canopy mist nets to collect detailed data on vertical bird distribution in primary rain forest in Wanang Conservation Area in Papua New Guinea (Madang Province). In total 850 birds from 86 species were caught. Bird abundance was highest in the canopy followed by the understory and lowest in the midstory. Overall bird diversity increased towards the canopy zone. Insectivorous birds represented the most abundant and species-rich trophic guild and their abundances decreased from the ground to canopy. The highest diversity of frugivorous and omnivorous birds was confined to higher vertical strata. Insectivorous birds did not show any pattern of diversity along the vertical gradient. Further, insectivores preferred strata with thick vegetation, while abundance and diversity of frugivores increased with decreasing foliage density. Our ground-to-canopy (0–27 m) mist netting, when compared to standard ground mist netting (0–3 m), greatly improved bird diversity assessment and revealed interesting patterns of avian community stratification along vertical forest strata.     

Patterns of liana community diversity and structure in a tropical rainforest reserve,Ghana: effects of human disturbance

Most studies have concluded that liana diversity and structure increase with disturbance. However, a contradictory pattern has emerged recently calling for more research in the area. Liana diversity and structure were investigated in three forest types that differ in disturbance intensity (nondisturbed, moderately disturbed and heavily disturbed forest: NDF, MDF and HDF, respectively) in the Atewa Range Forest Reserve, Ghana. In each forest type, 10 square plots of 0.25 ha were demarcated. Lianas with diameter ≥1 cm located on trees with diameter ≥10 cm were enumerated. A total of 429 individuals representing 40 species, 29 genera and seventeen families were identified in the study. Shannon diversity and species richness of lianas were significantly lower in the HDF (P < 0.05). Liana density and basal area differed significantly across all forest types (P < 0.0001). The importance value index (IVI) of most liana species varied greatly across the forest types. The current study has provided evidence to support the pattern of decreasing liana diversity and structure with disturbance in some tropical forests. Further studies are recommended to gain more understanding of the factors that are responsible for the divergent liana responses to disturbance in tropical forests.     

Effects of human disturbance on liana community diversity and structure in a tropical rainforest,Malaysia: implication for conservation

Aim Due to the important role of lianas in the functioning of forest ecosystem, knowledge of the factors that affect them are important in the management of forests. Currently, there are conflicting reports on the response of liana communities to disturbance, calling for more research in the area. The present study was carried out to investigate the response of liana diversity and structure to human disturbance within two major forests in the Penang National Park, Malaysia. The study also looked at the implication of the findings for conservation.Methods A total of 15 40 × 40-m 2 (or 40-m × 40-m) plots each were randomly located across a range of habitats in a primary forest and disturbed secondary forest. Trees with diameter at breast height ≥10 cm were examined for lianas with diameter ≥2 cm. Both lianas and trees were enumerated and compared between the two forests. Diversity and structural variables of lianas were compared between the two forests using the t -test analysis. Tree abundance was also compared between the two forests with t -test, while linear regression analysis was run to determine the effects of tree abundance on liana abundance.Important findings A total of 46 liana species belonging to 27 genera and 15 families were identified in the study. Human disturbance significantly reduced liana species richness and species diversity in the secondary forest. Liana abundance remained the same in both forests whereas liana basal area was significantly higher in the primary forest. Twiners and hook climbers were significantly more abundant in the primary and secondary forest, respectively. Large diameter lianas were more abundant in the primary forest compared with the secondary forest. The diameter distribution of most families in the primary forest followed the inverted J-shaped curve whereas only a few of the families in the secondary forest did so. Tree abundance was significantly higher in the primary forest. The abundance of lianas significantly depended on tree abundance in all the forests. The study has provided evidence of negative effects of human disturbance on liana diversity and structure that does not auger well for biodiversity in the forest. In view of the critical role of lianas in maintaining biodiversity in the forest ecosystem, lianas in the national park should be protected from further exploitation.     

Gregarious flowering in a lowland tropical rainforest: A possible response to disturbance by Cyclone Winifred

Observations in tropical lowland rainforests damaged by Cyclone Winifred on 1 February 1986 suggest that the disturbance has been followed by an unusual burst of flowering. Fifty-four species of concurrently flowering shrubs and trees were recorded in early March along a 4 km road transect in a cyclone-damaged forest. Approximately 80% of the smaller tree and shrub species observed were flowering. Twelve species which had flowered and fruited prior to the cyclone flowered again. Some species which normally flower following periods of partial or complete deciduousness in the drier months of the year flowered after being defoliated by the cyclone. Widespread defoliation of the rainforests, together with the hot, dry weather which followed the cyclone, exposed the understorey layers to abrupt increases in temperature, insolation, and water stress. It is postulated that these environmental changes may have effected the synchronization of flowering of a larger number of species than would normally occur. It is suggested that longterm changes in the species composition of the damaged forests as a result of coincidences of seed availability and regenerative space may occur.     

Ligninolytic activity of tropical rainforest basidiomycetes

A total of 116 strains of Brazilian tropical rainforest basidiomycetes were evaluated in terms of their ability to oxidize the dye rhemazol brilliant blue R (RBBR) and guaiacol. Laccase and peroxidase activities were detected by the drop test using solutions of α-naphthol and pyrogallol, respectively. RBBR and guaiacol oxidation occurred in 96.6 and 87.1% of the strains tested, respectively. One hundred strains oxidized both substrates. In the drop test, most strains presented laccase (96.6%) and peroxidase (92.2%) activity. The quick screening method used here can be useful to identify ligninolytic fungal strains to be used in various biotechnological applications. This revised version was published online in November 2006 with corrections to the Cover Date.     

Evolutionary consequences of human disturbance in a rainforest bird species from Central Africa

Relatively little attention has been directed towards understanding the impacts of human disturbance on evolutionary processes that produce and maintain biodiversity. Here, we examine the influence of anthropogenic habitat changes on traits typically associated with natural and sexual selection in the little greenbul (Andropadus virens), an African rainforest bird species. Using satellite remote-sensing and field survey data, we classified habitats into nonhuman-altered mature and human-altered secondary forest. Mature rainforest consisted of pristine rainforest, with little or no human influence, and secondary forest was characterized by plantations of coffee and cacao and high human impacts. Andropadus virens abundance was higher in secondary forest, and populations inhabiting mature rainforest were significantly larger in wing and tarsus length and bill size; characters often correlated with fitness. To assess the extent to which characters important in sexual section and mate choice might be influenced by habitat change, we also examined differences in plumage colour and song. Plumage colour and the variance in plumage luminance were found to differ between forest types, and song duration was found to be significantly longer in mature forest. The possible adaptive significance of these differences in traits is discussed. Despite relatively high levels of gene flow across habitats, amplified fragment length polymorphism analysis revealed that a small proportion of high-F(ST) loci differentiated mature from secondary forest populations. These loci were significant outliers against neutral expectations in a simulation analysis, suggesting a role for divergent selection in differentiation across habitats. A distance-based redundancy analysis further showed that forest type as defined by remote-sensing variables was significantly associated with genetic dissimilarities between habitats, even when controlling for distance. The observed shifts in morphology, plumage and song were consistent with divergent selection on heritable variation, but a role for plasticity cannot be ruled out. Results suggest that anthropogenic habitat changes may have evolutionary consequences, with implications for conservation and restoration.     

The influence of life form on carbon and nitrogen relationships in tropical rainforest ferns

Tropical ferns are characterized by a high diversity of plant life forms, yet there have been few large-scale studies on the functional ecology of these different forms. We examined epiphytic, hemiepiphytic, and terrestrial ferns, and asked whether there are differences in the mineral nutrition and water relations across different growth forms of a diverse assemblage of species. We measured specific leaf area, leaf nitrogen concentrations, and natural abundance of the stable isotopes δ¹⁵N and δ¹³C of 48 fern species from 36 genera across a wide range of habitats at La Selva Biological Station in Costa Rica. We found that epiphytes were significantly different in all measured variables from hemiepiphytic and terrestrial species, and that terrestrial and soil-rooted hemiepiphytes were indistinguishable in all variables excluding SLW. A multivariate analysis revealed that aspects of N nutrition were the most reliable at separating epiphytic species from other life forms. Our study demonstrates that the natural abundance of both C and N as well as N relations and leaf morphology are useful when segregating different plant life forms, and that the N cycle of epiphytic and terrestrial habitats function independently from each other.     

Valuation and sustainable use of tropical rainforest

Studies of the extraction of non-timber forest products have shown that the standing rainforest may be more valuable than alternatives involving deforestation

Although this article is about placing a value on rainforest, it begins by stressing the importance and value of rainforest for its environmental function, particularly for the control of world climate patterns. It is then shown how rainforest peoples depend on the plants around them and in some study areas were found to have a use for every tree on the one-hectare plots. It is therefore not surprising that the rainforest can contain many non-timber forest products (NTFPs) of commercial potential, some of which such as rubber latex and Brazil nuts have been in the market economy for many years. A summary is given of various attempts to place a value on rainforest for its NTFPs. Each of the three studies showed that the extraction of these products could be more valuable than alternative land uses involving deforestation. Various rainforest countries such as Brazil, Guatemala, and Indonesia have set up extractive reserves where local people are allowed to extract NTFPs but not to clear cut the forest. Extractive reserves have slowed down deforestation in some areas, but only provide a meagre subsistence existence for their inhabitants, so while they are useful, they are not a panacea that will solve all the conservation problems of tropical rainforest.     

Ecology of tropical butterflies in rainforest gaps

Tropical forest gaps are ephemeral and patchily distributed within forest areas and have very different light environments compared with closed-canopy forest. We used fruit-baited traps to investigate if gaps are exploited by more opportunistic butterfly species compared with closed-canopy forest. Gaps supported a higher diversity of butterflies in terms of species evenness but closed-canopy sites contained species with more restricted geographical distributions. There was little similarity between the assemblages of butterflies trapped in the canopy and those in either gap or closed-canopy sites, but the greater similarity was with gaps, and increased diversity in gaps was partly due to canopy species turning up in gaps. Dispersal rates (as measured by recapture rates) were higher in gaps and there was evidence that butterflies in gaps had relatively larger and broader thoraxes, indicating a flight morphology adapted for faster flight. These results support the notion of a distinctive gap fauna comprising more widespread, mobile species. Habitat modification that opens up the canopy is likely to result in an increase in these widespread species and a decline in understorey species with restricted distributions.     

Blind population genetics survey of tropical rainforest trees

Rainforest tree species can be difficult to identify outside of their period of reproduction. Vascular tissues from Carapa spp. individuals were collected during a short field trip in French Guiana and analysed in the laboratory with nuclear and chloroplast markers. Using a Bayesian approach, > 90% of the samples could be assigned to one of two distinct clusters corresponding to previously described species, making it possible to estimate the genetic structure of each species and to identify cases of introgression. We argue that this blind procedure represents a first-choice rather than a fallback option whenever related taxa are investigated.     

Positive relationship between fruit removal by animals and seedling recruitment in a tropical forest

Fleshy-fruited plants rely on animal frugivores to disperse their seeds, and seed removal by frugivores may leave an imprint on seedling recruitment. However, to what extent plant–frugivore interactions are related to seedling recruitment has rarely been quantified at the community level, especially in species-rich tropical forests. In this study, we tested the effect of different plant traits on fruit removal by frugivores and tested the relative importance of fruit removal, plant traits and abiotic factors for seedling recruitment. We quantified plant–frugivore interactions of 22 fleshy-fruited plant species consumed by 56 diurnal frugivore species, and counted the number of seedlings that emerged along an elevational gradient in the Colombian Andes. We measured a set of plant traits (i.e., crop size; fruit size; seed load and mass; fruit nutritional contents), estimated the density of adult plants and recorded relevant abiotic factors (light, temperature and humidity). We found that fruit removal by frugivores was positively associated with crop size, but negatively associated with fruit length and unrelated to seed load and fruit nutritional content. Seedling densities were positively related to the density of adult plants, seed mass and fruit removal by animals. We found no relationship between abiotic factors and seedling recruitment. Our results indicate that fruit abundance and morphology are important determinants of fruit removal and that fruit removal is positively associated with seedling recruitment accounting for effects of species abundance and plant traits. We conclude that plant traits shape fruit removal and seedling recruitment at the community level, while these two crucial processes of forest regeneration are directly linked by seed dispersal of animals.     

Fragmentation and local disturbance of forests reduce frugivore diversity and fruit removal in Ficus thonningii trees

Clearance, fragmentation, and degradation of tropical forests have resulted in declines of biodiversity. This loss of biodiversity is endangering important ecosystem processes such as seed dispersal. If anthropogenic disturbances affect seed dispersal of keystone plants, effects on tropical ecosystems might be especially pronounced. We studied frugivore assemblages and fruit removal from 25 Ficus thonningii trees in the heavily fragmented and disturbed Kakamega Forest, western Kenya. During 400 observation hours we recorded 36 frugivores visiting F. thonningii trees. We recorded significantly fewer frugivorous species in fragments compared to the main forest and in highly, compared to little, disturbed sites. Effects of fragmentation and local disturbance on the number of individuals were not significant but showed similar trends to those in the previous analyses. Furthermore, fruit removal from focal trees was slightly reduced in fragmented and significantly reduced in highly disturbed sites. These results suggest that mutualistic interactions of keystone species can be particularly sensitive to human forest disturbance with potential long-term effects on the biodiversity of tropical forests.     

Determinants of mortality across a tropical lowland rainforest community

Tree mortality is an important process determining forest dynamics. However, in species‐rich tropical forests it is largely unknown, how species differ in their response of mortality to resource availability and individual condition. We use a hierarchical Bayesian approach to quantify the impact of light availability, tree size and past growth on mortality of 284 woody species in a 50‐ha long‐term forest census plot in Barro Colorado Island, Panama. Light reaching each individual tree was estimated from yearly vertical censuses of vegetation density. Across the community, 78% of the species showed increasing mortality with increasing light. Considering species individually, just 29 species showed a significant response to light, all with increasing mortality at high light. Past growth had a significant impact on all but three species, with higher growth leading to lower mortality. For the majority of species, mortality decreased sharply with diameter in saplings, then levelled off or increased slightly towards the maximum diameter of the species. Diameter had the biggest impact on mortality, followed by past growth and finally light availability. Our results challenge many previous reports of higher mortality in shade, and we suggest that it is crucial to control for size effects when assessing the impact of environmental conditions on mortality.     

榕树在西双版纳热带雨林生态系统中的作用

榕树是西双版纳热带雨林中的关键植物类群之一,能够为多种生物提供栖息地和食物,从而维持该地区热带雨林生态系统的物种多样性。一些种类的榕树有绞杀特性,在森林更新演替中能够起到积极的作用;还有些种类的榕树是先锋物种,在植被恢复中起重要作用。但是,近些年对西双版纳的过度开发已经使热带雨林片断化,榕树种群数量大量减少,榕果内的寄生蜂、食榕果动物也受到了不同程度的影响。保护好西双版纳热带雨林中关键植物类群榕树,是保护和恢复热带雨林生态系统的重要措施之一。     

How environmental and disturbance factors influence species composition in temperate Australian grasslands

Abstract. A distinctive feature of Australian vegetational history is the abruptness of change since European settlement, involving the influx of exotic species and the imposition of exogenous disturbances which are novel in both intensity and character. This can produce two sources of habitat variability: the natural patterns arising from environmental variation, as well as an overlying effect of disturbance. The relative importance of these two types of variables were compared in temperate herbaceous vegetation. Canonical Correspondence Analysis showed that environment and disturbance had similar contributions to floristic variability. Individually, lithology, altitude and soil disturbance were the strongest variables while slope position, grazing and water enrichment were slightly less important. Despite generally low levels of site specificity, groups of species associated with lithology, slope position, altitude and different disturbance regimes were identified. Exotic species were associated with higher levels of disturbance, but showed levels of environmental specialization similar to the native component. Through combination of this analysis with a previous analysis of species richness for the same data set, it became evident that environmental variation mostly resulted in species substitutions while disturbances led to losses of species, with partial replacement by exotics. Synthesizing these results, we identified three broad groups in relation to tolerance of levels of exogenous disturbance: (1) intolerant species - native taxa intolerant of severe disturbances and constituting the species - rich component of the vegetation; (2) tolerant species - exotic and native taxa occurring at both disturbed and undisturbed habitats and (3) disturbance specialists - predominantly exotic species, correlated with high levels of disturbance.     

The influence of herbivores on primary producers can vary spatially and interact with disturbance

Identifying the major drivers of ecosystem change remains a central area of ecological research. Although top–down drivers of change have received particular focus, we still have little understanding of how consistently these factors control an ecosystem's shift in both directions, between different ecosystem states. Using a crossed experiment in a shallow embayment in southeastern Australia, we investigated the roles of disturbance (kelp removal) and sea urchin herbivory (via increased density) to determine their contributions to shifts away from a kelp‐dominated community. In a second experiment, done in urchin barren areas at two sites, we tested whether reductions in ambient sea urchin densities allowed an algal shift in the reverse direction. In both experiments, we observed that high densities of sea urchins could negatively influence kelp and macroalgal abundance. However, in the kelp bed, a moderate or severe disturbance resulted in a comparable algal response, irrespective of urchin density. The influence of sea urchins also varied dramatically between the two urchin barren sites. Here, reducing urchin densities resulted in algal recovery at one site, but at the other site, substantial colonisation of barren areas by canopy‐forming brown algae and Ulvales occurred across all (low, medium, and high) urchin density treatments. Our findings illustrate multiple pathways of urchin barren creation and algal recovery, and reveal that shifts both to and from an urchin barren state can occur irrespective of herbivore pressure. These alternate pathways can operate over short spatial distances or with different regimes of disturbance.     

The effect of accessibility on rates of fruit removal from tropical shrubs: An experimental study

Summary In a series of field experiments using Costa Rican rain forest plants, we examined the effect of accessibility on fruit removal rates. We compared the effects of fruit placement in terminal and axillary infructescences on diurnal and nocturnal removal rates, visitation rates, and incidence of fruit damage. We used three different species of berries (Phytolacca rivinoides, Psychotria brachiata, and Psychotria pitteri) and worked in three different habitats (fallow fields, treefall gaps, and forest understory) and in two different seasons (July–September, a season of fruit abundance and December–January, a season of fruit scarcity.)We found that in oldfields especially, diurnal removal rates by birds were significantly greater from axillary than from terminal infructescences. Nocturnal removal from axillary infructescences-presumably by rodents-is also occassionally significant. From these data, from observations on climbing ability and fruit use in captive rodents, and from reports in the literature, we suggest that rodents are significant sources of fruit and seed loss in tropical shrubs. We hypothesize that placement of the infructescence on the plant affects fruit removal by both seed-dispersing birds and by the less agile, often seed-destroying rodents. The balance between the two rates is an important component of a plant's dispersal success.Diurnal fruit removal rates were higher during the season of fruit scarcity than during the season of fruit abundance and higher in old fields than in forest gaps or understory. Fruit damage rates-probably due to orthopterans-were slightly greater in gaps and understory than in old fields.