Pristine tropical peat swamp forests (PSFs) represent a unique wetland ecosystem of distinctive hydrology which support unique biodiversity and globally significant stores of soil carbon. Yet in Indonesia and Malaysia, home to 56% of the world's tropical peatland, they are subject to considerable developmental pressures, including widespread drainage to support agricultural needs. In this article, we review the ecology behind the functioning and ecosystem services provided by PSFs, with a particular focus on hydrological processes as well as the role of the forest itself in maintaining those services. Drawing on this, we review the suitability of current policy frameworks and consider the efficacy of their implementation. We suggest that policies in Malaysia and Indonesia are often based around the narrative of oil palm and other major monocrops as drivers of prosperity and development. However, we also argue that this narrative is also being supported by a priori claims concerning the possibility of sustainability of peat swamp exploitation via drainage-based agriculture through the adherence to best management practices. We discuss how this limits their efficacy, uptake and the political will towards enforcement. Further, we consider how both narratives (prosperity and sustainability) clearly exclude important considerations concerning the ecosystem value of tropical PSFs which are dependent on their unimpacted hydrology. Current research clearly shows that the actual debate should be focused not on how to develop drainage-based plantations sustainably, but on whether the sustainable conversion to drainage-based systems is possible at all.
Survival rates of large trees determine forest biomass dynamics. Survival rates of small trees have been linked to mechanisms that maintain biodiversity across tropical forests. How species survival rates change with size offers insight into the links between biodiversity and ecosystem function across tropical forests. We tested patterns of size-dependent tree survival across the tropics using data from 1,781 species and over 2 million individuals to assess whether tropical forests can be characterized by size-dependent life-history survival strategies. We found that species were classifiable into four 'survival modes' that explain life-history variation that shapes carbon cycling and the relative abundance within forests. Frequently collected functional traits, such as wood density, leaf mass per area and seed mass, were not generally predictive of the survival modes of species. Mean annual temperature and cumulative water deficit predicted the proportion of biomass of survival modes, indicating important links between evolutionary strategies, climate and carbon cycling. The application of survival modes in demographic simulations predicted biomass change across forest sites. Our results reveal globally identifiable size-dependent survival strategies that differ across diverse systems in a consistent way. The abundance of survival modes and interaction with climate ultimately determine forest structure, carbon storage in biomass and future forest trajectories.
Tropical beta diversity, and particularly that of herbivorous insects in rainforests, is often considered to be enormous, but this notion has recently been challenged. Because tropical beta diversity is highly relevant to our view on biodiversity, it is important to gain more insights and to resolve methodological problems that may lead to contradictions in different studies. We used data on two ecologically distinct moth families from Southeast Asia and analyzed separately the contribution of beta components to overall species richness at three spatial scales. Observed diversity partitions were compared under different types of null models. We found that alpha diversity was lower than expected on the basis of null models, whereas hierarchical beta components were larger than expected. Beta components played a significant role in shaping gamma diversity, and their contribution can be high (multiplicative beta >5). We found a reduction in beta components when comparing primary forests to agricultural sites (cf. "biotic homogenization"), but even in these habitats, beta components were still substantial. Our analyses show that beta components do play an important role in our data on tropical herbivorous insects and that these results are not attributable to lumping different habitats when sampling environmental gradients.
Diatom abundance, biovolume and diversity were measured over a 2-year period along the Straits of Malacca at two stations with upper (Klang) and lower (Port Dickson) states of eutrophication. Diatom abundance, which ranged from 0.2 × 10(4) to 21.7 × 10(4) cells L(-1) at Klang and 0.9 × 10(3)- 41.3 × 10(3) cells L(-1) at Port Dickson, was influenced partly by nutrient concentrations. At Klang, the diatoms were generally smaller and less diverse (H' = 0.77 ± 0.48) and predominated by Skeletonema spp. (60 ± 32% of total diatom biomass). In contrast, diatoms were larger and more diverse (H' = 1.40 ± 0.67) at Port Dickson. Chaetoceros spp. were the most abundant diatoms at Port Dickson but attributed only 48 ± 30% of total diatom biomass. Comparison of both Klang and Port Dickson showed that their diatom community structure differed and that eutrophication reduced diatom diversity at Klang. We also observed how Si(OH)4 affected the abundance of Skeletonema spp. which in turn influenced the temporal variation of diatom community at Klang. Our results highlighted how eutrophication affects diatom diversity and community structure.
A comparative study of understorey birds inhabiting different habitats, that is, virgin jungle reserve (VJR) and regenerated forest (RF), was conducted in Ulu Gombak Forest Reserve and Selangor and Triang Forest Reserve, Negeri Sembilan, Peninsular Malaysia. The objective of this study was to assess the diversity of understorey birds in both habitats and the effects of forest regeneration on the understorey bird community. The mist-netting method was used to capture understorey birds inhabiting both habitats in both locations. Species composition and feeding guild indicated that understorey bird populations were similar in the two habitats. However, the number of secondary forest species such as Little spiderhunter (Arachnothera longirostra) in VJR is increasing due to its proximity to RF. This study discovered that RFs in both study areas are not yet fully recovered. However, based on the range of species discovered, the RFs have conservation value and should be maintained because they harbour important forest species such as babblers and flycatchers. The assessment of the community structure of understorey birds in VJR and RF is important for forest management and conservation, especially where both habitats are intact.
Proteobacteria produce N-acylhomoserine lactones as signaling molecules, which will bind to their cognate receptor and activate quorum sensing-mediated phenotypes in a population-dependent manner. Although quorum sensing signaling molecules can be degraded by bacteria or fungi, there is no reported work on the degradation of such molecules by basidiomycetous yeast. By using a minimal growth medium containing N-3-oxohexanoylhomoserine lactone as the sole source of carbon, a wetland water sample from Malaysia was enriched for microbial strains that can degrade N-acylhomoserine lactones, and consequently, a basidiomycetous yeast strain WW1C was isolated. Morphological phenotype and molecular analyses confirmed that WW1C was a strain of Trichosporon loubieri. We showed that WW1C degraded AHLs with N-acyl side chains ranging from 4 to 10 carbons in length, with or without oxo group substitutions at the C3 position. Re-lactonisation bioassays revealed that WW1C degraded AHLs via a lactonase activity. To the best of our knowledge, this is the first report of degradation of N-acyl-homoserine lactones and utilization of N-3-oxohexanoylhomoserine as carbon and nitrogen source for growth by basidiomycetous yeast from tropical wetland water; and the degradation of bacterial quorum sensing molecules by an eukaryotic yeast.
The tropics cover a large section of the world in which both developed and developing countries are situated. Rapid socioeconomic development, modernization, urbanization, and globalization have affected both the food market and physical activity (PA), which in turn have propelled the obesity epidemic in the tropics. There is growing concern that overweight and obesity are emerging as major health problems among children and adolescents in the tropics, despite the fact that undernutrition still exists in many of these countries. Physical inactivity, a low metabolic rate, and lack of physical fitness (PF) have been linked to overweight and obesity. Moreover, PF in several tropical countries is declining, and these changes may be a threat to future health, as low PA and PF levels are important risk factors for noncommunicable chronic diseases. Previous studies have reported that the relationships among PA, PF, overweight, and obesity are inconsistent and inconclusive. There is no indication that variances in the energy cost of physical activities lead to obesity. Despite a lack of definite evidence to prove a causal relationship, there is enough certainty that physical inactivity and low fitness levels are linked to overweight and obesity. Hence, people living in tropical countries need to be encouraged to lead a healthier lifestyle by increasing their PA levels and reducing sedentary behaviors to prevent overweight or obesity.
The characteristic flavor of exotic tropical fruits is one of their most attractive attributes to consumers. In this article, the enormous diversity of exotic fruit flavors is reviewed. Classifying some of the exotic fruits into two classes on the basis of whether esters or terpenes predominate in the aroma was also attempted. Indeed, as far as exotic tropical fruits are concerned, the majority of fruits have terpenes predominating in their aroma profile. Some of the fruits in this group are the Amazonian fruits such as pitanga, umbu-caja, camu-camu, garcinia, and bacuri. The ester group is made up of rambutan, durians, star fruit, snake fruit, acerola, tamarind, sapodilla, genipap, soursop, cashew, melon, jackfruit, and cupuacu respectively. Also, the role of sulphur-volatiles in some of the exotic fruits is detailed.
Deforestation in the tropics is an important source of carbon C release to the atmosphere. To provide a sound scientific base for efforts taken to reduce emissions from deforestation and degradation (REDD+) good estimates of C stocks and fluxes are important. We present components of the C balance for selectively logged lowland tropical dipterocarp rainforest in the Malua Forest Reserve of Sabah, Malaysian Borneo. Total organic C in this area was 167.9 Mg C ha⁻¹±3.8 (SD), including: Total aboveground (TAGC: 55%; 91.9 Mg C ha⁻¹±2.9 SEM) and belowground carbon in trees (TBGC: 10%; 16.5 Mg C ha⁻¹±0.5 SEM), deadwood (8%; 13.2 Mg C ha⁻¹±3.5 SEM) and soil organic matter (SOM: 24%; 39.6 Mg C ha⁻¹±0.9 SEM), understory vegetation (3%; 5.1 Mg C ha⁻¹±1.7 SEM), standing litter (<1%; 0.7 Mg C ha⁻¹±0.1 SEM) and fine root biomass (<1%; 0.9 Mg C ha⁻¹±0.1 SEM). Fluxes included litterfall, a proxy for leaf net primary productivity (4.9 Mg C ha⁻¹ yr⁻¹±0.1 SEM), and soil respiration, a measure for heterotrophic ecosystem respiration (28.6 Mg C ha⁻¹ yr⁻¹±1.2 SEM). The missing estimates necessary to close the C balance are wood net primary productivity and autotrophic respiration.Twenty-two years after logging TAGC stocks were 28% lower compared to unlogged forest (128 Mg C ha⁻¹±13.4 SEM); a combined weighted average mean reduction due to selective logging of -57.8 Mg C ha⁻¹ (with 95% CI -75.5 to -40.2). Based on the findings we conclude that selective logging decreased the dipterocarp stock by 55-66%. Silvicultural treatments may have the potential to accelerate the recovery of dipterocarp C stocks to pre-logging levels.
There is accumulating evidence that similar suites of plant traits may affect leaf palatability and leaf litter decomposability. However, the possible association between leaf herbivory and litter decomposition rates across species in species-diverse natural ecosystems such as tropical rain forests remains unexplored, despite its importance in estimating the herbivory effects on carbon and nutrient cycling of ecosystems. We found no strong association between leaf herbivory and litter decomposition rates across 40 tree species in a Malaysian tropical rain forest, even though the leaf and litter traits were tightly correlated. This is because the leaf and litter traits related to herbivory and decomposition rates in the field were inconsistent. Leaf toughness accounted for only a small part of the variation in the herbivory rate, whereas a number of litter traits (the leaf mass per area, lignin to nitrogen ratio, and condensed tannin concentration) accurately predicted the decomposition rate across species. These results suggest that herbivory rate across species may not be strongly related to single leaf traits, probably because plant-herbivore interactions in tropical rain forests are highly diverse; on the other hand, plant-decomposer interactions are less specific and can be governed by litter chemicals. We also investigated two factors, phylogeny and tree functional types, that could affect the relationship between herbivory and decomposition across species. Phylogenetic relatedness among the species did not affect the relationship between herbivory and decomposition. In contrast, when the plants were segregated according to their leaf emergence pattern, we found a significant positive relationship between herbivory and decomposition rates for continuous-leafing species. In these species, the condensed tannin to N ratios in leaves and litter were related to herbivory and decomposition rates, respectively. However, we did not observe a similar trend for synchronous-leafing species. These results suggest that the relationship between herbivory and decomposition may be more greatly affected by functional types than by phylogenetic relatedness among species. In conclusion, our results suggest that well-defended leaves are not necessarily less decomposable litter in a tropical rain forest community, implying that herbivory may not generate positive feedback for carbon and nutrient cycling in this type of ecosystem.
Tree seedlings in tropical rain forests are subject to both damage from natural enemies and intense interspecific competition. This leads to a trade-off in investment between defense and growth, and it is likely that tree species specialized to particular habitats tailor this balance to correspond with local resource availability. It has also been suggested that differential herbivore impacts among tree species may drive habitat segregation, favoring species adapted to particular resource conditions. In order to test these predictions, a reciprocal transplant experiment in Sabah, Malaysia, was established with seedlings of five species of Dipterocarpaceae. These were specialized to either alluvial (Hopea nervosa, Parashorea tomentella) or sandstone soils (Shorea multiflora, H. beccariana), or were locally absent (S. fallax). A total of 3000 seedlings were planted in paired gap and understory plots in five sites on alluvial and sandstone soils. Half of all seedlings were fertilized. Seedling growth and mortality were recorded in regular samples over 3.5 years, and rates of insect herbivore damage were estimated from censuses of foliar tissue loss on marked mature leaves and available young leaves. Greater herbivory rates on mature leaves had no measurable effects on seedling growth but were associated with a significantly increased likelihood of mortality during the following year. In contrast, new-leaf herbivory rates correlated with neither growth nor mortality. There were no indications of differential impacts of herbivory among the five species, nor between experimental treatments. Herbivory was not shown to influence segregation of species between soil types, although it may contribute toward differential survival among light habitats. Natural rates of damage were substantially lower than have been shown to influence tree seedling growth and mortality in previous manipulative studies.
This article presents findings of the thermal comfort study in hospitals. A field survey was conducted to investigate the temperature range for thermal comfort in hospitals in the tropics. Thermal acceptability assessment was conducted to examine whether the hospitals in the tropics met the ASHRAE Standard-55 80% acceptability criteria. A total of 114 occupants in four hospitals were involved in the study. The results of the field study revealed that only 44% of the examined locations met the comfort criteria specified in ASHRAE Standard 55. The survey also examined the predicted percentage of dissatisfied in the hospitals. The results showed that 49% of the occupants were satisfied with the thermal environments in the hospitals. The field survey analysis revealed that the neutral temperature for Malaysian hospitals was 26.4 degrees C. The comfort temperature range that satisfied 90% of the occupants in the space was in the range of 25.3-28.2 degrees C. The results from the field study suggested that a higher comfort temperature was required for Malaysians in hospital environments compared with the temperature criteria specified in ASHRAE Standard (2003). In addition, the significant deviation between actual mean vote and predicted mean vote (PMV) strongly implied that PMV could not be applied without errors in hospitals in the tropics.
The responses of tropical forests to global anthropogenic disturbances remain poorly understood. Above-ground woody biomass in some tropical forest plots has increased over the past several decades, potentially reflecting a widespread response to increased resource availability, for example, due to elevated atmospheric CO2 and/or nutrient deposition. However, previous studies of biomass dynamics have not accounted for natural patterns of disturbance and gap phase regeneration, making it difficult to quantify the importance of environmental changes. Using spatially explicit census data from large (50 ha) inventory plots, we investigated the influence of gap phase processes on the biomass dynamics of four 'old-growth' tropical forests (Barro Colorado Island (BCI), Panama; Pasoh and Lambir, Malaysia; and Huai Kha Khaeng (HKK), Thailand). We show that biomass increases were gradual and concentrated in earlier-phase forest patches, while biomass losses were generally of greater magnitude but concentrated in rarer later-phase patches. We then estimate the rate of biomass change at each site independent of gap phase dynamics using reduced major axis regressions and ANCOVA tests. Above-ground woody biomass increased significantly at Pasoh (+0.72% yr(-1)) and decreased at HKK (-0.56% yr(-1)) independent of changes in gap phase but remained stable at both BCI and Lambir. We conclude that gap phase processes play an important role in the biomass dynamics of tropical forests, and that quantifying the role of gap phase processes will help improve our understanding of the factors driving changes in forest biomass as well as their place in the global carbon budget.
The recurrent patterns in the commonness and rarity of species in ecological communities--the relative species abundance--have puzzled ecologists for more than half a century. Here we show that the framework of the current neutral theory in ecology can easily be generalized to incorporate symmetric density dependence. We can calculate precisely the strength of the rare-species advantage that is needed to explain a given RSA distribution. Previously, we demonstrated that a mechanism of dispersal limitation also fits RSA data well. Here we compare fits of the dispersal and density-dependence mechanisms for empirical RSA data on tree species in six New and Old World tropical forests and show that both mechanisms offer sufficient and independent explanations. We suggest that RSA data cannot by themselves be used to discriminate among these explanations of RSA patterns--empirical studies will be required to determine whether RSA patterns are due to one or the other mechanism, or to some combination of both.
Four insect repellent products (RPs) (RP 1, Experimental Repellent Lotion [Bayrepel 12%]; RP 2, Experimental Repellent Cream [Bayrepel 5%]; RP 3, Off! Insect Repellent II Aerosol [deet 15%]; and RP 4, Off! Skintastic II Cream [deet 7.5%]) were evaluated simultaneously for their efficacy against vector and nuisance mosquitoes. The aim of this study was to compare the relative efficacy of RPs based on a new repellent compound, Bayrepel (1-piperidinecarboxylic acid, 2-(2-hydroxyethyl)-1-methylpropylester), with deet (N,N-diethyl-m-toluamide)-based RPs. An 8-h field efficacy of above repellents was evaluated against the day-biting mosquito (Aedes albopictus) and night-biting mosquitoes (Culex quinquefasciatus and Anopheles spp.). Evaluation was carried out by exposing humans with repellent-treated bare limbs to mosquitoes landing and to mosquitoes landing and biting. Repellent product 1 or 2 was applied on the left arm and leg, whereas RP 3 or 4 was applied on the right arm and leg, respectively. Application of these 4 RPs significantly reduced (P < 0.05) the landing and the landing and biting of day-biting and night-biting mosquitoes. All 4 RPs were found to be equally effective (P < 0.05) against Ae. albopictus and Cx. quinquefasciatus. However, for protection against Anopheles spp., RPs 1 and 3 exhibited significantly (P < 0.05) better repellency effect than RPs 2 and 4.
With a focus on the Danum Valley area of Sabah, Malaysian Borneo, this special issue has as its theme the future of tropical rainforests in a changing landscape and climate. The global environmental context to the issue is briefly given before the contents and rationale of the issue are summarized. Most of the papers are based on research carried out as part of the Royal Society South East Asia Rainforest Research Programme. The issue is divided into five sections: (i) the historical land-use and land management context; (ii) implications of land-use change for atmospheric chemistry and climate change; (iii) impacts of logging, forest fragmentation (particularly within an oil palm plantation landscape) and forest restoration on ecosystems and their functioning; (iv) the response and resilience of rainforest systems to climatic and land-use change; and (v) the scientific messages and policy implications arising from the research findings presented in the issue.
Shirley is a 42 year old woman who has rung you 5 days after returning from a 3 week resort holiday in Malaysia and Thailand. You saw her before her trip and administered a hepatitis A vaccine and advised her that she did not require anti malarial drugs as she was only going to large cities and beach resorts. She says she has had a high fever, headache and body aches for several days and that she feels exhausted, but is well enough to come to the surgery. When you see her later that morning, she looks fairly well, although she is moving rather gingerly. She says she has been resting, is drinking lots of fluids, has some anorexia, but no other significant symptoms. Examination reveals a temperature of 38 degrees C and she has a fine morbilliform rash on her body, limbs and neck. There are no other abnormal findings.
The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fisher's alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between ∼ 40,000 and ∼ 53,000, i.e., at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of ∼ 19,000-25,000 tree species. Continental Africa is relatively depauperate with a minimum of ∼ 4,500-6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa.