Fragmented Tropical Rainforest Research Articles

Avian functional diversity retained in a tropical rainforest fragment after more than 120 years of turnover

Deforestation is linked to the increasing prevalence of small forest fragments worldwide and an associated loss in functional diversity. However, our long-term understanding on how biodiversity and functional roles respond in such isolated fragments is limited, especially in Southeast Asia. We compared the bird community in a small primary rainforest fragment in the Singapore Botanic Gardens, a UNESCO World Heritage Site, using historical records in 1898 and contemporary surveys conducted in 1998 and 2018–2021. Species composition was expectedly dissimilar between the 1898 and contemporary bird communities (50%), driven mostly by turnover (45.5%) rather than nestedness (4.5%). Despite the changes in community composition and species extirpations, both species richness and functional diversity were retained. Our results suggest that small forest fragments can form novel bird communities that are functionally similar to previous communities that inhabited the fragment, leading to the retention of functional diversity. Such functional redundancy may be encouraged through habitat restoration initiatives adjacent to fragmented forests.

Woody debris removal modifies carbon stocks and soil properties in a fragmented tropical rainforest

AbstractWe examined whether and how woody debris removal for domestic fuel affects carbon storage and soil properties in an Indian rainforest. Fuelwood removal reduced aboveground carbon stocks, increased soil bulk density, and possibly reduced soil phosphorus stocks. Equitably balancing this subtle trade‐off between climate‐regulating and vital, widely utilized provisioning functions, is a challenge for tropical forest research and management.

Drought tolerance in dipterocarp species improved through interspecific hybridization in a tropical rainforest

Gene transfer through interspecific hybridization can enhance functions such as growth performance, although its role in the ecophysiological functions of tropical tree species remains unclear. Hybrid seedlings of genus Shorea (Dipterocarpaceae), which dominates the canopy layer, are found in fragmented tropical rainforests in Southeast Asia. To elucidate changes in dipterocarp environmental adaptability due to hybridization, we studied the ecophysiological traits of dipterocarp seedlings including leaf morphology, photosynthesis, and drought tolerance in two parent species (Shorea curtisii and Shorea leprosula) and their hybrids, including F1 and backcross hybrids. Then, we induced drought stress to investigate drought tolerance in these seedlings. Photosynthetic ability was higher in S. leprosula than in S. curtisii, with the F1 and backcross hybrids showing intermediate characteristics. By contrast, drought tolerance, as indicated by stem hydraulic safety, cuticle thickness, and leaf mass per area, was higher in S. curtisii, lower in S. leprosula, and intermediate in their hybrids. The leaf turgor loss point decreased in S. curtisii due to osmotic adjustment under drought conditions, which led to lower predawn leaf water potential and higher water absorption ability from drier soil. By contrast, these changes were smaller and drought tolerance was weaker in S. leprosula. The hybrids including backcrosses had higher drought tolerance than S. leprosula, suggesting that gene transfer through introgression may facilitate the acquisition of drought tolerance. Although increased drought stress due to climate change and forest degradation are likely to limit seedling regeneration in S. leprosula, drought-tolerant genes obtained through hybridization with S. curtisii may contribute to its survival.

Phylogenetic and functional structure of tree communities at different life stages in tropical rain forest fragments

Tropical rain forest fragmentation is considered one of the principal drivers of biodiversity loss worldwide. Fragmentation and defaunation of tropical rain forests affect the maintenance of their biodiversity in a myriad of ways. Old-growth forest plant and animal species are more likely to suffer from local extinction, not only because fragments frequently represent low quality habitats but also because of the loss of biotic interactions such as seed dispersal. In this study, we evaluated the maintenance of tree species diversity in the face of habitat fragmentation in southern Mexico using different approaches. Firstly, we used community phylogeny at different tree life stages (i.e., seeds, seedlings and adults). Secondly, we categorised plant species in different life stages into functional groups according to seed size (small seeds < 1 cm length and large seeds > 1 cm length) and, finally, by dispersal syndrome (predominantly primate dispersed). We searched for three sites of continuous forest as experimental controls where two important seed dispersers coexist, the howler ( Alouatta pigra ) and spider ( Ateles geoffroyi ) monkeys, and six forest fragments of similar sizes (ca. 3–6 ha). Three fragments were occupied only by howler monkeys, and three had no primates. We compared entire assemblages as well as assemblages of small-seeded and large-seeded species separately to determine the phylogenetic structure and patterns of species richness and the density of adult trees (> 10 cm dbh), seedlings (10–100 cm tall) and seed assemblages. Fragments and continuous forest differed in taxonomic species richness and density at all life stages when large-seeded species mainly dispersed by primates were solely considered, with numbers in unoccupied fragments being consistently lower than in continuous forests and occupied fragments. Phylogenetic clustering occurred in all habitats and for all life stages, predominantly for the seedling stage, indicating that the understory community is assembled via environmental filtering (including both biotic and abiotic processes). Habitats occupied by primates tended to present a higher phylogenetic clustering than unoccupied fragments, suggesting that primates select phylogenetically-related species in their diets and, importantly, that these foraging behaviours influence seedling recruitment patterns. The loss of taxonomic and functional biodiversity and the non-random extinction of tree species principally dispersed by primates, represents part of the evolutionary history that is being lost throughout fragmentation.

Small mammals reduce distance dependence and increase seed predation risk in tropical rainforest fragments

AbstractSeed predation and reduced predation risk with distance from conspecific trees are important influences on tree regeneration in tropical forests. Shifts in animal communities, such as an increase in rodents and other small mammals due to forest fragmentation, could alter patterns of seed predation and affect tree regeneration and community dynamics in forest fragments. We performed a field experiment on four native rainforest tree species in the Western Ghats, India, to test whether fragmentation increases seed predation by mammals and alters the distance dependence of seed predation. We monitored seed predation within open and mammal exclosure plots, near and far from the canopies of conspecific trees, in contiguous and fragmented forests. Seed predation of Cullenia exarillata, Ormosia travancorica, and Syzygium rubicundum was markedly higher in forest fragments, and more so within open plots than exclosures, while the predominantly insect‐predated Acronychia pedunculata experienced similar predation in contiguous forests and fragments. Seed predation of C. exarillata and S. rubicundum was unrelated to distance from conspecific trees in open plots in both contiguous forests and fragments, in contrast to exclosures that showed marked near versus far differences in seed predation. Our findings suggest that by increasing overall seed predation risk and imposing similar seed predation risk near and far from adults variably across the tree species, small mammals could alter processes that shape tree diversity and species composition in fragmented tropical rainforests.

Valuation of Key Freshwater Ecosystem Services: A Case Study in Yagirala Rainforest

Tropical lowland rainforests in Sri Lanka are subjected to degradation due mainly to conversion to other uses and population pressure. Valuation of ecosystem services has become important in terms of conservation of such landscapes. This study intends to estimate economic value of key freshwater aquatic ecosystem services associated with tributary ecosystem in the Yagirala Forest Reserve, a fragmented tropical lowland rainforest in south-west Sri Lanka. Surface water discharged from the tributary and the ornamental fish were identified as main provisioning services and recreation and education were identified as cultural services of the tributary. Physical measurements on freshwater resource and fish fauna were carried out at eleven sampling points along the selected tributary during the rainy season. Water flow was measured at the end point of the tributary, which connects to the main stream using flow rate measuring method. Economic value of water used for agriculture/industrial and potable/domestic use were estimated based on the tariff rates available. Ornamental fish fauna was counted using transects and valued using market prices related to export trade. Cultural services were valued based on visitor data maintained at the Research Centre at Yagirala. Economic value of water available for agricultural activities and industrial purposes were estimated as LKR 39 million and 3 million respectively. Value of water used for domestic purposes was LKR 9 million. Economic value of potential ornamental fish of the tributary was estimated as LKR 41 thousand for three species and considering sustainable extraction. Cultural services were estimated as LKR 14 thousand. The total value of the selected ecosystem services of the tributary for 3 months was estimated as LKR 51 million. The study highlights the importance of combining physical data in the economic valuation. The estimated values could provide justification for the protection of these ecosystems and investments for further value additions.&#x0D; Keywords: Ecosystem services, Yagirala forest reserve, Economic value, Fresh water

Effects of tropical rainforest fragmentation on bird species: a case study from the Bemanevika Protected Area, northwestern Madagascar

The effects of forest fragmentation on forest bird species in the Bemanevika Protected Area (PA), northwestern Madagascar, were investigated during two breeding seasons from October 2016 to January 2018. The forest of Bemanevika is composed of large patches of fragmented tropical rainforest. Seven forest fragments ranging from 10 to 1 050 ha were surveyed. Two methods were used to collect data along transects orientated from the forest edge toward the interior of the forest: mist-netting and point-counts. In all, 27 non-forest birds and 65 forest birds were recorded at all fragments. According to their distribution along an edge-interior gradient, these 65 forest species are classified into three main groups: 15 (23.1%) edge species, 12 (18.5%) forest interior species and 38 (58.5%) ubiquitous species. Larger forest fragments host more forest bird species than smaller forest fragments. Of the 65 forest birds, 14, including the 12 forest interior species, were not found in the four smaller fragments (10–29 ha). The density of forest interior species was positively correlated to forest fragment size. The general trend was that forest interior species were the most sensitive to forest fragmentation (e.g. Madagascar Serpent-eagle Eutriorchis astur, Pitta-like Ground-roller Atelornis pittoides and Schlegel’s Asity Philepitta schlegeli). Large raptors, terrestrial species and understory species were the first to disappear from the small fragments. Fragmented forests provide habitat for bird species, even for those vulnerable to forest fragmentation, therefore the maintenance of large enough forest fragments should be considered in all conservation strategies aimed to protect forest birds.

Germination success of large‐seeded plant species ingested by howler monkeys in tropical rain forest fragments

Primates are important seed dispersers, especially for large-seeded (>1 cm long) tropical species in continuous and fragmented rainforests. In three forest fragments within the Montes Azules Biosphere Reserve, southern Mexico, we investigated the effect of seed passage through the gut of howler monkeys (Alouatta pigra) on the germination rate and maximum germination (%) of native, large-seeded species. One group of howler monkeys, per fragment, was followed and fresh feces collected. Large seeds were removed to compare their germination success with non-ingested seeds of the same species collected underneath parent plants. Feces contained large seeds from seven tree species (Ampelocera hottlei, Castilla elastica, Dialium guianense, Garcinia intermedia, Pourouma bicolor, Spondias mombin, Trophis racemosa) and one liana species (Abuta panamensis). Except for G. intermedia, ingested seeds germinated significantly faster than non-ingested seeds, which had negligible germination. Ingested seeds of D. guianense, P. bicolor, S. mombin, T. racemosa, and A. panamensis had significantly greater germination, while G. intermedia had significantly lower germination and seed ingestion had no apparent effect for A. hottlei and C. elastica. In general, seed ingestion by howler monkeys confers faster germination compared with non-ingested seeds. Faster germination reduces predation probabilities and increases seedling establishment in forest fragments. Primate dispersal services contribute to germination heterogeneity within plant populations of old-growth forest species and to their persistence in forest fragments.

Landscape structure shapes the diversity of tree seedlings at multiple spatial scales in a fragmented tropical rainforest.

The maintenance of seedling diversity of animal-dispersed tree species is fundamental for the structure and function of forest patches in fragmented tropical rainforests. Nonetheless, the effects of landscape structure at different spatial scales on α- and β-diversity of tree seedling communities are recently explored. Using a multi-scale approach, we assessed the relative effect of landscape composition and configuration on α- and β-diversity of animal-dispersed seedlings within 16 forest patches in the Lacandona rainforest, Mexico. We assessed these effects at 13 spatial scales (from 300 to 1500 m radius, at 100 m intervals) for three metrics of effective number of species considering α- and β-diversity. We found that α-diversity was largely affected by landscape composition and β-diversity by landscape configuration. On the one hand, the amount of secondary forest influenced α-diversity. Additionally, species richness increased in landscapes with highly aggregated forest patches. On the other hand, β-diversity was affected positively by forest fragmentation and negatively by the edge contrast of forest patches with the surrounding matrix. Our findings indicate that landscape configuration is a strong driver of seedling diversity in highly deforested rainforests. Promoting forest patches and secondary forests through payment for ecosystem services' programs, favoring matrix quality within land-sharing schemes of smallholder agriculture and secondary forest management, and identifying restoration opportunities for assisted or unassisted natural regeneration are urgently needed for conservation of seedling diversity in human-modified tropical landscapes.

Environment shapes the spatial organization of tree diversity in fragmented forests across a human-modified landscape.

Biodiversity patterns are shaped by the combination of dispersal, environment, and stochasticity, but how the influence of these drivers changes in fragmented habitats remains poorly understood. We examined patterns and relationships among total (γ) and site-level (α) diversity, and site-to-site variation in composition (β-diversity) of tree communities in structurally contiguous and fragmented tropical rainforests within a human-modified landscape in India's Western Ghats. First, for the entire landscape, we assessed the extent to which habitat type (fragment or contiguous forest), space and environment explained variation in α-diversity and composition. Next, within fragments and contiguous forest, we assessed the relative contribution of spatial proximity, environmental similarity, and their joint effects in explaining β-diversity. We repeated these assessments with β-diversity values corrected for the confounding effects of α- and γ-diversity using null models (β-deviation). Lower γ-diversity of fragments resulted from both lower α- and β-diversity compared to contiguous forests. However, β-deviation did not differ between contiguous forests and fragments. Fragmented and contiguous forest clearly diverged in floristic composition, which was attributable to β-diversity being driven by differences in elevation and MAP. Within fragmented forest, neither space nor environment explained β-diversity, but β-deviation increased with greater elevational differences. In contiguous forests by comparison, environment alone (mainly elevation) explained the most variation in β-diversity and β-deviation of both species' occurrences and abundances. Spatial gradients in environmental conditions played a larger role than dispersal limitation in shaping diversity and composition of tree communities across forest fragments. Thus, location of remnant patches at different elevations was a key factor underlying site-to-site variability in species abundances across fragments. Understanding the environmental characteristics of remnant forests in human-modified landscapes, combined with knowledge of species-environment relationships across different functional groups, would therefore be important considerations for management and restoration planning in human-modified landscapes.

Tropical rainforest fragmentation affects plant species richness, composition and abundance depending on plant-size class and life history

Background: Tropical rain forests have been impacted by land use change, leading to major deforestation and fragmentation. Understanding how fragmentation impacts plant communities is central for tropical conservation.&#x0D; Questions: i) How does species richness vary across a range of fragment sizes, and does it vary with plant size-structure? ii) how are species composition and floristic similarity affected by forest fragmentation? iii) does habitat fragmentation affect the representation of species with different life-history and regeneration patterns?&#x0D; Studied species: We sampled overall plant communities and calculated diversity metrics of mature-forest and light-demanding species, considering plants of different size-categories (defined by diameter at breast height, DBH).&#x0D; Study site: This study was carried out at Los Tuxtlas, Veracruz, Mexico. An area originally dominated extensive evergreen tropical forest, but currently highly fragmented&#x0D; Methods: We sampled plants in five forest fragments representing (2 - 36 ha), and a large patch of continuous forest (700 ha). Within each site we established ten-50 × 2 m transects and registered all woody plants with DBH &gt; 1 cm.&#x0D; Results: Species richness declined as fragment size became smaller. Such decline was significant considering all plants (DBH &gt; 1.0 cm) but became non-significant as plant size-category increased (DBH &gt; 2.5, or &gt; 10 cm.). Small fragments had distinguishable assemblages compared to continuous forest and also a reduction in the representation of mature-forest species compared to light-demanding species.&#x0D; Conclusions: Our findings confirm that fragmentation affects tropical plant species diversity, but the effect is differential, depending on plant size-category and life history.

Fine-scale barriers to connectivity across a fragmented South-East Asian landscape in six songbird species.

Habitat fragmentation is a major extinction driver. Despite dramatically increasing fragmentation across the globe, its specific impacts on population connectivity across species with differing life histories remain difficult to characterize, let alone quantify. Here, we investigate patterns of population connectivity in six songbird species from Singapore, a highly fragmented tropical rainforest island. Using massive panels of genome‐wide single nucleotide polymorphisms across dozens of samples per species, we examined population genetic diversity, inbreeding, gene flow and connectivity among species along a spectrum of ecological specificities. We found a higher resilience to habitat fragmentation in edge‐tolerant and forest‐canopy species as compared to forest‐dependent understorey insectivores. The latter exhibited levels of genetic diversity up to three times lower in Singapore than in populations from contiguous forest elsewhere. Using dense genomic and geographic sampling, we identified individual barriers such as reservoirs that effectively minimize gene flow in sensitive understorey birds, revealing that terrestrial forest species may exhibit levels of sensitivity to fragmentation far greater than previously expected. This study provides a blueprint for conservation genomics at small scales with a view to identifying preferred locations for habitat corridors, flagging candidate populations for restocking with translocated individuals and improving the design of future reserves.

Diversity metrics of spider communities associated with an understorey plant in tropical rain forest fragments

AbstractHuman activities change the biodiversity of ecological communities in at least three dimensions: ecologically, taxonomically and functionally. Gathering information on these three dimensions allows the improvement of biodiversity assessments and the increased understanding of anthropogenic impact on natural communities. In this study, we analysed the spider community associated with the tropical plant Heliconia aurantiaca in two contrasting habitat types: continuous forest and forest fragments in south-eastern Mexico. We examined the foliage, stems and bracts of H. aurantiaca individuals in both habitats. We categorized each spider species according to its behavioural and functional traits. We analysed ecological diversity using Hill numbers, taxonomic distinctness and functional diversity using the FRic index. Overall, we collected a total of 110 spiders, of which 44 individuals from 29 species were found in continuous forests, with 66 individuals from 36 species in forest fragments. We found greater ecological diversity in continuous forest than in fragments. In contrast, we found lower functional diversity in continuous forest than in fragments. Taxonomic diversity showed no significant difference between habitats. Forest fragmentation affected the biodiversity of spiders by disrupting species composition and function, which may lead to other ecological changes such as predator–prey interactions and other aspects of ecosystem functioning.

Spatio‐temporal scaling of biodiversity in acoustic tropical bird communities

Automated analysis of acoustic communities is a rapidly emerging approach for the characterization and monitoring of biodiversity. To evaluate its utility, we should verify that such ‘bioacoustics’ can accurately detect ecological signal in spatiotemporal acoustic data. Targeting the ‘Biological Dynamics of Forest Fragments Project’ sites in Brazil, we ask: What is the relative contribution of the spatial, temporal and habitat dimension to variation in bird acoustic communities in a previously fragmented tropical rainforest? Does the functional diversity of bird communities scale similarly to space and time as does species diversity, when both are recorded by bioacoustics means? Overall, is the imprint of landscape fragmentation 30 years ago still audible in the present‐day soundscape? We sampled forty‐four sites in secondary forest and 107 sites in old‐growth forest, resulting in 11 000 h of audio recordings. We detected 60 bird species with satisfactory precision and recovered a linear log–log relation between sampling time and species diversity. Sites in primary forest host more species than sites in secondary forest, but the difference decreased with sampling time, as the slope was slightly higher in secondary than primary forests. Functional diversity, as exposed by vocalizing birds, accumulates faster than does species diversity. The similarity among local communities decreases with distance in both time and space, but stability in time is remarkably high: two acoustic samples from the same site one year (or more) apart prove more similar than two samples taken at the same time but from sites situated just a few hundred meters apart. These findings suggest that habitat modification can be heard as a long‐lasting imprint on the soundscape of regenerating habitats and identify soundscape–area and soundscape–time relations as a promising tool for biodiversity research, applied biomonitoring and restoration ecology.

Effects of restoration on tree communities and carbon storage in rainforest fragments of the Western Ghats, India

AbstractEcological restoration is a leading strategy for reversing biodiversity losses and enhancing terrestrial carbon sequestration in degraded tropical forests. There have been few comprehensive assessments of recovery following restoration in fragmented forest landscapes, and the efficacy of active versus passive (i.e., natural regeneration) restoration remains unclear. We examined 11 indicators of forest structure, tree diversity and composition (adult and sapling), and aboveground carbon storage in 25 pairs of actively restored (AR; 7–15 yr after weed removal and mixed‐native tree species planting) and naturally regenerating (NR) plots within degraded rainforest fragments, and in 17 less‐disturbed benchmark (BM) rainforest plots in the Western Ghats, India. We assessed the effects of active restoration on the 11 indicators and tested the hypothesis that the effects of active restoration increase with isolation from contiguous and relatively intact rainforests. Active restoration significantly increased canopy cover, adult tree and sapling density, adult and sapling species density (overall and late‐successional), compositional similarity to benchmarks, and aboveground carbon storage, which recovered 14–82% toward BM targets relative to NR baselines. By contrast, tree height–diameter ratios and the proportion of native saplings did not recover consistently in actively restored forests. The effects of active restoration on canopy cover, species density (adult), late‐successional species density (adult and sapling), and species composition, but not carbon storage, increased with isolation across the fragmented landscape. Our findings show that active restoration can promote recovery of forest structure, composition, and carbon storage within 7–15 yr of restoration in degraded tropical rainforest fragments, although the benefits of active over passive restoration across fragmented landscapes would depend on indicator type and may increase with site isolation. These findings on early stages of recovery suggest that active restoration in ubiquitous fragmented landscapes of the tropics could complement passive restoration of degraded forests in less fragmented landscapes, and protection of intact forests, as a key strategy for conserving biodiversity and mitigating climate change.

Howling on the edge: Mantled howler monkey (Alouatta palliata) howling behaviour and anthropogenic edge effects in a fragmented tropical rainforest in Costa Rica

AbstractThe function of long calling is a subject of interest across animal behaviour study, particularly within primatology. Many primate species have male‐specific long‐distance calls, including platyrrhines like the folivorous howler monkey (Alouatta spp.). Howler monkeys may howl to defend resources such as feeding trees or areas of rich vegetation from other monkey groups. This study tests the ecological resource defence hypothesis for howling behaviour in the mantled howler monkey (Alouatta palliata) and investigates how anthropogenic forest fragmentation may influence howling behaviour. More specifically, this study examines how howling bout rate, duration, precursors and tree species richness, DBH, and canopy cover vary in 100 m anthropogenic edge and interior forest zones at La Suerte Biological Research Station (LSBRS), a fragmented tropical rainforest in Costa Rica. Results show that tree species richness and canopy cover are higher in forest interior at this site, suggesting that monkeys should howl at greater rates in the interior to defend access to these higher‐quality vegetation resources. Overall, our results supported the ecological resource defence hypothesis. The main howl precursor was howling from neighbouring groups. Although howling rate did not differ between forest zones, howling bouts from forest interior were longer, had a greater number of howls per bout and were preceded by different precursors than howls from anthropogenic edge zones, including more howls from neighbouring groups. Our findings provide some of the first evidence for behavioural edge effects in primate vocal communication behaviour.

Tropical forest conversion to rubber plantation affects soil micro- & mesofaunal community & diversity

Tropical rainforests play important roles in carbon sequestration and are hot spots for biodiversity. Tropical forests are being replaced by rubber (Hevea brasiliensis) plantations, causing widespread concern of a crash in biodiversity. Such changes in aboveground vegetation might have stronger impacts on belowground biodiversity. We studied tropical rainforest fragments and derived rubber plantations at a network of sites in Xishuangbanna, China, hypothesizing a major decrease in diversity with conversion to plantations. We used metabarcoding of the 18S rRNA gene and recovered 2313 OTUs, with a total of 449 OTUs shared between the two land-use types. The most abundant phyla detected were Annelida (66.4% reads) followed by arthropods (15.5% reads) and nematodes (8.9% reads). Of these, only annelids were significantly more abundant in rubber plantation. Taken together, α- and β-diversity were significantly higher in forest than rubber plantation. Soil pH and spatial distance explained a significant portion of the variability in phylogenetic community structure for both land-use types. Community assembly was primarily influenced by stochastic processes. Overall it appears that forest replacement by rubber plantation results in an overall loss and extensive replacement of soil micro- and mesofaunal biodiversity, which should be regarded as an additional aspect of the impact of forest conversion.

Effects of environmental parameters on beetle assemblage in a fragmented tropical rainforest of South America

As a result of habitat fragmentation, the environmental structures of forest remnants change and alter their microclimatic conditions. Edaphic beetles comprise several families that are considered effective bioindicators. In this study, we analyzed how environmental parameters and fragment size affect edaphic beetle assemblage in a fragmented rainforest landscape in Brazil. Beetles were sampled in 12 forest fragments using pitfall traps. Fragment size, tree density and diameter, litter depth and dry weight, and canopy cover were measured in each forest fragment. Staphylinidae and Carabidae were the beetle families with the highest species richness, whereas Scarabaeidae and Nitidulidae were the most abundant families. Beetle abundance was positively affected by litter dry weight and fragment size. In addition, species composition was significantly affected by fragment area. In conclusion, forest patch size is an important parameter for maintaining edaphic beetle assemblages in tropical rainforests, causing major shifts in its abundance and species distribution.

Overlapping flowering periods among Shorea species and high growth performance of hybrid seedlings promote hybridization and introgression in a tropical rainforest of Singapore

A considerable extent of interspecific hybridization among dominant canopy dipterocarp species was recently found in a tropical rain forest fragment in Singapore. However, information about the fertility of the hybrids and the growth of their successive hybrids remains limited. We studied the flowering phenology of four dipterocarp species in the genus Shorea (S. curtisii, S. leprosula, S. parvifolia, and S. macroptera) and two hybrids (S. curtisii × S. leprosula and S. leprosula × S. parvifolia) and studied the performances of seedlings reproduced from them. We observed that S. macroptera bloomed first, without overlap with congeneric species, followed by the other Shorea species and the two first filial (F1) hybrids. S. curtisii and S. leprosula, the species forming hybrids are most likely to succeed in this forest, completely overlapped with their hybrids. Fruits collected from the hybrids were viable, and these hybrid seedlings showed greater survival and a higher growth rate than those from pure species under greenhouse conditions. They included various cross types such as a backcross with each parent species. These results may imply that successive hybrids and introgression spontaneously occur among Shorea species. It may be important to consider the risk of hybridization for the management of tropical forests, particularly in degraded tropical rainforests where mechanisms of ecological isolation between closely related species might be altered.

Effects of forest degradation on the moonrat Echinosorex gymnura in Sabah, Malaysian Borneo

Commercial timber extraction and agricultural expansion lead to substantial degradation and loss of tropical rainforests, posing a severe threat to biodiversity in South-east Asia. Although the impacts of these disturbances are well understood for some species, they remain largely unknown for most species, impeding any directed conservation efforts. One of these little known, presumably forest-dwelling species is the moonrat Echinosorex gymnura, an insectivorous mammal ranging from southern Myanmar and southern Thailand to Sumatra and Borneo. While the moonrat is currently listed as Least Concern on The IUCN Red List of Threatened Species, large parts of its range have been severely degraded due to unsustainable logging practices and the conversion of forest to oil palm plantations. We conducted a systematic large-scale camera trap survey in three forest reserves under different forest management strategies in Sabah, Malaysian Borneo. We recorded a total of 67 independent moonrat detections at 22 of 180 camera trap stations over 12,281 camera trap days. We analysed moonrat habitat associations using occupancy modelling and a set of 9 different environmental covariates. Canopy closure and forest quality were positively associated with moonrat occurrence and were the most important determinants of the species’ occurrence in our study area. Proximity to plantations (oil palm and industrial timber) and elevation negatively affected moonrat occurrence. Our results thus indicate that the moonrat strongly depends on high-quality lowland forest and is unlikely to occur close to plantations. Moonrat occupancy was highest in the sustainably managed forest reserve, suggesting that this species responds much better to reduced-impact logging compared to conventional logging practices. Our first ecological survey indicates that the moonrat may be more threatened by the continued conversion, degradation, and fragmentation of tropical lowland rainforests than previously assumed.