Kwek Yan Chong

Mitigating the impact of oil‐palm monoculture on freshwater fishes in Southeast Asia

Anthropogenic land-cover change is driving biodiversity loss worldwide. At the epicenter of this crisis lies Southeast Asia, where biodiversity-rich forests are being converted to oil-palm monocultures. As demand for palm oil increases, there is an urgent need to find strategies that maintain biodiversity in plantations. Previous studies found that retaining forest patches within plantations benefited some terrestrial taxa but not others. However, no study has focused on aquatic taxa such as fishes, despite their importance to human well-being. We assessed the efficacy of forested riparian reserves in conserving freshwater fish biodiversity in oil-palm monoculture by sampling stream fish communities in an oil-palm plantation in Central Kalimantan, Indonesia. Forested riparian reserves maintained preconversion local fish species richness and functional diversity. In contrast, local and total species richness, biomass, and functional diversity declined markedly in streams without riparian reserves. Mechanistically, riparian reserves appeared to increase local species richness by increasing leaf litter cover and maintaining coarse substrate. The loss of fishes specializing in leaf litter and coarse substrate decreased functional diversity and altered community composition in oil-palm plantation streams that lacked riparian reserves. Thus, a land-sharing strategy that incorporates the retention of forested riparian reserves may maintain the ecological integrity of fish communities in oil-palm plantations. We urge policy makers and growers to make retention of riparian reserves in oil-palm plantations standard practice, and we encourage palm-oil purchasers to source only palm oil from plantations that employ this practice.

Disregarding human pre-introduction selection can confound invasive crayfish risk assessments.

Trait-based risk assessments of invasive species focus on identifying intrinsic biological or ecological traits associated with invasion success, which allows for a new species’ invasion risk to be assessed a priori, thus facilitating cost-effective prevention strategies. However, human preferences for species traits—preferences that might affect which species enter into different pathways of invasion—exist for taxa closely associated with people. Disregarding such preferences can confound correlations between species traits and invasion success. Here we develop a risk assessment for crayfish, a group of culturally and ecologically important decapod crustaceans with numerous harmful invasive species, that explicitly accounts for species traits as well as human preferences as they are expressed in different pathways (e.g., aquaculture, live angling bait for fishing, harvesting). Our results indicate that species traits and human preferences are confounded for introduction and establishment risk models, but subsequent spread risk is not associated with human preferences and can be predicted by clutch size. Although not commonly addressed, this study demonstrates that accounting for human preferences in trait-based risk assessments is important for taxa closely associated with people, as pre-introduction human selection of traits may bias such analyses.

Towards a global database of weed risk assessments: a test of transferability for the tropics

Worldwide spread and establishment of alien plant species continues to accelerate and damage ecological and agricultural systems. Early warning and prevention of high-risk introductions is the most cost-effective approach to minimise losses while maximising benefits, and the Australian Weed Risk Assessment (A-WRA) system has been the most well-developed and successful predictive scheme. However, any system would be limited if the results or scores were confined to the locality of assessment. We compiled A-WRA scores conducted in four tropical to sub-tropical regions and tested the accuracy of these scores for predicting naturalisations for a separate well-documented, equatorial, exotic flora where weed risk assessments have never been conducted. Receiver Operating Characteristic (ROC) curves reflect high accuracies of predictions, comparable to those in other studies. No significant differences in accuracy were found between each regional subset and the compiled set of scores. Our results show that A-WRA scores assessed at one locality can be used for others of similar climate, increasing the utility of every species’ assessment. A global database of A-WRA scores would enable rapid local decision-making in border controls on imported plant species. A growing record of species assessments would also facilitate monitoring evolutionary and ecological aspects of invasive species.

Moving Away from Paper Corridors in Southeast Asia

[Extract] Among biodiversity conservation solutions, corridors often receive much public and political support. Nonbiologists can easily connect with the concept (Van Der Windt & Swart 2008), and corridors have the potential to reach a middle ground between land development and biodiversity conservation. However, this political convenience can be taken too far, especially given that corridors need substantial research and planning to be successful. At best, a poorly implemented corridor is a waste of public funds; at worst, it is a consolation measure that legitimizes habitat destruction. Corridors may even accelerate the decline of rare native species by allowing invasive species to spread easily across the landscape (Beier et al. 2008). Recently, attention has been directed toward distilling the best practices in designing linkages (Beier et al. 2008; Lacher & Wilkerson 2013) to help practitioners maximize ecological connectivity while avoiding common pitfalls.

Leaf litter depth as an important factor inhibiting seedling establishment of an exotic palm in tropical secondary forest patches

Intact tropical rainforests on continents and continental islands are considered to be relatively resistant to invasions by introduced plant species, but fragmentation and degradation may render them susceptible, especially to species from predominantly shade-tolerant families with centres of diversity in the tropics, such as palms. We investigated the seedling establishment patterns of the most common exotic palm species in Singapore’s secondary forest patches, the Macarthur palm (Ptychosperma macarthurii), in relation to landscape-level planting intensity, abiotic conditions, and recipient community composition. We first used conditional inference forests to narrow down the set of possible explanatory variables, followed by fitting generalised linear models with the forest patch and individual plots as random intercepts, to account for the nesting of plots within patches and overdispersion, respectively. The number of cultivated adults in the vicinity was not an important variable. Instead, leaf litter was the most important predictor of seedling density. Thick leaf litter in the disturbed and younger secondary forest matrix that surrounds old growth forest patches may therefore serve as a buffer against invasions, especially by small-seeded exotics. However, if adults of exotic species are allowed to establish unchecked, for example along forest trails that lead into the interior of the forested landscape, the seed rain may eventually reach old growth forest where leaf litter is typically thin. Further studies are required to determine if second-generation adults within invaded habitats contribute disproportionately more to propagule pressure than first-generation cultivated plants outside the invaded habitat.

Pitcher plant facilitates prey capture in a sympatric congener

Carnivorous plants avoid below-ground competition for nitrogen by utilizing an alternative nitrogen resource—invertebrate prey, but it remains unclear if sympatric carnivorous plants compete for prey resources. The aim of this study was to investigate if exploitative prey-resource competition occurs between the two sympatric pitcher plant species, Nepenthes rafflesiana and N. gracilis in Singapore. We first investigated if prey-resource partitioning occurs between these two species, and then investigated niche shift in N. gracilis by examining its pitcher contents along an in situ gradient of N. rafflesiana interspecific competition. Our results showed clear evidence of resource partitioning between the two species, but contrary to the expectation of competition, proximity to N. rafflesiana pitchers correlated with higher total prey numbers in N. gracilis pitchers. Our multivariate model of prey assemblages further suggested that N. rafflesiana facilitates N. gracilis prey capture, especially in several ant taxa that are trapped by both species. Concurrently, we found strong evidence for intraspecific competition between N. gracilis pitchers, suggesting that prey resources are exhaustible by pitcher-predation. Our results show that resource partitioning can be associated with facilitative interactions, instead of competition as is usually assumed. Facilitation is more typically expected between phylogenetically distant species, but divergences in resource acquisition strategies can permit facilitation between congeners.

Herbarium records do not predict rediscovery of presumed nationally extinct species

Rediscoveries of species previously thought to be extinct present a dilemma to conservation biology. On one hand, such instances offer the chance to change the course of events away from one that would have led to extinctions. On the other hand, public support for conservation may wane if scientists are frequently seen to overstate and prematurely declare extinctions. Recent studies have adopted a probabilistic approach to infer extinction, using sightings or collections and statistical models to calculate the chance that a species may still be extant. We conduct the first broad-scale test of such models using a recently compiled national red list and national herbarium collection records, including collections of presumed nationally extinct species made after the red list publication, which constitute “rediscoveries”. There was little evidence that the probabilities calculated by these models were associated with rediscoveries over a 3.5-year period. Current probabilistic models of extinction using sighting records could hence be inadequate for use with most natural history collection data.

Dipteran larvae and microbes facilitate nutrient sequestration in the Nepenthes gracilis pitcher plant host

The fluid-containing traps of Nepenthes carnivorous pitcher plants (Nepenthaceae) are often inhabited by organisms known as inquilines. Dipteran larvae are key components of such communities and are thought to facilitate pitcher nitrogen sequestration by converting prey protein into inorganic nitrogen, although this has never been demonstrated in Nepenthes. Pitcher fluids are also inhabited by microbes, although the relationship(s) between these and the plant is still unclear. In this study, we examined the hypothesis of digestive mutualism between N. gracilis pitchers and both dipteran larvae and fluid microbes. Using dipteran larvae, prey and fluid volumes mimicking in situ pitcher conditions, we conducted in vitro experiments and measured changes in available fluid nitrogen in response to dipteran larvae and microbe presence. We showed that the presence of dipteran larvae resulted in significantly higher and faster releases of ammonium and soluble protein into fluids in artificial pitchers, and that the presence of fluid microbes did likewise for ammonium. We showed also that niche segregation occurs between phorid and culicid larvae, with the former fragmenting prey carcasses and the latter suppressing fluid microbe levels. These results clarify the relationships between several key pitcher-dwelling organisms, and show that pitcher communities facilitate nutrient sequestration in their host.

Seed production and survival of four dipterocarp species in degraded forests in Singapore

Background: Seed production, germination, and seedling survival are crucial processes during community masting events in dipterocarp-dominated rain forest in South-east Asia. Aims: We examine how these processes function in fragmented remnants of dipterocarp forest in Singapore. Methods: Fruits were captured in seed traps and seed fates on the ground were tracked up to 5 months after fruiting for four dipterocarp species during a masting event in 2014; camera traps under each tree recorded seed predators. Results: Long-tailed macaques were the major seed predators, claiming 34% of pre-dispersal seeds. Insect seed predation, primarily by moth larvae, played a relatively minor role, claiming only 9% of seed pre-dispersal and 0.7% post-dispersal. The mean proportion of seeds that escaped post-dispersal predation but failed to germinate was between 5% and 37% for the four species. Conclusions: The non-viability of dipterocarp seeds can be at least as great a concern for forest regeneration as the rate of vertebrate pre-dispersal predation.

Pollination of Ficus elastica : India rubber re-establishes sexual reproduction in Singapore

Ficus elastica, otherwise known as India Rubber (although its geographical origins are unclear), was an important source of latex in the early 19th century and was widely cultivated in tropical Asia. Like all figs, F. elastica is dependent on tiny, highly specific wasps for pollination, and detailed studies based out of Singapore in the 1930s suggested that through the loss of its pollinator F. elastica was extinct in the wild. However, around 2005 wild seedlings of F. elastica began appearing in Singapore. We identified the pollinator as Platyscapa clavigera, which was originally described from F. elastica in Bogor in 1885. A visit to Bogor Botanical Gardens revealed that not only was F. elastica being pollinated by P. clavigera in the gardens, but there was clear evidence it had been reproducing naturally there over many decades. Although Singapore has a native fig flora of over 50 species, F. elastica went unpollinated for at least 70 years and probably from the time it was introduced during the 19th century. These observations illustrate the extraordinary specificity of this interaction and, through the fig’s ability to wait for its pollinators, demonstrates one way in which such highly specific interactions can be evolutionarily stable.