Carsten A. Brühl

How will oil palm expansion affect biodiversity

Oil palm is one of the worlds most rapidly increasing crops. We assess its contribution to tropical deforestation and review its biodiversity value. Oil palm has replaced large areas of forest in Southeast Asia, but land-cover change statistics alone do not allow an assessment of where it has driven forest clearance and where it has simply followed it. Oil palm plantations support much fewer species than do forests and often also fewer than other tree crops. Further negative impacts include habitat fragmentation and pollution, including greenhouse gas emissions. With rising demand for vegetable oils and biofuels, and strong overlap between areas suitable for oil palm and those of most importance for biodiversity, substantial biodiversity losses will only be averted if future oil palm expansion is managed to avoid deforestation.

Biofuel plantations on forested lands: double jeopardy for biodiversity and climate

The growing demand for biofuels is promoting the expansion of a number of agricultural commodities, including oil palm (Elaeis guineensis). Oil-palm plantations cover over 13 million ha, primarily in Southeast Asia, where they have directly or indirectly replaced tropical rainforest. We explored the impact of the spread of oil-palm plantations on greenhouse gas emission and biodiversity. We assessed changes in carbon stocks with changing land use and compared this with the amount of fossil-fuel carbon emission avoided through its replacement by biofuel carbon. We estimated it would take between 75 and 93 years for the carbon emissions saved through use of biofuel to compensate for the carbon lost through forest conversion, depending on how the forest was cleared. If the original habitat was peatland, carbon balance would take more than 600 years. Conversely, planting oil palms on degraded grassland would lead to a net removal of carbon within 10 years. These estimates have associated uncertainty, but their magnitude and relative proportions seem credible. We carried out a meta-analysis of published faunal studies that compared forest with oil palm. We found that plantations supported species-poor communities containing few forest species. Because no published data on flora were available, we present results from our sampling of plants in oil palm and forest plots in Indonesia. Although the species richness of pteridophytes was higher in plantations, they held few forest species. Trees, lianas, epiphytic orchids, and indigenous palms were wholly absent from oil-palm plantations. The majority of individual plants and animals in oil-palm plantations belonged to a small number of generalist species of low conservation concern. As countries strive to meet obligations to reduce carbon emissions under one international agreement (Kyoto Protocol), they may not only fail to meet their obligations under another (Convention on Biological Diversity) but may actually hasten global climate change. Reducing deforestation is likely to represent a more effective climate-change mitigation strategy than converting forest for biofuel production, and it may help nations meet their international commitments to reduce biodiversity loss.

Climatic drivers of hemispheric asymmetry in global patterns of ant species richness.

Although many taxa show a latitudinal gradient in richness, the relationship between latitude and species richness is often asymmetrical between the northern and southern hemispheres. Here we examine the latitudinal pattern of species richness across 1003 local ant assemblages. We find latitudinal asymmetry, with southern hemisphere sites being more diverse than northern hemisphere sites. Most of this asymmetry could be explained statistically by differences in contemporary climate. Local ant species richness was positively associated with temperature, but negatively (although weakly) associated with temperature range and precipitation. After contemporary climate was accounted for, a modest difference in diversity between hemispheres persisted, suggesting that factors other than contemporary climate contributed to the hemispherical asymmetry. The most parsimonious explanation for this remaining asymmetry is that greater climate change since the Eocene in the northern than in the southern hemisphere has led to more extinctions in the northern hemisphere with consequent effects on local ant species richness.

Altitudinal distribution of leaf litter ants along a transect in primary forests on Mount Kinabalu, Sabah, Malaysia

The ant communities of the leaf litter were studied along an elevational gradient on Mount Kinabalu in primary rain forest systems ranging from dipterocarp hill forest to dwarf forest of the highest altitudes (560, 800, 1130, 1360, 1530, 1740, 1930, 2025, 2300, 2600 m a.s.l.). The litter ant fauna along the gradient included 283 species of 55 genera. The number of ant species in the leaf litter decreased exponentially without evidence of a peak in species richness at mid-elevations. This result is in contrast to many findings on altitudinal gradients in ants and other animal groups. Most ant species have a very limited altitudinal range leading to high turnover values when comparing communities of different altitudes. Of the ant species, 74% were even restricted to one site. As evident from this study, altitudinal ranges of species are very narrow. Elevational gradients are therefore extremely species-rich and might serve as a prime example of hot spots of biodiversity. This fact is of great concern when implementing conservation strategies.

Stratification of ants (Hymenoptera, Formicidae) in a primary rain forest in Sabah, Borneo

The ant fauna of a rain forest in Sabah, Malaysia was sampled by using different collecting methods in three strata. In total, 524 morphospecies of ants could be distinguished. They belong to seven subfamilies and 73 genera. So far, the ant community described is the most species rich published for a primary tropical rain forest. Regarding the stratification in the forest, the leaf litter com- munity comprised as many ant species as the lower vegetation or canopy. Further- more the litter stratum had the highest generic diversity. The stratification of ants in rain forests seems to be a very strict one with the majority of species (75%) being related to only one stratum. This is in contrast to findings on the stratifica- tion of beetles in rain forests. The stratification and a radiation of some groups into vegetation and canopy, where a broad spectrum of permanent habitats exist, is responsible for the high diversity of ants in tropical rain forests.

Terrestrial pesticide exposure of amphibians: an underestimated cause of global decline?

Amphibians, a class of animals in global decline, are present in agricultural landscapes characterized by agrochemical inputs. Effects of pesticides on terrestrial life stages of amphibians such as juvenile and adult frogs, toads and newts are little understood and a specific risk assessment for pesticide exposure, mandatory for other vertebrate groups, is currently not conducted. We studied the effects of seven pesticide products on juvenile European common frogs (Rana temporaria) in an agricultural overspray scenario. Mortality ranged from 100% after one hour to 40% after seven days at the recommended label rate of currently registered products. The demonstrated toxicity is alarming and a large-scale negative effect of terrestrial pesticide exposure on amphibian populations seems likely. Terrestrial pesticide exposure might be underestimated as a driver of their decline calling for more attention in conservation efforts and the risk assessment procedures in place do not protect this vanishing animal group.

Size does matter - effects of tropical rainforest fragmentation on the leaf litter ant community in Sabah, Malaysia

Primary tropical lowland rainforest in Sabah, Malaysia, has been largely reduced to small to medium-sized, often isolated, forest islands surrounded by a highly altered agricultural landscape. The biodiversity patterns of leaf litter ant communities were monitored in two forest fragments of differing size as well as in a contiguous forest over the course of two years. Species number and diversity in the forest isolates was significantly lower, reaching only 47.5% of the species number collected in the contiguous forest. Species density was also lower, which had led to a thinning of the ant community in the fragments. Community composition was substantially altered in the forest remnants, and an increase of tramp species with smaller fragment size was detected. These results were unexpected and alarming, as the medium-sized forest is with its 42.9 km2 a comparatively large primary forest fragment for Sabah.

Amphibians at risk? Susceptibility of terrestrial amphibian life stages to pesticides

Current pesticide risk assessment does not specifically consider amphibians. Amphibians in the aquatic environment (aquatic life stages or postmetamorphic aquatic amphibians) and terrestrial living juvenile or adult amphibians are assumed to be covered by the risk assessment for aquatic invertebrates and fish, or mammals and birds, respectively. This procedure has been evaluated as being sufficiently protective regarding the acute risk posed by a number of pesticides to aquatic amphibian life stages (eggs, larvae). However, it is unknown whether the exposure and sensitivity of terrestrial living amphibians are comparable to mammalian and avian exposure and sensitivity. We reviewed the literature on dermal pesticide absorption and toxicity studies for terrestrial life stages of amphibians, focusing on the dermal exposure pathway, that is, through treated soil or direct overspray. In vitro studies demonstrated that cutaneous absorption of chemicals is significant and that chemical percutaneous passage, P (cm/h), is higher in amphibians than in mammals. In vivo, the rapid and substantial uptake of the herbicide atrazine from treated soil by toads (Bufo americanus) has been described. Severe toxic effects on various amphibian species have been reported for field-relevant application rates of different pesticides. In general, exposure and toxicity studies for terrestrial amphibian life stages are scarce, and the reported data indicate the need for further research, especially in light of the global amphibian decline.

Pollen foraging and resource partitioning of stingless bees in relation to flowering dynamics in a Southeast Asian tropical rainforest

Summary: We used microscopic pollen analysis to investigate the diversity and similarity of pollen diets of six colonies of stingless bees (Apidae; Meliponini) located within one monospecific (three colonies of Trigona collina) and one mixed nesting aggregation (one colony of T. collina, and one colony of each of the close relatives T. melina and T. melanocephala) in lowland tropical rain forest in Sabah, Malaysia. Samples of 20 corbicular loads, collected six times over a period of three months from each colony, contained a total of 74 different morphotypes of pollen grains with an average between 4.7 to 8.5 per sample for the different colonies. In an analysis on total diet composition intraspecific similarity was much greater than interspecific similarity. The focal colony of Trigona collina from the mixed aggregation distinctly clustered according to species rather than nest location, suggesting that some interspecific resource partitioning occurs. The sampling period was accompanied by a drastic increase in flowering activity as evidenced by data from a flower phenology transect. At times of limited flowering similarity of pollen diets was generally low, both within and between species. It is hypothesized that this is so because bees are forced to forage from scattered subsets of flower patches spread out over a large foraging range. In times of increased flowering pollen diet similarity significantly increased between colonies of the monospecific aggregation, presumably because colonies concentrated on more profitable sources in closer proximity. In contrast, similarity remained low within the mixed aggregation, suggesting that innate differences in foraging preferences precluded any effect of diet convergence.

Review on environmental alterations propagating from aquatic to terrestrial ecosystems.

Terrestrial inputs into freshwater ecosystems are a classical field of environmental science. Resource fluxes (subsidy) from aquatic to terrestrial systems have been less studied, although they are of high ecological relevance particularly for the receiving ecosystem. These fluxes may, however, be impacted by anthropogenically driven alterations modifying structure and functioning of aquatic ecosystems. In this context, we reviewed the peer-reviewed literature for studies addressing the subsidy of terrestrial by aquatic ecosystems with special emphasis on the role that anthropogenic alterations play in this water-land coupling. Our analysis revealed a continuously increasing interest in the coupling of aquatic to terrestrial ecosystems between 1990 and 2014 (total: 661 studies), while the research domains focusing on abiotic (502 studies) and biotic (159 studies) processes are strongly separated. Approximately 35% (abiotic) and 25% (biotic) of the studies focused on the propagation of anthropogenic alterations from the aquatic to the terrestrial system. Among these studies, hydromorphological and hydrological alterations were predominantly assessed, whereas water pollution and invasive species were less frequently investigated. Less than 5% of these studies considered indirect effects in the terrestrial system e.g. via food web responses, as a result of anthropogenic alterations in aquatic ecosystems. Nonetheless, these very few publications indicate far-reaching consequences in the receiving terrestrial ecosystem. For example, bottom-up mediated responses via soil quality can cascade over plant communities up to the level of herbivorous arthropods, while top-down mediated responses via predatory spiders can cascade down to herbivorous arthropods and even plants. Overall, the current state of knowledge calls for an integrated assessment on how these interactions within terrestrial ecosystems are affected by propagation of aquatic ecosystem alterations. To fill these gaps, we propose a scientific framework, which considers abiotic and biotic aspects based on an interdisciplinary approach.