Impact of rainforest conversion into monoculture plantation systems on pseudoscorpion density, diversity and trophic niches

Abstract

Indonesia’s biodiversity is at risk due to large forest areas being transformed into rubber and oil palm monoculture plantations. The effects of this land-use change on local fauna have been studied in a variety of organisms, including invertebrates from leaf litter and soil habitats. Litter and soil organisms are important drivers of essential ecosystem functions, such as nutrient cycling and carbon sequestration, which are impacted heavily by monoculture plantations. Pseudoscorpions (Arachnida: Pseudoscorpiones) are predatory arthropods in such litter and soil habitats and are an ubiquitous, although typically not very abundant, component of the soil animal food web. Since virtually nothing is known on their functional role diversity in tropical soil food webs, this study aims at contributing filling this gap of knowledge. We studied the impact of the conversion of rainforest into rubber and oil palm plantations on the density and diversity of pseudoscorpions in two landscapes of Jambi province, Sumatra, Indonesia, and applied stable isotope analysis to investigate changes in their trophic niches. Among 266 sorted individuals, only one described species was recorded, while the others were sorted to a total of nine morphospecies. Pseudoscorpions in the study region predominantly colonized mineral soil rather than the litter layer. As expected, the density declined from rainforest to rubber (-83%) and oil palm (-87%), and the number of species declined from rainforest to rubber (-37%) but in particular to oil palm (-47%). The density in riparian areas was five times lower than in non-riparian sites, however, species richness was almost the same. Further, the community composition of pseudoscorpions differed between land-use systems and landscapes; no species was present across all land-use systems, and the majority of species was only present in one land-use system indicating high habitat dependence. Stable isotope analysis suggested that the pseudoscorpion community shifted from species associated with the detritus-based energy channel in rainforest to species associated with the plant-based energy channel in monoculture plantations, indicating shifts in the use of basal resources by the soil community cascading up into predators. Overall, the results indicate that tropical pseudoscorpion communities comprise high-level predators that prefere to inhabit soil rather than litter and respond sensitively to land-use change. Due to this sensitivity, pseudoscorpion abundance may serve as bioindicator for ecosystem changes in the tropics. To mitigate negative effects of changes in land use in tropical ecosystems on cryptic and unexplored soil biodiversity, reduced herbicide use resulting in increased understory vegetation and mulching practices might be adopted.

Keywords

• stable isotopes
• soil
• predation
• Indonesia
• land-use change
• rubber