Shift in trophic niches of soil microarthropods with conversion of tropical rainforest into plantations as indicated by stable isotopes (15N, 13C)

Abstract

Land-use change is threatening biodiversity worldwide, affecting above and below ground animal communities by altering their trophic niches. However, shifts in trophic niches with changes in land use are little studied and this applies in particular to belowground animals. Oribatid mites are among the most abundant soil animals, involved in decomposition processes and nutrient cycling. We analyzed shifts in trophic niches of six soil-living oribatid mite species with the conversion of lowland secondary rainforest into plantation systems of different land-use intensity (jungle rubber, rubber and oil palm monoculture plantation) in two regions of southwest Sumatra, Indonesia. We measured stable isotope ratios (13C/12C and 15N/14N) of single oribatid mite individuals and calculated shifts in stable isotope niches with changes in land use. Significant changes in stable isotope ratios in three of the six studied oribatid mite species indicated that these species shift their trophic niches with changes in land use. The trophic shift was either due to changes in trophic level (δ15N values), to changes in the use of basal resources (δ13C values) or to changes in both. The trophic shift generally was most pronounced between more natural systems (rainforest and jungle rubber) on one side and monoculture plantations systems (rubber and oil palm plantations) on the other, reflecting that the shifts were related to land-use intensity. Although trophic niches of the other three studied species did not differ significantly between land-use systems they followed a similar trend. Overall, the results suggest that colonization of very different ecosystems such as rainforest and intensively managed monoculture plantations by oribatid mite species likely is related to their ability to shift their trophic niches, i.e. to trophic plasticity.

Trophic niche differentiation and utilisation of food resources in Collembola is altered by rainforest conversion to plantation systems

“…Results of our study indicate that rainforest conversion into agricultural plantations is associated with changes in basal resources (Δ 13 C values) of Collembola, but does not significantly affect their average trophic positions (Δ 15 N values). These findings are in line with the results of the study of Krause et al (2019) investigating oribatid mites at the same study sites and showing that the shift in trophic niches to be mainly due to changes in the use of basal resources rather than trophic levels. Similar to previous studies on centipedes, oribatid mites and other soil animal taxa ( Klarner et al, 2017 ; Susanti et al, 2019 ; Krause et al, 2019 ), we also found the conversion of rainforest into plantations to be associated in Collembola with a shift from detritivory towards herbivory (i.e., lower 13 C enrichment).…”

“…These findings are in line with the results of the study of Krause et al (2019) investigating oribatid mites at the same study sites and showing that the shift in trophic niches to be mainly due to changes in the use of basal resources rather than trophic levels. Similar to previous studies on centipedes, oribatid mites and other soil animal taxa ( Klarner et al, 2017 ; Susanti et al, 2019 ; Krause et al, 2019 ), we also found the conversion of rainforest into plantations to be associated in Collembola with a shift from detritivory towards herbivory (i.e., lower 13 C enrichment). In rainforest and jungle rubber, δ 13 C values of Collembola were 2.0–5.0‰ higher compared to leaf litter, which resembles the shift observed in temperate forest ecosystems ( Pollierer et al, 2009 ).…”

“…Conversion of rainforest may have less affected the mineral soil- and root-based resources than litter resources, and this may explain the high abundance of euedaphic Pseudosinella sp.1 in plantations. Similarly, Krause et al (2019) found the trophic niche of dominant species of oribatid mites to change little with the conversion of rainforest into plantations. This suggests that trophic niches of certain species may be little affected by land-use change despite strong changes in the overall food-web structure.…”

“…Uneven decline in energy flux across size classes and trophic levels was documented for meso- and macrofauna soil communities leading to strong alterations in soil food-web structure ( Potapov, Tiunov & Scheu, 2019 ). Different basal resources available in different land-use systems result in changes in trophic niches of decomposer and predatory soil invertebrates, and results in reduced abundance of primary decomposers and in soil animals shifting their feeding habits towards herbivory ( Klarner et al, 2017 ; Krause et al, 2019 ; Susanti et al, 2019 ). Land-use change may also result in reduced trophic niche differentiation among species in belowground communities ( Korotkevich et al, 2018 ), but this has not been investigated in tropical ecosystems.…”

“…Trophic positions and length of trophic chains can be assessed using δ 15 N values, whereas the range of δ 13 C values reflects variability in the use of basal resources ( Potapov, Tiunov & Scheu, 2019 ). Stable isotope composition of consumers follows that in food resources, thus allowing to reveal potential diet switching with land-use change ( Klarner et al, 2017 ; Krause et al, 2019 ; Susanti et al, 2019 ).…”