Community structure, trophic position and reproductive mode of soil and bark-living oribatid mites in an alpine grassland ecosystem

Abstract

The community structure, stable isotope ratios (15N/14N, 13C/12C) and reproductive mode of oribatid mites (Acari, Oribatida) were investigated in four habitats (upper tree bark, lower tree bark, dry grassland soil, forest soil) at two sites in the Central Alps (Tyrol, Austria). We hypothesized that community structure and trophic position of oribatid mites of dry grassland soils and bark of trees are similar since these habitats have similar abiotic characteristics (open, dry) compared with forest soil. Further, we hypothesized that derived taxa of oribatid mites reproducing sexually dominate on the bark of trees since species in this habitat consume living resources such as lichens. In contrast to our hypothesis, the community structure of oribatid mites differed among grassland, forest and bark indicating the existence of niche differentiation in the respective oribatid mite species. In agreement with our hypothesis, sexually reproducing taxa of oribatid mites dominated on the bark of trees whereas parthenogenetic species were more frequent in soil. Several species of bark-living oribatid mites had stable isotope signatures that were similar to lichens indicating that they feed on lichens. However, nine species that frequently occurred on tree bark did not feed on lichens according to their stable isotope signatures. No oribatid mite species could be ascribed to moss feeding. We conclude that sexual reproduction served as preadaptation for oribatid mites allowing them to exploit new habitats and new resources on the bark of trees. Abiotic factors likely are of limited importance for bark-living oribatid mites since harsh abiotic conditions are assumed to favor parthenogenesis.

Community structure of soil oribatida (acari) two years after windthrow in the high tatra mountains

“…On the other hand, species from the family Eremaeidae were present only in EXT stand. The occurrence of Eremaeus hepaticus, Eueremaeus oblongus and Eueremaeus silvestris is often associated with surface residues (tree bark, branches, decaying wood) left after forest harvesting (Maraun et al 2009;Fischer et al 2010). Maraun & Scheu (2000) observed that Oppiidae are generally abundant in forest soils whereas in strongly disturbed habitats their density is lower, which is in agreement with the distribution of this family in the present study.…”

Cyanobacteria produce a high variety of hepatotoxic peptides in lichen symbiosis

“…In terrestrial ecosystems, cyanolichens represent a potential source of hepatotoxins for grazers, which might also introduce toxins into food chains. Many molluscs and arthropods, but also mammals such as voles, squirrels, snub-nosed monkeys, and ruminants, are known to feed on lichens (30)(31)(32)(33)(34). Mollusc grazing has been suggested to be the limiting ecological factor for some cyanolichens in boreal rain forests in Norway (31).…”

Oribatid mite communities on the bark of dead wood vary with log type, surrounding forest and regional factors

“…Oribatid mite communities on bark overlap only little with those in soil, thereby the bark of trees represents a distinct habitat (Wunderle, 1992;Proctor et al, 2002;Erdmann et al, 2006;Fischer et al, 2010a). However, it is little studied if oribatid mite communities from dead wood on the forest floor resemble those of the soil or those of the bark of trees or if dead wood is colonized by a specific oribatid mite community (but see Skubała and Ma slak, 2009;Huhta et al, 2012).…”

“…It has been shown that oribatid mites in soil mostly feed on litter and fungi, whereas oribatid mites on the bark of trees often feed on lichens or mosses (Schuster, 1956;Luxton, 1972;Siepel and de Ruiter-Dijkman, 1993;Erdmann et al, 2007;Fischer et al, 2010a;Maraun et al, 2011). However, the trophic ecology of oribatid mite from dead wood has never been studied.…”

“…This is based on the assumption that the advantage of having genetically different progeny diminishes when resources are not limited and thus favors faster reproducing asexual species. The percentage of parthenogenetic individuals in soil is high ($50-80%) compared to the bark of living trees ($5-10%) (Fischer et al, 2010a;Maraun et al, 2012). How the ratio between parthenogenetic and sexual oribatid mites changes after death of trees and how dead wood is colonized by soil living oribatid mite species is unknown.…”