Specialization of oribatid mites to forest microhabitats—the enigmatic role of litter

Abstract

The degree of ecological specialization influences the biological performance of species in their natural environment and affects the coexistence of different taxa. However, on a small scale, the diversity of microarthropods that coexist in forest soils and leaf litter seems inordinately high, a situation known as the “enigma of soil animal species diversity”. Since recent studies point to the importance of small‐scale heterogeneity to explain this phenomenon, we use interaction networks between microhabitats and their inhabitants to resolve and quantify the community structure (species composition, richness, and diversity) of oribatid mites (Oribatida) in five discrete, patchy substrates—dead wood, lichens, mosses, sod, and tree bark—and in the general leaf litter. Since oribatid mites are ubiquitous in all these microhabitats in temperate forests, the analysis of their community structure in the light of generalization and specialization might help us understand the ecological role of litter. We investigated whether litter acts as a specific microhabitat with the intrinsic characteristics that enable the “enigmatic” high diversity of oribatid mites (Habitat‐Hypothesis), if litter acts as a source from which oribatid mite species more or less randomly invade different associated microhabitat‐patches (Source‐Hypothesis), or if litter only connects patchily distributed microhabitats with specific species compositions (Connector‐Hypothesis). In total, 25,162 adult oribatid mite individuals were analyzed, most belonging to the derived group Brachypylina. Species richness, density, and diversity differed among microhabitats with highest values found in mosses and dead wood and lowest on tree bark. In general, specialization of oribatid mite species was low—highest on tree bark and in grass sod—but differed slightly among oribatid mite taxa (Enarthronota, Mixonomata, Nothrina, Brachypylina). The Connector‐ and Habitat‐Hypotheses can explain the distribution of most oribatid mite species but the Source‐Hypothesis explains the distribution patterns for only a few species.

Chemical communication in springtails: a review of facts and perspectives

“…Conversely, negative interactions, whether symmetrical or asymmetrical, will result in either niche shifts or checkerboard distributions, according to different or similar ecological species requirements, respectively. A better knowledge of chemical communication systems might thus contribute to explain fine-scale niche segregation (Anderson 1978;Zhao et al 2013) and competition-mediated over-dispersion of functional traits (Widenfalk et al 2016), as observed in soil samples, and then to finally resolve the famous "enigma of soil animal species diversity" (Anderson 1975;Maraun et al 2003;Wehner et al 2016).…”

Storage and release of hydrogen cyanide in a chelicerate ( Oribatula tibialis )

“…Adult specimens of Oribatula tibialis (Nicolet) were collected from moss and litter taken from a mixed forest stand near Groß-Gerau, Hesse, Germany, using a thermal-gradient extractor over 24 h (for further methods and habitat characterization, see 44).…”

Seasonal fluctuation of oribatid mite communities in forest microhabitats

“…The approximately 16,000 described species ( Schatz et al, 2011 ) are collectively ubiquitous, yet individual species are unevenly distributed in all major forests and grasslands, and also in aquatic habitats all over the world ( Wallwork, 1983 ; Schatz, 2005 ; Schatz & Behan-Pelletier, 2008 ). In temperate forests, oribatid mite species tend to inhabit different microhabitat patches and therefore their communities are unequally distributed among mineral soil, litter, mosses, lichens, dead wood or tree bark ( Aoki, 1967 ; Arroyo, Kenny & Bolger, 2013 ; Wehner et al, 2016 ). This specificity may be caused by differences in microhabitat structure (e.g., small vs wide pores, continuous (litter) vs. insular (tree bark, moss); Nielsen et al, 2008 ), microclimatic conditions (e.g., moisture, exposure; Nielsen et al, 2010 ), spatial resource heterogeneity ( Nielsen et al, 2010 ) or biotic interactions (e.g., predation; Hammer, 1972 ; Gao et al, 2014 ).…”

“…In general, most adult oribatid mite species tend to prefer distinct microhabitats (e.g., litter, moss patches, dead wood, lichens, grassy sods, bark of trees) if conditions are favourable ( Wehner et al, 2016 ). For example, Wehner et al (2016) reported that the microhabitat ‘litter’ provides the most stable ecological conditions and seems to function as habitat for litter specialists (e.g., Hypochthonius rufulus ; Habitat-Hypothesis) and “refuge” for generalists during unfavourable conditions (e.g., Chamobates cuspidatus , Carabodes spp. ; “Connector-Hypothesis”).…”