Abstract
Exotic earthworms are drivers of biotic communities in invaded North American forest stands. Here we used ecologically important oribatid mite (Arachnida: Acari) communities, as model organisms to study the responses of litter- and soil-dwelling microarthropod communities to exotic earthworm invasion in a northern temperate forest. Litter- and soil-dwelling mites were sampled in 2008–2009 from forest areas: (1) with no earthworms; (2) those with epigeic and endogeic species, including Lumbricus rubellus Hoffmeister; and (3) those with epigeic, endogeic, and anecic earthworms including L. terrestris L. Species richness and diversity of litter- and soil-dwelling (0–2 cm soil depth) oribatid mites was 1–2 times higher in sites without earthworms than in sites with worms. Similarly, litter-dwelling oribatid mites were between 72 and 1,210 times more abundant in earthworm-free sites than in sites with worms. Among earthworm invaded sites, abundance of litter-dwelling oribatid mites in sites without the anecic L. terrestris was twice as high in May and 28 times higher in October, compared to sites with L. terrestris. Species richness, diversity, and abundance of oribatid mites were greater in litter-layers than in the soil-layers that showed a varied response to earthworm invasion. Species compositions of both litter- and soil-dwelling oribatid mite communities of forests with no earthworms were markedly different from those with earthworms. We conclude that exotic earthworm invasions are associated with significant declines of species diversity, numbers, and compositional shifts in litter- and soil-inhabiting communities. These faunal shifts may contribute to earthworm effects on soil processes and food web dynamics in historically earthworm-free, northern temperate forests.
Highlights
During the last few centuries, northern temperate forests of North America have experienced many anthropogenic disturbances, such as habitat loss and fragmentation, changes in natural disturbances regimes, and the introduction of exotic species [1,2,3,4]
In October, more species were shared between no earthworm and earthworm invaded habitats without anecic species
Our results indicated that the invasion by earthworms changed the richness, diversity, abundance, and composition of oribatid mites in a northern temperate forest
Summary
During the last few centuries, northern temperate forests of North America have experienced many anthropogenic disturbances, such as habitat loss and fragmentation, changes in natural disturbances regimes, and the introduction of exotic species [1,2,3,4]. Earthworms are generally classified into three groups: epigeic, endogeic, and anecic [11,14,15,16] Epigeic species such as Lumbricus rubellus Hoffmeister are litter-dwelling species that use shallow burrows, and feed on leaf litter and other coarse organic matter. Endogeic species, such as Aporrectodea caliginosa (Savigny) and Octalasion tyrtaeum (Savigny), dwell in deep burrows in the mineral soil where they ingest mineral soil to digest organic matter and microflora. Amongst the three guilds of earthworms, anecic species cause the greatest soil disturbance (rapid reduction of litter layer and intermixing of the litter and mineral layers), followed by endogeic (disturbance of mineral layer), and epigeic (rapid reduction of litter layer) species [7]
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