Belowground competition among invading detritivores

Abstract

. The factors regulating soil animal communities are poorly understood. Current theory favors niche complementarity and facilitation over competition as the primary forms of non-trophic interspecifi c interaction in soil fauna; however, competition has frequently been suggested as an important community-structuring factor in earthworms, ecosystem engineers that infl uence belowground processes. To date, direct evidence of competition in earthworms is lacking due to the diffi culty inherent in identifying a limiting resource for saprophagous animals. In the present study, we offer the fi rst direct evidence of interspecifi c competition for food in this dominant soil detritivore group by combining fi eld observations with laboratory mesocosm experiments using 13 C and 15 N double-enriched leaf litter to track consumption patterns. In our experiments, the Asian invasive species Amynthas hilgendorfi was a dominant competitor for leaf litter against two European species currently invading the temperate deciduous forests in North America. This competitive advantage may account for recent invasion success of A. hilgendorfi in forests with established populations of European species, and we hypothesize that specifi c phenological differences play an important role in determining the outcome of the belowground competition. In contrast, Eisenoides lonnbergi , a common native species in the Eastern United States, occupied a unique trophic position with limited interactions with other species, which may contribute to its persistence in habitats dominated by invasive species. Furthermore, our results supported neither the hypothesis that facilitation occurs between species of different functional groups nor the hypothesis that species in the same group exhibit functional equivalency in C and N translocation in the soil. We propose that species identity is a more powerful approach to understand earthworm invasion and its impacts on belowground processes.

Species-specific effects of earthworms on microbial communities and the fate of litter-derived carbon

“…Xia et al, 2011;Crumsey et al, 2013), is consistent with the theoretical responses of soil microbes following a C pulse event, and can be readily explained by the enzyme-driven theoretical models of microbial C and N limitation (Schimel and Weintraub, 2003;Waring et al, 2013). Earthworms are also known to change the fate of litterderived C through a combination of their feeding, burrowing, and casting behaviors (Fahey et al, 2013a;Chang et al, 2016). Therefore, the contribution of litter-derived C to soil respiration may still be altered even under situations where total soil respiration is not affected.…”

Historical land use and stand age effects on forest soil properties in the Mid-Atlantic US

“…Increasing human population on the region leads to increased N-deposition and new species introduction. As an example, in one of our old forest stands, Treefall, several Asian earthworm species are currently invading from the neighboring residential areas (Chang et al, 2016). These future influences will cause trajectories of forest soils to diverge further away from the pre-Colonial states even affecting those forests that have not been cut or managed previously.…”

Asian pheretimoid earthworms in North America north of Mexico: An illustrated key to the genera Amynthas, Metaphire, Pithemera, and Polypheretima (Clitellata: Megascolecidae)

“…It has been shown to be the superior competitor when interacting with Lumbricus rubellus, an epi-endogeic European earthworm common in the US, for leaf litter. It does not appear to affect Eisenoides lonnbergi, a large native lumbricid common in riparian areas, wetlands, and some upland habitats in the eastern US (Chang et al 2016a). 16.…”

“…One species, A. agrestis, has been shown to compete with native millipedes for food resources, and may reduce species richness and diversity in the latter (Snyder et al 2011(Snyder et al , 2013. Moreover, many of the forests invaded by Amynthas and Metaphire have native earthworm fauna and/or have already gone through significant changes due to invasion by European lumbricid earthworms, primarily of the genera Lumbricus, Aporrectodea, and Octolasion (Chang et al 2016a). The impacts of Asian earthworms will depend on how Amynthas and Metaphire interact with resident native and non-native species, and whether earthworm communities dominated by Asian earthworms function differently from those primarily composed of European species.…”

“…In forests already dominated by European species, interspecific competition as a result of Amynthas or Metaphire invasion may lead to changes in earthworm community structure. Competition for leaf litter has been demonstrated between M. hilgendorfi and Lumbricus rubellus, one of the most common European earthworm species, with M. hilgendorfi being the superior competitor (Chang et al 2016a). Lumbricus rubellus also suffered reduced biomass in the presence of A. agrestis (Zhang et al 2010).…”