No evidence of co-facilitation between a non-native Asian earthworm (Amynthas tokioensis) and invasive common buckthorn (Rhamnus cathartica) in experimental mesocosms
Non-native invasive earthworms are known drivers of forest change in north temperate forests. Much understanding of earthworm invasion is based on species of European origin, but concern about Asian pheretimoid earthworms (e.g. Asian jumping worms, Amynthas spp.) is increasing. Some effects of Amynthas spp. on soil properties and biota have been studied, but little is known about interaction of Amynthas spp. with plants. Potential interaction between Amynthas spp. and invasive buckthorn (Rhamnus cathartica) is of particular interest given hypothesized co-facilitation between R. cathartica and European earthworms—cited by some as components of an “invasional meltdown”. We used reciprocal mesocosm experiments in Wisconsin, USA, to test for co-facilitation between Amynthas tokioensis and R. cathartica. We asked: (1) Are jumping worms more successful in environments invaded by buckthorn? (2) Does jumping worm activity increase buckthorn germination and establishment? Counter to expectations, co-facilitation was not supported, and we found evidence to the contrary. There was no increase in litter loss (indicative of consumption by jumping worms) or jumping worm fecundity in buckthorn-invaded environments, and buckthorn germination was unaffected by increased jumping worm densities. Counter to our hypothesis, jumping worm fecundity was greater in buckthorn-free soils than in buckthorn-invaded soils. Our results show no experimental evidence of co-facilitation by either of these invasive species, and highlight potential differences in ecological impact of non-native invasive earthworm taxa that vary in life-history and functional dynamics.
KeywordsAsian jumping worm Amynthas tokioensis Earthworms Rhamnus cathartica Wisconsin
We thank Kristin Braziunas, Rose Graves, Winslow Hansen, and especially Daniela Robledo for field assistance, and Chris Kucharik, Claudio Gratton, Ellen Damschen, Steve Carpenter, Jiangxiao Qiu and Katie Laushman for helpful comments on development of these ideas. Thanks to Eric Pedersen for field assistance and statistical advice. Two anonymous reviewers also provided constructive comments on this manuscript. We appreciate logistical support from Susan Carpenter and Bradley Herrick, and thank the University of Wisconsin–Madison Arboretum for providing the field facility. Thanks to Marie Johnston for technical expertise with earthworm identification and cocoon processing, as well as arboretum volunteers for cocoon processing assistance. We acknowledge funding from the US National Science Foundation, especially the Long-term Ecological Research (DEB-1440297) and Water, Sustainability and Climate (DEB-1038759) Programs, and support to MGT from the University of Wisconsin-Madison Vilas Trust. CZ acknowledges support from a Natural Science and Engineering Research Council of Canada doctoral fellowship, National Geographic Young Explorer Grant (Grant Number 9857-16), and PEO Scholar Award. CZ and MGT conceived the ideas and designed methodology; CZ collected and analyzed the data and led the writing of the manuscript. Both authors contributed critically to all drafts and gave final approval for publication.
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