An invasive slug exploits an ant-seed dispersal mutualism

Abstract

Plant-animal mutualisms, such as seed dispersal, are often vulnerable to disruption by invasive species. Here, we show for the first time how a non-ant invasive species negatively affects seed dispersal by ants. We examined the effects of several animal species that co-occur in a temperate deciduous forest-including native and invasive seed-dispersing ants (Aphaenogaster rudis and Myrmica rubra, respectively), an invasive slug (Arion subfuscus), and native rodents-on a native myrmecochorous plant, Asarum canadense. We experimentally manipulated ant, slug, and rodent access to seed depots and measured seed removal. We also video-recorded depots to determine which other taxa interact with seeds. We found that A. rudis was the main disperser of seeds and that A. subfuscus consumed elaiosomes without dispersing seeds. Rodent visitation was rare, and rodent exclusion had no significant effect on seed or elaiosome removal. We then used data obtained from laboratory and field mesocosm experiments to determine how elaiosome robbing by A. subfuscus affects seed dispersal by A. rudis and M. rubra. We found that elaiosome robbing by slugs reduced seed dispersal by ants, especially in mesocosms with A. rudis, which picks up seeds more slowly than M. rubra. Taken together, our results show that elaiosome robbing by an invasive slug reduces seed dispersal by ants, suggesting that invasive slugs can have profound negative effects on seed dispersal mutualisms.

Interactions between seed‐dispersing ant species affect plant community composition in field mesocosms

“…In previous work, we found that M. rubra dispersed more seeds than Aphaenogaster sp. in natural settings (along with laboratory and mesocosm settings, similar to this study; Meadley-Dunphy et al, 2016;Prior et al, 2014Prior et al, , 2015. Garnas et al (2014) found that M. rubra recruited to baits faster than native ant species in its invasive range in Maine.…”

“…In previous work, we found that M. rubra dispersed more seeds than Aphaenogaster sp. in natural settings (along with laboratory and mesocosm settings, similar to this study; Meadley‐Dunphy et al., 2016; Prior et al., 2014, 2015). Garnas et al.…”

“…In particular, in previous work, we found that ant species vary in how quickly they recruit to, remove, process and re‐disperse seeds outside of nests (Prior et al., 2015; Prior, Saxena, & Frederickson, 2014), along with where they deposit seeds in relation to their nests and adult and dispersed plants (Meadley‐Dunphy, Prior, & Frederickson, 2020). Myrmica rubra is better at discovering seeds than Aphaenogaster sp., finding and moving seeds more quickly (Meadley‐Dunphy, Prior, & Frederickson, 2016; Prior et al., 2014, 2015), and to more distant locations (Meadley‐Dunphy et al., 2020). This previous work shows that the two seed‐dispersing ants directly impact and cause divergence of myrmecochore communities (Meadley‐Dunphy et al., 2020; Prior et al., 2015).…”

Antagonistic and mutualistic interactions alter seed dispersal of understory plants at forest edges

“…We predicted that rodents would be a major interactor with seeds and that seed predation by rodents would be higher at forest edges than in interiors, which has been found in other studies (Kollmann andBuschor 2003, Ness andMorin 2008). We found evidence that rodents consumed seeds as seed casings were left on depots (as in Ness and Morin 2008, Kwit et al 2012, Meadley-Dunphy et al 2016. In our experiment, we also found that the rodent exclosure treatment affected seed removal, but these results may have been influenced by the effect of slugs.…”

“…Treatments were applied to seed depots, which were 15.5 9 17 cm rectangles of corrugated plastic sheets with petri dishes attached with glue. We have used similar depots in previous experiments, finding that they do not inhibit dispersal or interaction with seeds by ants or other organisms (Meadley-Dunphy et al 2016).…”