Climate change alters slug abundance but not herbivory in a temperate grassland

Discussion Despite prior work illustrating that slug herbivory can significantly reduce plant production in pastures [1, 16] and our hypothesis that it would do so at this site, we found little-to-no evi- dence that slugs impact plant production or plant species composition in our central Kentucky pasture. Overall, our results indicate that slug herbivory is relatively limited at this site, despite catching 325 slugs during the 2013 growing season. In addition to eating aboveground plant material, slugs consume litter and detritus [42]. This is a possible explanation for why few significant effects on live aboveground plant biomass were recorded. Slugs at this site may have primarily consumed detritus, which we did not mea- sure. Previous research on the effects of slug exclusion has focused mainly on establishment and development of plants, finding that slugs can influence the development of pastures and other ecosystems through seedling herbivory [1, 27, 43, 44]. Because the pasture for this project was established with perennial species more than three years prior to the beginning of this experiment, it is possible that the primary influence of slugs on seedling survival and its subse- quent impacts on the resulting plant community dynamics was missed. Several plant species present in the pasture were annuals (comprising on average 18% of the biomass), sprouting new seedlings each spring and autumn. Still, few effects of slug herbivory were observed, sug- gesting overall effects were negligible.

Fig 2. Average (± S.E.) aboveground plant biomass harvested from the control and slug exclosure rings for each climate treatment over the seven harvest dates. The asterisk denotes a significant difference in plant biomass between the control and slug exclosure rings in the heated plots only in May of 2013. https://doi.org/10.1371/journal.pone.0283128.g002 Fig 3. Average (± S.E.) plant biomass per ring harvested in each climate treatment from October 2011 to October 2013. Capital letters denote significant differences across the harvests, and lowercase letters denote significant across climate treatments within each harvest. https://doi.org/10.1371/journal.pone.0283128.g003 PLOS ONE Slug herbivory & climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0283128 March 14, 2023 9 / 17