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

composition of vegetative stands through highly selective foraging [17]. For example, in pas- ture and grassland settings, gastropods have been reported to selectively graze seedlings [16], although this depends on plant species [18], seedling age [18], and nitrogen (N) content [19]. Plant N content is an important factor determining grazing preference for gastropods, with plant material containing greater N preferred when all else is equal [19]. However, as shown by Mattson [19], seedling age appears to be the dominant factor governing palatability for gas- tropods, due, in part, to young shoots having fewer physical barriers (e.g. production of plant defense compounds) to herbivory in addition to increased N availability. While seedling age may govern grazing selection in monocultures, species identity and abundance can be greater drivers of grazing selection in polycultures [18]. Hanley et al. [18] documented that when mul- tiple species of rosette forbs were grown in polyculture (versus monoculture), rates of herbiv- ory were more dependent on plant species than seedling age. Given these complex factors governing food selection by gastropods, the high species richness and variation of plant age and growth form in most grasslands makes it difficult to predict the effect of slug herbivory on plant community composition [16]. Furthermore, slug herbivory is likely to be impacted by climate change through both direct and indirect interactions [12, 15]. Climate change is expected to increase global average annual

temperatures by 1.4–5.8˚C and alter hydrological regimes world-wide, in part by altering the timing and magnitude of rain events [20]. Changes in these abiotic parameters could directly and significantly affect slug abundance, habitat suitability and/or geographic range [11, 21, 22]. Gastropods are highly sensitive to abiotic factors, strongly preferring cool, moist condi- tions [12, 22, 23]. For instance, the urban heat island effect decreases gastropod survival in oth- erwise suitable environments [23]. Increasing temperatures have resulted in increased mortality of larval [24] and juvenile [25] gastropods and could cause local extinctions of some species. While gastropods typically prefer wetter places in fields, with densities determined pri- marily by soil moisture, the effect of moisture availability is highly seasonal and changes dra- matically from year-to-year [12, 22]. Gastropods have also been shown to expand their range, for example, moving upslope in Swiss National Park—the first such documented case of gas- tropods with low dispersal capacity moving in response to climate change [26]. Climate change may also have indirect effects on slugs if it alters plant community composi- tion and quantity, quality, or N concentration of the plant material. In an experimental grass- land in the United Kingdom, climate manipulations of winter warming and altered summer precipitation were shown to affect slug relative abundance, but this result was attributed pri- marily to changes in vegetation due to climate treatments [12]. However, in some systems,

since slugs can influence the composition of vegetation through seedling herbivory, any direct effects on the slug community from climate change may result in concomitant changes to the plant community [27]. In a factorial study of warming, N addition, and slug exclusion, Moise and Henry [15] found that long-term warming (three years) in an old-field pasture reduced overall plant productivity but that slug exclusion in warmed plots negated the negative effect on biomass of warming alone. These results suggest that the negative effect of warming on grassland productivity was mostly a direct effect of warming increasing slug herbivory [15]. Managed grassland research has shown slugs can have significant effects on plant produc- tion and species composition [10, 28]. However, little research on slug herbivory or ecology has been conducted in pastures in North America. It is important to understand what, if any, effects slugs have on pasture productivity in the transitional climatic zone of the United States, which are typically dominated by tall fescue pastures [14 million hectares east of the Missis- sippi River [29] and >2 million hectares in Kentucky [30] that support animal grazing and other ecosystem services [31]. Unfortunately, not enough is known about slug herbivory and ecology in transitional climatic zone pastures to predict responses to climate change PLOS ONE Slug herbivory & climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0283128 March 14, 2023 2 / 17 was additionally supported with funding provided to R.L.M from the Kentucky Agricultural

Experiment Station (KY006045; https://research.ca. uky.edu) and from the University of Kentucky College of Agriculture, Food and Environment (http://www.ca.uky.edu). No funders played any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared no competing interests exist.