Selective plant foraging and the top-down suppression of native diversity in a restored prairie.
Clarifying what species are being consumed at what times can improve our understanding of how anthropogenic change affects food web dynamics, with implications for community assembly including restoration. This includes human-based changes to plant communities via species introductions, which can interact with consumer feeding preferences to indirectly alter assembly outcomes including reduced restoration success if planted species are preferentially targeted. We used DNA barcoding of plant material in rodent scat, combined with field-based feeding trials, rodent trapping, and rodent exclosures to test for dietary preferences and assembly impacts of native rodents on a restored and regionally rare tallgrass prairie of central North America. We examined whether native rodents preferred non-targeted and mostly non-native oldfield plants that are more locally abundant, thus protecting the rarer native planted species from consumption, or if rodents preferred native plants regardless of abundance. Our results supported the latter outcome. Barcoding revealed that native rodents consumed mostly non-planted oldfield species for 10 months of the year (92% of the diet). The exceptions were August-September, when planted prairie species accounted for 87% of plants consumed and coincided with their peak seed production. Cafeteria trials suggested diet seasonality to be explained by food limitation - native prairie seeds were consumed year-round when made available. Non-targeted oldfield species thus appeared to be of sufficient quality to support rodent populations (peaking at 23 individuals ha-1 in summer), but without rescuing rarer prairie species from targeted granivory and resulting in reduced prairie diversity outside of experimental exclosures. Synthesis and applications. Our work illustrates how anthropogenic-based changes to producer communities may affect feeding pathways in grassland food webs, potentially facilitating establishment by non-target species via indirect consumer effects that can be difficult to detect. These findings suggest that rodents may reduce the restoration success of tallgrass prairie in our region, with some planted species likely to suffer future recruitment difficulties due to granivory. Managers may need to consider multiple trophic levels with restoration, not just the commonly planted producer communities but also the consumers and predators associated with them.