Incidental Ingestion of Plant-Dwelling Arthropods by Sheep and Cattle in the Same Habitat

Large mammalian herbivores influence grassland ecosystems through plant consumption, return of excreta and trampling, and by altering nutrient cycles and soil properties. These herbivore-mediated changes impact other animals in the habitat, particularly plant-dwelling arthropods. While plant-mediated effects of large mammalian herbivores on arthropod populations are well documented, direct effects, such as incidental ingestion of arthropods, remain understudied. Large mammalian herbivores incidentally ingest a variety of plant-dwelling arthropods; however, it remains unclear how this interaction is influenced by the dietary choices of different mammal species within the same habitat. Using a DNA metabarcoding analysis of fecal samples, we investigated the ingestion of plant-dwelling arthropods by sheep and cattle grazing in northeast Asian grasslands. Fecal samples were collected from replicated plots throughout the grazing season, including previously grazed and ungrazed plots. A COI marker was used to amplify arthropod DNA, followed by high-throughput sequencing. Results revealed that both sheep and cattle ingest a variety of plant-dwelling arthropods, including herbivores, parasitoids, and predators, with a high proportion of endophages (species developing in plant tissue). Significant differences were observed in ingestion between sheep and cattle—sheep (selective grazers) ingested a wider variety of plant-dwelling arthropods compared to cattle, whose diet consisted primarily of grasses, highlighting the impact of dietary choices on arthropod ingestion. Grazing regime influenced the ingestion of plant-dwelling arthropods in sheep, with differences observed between previously grazed and ungrazed plots. Our findings demonstrate that the ingestion of plant-dwelling arthropods by large mammalian herbivores is a dynamic and widespread phenomenon, varying across mammalian species and seasons.