Aboveground vegetation communities affect dung seedling richness and density based on the diet selection of large herbivores

Abstract

The function of the dung seed bank from large generalist herbivores in grassland ecosystems is often overlooked. The dung seed bank is the product of the canopy seed bank ingested by herbivores that then accumulates in their feces. However, the mechanisms by which aboveground vegetation composition and structure affect the dung seed bank remain unclear, especially when considering the forage preferences effects of large generalist herbivores. We conducted a 4-year (2019–2022) rotational grazing experiment with yaks in an alpine meadow during the warm season on the northeastern Qinghai-Tibetan Plateau and investigated the aboveground vegetation community height, richness, and biomass; the forage preferences of the yaks; and the richness and density of dung seedlings. Aboveground vegetation community height, richness, and biomass showed fluctuations across the years and seasons. During the warm season, the dung seedling richness and density were 0.042 ± 0.013 species/g dung and 0.112 ± 0.043 seedlings/g dung, respectively. Among the 63 species of plants that were present as aboveground vegetation and that germinated from the dung samples, 65.08 % had a neutral preference for foraging by the yaks. Significant differences between yak dung seedlings and aboveground vegetation composition indicated the potential for dung seedlings to promote microhabitat patchiness around dung deposition sites. Aboveground vegetation community height had a negative effect on the dung seed bank, whereas richness and biomass had a positive effect. Our findings suggest that the aboveground vegetation community structure affects the size and composition of the dung seed bank through its effect on the diet selection of large generalist herbivores. We emphasize that the complementary roles of the herbivore dung seed bank and the soil seed bank should be considered when assessing the contribution of the soil seed bank to aboveground vegetation regeneration.