Seed dispersal and germination by yak gut passage in an alpine meadow community on the Qinghai-Tibetan Plateau

Natural regeneration of plant communities is often limited by seed dispersal, particularly in the alpine meadows of the Qinghai-Tibetan Plateau, where many of meadows are deteriorating into bare land. Endozoochorous seed dispersal by grazing herbivores is a potentially effective mechanism for plant movement, yet its ecological significance remains poorly understood. In this study, we examined the role of gut passage in seed dispersal by feeding known quantities of seeds from 24 alpine meadow species to four yaks. The pattern of undamaged seeds defecated by yaks followed a consistent Gaussian model: y=-0.03+0.98e-2((x-51.10)/30.80)2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$y = - 0.03 + 0.98e<^>{{ - 2((x - 51.10)/30.80)<^>{2} }}$$\end{document}, with the majority of the seeds (approximately 96%) being defecated within 72 h after ingestion, with a range of 12-108 h. The average seed recovery rate was 30.1%, varying between 1.8 and 66.6%, and showed a negative correlation with the seed shape index. Moreover, the time seeds spent passing through the yak gut was positively correlated with the seed shape index, though no significant relationship was observed with the seed mass. Gut passage through yaks considerably increased seed germinability in five species of Cyperaceae and one species of Polygonaceae, which are primarily physiologically dormant and dominant plants in alpine meadows. These findings suggest that seed ingestion by grazing yaks may play a crucial role in shaping the plant community dynamics of alpine species on the Qinghai-Tibetan Plateau.