Estimated epizoochory seed dispersal distances by grazing yak across seasons in an alpine meadow

TL;DR

This study shows that yaks can disperse plant seeds over long distances, especially in spring, helping maintain plant diversity in alpine meadows.

Contribution

The study quantifies seasonal seed dispersal distances by yaks and identifies the role of seed structures in retention.

Findings

Seed dispersal distances by yaks vary seasonally, with the highest in spring and lowest in winter.

Seeds with adhesive structures like mucilage can be dispersed up to ~35 km by yaks.

Seasonal grazing allows diaspores to move between pastures due to slow seed loss from yak fur.

Abstract

Epizoochorous dispersal of grassland plants by large herbivores is an important way by which grassland plants achieve population expansion over long distances. However, little is known about the maximum distance that seeds can be dispersed by domestic animals under seasonal grazing, which is the most common type of grassland management worldwide, especially in alpine regions.

To this end, we estimated the distance over which epizoochory dispersal occurs via yaks (Poephagus grunniens) for seven common plant species seeds in an alpine meadow under seasonal grazing using a simulated yak-fur seed adhesion test combined with observations of grazing behavior.

The results showed that, as yak primary (e.g., walking time) and secondary (e.g., foraging rate) behavioral patterns differed significantly across seasons (P< 0.05), the epizoochory dispersal distances of plant seeds also had clear seasonal dynamics, manifesting as spring > summer > autumn > winter, and that the length of seed adhesive structures correlated positively with the retention rate as well as retention time on yak fur. The relatively slow loss of diaspores observed in this study mainly shows that moving yak from one seasonal pasture to the following allows the dispersal of diaspores between two successive pastures. The dispersal scale was even wider (maximum dispersal distance of ~35 km) for seeds with special appendages (i.e., mucilage, sticking to the fur due to mucilage presence).

Our results highlight that yaks are substantial seed dispersal vectors for alpine meadow plants and that seasonal grazing is a suitable management method for coping with habitat fragmentation as well as plant diversity conservation in alpine areas from the perspective of seed dispersal.

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