Dispersal of semi-fleshy fruits to rock crevices by a rock-restricted rodent

Abstract

Seed dispersal allows successive generations of plants to be mobile in space and time. Heeria argentea’s unusual fruit and its ubiquity in extremely rocky habitats, suggests that this tree requires a specialist disperser. We therefore investigated the dispersal ecology of H. argentea and Hartogiella schinoides. We found M. namaquensis rapidly removed H. argentea and H. schinoides fruits, moving them short distances within and between rock outcrops, and consumed only the pericarps. Birds were observed consuming H. schinoides, but not H. argentea fruits, suggesting M. namaquensis is its sole, specialist disperser. Most H. argentea seeds (65%) with removed pericarps germinated successfully, while intact fruits did not. We show rock outcrops represent fire refugia, allowing H. argentea trees to grow to large sizes, with small stems and a co-occurring, wind-dispersed tree, Widdringtonia nodiflora found away from these sites. This rodent–tree mutualism is perhaps the clearest global example of directed dispersal and shows that these endemic trees are highly adapted for survival in the southwestern Cape habitat and are not tropical relicts.

Significance: 

• The fruits of rock-restricted Cape trees are directly dispersed by rock rats to rock outcrops. This is the first description of rodent dispersal of fleshy fruits in South Africa.
• This species-specific interaction allows for rapid germination of seeds and protection from frequent fires for adults. This rodent–tree mutualism is perhaps the clearest global example of directed seed dispersal.

Supplementary Video 1:

https://youtu.be/qOgylIJSKpI

Supplementary Video 2:

https://youtu.be/4jWIUrtzpUk

Supplementary Video 3:

https://youtu.be/FtBmh-3oYi4