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
 
 
Highlights
IntroductionVia their seeds, to be mobile in space and time. The spatio-temporal locations at which seeds arrive have a major influence on the subsequent fitness of offspring, as location is a major determinant of seed and seedling survival
Seed dispersal allows plants, via their seeds, to be mobile in space and time
We placed 5–10 H. argentea fruits at depots for 3 days, with six depots per site; four sites were in rock outcrops and two sites were in adjacent non-rocky proteoid shrublands
Summary
Via their seeds, to be mobile in space and time. The spatio-temporal locations at which seeds arrive have a major influence on the subsequent fitness of offspring, as location is a major determinant of seed and seedling survival. In the southwestern Cape, these forests are restricted to growing in extremely rocky habitats, such as on cliffs and amongst rock outcrops and screes.[1]. The dynamics of these forests are different to that of the adjacent shrublands (known as fynbos) where post-fire recruitment from long-lived seed banks of non-fleshy fruits dominates.[2] For example, many Proteaceae as well as Widdringtonia nodiflora (mountain cypress; Cupressaceae) are serotinous trees with dry, wind-dispersed seeds that grow in the open shrublands. Yellow-green, leathery-coated fruits up to 30 mm in diameter with a 3 mm thin, fleshy pericarp surrounding a single, soft, chlorophyllous seed (Figure 1a,b).
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