Question: Is Opuntia stricta more frequent, and its patches larger, under trees suitable for baboon roosting? If so, does it mean that baboons are major dispersal agents and that plants established under these trees are important foci of Opuntia stricta spread?

Location: Skukuza, Kruger National Park, South Africa.

Method: We surveyed an area invaded by Opuntia stricta in the Skukuza region of KNP. The survey included plots under potential baboon roosting trees, plots under trees unlikely to support baboons, and paired randomly located open sites.

Results: The null hypothesis – tree-Opuntia spatial independence – can be rejected for Acacia nilotica, but not for Spirostachys africana. Opuntia plants are positively associated with Acacia trees suitable for baboon roosting. However, there is no significant difference between frequency of Opuntia under Acacia trees suitable and unsuitable for baboon roosting. It appears that all Acacia trees can serve as nurse trees for Opuntia. Compared to plots under Acacia trees, frequencies of old and robust Opuntia plants are significantly higher in open areas and under dead trees.

Conclusions: While baboons may be responsible for long distance Opuntia dispersal (over km), their role is not detectable at a local scale. On the other hand, elephants seem to contribute substantially to the local vegetative propagation of this species. Opuntia establishment and growth are more influenced by micro-habitat than previously thought.

Nomenclature: Germishuizen & Meyer (2003) for plant species.