Opposing forces of seed dispersal and seed predation for an invasive cactus in East Africa

Dudenhoeffer, Megan
The invasive prickly-pear cactus (Opuntia stricta), has reduced rangeland quality and altered understory-plant communities throughout much of the globe. In the Lakipia Highlands of central Kenya, olive baboons (Papio anubis) frequently consume O. stricta fruits and disperse the seeds via defecation. This animal-mediated dispersal can increase germination and subsequent survival of plants, which is of concern to both ranchers and conservationists due to O. stricta's ability to outcompete native plants consumed by livestock and wildlife. However, consumption of seeds by rodents (seed predation) may offset the potential benefits of seed dispersal for cactus establishment. We investigated whether seed predation by an abundant rodent—the fringe-tailed gerbil (Gerbilliscus robustus)—could reduce or altogether offset the benefits of seed dispersal for O. stricta establishment. We tested if foraging by gerbils was biased towards seeds in baboon feces. Using remotely-triggered cameras, we monitored paired sites, each consisting of a control pile of seeds and a pile of baboon feces containing seeds. We then used a Cox regression model to determine that seed predation was higher for seeds embedded within baboon feces than for control seed piles. These data suggest that high abundances of rodents—characteristic of areas from which large ungulates have been extirpated—may disrupt the process of seed dispersal and reduce rates of cactus establishment. Future research should focus on if and how seed predation by gerbils ultimately affects the spread of this invasive plant.
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