Restio culm felling is a consequence of pre-dispersal seed predation by the rodent Rhabdomys pumilio in the Fynbos

Seed mortality represents a substantial cost for plants and can have a large effect on plant reproductive fitness. Here we report evidence for pre-dispersal seed mortality by a novel mechanism: culm felling in female nut-seeded restios by rodents. We noted strong female-specific culm felling in the nut-fruited Cannomois congesta Mast. (Restionaceae) from the South Western Cape, South Africa. Camera-trap analysis showed that this culm felling is carried out by the striped mouse, Rhabdomys pumilio Spar. (Muridae) and is primarily aimed at obtaining ripe seeds held at the tips of female culms rather than eating the culm. All seeds acquired by R. pumilio were found to be consumed. We recorded a mean loss of 81% culms/seeds in affected female C. congesta plants in contrast to very few culm losses from males. This highly selective rodent behaviour is presumably due to detectable differences in the nutritional reward associated with terminal male/female inflorescences (large nut-like seeds vs. pollen). Pre-dispersal seed predation through culm felling could significantly reduce the fecundity of ant-dispersed restios such as C. congesta because fewer seeds manage to fall to ground where mutualistic ground foraging ants compete with rodents for seeds. Culm losses through felling could also have physiological and nutritional implications. Future research should explore the generality of this phenomenon amongst the Restionaceae, and quantify the associated physiological and reproductive costs.