Seed Dispersal by Frugivores and Germination Success of the Invasive Alien Shrub Pyracantha Angustifolia in the Eastern Free State Province, South Africa

Invasive alien plants can use animal-plant interactions to increase their invasiveness. This study investigated the role of frugivorous birds in seed dispersal and germination of the alien plant Pyracantha angustifolia (Rosaceae) in South African high elevation grasslands. We monitored which bird species fed on the fruit of the invasive P. angustifolia in some farms in the Eastern Free State Province using camera-traps and direct surveillance. Nine bird species visited P. angustifolia shrubs to perch or feed on fruits, but only one bird (Speckled Mousebird) fed on the fruits during timed observations. To assess the effect of ingestion by avian frugivores on P. angustifolia germination, P. angustifolia fruits were fed to captive Cape White-eyes (Zosterops virens), Dark-capped Bulbuls (Pycnonotus tricolor), Purple-crested Turacos (Gallirex porphyreolophus), Red-winged Starlings (Onychognathus morio) and Speckled Mousebirds (Colius striatus). Seeds collected from bird excreta, whole fruits, and depulped fruits were grown under greenhouse conditions and germination rates recorded. All captive bird species, except for Cape White-eyes, ingested the seeds; Cape White-eyes only fed on fruit pulp that they had manually removed. Bird species with relatively larger body mass had longer seed retention times compared with the smaller bird species. Germination success of both depulped and ingested P. angustifolia seeds was high (> 80%) and that of whole fruits low (7%). Ingestion by the four avian frugivore species did not affect germination rate and success; instead, the birds facilitate the spread and germination of seeds by removing the fruit pulp and spreading the seed away from the parent shrubs.