Seed dispersal by frugivores and germination of the invasive alien shrub Pyracantha angustifolia (Franch.) C.K. Schneid. in 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, germination success and germination time of the alien plant Pyracantha angustifolia (Franch.) C.K. Schneid. (Rosaceae) in South African high elevation grasslands. We monitored which bird species fed on the fruit of the invasive P. angustifolia in farms in the Free State Province using timed-focal and opportunistic observations, and camera traps aimed at fruiting branches and fallen fruits on the ground. Nine bird species visited P. angustifolia shrubs to perch or feed on fruits, but only one (Speckled Mousebird) fed on the fruits during timed-focal observations. Camera trap footage and opportunistic observations revealed a further three bird species (African Pied Starlings, Crested Barbets, Red-eyed Barbets), domestic horses and goats, and two rodent species feeding on fruits. To assess the effect of ingestion by avian frugivores on P. angustifolia germination success and time, 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); frugivores present in the invasive range of P. angustifolia in South Africa. Seeds collected from bird excreta, whole fruits, and depulped fruits were grown under greenhouse conditions and germination times recorded. All captive bird species, except for Cape White-eyes, ingested the seeds; Cape White-eyes fed on fruit pulp only. 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 significantly higher (> 80%) than for seeds from whole fruits (7%). Ingestion by the four avian frugivore species did not affect germination time 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.