The effect of frugivorous birds on seed dispersal and germination of the invasive Brazilian pepper tree (Schinus terebinthifolius) and Indian laurel (Litsea glutinosa)

Abstract

Biological invasions are a major threat to biodiversity in most parts of the world. The success of invasive fleshy fruiting plants is linked to the role of native avian frugivores. By ingesting and excreting/regurgitating viable seeds, avian frugivores are able to promote germination and disperse the seeds of these invasive fleshy fruiting plants. The Brazilian pepper tree (Schinus terebinthifolius) and the Indian laurel (Litsea glutinosa) are both invasive species in South Africa, particularly in KwaZulu-Natal. We examined the effect of native birds (Cape white-eyes (Zosterops virens), red-winged starlings (Onychognathus morio), speckled mousebirds (Colius striatus) and dark-capped bulbuls (Pycnonotus tricolor) on germination and dispersal of S. terebinthifolius and L. glutinosa seeds by comparing them to those of whole and manually de-pulped S. terebinthifolius and L. glutinosa fruit. By comparing the seed retention times and fruit consumed by the various avian species, we examined which avian species were likely to have the most effect on germination and dispersal of S. terebinthifolius and L. glutinosa. We found that all avian species readily consumed the fruit of S. terebinthifolius and that (through pulp removal by gut passage) these avian species played a vital role in the germination time and success of S. terebinthifolius. Most of the avian species consumed L. glutinosa fruit (though not as much as S. terebinthifolius), with speckled mousebirds being the only exception. However, ingestion of L. glutinosa fruit had no positive effect on germination as none of the seeds germinated (including the control seeds). Variances in body mass and bill size could potentially mean that larger birds play a greater role in seed dispersal as they ingested a greater number of seeds. Further studies need to be conducted on L. glutinosa in order to determine the conditions in which it germinates in the field and how these may be replicated for germination experiments in the laboratory.