Many highly invasive plant species have fleshy fruits which are eaten by native frugivorous animals. These frugivores play an important role in long-distance seed dispersal, and may also affect germination success. The aim of this study was to determine whether generalist frugivores enhance or decrease seed germination of invasive alien species through pulp removal or seed coat abrasion, besides serving as dispersal agents. Fruits of four fleshyfruited invasive alien plant species, namely Solanum mauritianum, Cinnamomum camphora, Lantana camara and Psidium guajava, were fed to three generalist avian frugivorous species, which have been observed feeding on these fruits in the wild. Seed retention time was recorded as this affects dispersal distance and the duration that seeds are exposed to the effects of the gut. Seeds removed from excreta, seeds from manually de-pulped fruit, and whole fruit were planted in soil trays housed in a greenhouse. Daily germination counts were done. Seed retention times differed significantly between bird species for all fruits, except those of C. camphora. However, all frugivores had a similar effect on the germination success of seeds of S. mauritianum, L. camara and P. guajava, showing that gut retention time was not important. Germination of seeds from manually de-pulped fruits did not differ from that of ingested seeds of all plant species, suggesting that seed coat abrasion was also not important. Pulp removal resulted in significantly higher germination rates, both in the two species with larger, multi-seeded fruit (S. mauritianum and P. guajava), and in the two species having single-seeded fruit with waxy exocarps (C. camphora and L. camara). Pulp removal also resulted in significantly earlier germination of L. camara and P. guajava seeds. Therefore, frugivores not only accelerate dispersal, but also greatly enhance seed germination of all fleshy-fruited invasive alien species in this study.

The spread of invasive alien plants into natural habitats is of growing global concern. Several studies have investigated the role that avian frugivores play in the dispersal of these seeds and their effects on germination success. Fruit bats have however received little attention as important dispersal agents of invasive alien plants, despite their recognized role as long distance dispersal agents of various native flora. We investigated whether Wahlberg's epauletted fruit bats, Epomophorus wahlbergi, would positively influence the germination of seeds of invasive alien plants. These fruit bats were fed fruits of four invasive alien plant species-Psidium guajava, Melia azedarach, Eriobotrya japonica, and Morus alba. Epomophorus wahlbergi were able to process more fruit per gram body mass than birds have been observed to do. Spat and de-pulped control seeds had similar germination success and germinated at approximately the same time for most species. While seeds retained in whole fruit had significantly less germination success than spat seeds for all species, except M. azedarach, they mostly germinated at approximately the same time.Epomophorus wahlbergi can swallow small seeds (\ 2 mm), while seeds larger than this are generally spat out. Large fruit are usually carried away to feeding roosts where seeds are dropped, thereby dispersing seeds and fruits which are too large for some bird species to ingest. Epomophorus wahlbergi should not be underestimated as dispersers of these invasive alien plants as they consume proportionally large amounts (0.62 ± 0.09 to 0.99 ± 0.11 g.g -1 body mass) of fruit, except for M. azedarach, and positively affect their seed germination rates.

Many highly invasive plants are fleshy-fruited and owe their invasiveness largely to mutualisms formed with local dispersers. The energetic benefits gained by frugivores from ingestion of fruits of invasive alien plants remain poorly documented. We assess whether avian frugivores process fruits of invasive alien plants effectively to meet their daily energetic requirements. Four fleshy-fruited plant species that are invasive in southern Africa were considered -Solanum mauritianum, Cinnamomum camphora, Lantana camara and Psidium guajava. Their fruits were fed to three common generalist frugivores -Red-winged Starling Onychognathus morio, Speckled Mousebird Colius striatus and Dark-capped Bulbul Pycnonotus tricolor -to determine the efficiency of digestion. Energetic parameters calculated for all fruit diets varied significantly between frugivore species. Speckled Mousebirds and Dark-capped Bulbuls maintained body mass and efficiently processed all four fruit types, whereas Red-winged Starlings only did so on C. camphora and S. mauritianum diets. These results explain why these fruits are attractive to local avian frugivores. Furthermore, these avian frugivores processed large quantities of invasive fruits, thereby serving as potentially efficient dispersers.

While fleshy‐fruited invasive alien plants are recognized as some of the worst invaders on a global scale, until recently, little consideration has been given to the frugivores that feed on these fruits and, more specifically, the fruit traits, which may influence this. We investigated a series of morphological and nutritive fruit traits for ca 30 species of fleshy‐fruited invasive alien and exotic species in South Africa. Invasive alien fruit traits were compared with comparable traits of a similar sample size of indigenous fleshy fruits, which occur in the same area. Finally, the similarity of traits for the same invasive alien species was compared with those fruits in Australia. Invasive alien fleshy fruits were similar in morphology, but greater in some nutritive aspects when compared with indigenous fruits. Furthermore, they were very similar in all aspects to their counterparts in Australia. Most seeds of invasive fleshy fruits were small and light, which may explain some of their invasive success, as benefits associated with small seededness may promote invasive potential. Nutritionally, most invasive alien fleshy‐fruits were hexose‐dominant, containing low lipid and nitrogen content. While frugivore preference trends remain to be formally investigated, this study provides insights into fruit traits, which may tentatively outline why invasive fruits are universally fed on and thus successfully spread.

No abstract