Functional traits vary among fleshy-fruited invasive plant species and their potential avian dispersers

Habitat fragmentation has a multitude of negative effects on biodiversity, including the facilitation of alien plant invasion. Of concern in South Africa is the spread of fleshy-fruited invasive plant species, which in many places are replacing indigenous vegetation in frequently disturbed and fragmented habitats. The availability of dispersers is among the most important factors for the successful invasion of fleshy fruited invasive plant species. Dispersers differ in their dispersal capacity, and the success of frugivore dispersed plants depends both on animal and plant traits. Here, we used the functional traits of fleshy-fruited invasive plants to test for specific associations with avian functional traits in Indian Ocean Coastal Belt Forests, KwaZulu-Natal Province, South Africa. We predicted that fleshy-fruited invasive plant species that were more likely to persist in disturbed Indian Ocean Coastal Belt Forests were small-seeded, open habitat species with longer fruiting period lengths. The use of multivariate analyses showed that avian seed dispersers and fleshy-fruited invasive plant species differed in the functional traits between species with each group (i.e. plants and avian dispersers) that were important for seed dispersal. For fleshy-fruited plants, morphological traits (seed size, fruit size) and phenological traits (fruiting period length) were more variable between the species. For avian species, the variation was in their morphology (body size, gape width, bill length), abundance and habitat specificity. As predicted, avian species that were potentially dispersing invasive plants were forest generalist and relatively abundant species persisting in the fragmented forest. Fleshy-fruited invasive plant species that were predicted to be effectively dispersed were small-seed, open habitat species with longer fruiting length including lantana (Lantana camara), white mulberry (Morus alba), Brazilian pepper (Schinus terebinthifolius) and bugweed (Solanum mauritianum). Overall, our study showed that easily measured traits were important for understanding forest invasion dynamics and give insights to management strategies that can be developed to minimise further infestations.