This overarching question was recently addressed in a series of comparative studies of bird foraging activity on fruits of alien and native plants in the globally
renowned Cape Floristic Region. The work formed part of the PhD thesis of Thabiso Mokotjomela. A few key findings from this research are summarized below.
Fruits of some established alien plants (e.g. Solanum mauritianum) were found to be more attractive to birds than those of nearby native fleshy fruited
species, supporting the notion that frugivorous birds concentrate their activities where resources are most abundant and fruits are more nutritious
(Mokotjomela et al. 2013. Plant Ecol. 214:49-59).
It has been estimated that 63 of the 224 terrestrial bird species present in southern Africa have migrated into the Cape Floristic Region in response to
the introduction of alien trees and shrubs. These migrant birds have presumably also contributed to the expansion of alien plant distributions though seed dispersal.
Lantana camara L. (Verbenaceae) is one such example that was introduced into South Africa as an ornamental and hedging plant from central tropical America in 1858
(click here for further details of the history of this species in South Africa).
Mature plants of L. camara can produce up to 12,000 single seed bearing fruits annually and up to several thousand per m2. [Photo Credit: Charlene Janion]
When fleshy fruited emerging alien species were included, it was found that birds displayed significantly higher visitation frequencies on these species compared to
both established and native species (Mokotjomela et al. 2013. S. Afr. J. Bot.
86:73-78). Seeds of established alien plants had dispersal distances (based on bird ring recapture records, flight speeds and seed gut retention time) much greater
than previously reported (Mokotjomela et al. 2013. Plant Ecol. 214:1127-1137).
To limit preferential fruit consumption and the consequent dispersal of emerging aliens into natural areas, alien plant control measures should focus on eradicating localised
populations of emerging aliens. To mitigate disruption of natural seed dispersal patterns, selected native plants with similar fruiting attributes should be identified as suitable replacements
for aliens in control and restoration programs.
Read the papers:
Mokotjomela, T.M., Musil, C.F, Esler, K.J. (2013). Frugivorous birds visit fruits of emerging alien shrub species more frequently than those of established alien and native shrub species in the South African Mediterranean climate region. South African Journal of Botany, 86:73-78.
Mokotjomela, T.M., Musil, C.F, Esler, K.J. (2013). Do frugivorous birds concentrate their foraging activities on those alien plants with the most abundant and nutritious fruits in the South African Mediterranean-climate region? Plant Ecology, 214:49-59.
Mokotjomela, T.M., Musil, C.F, Esler, K.J. (2013). Potential seed dispersal distances of native and non-native fleshy fruiting shrubs in the South African Mediterranean Climate Region. Plant Ecology, 214:1127-1137.
For more information, contact Karen Esler at firstname.lastname@example.org