Pollination and breeding systems of alien invasive plants in KwaZulu - Natal in South Africa.

Abstract

According to Baker (1955), success of plant invasions can be attributed to autogamous breeding

systems and generalist pollination systems. A test of Baker's rule was carried out on 19 invasive

alien plant species in KwaZulu-Natal, South Africa. Natural levels of fruit set in these plants was

high (median= 71.5% fruit set per plant). Breeding system experiments for 18 species showed that

17% of the species are allogamous, 72 % are autogamous and 11% are apomictic. This contrasts

markedly with a general flora of 1472 species in which 65% are allogamous, only 14% are

autogamous, and 21% are apomictic. Because the breeding systems of the alien species were largely

autogamous, pollinators make only a small contribution to the overall reproductive success. Seventy

one percent of the 14 alien species for which pollinators were obtained were pollinated by

honeybees, which are super-generalists and ubiquitous in a generalist pollination systems. However,

some species showed pre-adaptation to relatively specialized pollination systems, involving

hawkmoths, butterflies and Xylocopa bees respectively. Thus, alien plants were not visited by a wide

range of insects, but rather showed pre-adaption to one or more pre-existing guilds in the new

habitat. Pollen limitation experiments showed no evidence that reproductive success in populations

of the species is limited by pollen availability.