POPULATION ECOLOGY OF CHRYSANTHEMOIDES MONILIFERA IN SOUTH-AFRICA - IMPLICATIONS FOR ITS CONTROL IN AUSTRALIA

1. The population ecology of single species stands of Chrysanthemoides incana, C. monilifera monilifera, C. m. pisifera, and C. m. rotundata was examined at 12 study sites in South Africa. Comparisons are made with populations of C. m. monilifera and C. m. rotundata, which are in troduced invasive weeds of native vegetation in Australia. 2. In South Africa, adult plant density averaged 0 . 2 plants m(-2). Plants in th e sample were between 6 and 35 years old as determined by growth rings . Recruitment in Cape Province sites appeared to be restricted to a fe w years, probably following major disturbance such as fire. In Natal, recruitment declined as the population aged. Seedlings were rare, bein g present at only four sites and at densities lower than that of adult plants. 3. Insects and unidentified causes destroyed 10-58% of ovules before the flowers senesced. Larvae of seed-feeding flies, Mesoclanis species, destroyed a small fraction of the seeds (0 . 2-9% per site) and damage to seeds by other insects (chiefly larvae of Lepidoptera) a ccounted for 4-25% of ovules. Between 0 . 4 and 32% of ovules became v iable seeds. 4. Over all sites the seed bank under the canopy of plant s consisted of 410-4500 seeds m(-2), of which 0-6% were viable. There was a mean of 26 viable seeds m(-2) over all sites. Outside the canopy , total seed density ranged from 7 to 660 m(-2), of which 0-6% were vi able. Identifiable post-dispersal damage was mainly due to rodents (up to 62% of dispersed seed) and was higher in Cape Province than in Nat al. 5. Between 5 and 20% of the leaf surface area was consumed by herb ivores. 6. Chrysanthemoides populations in South Africa attain similar adult plant densities to Australian populations of Chrysanthemoides, but have lower percentage ground cover and much reduced recruitment on ce a population is established. It is likely that biological control a gents causing similar damage in Australia will need the help of other management techniques such as fire to reduce weed density and persiste nce.