Invasiveness and comparative life-history traits of exotic and indigenous Senecio species in Australia

A comparative ecological study of closely related invasive and non-invasive species, Senecio madagascariensis and S. lauttus (Asteraceae), investigate d what traits might confer invasive ability in very similar species. Life-h istory attributes of the weed S. madagascariensis were compared to five hab itat-specific subspecies of S. lautus: S. l. alpinus, S, l. dissectifolius, S. l. lanceolatus and two forms of S. l. maritimus. Field populations of e ach taxon were monitored to compare their population ecology. Relative rate s of phenological development were compared at a single location. Seed germ ination was studied in a laboratory experiment. Transplant experiments were conducted in a range of S. madagascariensis and S. lautus habitats to comp are performance in different environments. In monitored field populations S . madagascariensis produced seedlings and reproductive cohorts more frequen tly, flowered for longer periods, produced more seeds and had fewer germina ble achenes in the soil compared to S. lautus taxa, S. madagascariensis ach enes had higher rates of germination than S. lautus in both light and dark conditions. S. madagascariensis was found to have higher rates of survival than S. lautus taxa in 3 range of habitats and to be faster to flower in bo th transplant and standard glasshouse environments. Overall S. madagascarie nsis performed better than S. lautus ecotypes in terms of seedling, growth and fecundity measurements and second best For achenes. Despite relatively good performance in terms of life-history traits there is no evidence that S. madagascariensis is invading S. lautus habitats. We speculate that physi ological and morphological adaptations to specialised environments are a be tter explanation for success of Senecio taxa/ecotypes than generalised life -history trait performance. We suggest that invasiveness is essentially unp redictable, due to habitat/plant specific interactions between invader and area of introduction. In the absence of predictive theory, quarantine autho rities should use a combination of methods to assess invasive potential inc luding a database of known weeds, performance comparisons between congeneri c natives and exotics in a range of habitats at proposed point of introduct ion and monitoring of introduced species to determine if they spread.