Mortality and performance (total biomass) of five exotic (weedy) and five n
ative annual Asteraceae in Western Australia were compared along a mineral
nutrient gradient. Mortality did not differ between exotic and native speci
es but varied greatly within each group. The exotic species responded more
positively to higher nutrient additions than the native species, indicating
that the exotics might have a competitive advantage in a nutrient-enhanced
situation (e.g., after fire). The concept of 'phenotypic inertia' (PI), co
mbining survival and performance over a range of environments, is introduce
d as a means of evaluating the range of growing conditions tolerated. The t
wo species with highest PI (one exotic and one native) had the lowest morta
lity and uniformly moderate biomass for the nine nutrient treatments. The s
pecies with the lowest PI (a native) had complete failure at the two highes
t nutrient levels and low variable growth in the remainder. PI has potentia
l as a measure of environmental tolerance although, in the present study, t
he exotic species were not clearly superior to the native species in their
responses to a wide range of soil nutrient levels.