Achene mass variation in Ericameria nauseosus (Asteraceae) in relation to dispersal ability and seedling fitness

1, Ericameria nauseosus (Asteraceae) is a highly variable shrub species of western North America, whose achene mass varies sevenfold among subspecies and populations. We examined trade-offs between seedling fitness and disper sal ability by asking: does greater achene mass reduce dispersal ability, a nd is this potential disadvantage to large achenes compensated for by incre ased pappus investment? Does smaller achene mass reduce seedling fitness, a nd is this potential disadvantage to small achenes compensated for by incre ased relative growth rate (RGR)? 2. Dispersal ability was measured as fall rate in still air, while seedling fitness was measured as dry mass at two ages for 21 populations belonging to nine subspecies. 3. Fall rate was positively correlated with achene plume loading(-1/2), but because of variation in pappus investment and geometry, both plume loading (-1/2) and fall rate were only weakly positively correlated with achene mas s. Relative pappus investment did not show a consistent increase with achen e mass. 4. Seedling dry mass was strongly positively correlated with achene mass fo r 2-week-old seedlings grown without added nutrients. This correlation was significant but weak with added nutrients at 2 weeks, and by 4 weeks it was no longer significant. Seedling RGR was strongly negatively correlated wit h achene mass. 5. Achene mass variation was related to both seedling fitness and dispersal ability, but compensation was evident mainly as faster RGR in populations with small achenes.