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

Abstract

Abstract1. 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 dispersal ability by asking: does greater achene mass reduce dispersal ability, and is this potential disadvantage to large achenes compensated for by increased pappus investment? Does smaller achene mass reduce seedling fitness, and is this potential disadvantage to small achenes compensated for by increased 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 mass. Relative pappus investment did not show a consistent increase with achene mass.4. Seedling dry mass was strongly positively correlated with achene mass for 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 with 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.