| Abstrakt: |
(1) An experiment was performed to ascertain the relative success of plants derived from the ray and disc achenes of Heterotheca latifolia when in competition with one another and potentiatlly short of water. The treatments included pure and mixed sowings with regular watering, and mixed sowings with droughts beginning and ending at various times. The number of living plants was counted at various times during the experiment. Success was measured as total biomass at the end of the experiment, mean biomass per plant, mean height and width of plants, the number of plants alive at the end of the experiment, and the distribution of individual biomasses. (2) Disc achenes were more successful than ray achenes when a plentiful water supply resulted in a high overall biomass and density at the end of the experiment. The inferior performance of ray achenes is attributed to the combined effects of lower embryo provisioning, lower and later germination, and suppression by the early-germinating disc achenes. (3) Ray achenes were more successful than disc achenes when water was scarce and overall biomass and density were low at the end of the experiment. Their superior performance resulted from escaping the water shortage by dormancy. (4) While the disc achene strategy resulted in a higher mean performance across treatments, the ray achene strategy exhibited lower variance in performance. This result is discussed in terms of ideas about fitness in variable environments. [ABSTRACT FROM AUTHOR] |
