The Population Biology of Chamaelirium Luteum, A Dioecious Member of the Lily Family: Life History Studies

An investigation of the demographic characteristics and consequences of sexual dimorphism was undertaken with the long—lived dioecious forest floor herb, Chamaelirium luteum (L.) Gray. Following seven consecutive years of censusing, individuals within populations were assigned to one of three sex classes: males, females, and individuals of unknown sex (i.e., plants not observed to flower during the study). Individuals of unknown sex showed different characteristics than both males and females, and it is believed that these plants represent a juvenile class. The three sex classes differed in overall size: females were the largest, followed by males and then by putative juveniles. The putative juvenile class had the highest mortality rate, followed by females and then by males. Females produced larger inflorescences and flowered less often over a span of years than males. Age—specific and size—specific life history traits were also investigated. The populations were found to be structured according to age: seedlings 1—3 yr old had a much higher mortality rate than established adult plants. Furthermore, there was an interaction between sex and age in that males were found to have a younger age at first reproduction than females. The populations were also found to be structured according to plant size; changes in size from year to year, inflorescence size and flowering schedules in males and females, and mortality rates among juveniles were all correlated with plant size. The observed sexual dimorphism in life history traits between males and females indicates that there are differential °costs° associated with reproduction of the two sexes. The direct effects of flowering on plant size transitions were found to differ for the two sexes; flowering in a particular year resulted in a reduction in size in the following year for both sexes, but the reduction was greater for females. The potential impact of specialization of sex function on life history evolution within a plant species appears quite dramatic based on the findings of this study.