| A recurrent theme in the study of life history evolution has been the comparison between iteroparity and semelparity. I compared the semelparous annual plant, Zea mays ssp. parviglumis with the iteroparous perennial Z. diploperennis in demography, morphology and physiology. I conducted a demographic survey of two natural populations of each species in the Sierra de Manantlan Biosphere Reserve (RBSM), Jalisco, Mexico, recording survivorship and reproduction of marked plants and survivorship of seed until germination. I used the demographic information to parameterize population projection matrices and model population growth. Using sensitivity and elasticity analyses of the population matrix models, I determined which life stages were most influential on population growth.; I compared morphological and physiological traits between annual and perennial Zea in a common garden in the RBSM, and I conducted a parallel comparison of traits between the annual P. vulgaris and the perennial P. coccineus ssp. formosus. I measured the following traits: leaf area, leaf number, aboveground biomass, root biomass, leaf nitrogen concentration, stable hydrogen and oxygen ratios of stem and soil water, stable carbon isotope ratio in leaf material, leaf water potential and stomatal conductance. I also compared photosynthetic physiology and growth components in a greenhouse common garden, measuring the same traits as in the field common garden, as well as carbon assimilation at different light levels.; Interpopulation variation in Zea was as important as interspecific variation with respect to all demographic transitions. An aerial seed bank contributed to yearly recruitment in both annual and perennial Zea. Survival of seeds until germination was the most influential life stage in the annual while seedling survival was most important in the perennial. In the common garden, perennial Zea grew as large as the annual and reproduced within one growing season. Growth and allocation in Phaseolus followed expected patterns. In both genera, annuals had shallower rooting but similar water use behavior to their perennial congeners. In the greenhouse, differences in growth between annuals and perennials were due to greater leaf area per unit biomass in both Zea and Phaseolus, but differences were achieved via different underlying growth components in the two genera. |
