r- and K-Selection in Typha

A comparison of environmental and population parameters between sites differing in length of frost-free period indicated that populations from short growing season locations should be more subject to r-selection, while populations from locations with a long growing season should be more subject to K-selection. Properties of population samples of three species of Typha conformed to the theory. Specifically, the following hypotheses were confirmed: (i) r-selected genotypes have a greater developmental speed; (ii) r-selected genotypes have higher fecundity; (iii) r-selected genotypes produce more offspring, but invest less energy in each offspring; (iv) r-selected genotypes show less evidence of selection for traits increasing competitive ability in high density situations; (v) there is a selective trade-off between mechanisms contributing to colonization potential and those contributing to competitive potential. Superimposed on the selection pattern along the climatic gradient was an r-K dichotomy between the species occurring throughout the gradient, T. latifolia, and the two species, T. angustifolia and T. domingensis, restricted to different ends of the gradient.