Access Type

Open Access Dissertation

Date of Award

January 2012

Degree Type


Degree Name



Biological Sciences

First Advisor

D Carl Freeman

Second Advisor

Daniel M. Kashian


Although dioecious species are rare in nature, the sexual system appears in a diverse number of families and across all life forms and global locations. We looked at the population dynamics of natural populations to determine why many dioecious populations display biased sex ratios. We also looked at the role incestuous matings, seed and pollen dispersal patterns, and compensation play in the evolution of this sexual system using two theoretical models we developed. Finally, we studied aspen populations in the Midwest to determine how climate variables affect growth and decline. We found many dioecious species display male biased ratios and that life form and dispersal agents are good indicators. Our theoretical models imply that incest and dispersal specialization of unisexual individuals facilitate invasion, but through the interaction of specialization, incest, and compensation, unisexual invasion occurs much more consistently and under less stringent conditions then previously modeled. Finally, we found that declining aspen stands were much less responsive to climate variables than healthy stands and that a number of stand characteristics could be used to discriminate between responsive and non-responsive stands.

Included in

Biology Commons