Publication Date



Open access

Degree Type


Degree Name

Doctor of Philosophy (PHD)


Biology (Arts and Sciences)

Date of Defense


First Committee Member

Carol Horvitz

Second Committee Member

Barbara Whitlock

Third Committee Member

David Janos

Fourth Committee Member

Hans de Kroon


I addressed how light availability influences sexual and clonal offspring production, demographic performance and contribution to population dynamics by studying the Neotropical understory herb Calathea marantifolia across a light gradient in Costa Rica. To understand how demographic performance was influenced by light availability I conducted a transplant experiment in the field. Both seedlings and clonal offspring grew best when planted in high light areas, but seedlings showed a faster and more dramatic response. Survival of seedlings was greatest in high light sites but clonal offspring survival was greatest where light availability was low. To examine the demographic consequences of physiological integration between parent plants and their clonal offspring I combined an isotope tracing study with a severing experiment in natural populations. Very little water was transported between parent and offspring. Severing the connections between parent and offspring did not influence the demographic performance of parent plants, but clonal offspring were negatively affected, especially prior to rooting. I investigated the demographic cost of sexual reproduction by manipulating the sexual reproductive effort of plants in the field. Increasing the sexual reproductive effort of plants did not reduce their future demographic performance. However, subsequently produced clonal offspring displayed a small reduction in size due to their parent's increased reproduction. To understand the contribution of both reproductive modes for population growth rate I used field data collected in plots with high and low light. Data from the first census interval were used to develop a new size-structured integral projection model that includes both sexual and clonal recruitment. Population growth rate was faster in high light than in low light and a life table response experiment revealed that this difference was primarily due to improved survival and growth at large sizes and increased clonal reproduction in high light. By removing reproductive modes from the model, I found that sexual reproduction contributes more to population growth than clonal reproduction. When only sexual reproduction is included in the model population growth rate is fastest in high light environments. By contrast, when only clonal reproduction is included in the model population growth rate is fastest low light.


Calathea; Clonal Reproduction; Light Availability