Yellow Starthistle in Utah: An Investigation of Centaurea solstitialis Invasion Patterns, Processes, and Population Dynamics

Author

Julie Patrice Rieder, Utah State University

Date of Award:

5-1-2005

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Life Sciences: Biology

Committee Chair(s)

Edward W. Evans

Committee

Edward W. Evans

Committee

James A. MacMahon

Committee

Janis L. Boettinger

Committee

Eugene W. Schupp

Committee

William P. Kemp

Abstract

In a series of observational studies and experiments in the field, I investigated the general biology of yellow starthistle (Centaurea solstitialis) within a landscape in Utah in light of three main phases of invasion: arrival and establishment, spread, and equilibrium. During the establishment phase, the effect of disturbance on yellow starthistle establishment and performance was context dependent; disturbance positively influenced establishment and fecundity on relatively large disturbed plots that were artificially seeded, but had no significant effect on YST performance on small disturbed plots receiving ambient seed rain. Importantly, disturbance was not essential for establishment of yellow starthistle. During the process of spread, yellow starthistle exhibited a patchy distribution, did not consistently increase in spatial extent each year, and maintained the location of its patches over time. Individual yellow starthistle seedlings survived best when near conspecifics, but had similar or slightly higher reproductive output when far from conspecifics. The patterns of individual performance suggested that conspecific facilitation when near conspecifics, reduced intraspecific competition when far from conspecifics, and the avoidance of interspecific competition when surrounded by heterospecifics, may influence yellow starthistle population dynamics. To investigate one potential mechanism of conspecific facilitation, I examined nitrogen dynamics in soil beneath yellow starthistle and Bromus inermis. Soil beneath yellow starthistle accumulated more inorganic nitrogen over the dry summer months compared to soil beneath Bromus inermis. The soil inorganic nitrogen was more rapidly depleted beneath yellow starthistle than beneath Bromus inermis after fall wet-up, coinciding with establishment of yellow starthistle seedlings. These results suggest elevated levels of soil inorganic nitrogen beneath yellow starthistle may create a positive feedback loop, encouraging the establishment of yellow starthistle seedlings. Finally, during the equilibrium phase, yellow starthistle seedlings growing at reduced densities survived at higher rates compared to those seedlings at ambient densities. Importantly, total reproductive output was similar on reduced- and ambient-density plots, suggesting that even strong reductions in initial seedling density have relatively minor impacts on the maintenance of population size for yellow starthistle. Thus, even flowerhead predators that greatly reduce seed production, and therefore reduce seedling densities, may be ineffective at controlling yellow starthistle populations.

Comments

Ecology

Recommended Citation

Rieder, Julie Patrice, "Yellow Starthistle in Utah: An Investigation of Centaurea solstitialis Invasion Patterns, Processes, and Population Dynamics" (2005). Biology. 710.
https://digitalcommons.usu.edu/etd_biology/710