Undergraduate Honors Theses

Thesis Defended

Spring 2017

Document Type


Type of Thesis

Departmental Honors


Ecology and Evolutionary Biology

First Advisor

Katharine Suding

Second Advisor

Pieter Johnson

Third Advisor

Eve-Lyn Hinckley


Species invasions have become a problem of global concern because of their negative impacts on native ecosystems. In the Carrizo Plain of California, the invasive grass Hordeum murinum has become the focus of management because it threatens native grassland species. Previous studies have illustrated how resource availability and burrowing herbivore activity affect the growth of this grass, but more information on its germination is needed in order to obtain a full picture of its population dynamics. Seedbank samples were collected in different field conditions and then brought into the greenhouse to assess germination. Experimental field manipulations allowed evaluation of Hordeum germination in response to Giant Kangaroo Rat (Dipodomys ingens) burrowing and foraging activity, precipitation, and plant community cover. Presence of burrowing and increased precipitation resulted in an increase in the abundance of Hordeum germinants. The presence of Giant Kangaroo Rat foraging activity increased the abundance of Hordeum germinants across seasons. In addition, more Hordeum germinants grew when this trophic activity was absent and after an entire summer of dormancy had passed, which leads to further questions regarding seed conditioning. Relative abundance of Hordeum germinants had a linear, negative relationship with total plant cover in the field, suggesting competitive effects of the plant community on germination. The results from this study will contribute to a larger project developing population models for invasive grasses in order to understand what limits population growth and to aid management decisions.