Year of Award

2017

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Organismal Biology, Ecology, and Evolution

Department or School/College

Division of Biological Sciences

Committee Chair

Ragan M. Callaway

Commitee Members

John L. Maron, Dean E. Pearson, Erick Greene, Mark Hebblewhite

Abstract

One of the most well-known explanations for the success of invasive plants in novel environments is enemy release, which predicts that 1) invasive plants are limited by natural enemies in the native range but not the non-native range, and 2) native competitors in recipient communities remain limited by their natural enemies. Despite considerable empirical attention, very few studies have tested these basic predictions, especially with respect to generalist herbivores. We tested whether invasive cheatgrass (Bromus tectorum) has experienced enemy release from granivorous rodents – an important guild of generalists – using exclosures and experimental seed additions in western Asia (where cheatgrass is native) and the Great Basin Desert, USA (where cheatgrass is invasive). Rodent exclusion improved cheatgrass establishment in western Asia but had no effect in the Great Basin (Ch. 1), and rodent exclusion in the Great Basin improved the establishment of a suite of native grasses but not cheatgrass (Ch. 2). Interestingly, rodent exclusion benefited native grasses to the same extent as eliminating cheatgrass competition (Ch. 3). These results suggest that cheatgrass in the Great Basin has experienced enemy release from an important group of generalists, which may help explain its exceptional invasiveness. In addition, seed predation from native rodents and competition from cheatgrass can present equally important barriers to the establishment of native grasses in the Great Basin.

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© Copyright 2017 Jacob Elias Lucero