The introduction of invasive plants is altering habitats across the planet. Arid ecosystems are undergoing state changes from the spread of invasive grasses and subsequent alteration of fire regimes. Rodent species in the Great Basin Desert provide some biotic resistance against the spread of invasive species like Bromus tectorum (cheatgrass), but how they influence seed abundance in the presence of other native and invasive species in differing burned states is unknown. Is the success of invasive grasses being partially driven by rodent seed preference? In June 2017 we placed 3,200 petri dishes filled with soil across five full factorial replicated blocks in unburned, burned, and reburned plots where rodents were excluded or allowed access. Within each dish, 100 seeds from one of 11 different native or invasive species were placed, and dishes were removed after 1, 3, 7, and 14 days with the remaining seeds counted to study rodent granivory preference over time.
Results/Conclusions
We found that rodent seed predation impacted all species. Seed count steadily decreased at every collection point across the 2 week study period, indicating consistent rodent predation. Seed predation was highest in unburned plots and lowest in burned plots. Native shrub cover and a reduced amount of ambient seed sources may explain increased granivory in unburned plots. All grass species, invasive Bromus tectorum and natives Poa secunda, Pseudoroegneria spicata, and Elymus elymoides were consumed more than shrub or forb species. Native grass seeds were removed more than B. tectorum seeds. This suggests that rodents prefer larger native grass seeds but will preferentially consume invasive cheatgrass over native shrub and forb seeds, which tend to be smaller. Invasive forb seeds Halogeton glomeratus, Ceratocephala testiculata, and Sanguisora minor were removed more than the seeds of the native forb Sphaeralcea coccinea, and native shrubs Artimesia tridentata, and Atriplex canescens. The data suggest that seed size and texture may be more important than seed origin (native vs. exotic) in influencing rodent preference.