As invasive grasses and fire increase in frequency and extent in North American deserts, they have the potential to affect animal communities through bottom-up forces. We experimentally tested the effects of fire on rodent communities of the Great Basin and Mojave Deserts. Fire decreased the abundance, richness, and diversity of rodents in the Great Basin after fire. In the Mojave, abundance was unaffected and diversity and species richness were greater on burned than unburned plots 4 months after fire. The effects of fire on rodent communities tended to decrease over time. The differences in effects between the deserts may be due to differences in the foraging preferences of the dominant species at each site. As these species are primarily herbivorous, short-term changes to the rodent community could have long-term implications by affecting the recovery of the plant community after fire.

Ecosystems are transformed by changes in disturbance regimes including wildfire and herbivory. Rodent consumers can have strong top-down effects on plant community assembly through seed predation, but their impacts on post-germination seedling establishment via seedling herbivory need better characterization, particularly in deserts. To test the legacy effects of fire history, and native rodent consumers on seedling establishment, we evaluated factorial combinations of experimental exclusion of rodents and fire history (burned vs. unburned) on seedling survival of 14 native plant species that vary in their life history strategies and growth form in the Mojave Desert. Seedlings were placed into the experimental plots, and seedling survival was monitored daily for 8 days. The legacy effects of fire history had minimal effects on seedling survival, but rodent exclusion, year, and their interaction were strongly significant. Seedling survival rates were nearly sixfold greater in rodent exclusion plots compared to control plots in 2012 (53 vs. 9%) and 17-fold greater in 2013 (17 vs. 1%). The dramatic increase in seedling mortality from 2012 to 2013 was likely driven by an increase in rodent abundance and an outbreak of grasshoppers that appears to have intensified the rodent effect. There was strong variability in plant species survival in response to rodent herbivory with annual plants and forb species showing lower survival than perennial plants and shrub species. These results indicate that rodent consumers can strongly regulate seedling survival of native plant species with potentially strong regulatory effects on plant community development.

Abstract. Rodent consumers can have strong top-down effects on plant community development via seed predation, but their influence on seedling recruitment and how it varies depending on disturbance history and plant traits are largely unknown. Over a two-year period, we experimentally tested the influence of rodents and fire on seedling survival of 14 plant species with contrasting growth forms and life history traits in the Great Basin Desert. Seedling survival was dramatically increased by rodent exclusion and fire and was greater in 2013 than 2012. Rodent abundance was an order of magnitude lower in 2013 than 2012 and across both years showed a negative linear relationship with mean seedling survival of all 14 plant species (R 2 = À0.62). There was strong variability in plant species sensitivity to rodent herbivory with a more than 10-fold difference in mortality risk between the most sensitive species and the most resistant species and a high degree of variability in survival among all species. Mortality risk of forb species was double that of grass species and there was a trend toward higher mortality of native species compared to introduced species. The results suggest that rodent herbivory may be an important determinant of plant community assembly in desert ecosystems with plant life history strategies and growth form traits serving as important survival filters. Post-fire environments and low rodent years likely provide windows of opportunity for greater seedling recruitment due to a release from rodent herbivory pressure.