Rodent herbivory preferences and their implications for plant community assembly and invasion in a post-fire desert ecosystem

Herbivory influences plant evolution, the assembly of plant communities, and patterns of biological invasions. This study examined rodent herbivory patterns on the survival of native and non-native plant seedlings following fires in the Mojave Desert. We also assessed the extent of these effects on seedlings that use different life history strategies: grasses, forbs, and shrubs. Using a full-factorial design, we tested the individual and interactive effects of past fires and rodent exclusion on seedling survival. Five native and four non-native invasive plant species common in the Mojave Desert were grown to the seedling stage and placed in randomized order in the experimental plots. We assessed seedling survival after seven days. Survival was nearly two-fold greater for non-native seedlings (85%) than native seedlings (47%, p = 0.002). Rodents decreased native seedling survival from 59 to 36% (p = 0.002) but did not affect non-native seedling survival. Rodents decreased shrub (58–31%, p = 0.006) and forb seedling survival (76–57%, p = 0.04) but did not affect grass seedling survival. Rodents showed the greatest preference for Larrea tridentata (creosote), Sphaeralcea ambigua (desert globemallow), and Erodium circutarium (red stem stork's bill). Post-fire conditions significantly decreased the seedling survival of native shrub, Yucca brevifolia (Joshua tree), with 47% survival in unburned plots but no survival in burned plots (p = 0.003). Fire history did not significantly impact other species or influence patterns of rodent herbivory. These results suggest that low rodent preference for grass seedlings may partially contribute to the success of non-native grass invasions in the Mojave Desert.