Rodent herbivory differentially affects mortality rates of 14 native plant species with contrasting life history and growth form traits.

Abstract

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 8days. 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.