Niche opportunities for invasive annual plants in dryland ecosystems are controlled by disturbance, trophic interactions, and rainfall
Resource availability and biotic interactions control opportunities for the establishment and expansion of invasive species. Studies on biotic resistance to plant invasions have typically focused on competition and occasionally on herbivory, while resource-oriented studies have focused on water or nutrient pulses. Through synthesizing these approaches, we identify conditions that create invasion opportunities. In a nested fully factorial experiment, we examined how chronic alterations in water availability and rodent density influenced the density of invasive species in both the Mojave Desert and the Great Basin Desert after fire. We used structural equation modeling to examine the direct and mediated effects controlling the density of invasives in both deserts. In the first 2 years after our controlled burn in the Great Basin, we observed that fire had a direct effect on increasing the invasive forb Halogeton glomeratus as well as a mediated effect through reducing rodent densities and herbivory. 4 years after the burn, the invasive annual grass Bromus tectorum was suppressing Halogeton glomeratus in mammal exclusion plots. There was a clear transition from years where invasives were controlled by disturbance and trophic interactions to years were resource availability and competition controlled invasive density. Similarly, in the Mojave Desert we observed a strong early influence of trophic processes on invasives, with Schismus arabicus benefitted by rodents and Bromus rubens negatively influenced by rodents. In the Mojave Desert, post-fire conditions became less important in controlling the abundance of invasives over time, while Bromus rubens was consistently benefitted by increases in fall rainfall.
KeywordsNiche opportunity Invasive species Precipitation manipulation Fire Rodents
We appreciate the assistance of the Bureau of Land Management Salt Lake City Field office for providing National Environmental Policy Act clearance and conducting the experimental burn treatments in the Great Basin. We also acknowledge the Washington and Iron County Fire Marshals who conducted the experimental burns in the Mojave Desert. We acknowledge Tiffany Sharp and Brock McMillan for conducting the rodent surveys and Amy Clark and Justin Taylor for assistance with the vegetation surveys. This project was funded by United States Department of Agriculture National Institute of Food and Agriculture Grant: 2010-38415-21908 and by Brigham Young University’s Office of Research and Creative Activities.
Author contribution statement
RAG and SBS conceived and designed the experiments. RAG, RCO, TBB, and SBS performed the experiments, RAG, AR, and DCL analyzed the data. RAG and RCO wrote the manuscript; other authors provided editorial advice.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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