Effects of a nonnative, invasive lovegrass on Agave palmeri distribution, abundance, and insect pollinator communities

Nonnative Lehmann lovegrass (Eragrostis lehmanniana) has invaded large areas of the Southwestern United States, and its impact on native plants is not fully understood. Palmer’s agave (Agave palmeri), an important resource for many pollinators, is a key native plant potentially threatened by E. lehmanniana. Understanding potential impacts of E. lehmanniana on A. palmeri is critical for anticipating the future of the desert community where they coexist and for addressing management concerns about associated threatened and endangered species. Our study provides strong indications that E. lehmanniana negatively impacts A. palmeri in several ways. Areas of high E. lehmanniana abundance were associated with significantly lower densities and greater relative frequencies of small A. palmeri, suggesting that E. lehmanniana may exclude A. palmeri. There were no significant differences in species richness, abundance, or community composition when comparing flower associates associated with A. palmeri in areas of high and low E. lehmanniana abundance. However, we did find significantly lower connectedness within the pollination network associated with A. palmeri in areas with high E. lehmanniana abundance. Although E. lehmanniana forms thick stands that would presumably increase fire frequency, there was no significant association between E. lehmanniana and fire frequency. Interestingly, medium to high densities of A. palmeri were associated with areas of greater fire frequency. The complex ramifications of E. lehmanniana invasion for the long-lived A. palmeri and interlinked desert community warrant continued study, as these species are likely to continue to be found in close association due to their similar soil preferences.