PARENT SESSION
Monday, August 7, 5:00-6:30 pm
Poster Session 2 - Invasive species
Exhibit Hall, Ballroom Level, Cook Convention Center

Niche differences and competition promote invasion into coastal sage scrub communities.

Goldstein, Leah¹, Suding, Katharine¹, ¹ University of California, Irvine, Irvine, CA

ABSTRACT- Although it has often been speculated that differences in resource use between invasive species and a resident community may explain invasion success, there have been few mechanistic tests. Alternatively, invaders and residents could have strongly overlapping resource use patterns, leading to competitive exclusion by the invader. In California, exotic grass and forb species have successfully invaded coastal sage scrub communities, converting the shrub-dominated communities to exotic grasslands. To investigate if resource niche differences could explain the successful establishment of exotic grassland species within a coastal sage scrub community, we measured the resource use traits of seven native and non-native species at a grassland-coastal sage scrub ecotone. We measured four traits indicative of water and nitrogen use strategies: leaf ¹⁵N, leaf C:N, leaf ¹³C, and xylem water ¹⁸O and ²H. For all traits, invaders and native species did not show clear separation in their resource use characteristics. However, there were species-specific differences that could contribute to the success of individual invaders. For instance, Brassica nigra, an invasive forb, had higher ¹⁵N and lower C:N than neighboring native species, which may indicate that differences in N use contribute to its success. In contrast, the invasive annual grass Brachypodium distachyon had similar nitrogen use traits as native shrubs, but water isotope data suggest it is obtaining water from shallower soil depths. These results suggest that the mechanisms of invasion success are species and resource specific. Both competitive interactions among species with overlapping traits and resource partitioning mechanisms among species with niche differences may contribute to the establishment of invaders.

Key words: invasion, coastal sage scrub, stable isotopes