Print PageIn arid and semi-arid ecosystems seed consumers are ubiquitous and influence plant population establishment and composition through seed predation and dispersal. As a result, it is reasonable to assume that seed consumers may facilitate or suppress the spread of non-native species. However, the potential interactions between seed consumers and seeds of non-native invasive species are seldom examined. To evaluate the role of seed consumers on the invasion success of a non-native forb, Brassica tournefortii, at five replicate sites in the Mojave Desert USA, we examined seed removal patterns in open and under shrub microhabitats over multiple field seasons. We used wire cages to exclude access of seed consumers to experimental seeds, and quantified the mount of B. tournefortii seed carried back to the nest by harvester ants at 2 and 4 m away from randomly selected ant nests. The spatial distribution of B. tournefortiiplants was assessed by counting plants at the nest entrance (0 m), 2, 4, and 6 m away from the nest.
Results/Conclusions
Harvester ants were the main seed removers of B. tournefortii seeds. Ants removed 90% and 60% of offered seeds in open and undershrub habitat during summer, respectively. The proportion of seeds removed at 2 and 4 m away from ant nest was not significantly different; however, a larger proportion of seeds arrived to the nest when removed 2 m away from a nest. The spatial distribution of B. tournefortti plants differed as a function of distance from ant nests. Plant density was low at 0, 2, and 4 m away from the nest entrance while density increased at 6 m away from the nest entrance. Results indicate that harvester ants interact with B. tournefortii seed and can disperse the seeds of this non-native species. However, plant density was low near the nest entrance, suggesting that ant mediated seed dispersal does not promote plant establishment. Therefore, it appears that harvester ants may be acting as seed predators rather than seed dispersers.
phone 202-833-8773