PARENT SESSION
Poster Session 20: Invasive Species
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Bottom-up effects of non-native grasses on arthropod communities.
Wolkovich, Elizabeth1, Cottingham, Kathryn1, Bolger, Douglas1, 1 Dartmouth College, Hanover, NH
ABSTRACT- A system's dominant plant type often drives its community and ecosystem properties; invasion of a different functional type can alter the spatial patterning of vegetation, soil chemistry and physical structure. The invasion of non-native annual grasses (Bromus spp.) into semi-arid coastal sage scrub represents a dramatic change from shrub-domination to grass-domination. We conducted an observational study in coastal sage scrub of San Diego, California, from March to June 2004 to test the hypothesis that non-native grasses increase arthropod abundance due to increased aboveground plant biomass. We sampled arthropods with pitfalls installed under Artemisia californica and Eriogonum fasiculatum shrubs in areas of naturally high or low Bromus cover across three aspects (east/west, north, south) at two sites. Arthropod numbers generally decreased with increasing Bromus cover. Neither shrub species nor aspect were significant predictors of arthropod abundance. Acari and Formicidae, the two most abundant groups, showed similar decreases with increasing Bromus cover (for Acari: ln(acari) = 2.73 - 0.14 Bromus1/2 p=.02; for Formicidae: ln(Formicidae) = 2.89 - 0.13 Bromus1/2, p=.005). At the species level, the decline in ants was driven primarily by Pheidole vistana and Forelius mccooki, while other species, such as Solenopsis xyloni, showed no trend with Bromus. Soil carbon and nitrogen increased linearly with increasing Bromus cover, which may indicate that, even with reduced soil mesofauna abundance, Bromus litter is able to decompose and enter the soil. Bromus appears to cause complex changes in coastal sage shrub, perhaps because of its ability to alter physical, chemical, and biological properties. Experimental studies are now underway to determine if patterns of arthropod abundance are consistent across years, and how Bromus litter affects abiotic and functional properties of the soil.
Key words: invasive species, arthropods, semi-arid, bottom-up effects