Ant sampling in long-term scrub oak plots: ecological effects of Argentine ant invasions

Financial and logistical support from The Nature Conservancy has permitted the establishment and annual monitoring of nine pairs of invaded / uninvaded plots (each plot is circular with a 10-m radius) in island scrub oak woodland on Santa Cruz Island. Plots within each pair are matched for aspect and vegetation characteristics. These plots have now been sampled (using standardized approaches) for ants in four consecutive years (2010 - 2013). Consistent with research conducted elsewhere in Southern California, this sampling effort has revealed that invaded plots consistently support reduced native ant diversity compared to that observed in uninvaded plots. Evidence that decreased diversity is the direct result of invasion by L. humile comes from two formerly uninvaded plots that were invaded during the monitoring period. Diversity at these plots declined rapidly after invasion by L. humile.