Biological invasions occur when non-native species become established in areas outside of their original range. Biological invasions have tremendous ecological impacts and economical costs, causing extinction of native species and shifts in ecosystem function that are estimated to cost over $138 billion per year in the United States alone. Ecologists have developed several ideas that might explain why some exotic organisms are such good invaders. For example, exotic organisms might be good invaders because they leave their original predators behind when they invade a new place (an idea called the "enemy release hypothesis"). Although ecologists have come a long way in understanding biological invasions, our understanding of how invasions happen is still incomplete, as suggested by invasions that fail when they are predicted to succeed and vice versa.
Dr. John Orrock and Dr. Jim Reichman are examining a new idea that might explain why biological invasions happen: invasive plants might gain a foothold in native communities by changing the behavior or abundance of native animals in a way that increases the impact of native animals on native plants. Their work will take place in the grasslands of California, where 9.2 million hectares of grassland (almost 25% of the entire state) are dominated by non-native plants. By using fencing to alter the access of native animals, Dr. Orrock and Dr. Reichman will be able to determine whether native animals are the missing link that is promoting invasion. These results will impact restoration work and shed new light on the role that native animals play in affecting invasions. The results may suggest that understanding how potential invaders change the impact of native animals on native plants will increase understanding of how biological invasions happen.