Can natives fight back? Evolutionary response to cheatgrass invasion

Native perennial grass species in the intermountain west are experiencing a shift in the composition of interspecific competitors from primarily perennial species to exotic, annual grasses. One would predict that traits that confer an advantage to perennial grasses in the presence of these annual competitors would be favored over time, leading to shifts in population traits of perennial grasses in invaded communities. Here I present data from greenhouse and field studies that demonstrate that there are differences in potentially adaptive traits in a native perennial grass, squirreltail (Elymus sp.). Dormant squirreltail plants were collected from annual grass invaded and un-invaded sites near Bordertown, CA in August 2006, and transplanted into pots in a greenhouse. Individual plants were split into two equal halves, and one half was grown with competition from cheatgrass (Bromus tectorum), and the other half was grown without competition. Plants collected from invaded sites responded significantly more quickly to watering treatments, growing more leaves in the first week of watering. In addition, preliminary results show a significant competition by collection site interaction, such that squirreltail plants collected from invaded areas experienced a smaller decrease in plant size when grown with competition than did plants collected from un-invaded areas. These traits are adaptive when plants grow in the presence of annual species, and discussed is the possibility that annual grasses were the selective force that caused these population differences.