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Title: Native perennial grasses show evolutionary response to Bromus tectorum (Cheatgrass) invasion

Author
item GOERGEN, ERIN - University Of Nevada
item LEGER, ELIZABETH - University Of Nevada
item Espeland, Erin

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2011
Publication Date: 3/30/2011
Citation: Goergen, E., Leger, E., Espeland, E.K. 2011. Native perennial grasses show evolutionary response to Bromus tectorum (Cheatgrass) invasion. PLoS One. 6(3): e18145 (1-8). doi:10.1371/journal.pone.0018145.

Interpretive Summary: Although the introduction of invasive species can lead to the loss of native species, invasive species may also induce rapid evolutionary changes in remnant native plants. Invasive species are a direct selective force on native plants by competing with them for resources, but also change other selection pressures experienced by natives. For example, the introduced annual grass Bromus tectorum L. (cheatgrass) changes soil characteristics and increases the rate of the fire cycle in the arid west. In this experiment, we asked how much variation there was between five perennial grass species and their populations in the ability to grow successfully with cheatgrass. We would expect that if plants had evolved an adaptive response to cheatgrass, plants from invaded areas would respond better to being grown with cheatgrass compared to plants from uninvaded areas. To test this, 320 adult plants were collected from invaded and uninvaded communities from four locations near Reno, Nevada, USA. Each plant was divided in two (cloned) and transplanted into the greenhouse. One clone was grown with cheatgrass while the other was grown alone. We measured tolerance (ability of each clone to maintain its own size) and competitive ability (the ability of each clone to reduce size of B. tectorum). Plants from invaded populations consistently had earlier greenup and earlier flowering than those from uninvaded populations, and in two out of four sites, invaded populations were more tolerant of B. tectorum competition than uninvaded populations. Poa secunda and one population of E. multisetus had the strongest competitive effect on B. tectorum, and these two species were the only ones that flowered in competition with B. tectorum. Our study indicates that adaptation to B. tectorum is a function of both location and species identity, with some, but not all, populations of native grasses evolving in response to B. tectorum invasion within the Great Basin.

Technical Abstract: Invasive species can change selective pressures on native species by altering biotic and abiotic conditions in invaded habitats. Although invasions can lead to native species extirpation, they may also induce rapid evolutionary changes in remnant native plants. We investigated whether adult plants of five native perennial grasses exhibited trait shifts consistent with evolution in response to invasion by the introduced annual grass Bromus tectorum L. (cheatgrass), and asked how much variation there was between species and populations in the ability to grow successfully with the invader. Three hundred and twenty adult plants were collected from invaded and uninvaded communities from four locations near Reno, Nevada, USA. Each plant was divided in two and transplanted into the greenhouse. One clone was grown with B. tectorum while the other was grown alone, and we measured tolerance (ability to maintain size) and the ability to reduce size of B. tectorum for each plant. Plants from invaded populations consistently had earlier phenology than those from uninvaded populations, and in two out of four sites, invaded populations were more tolerant of B. tectorum competition than uninvaded populations. Poa secunda and one population of E. multisetus had the strongest suppressive effect on B. tectorum, and these two species were the only ones that flowered in competition with B. tectorum. Our study indicates that adaptation to B. tectorum is a function of both location and species identity, with some, but not all, populations of native grasses evolving in response to B. tectorum invasion within the Great Basin.