Abstract
Invasive species can change selective pressures on native plants 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 among 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 response to B. tectorum is a function of both location and species identity, with some, but not all, populations of native grasses showing trait shifts consistent with evolution in response to B. tectorum invasion within the Great Basin.
Highlights
Invasion by non-native species poses a threat to native plant communities through mechanisms operating at multiple scales
We examined populations of five common native perennial grass species from four locations where paired invaded/uninvaded sites were found in close proximity, addressing the following questions: 1) Which species are the most tolerant of B. tectorum competition? 2) Which species exert the strongest competitive effect on B. tectorum? 3) Does native plant phenology differ between invaded and uninvaded populations? and 4) Are tolerant and/or competitive plants present in higher frequencies in invaded communities? Questions 1 and 2 address performance differences among species, while questions 3 and 4 allow us to infer whether trait shifts are consistent with an evolutionary response to invasion
The widespread invasion of B. tectorum in the arid western US provides the opportunity to examine the response of native plants to the selective pressure of B. tectorum invasion in a variety of communities and across large areas
Summary
Invasion by non-native species poses a threat to native plant communities through mechanisms operating at multiple scales. By altering the abiotic and biotic environment, invasive species are changing selection pressures experienced by native plants that remain in invaded communities [6,7,8]. Isolated native plants often persist within disturbed environments, suggesting that these plants may possess traits that increase their performance in invaded conditions [6,7]. Comparing plants from invaded and uninvaded populations may provide insight on phenotypic traits that allow native plants to persist in invaded populations, and measuring changes in trait frequency can indicate whether invaded populations are potentially responding to selective pressures associated with invasion. While causal selective agents may be difficult to determine, a trait-based approach can allow us to identify phenotypes that will perform best when restoring invaded rangelands
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