Evolutionary Responses of Native Plants to Novel Community Members

Abstract

Both ecological and evolutionary processes can influence community assembly and stability, and native community members may respond both ecologically and evolutionarily as additional species enter established communities. Biological invasions provide a unique opportunity to examine these responses of native community members to novel species additions. Here, I use reciprocal transplant experiments among naturally invaded and uninvaded environments, along with experimental removals of exotic species, to determine whether exotic plant competitors and exotic insect herbivores evoke evolutionary changes in native plants. Specifically, I address whether the common native plant species Lotus wrangelianus has responded evolutionarily to a series of biological invasions by adapting to the presence of the exotic plant Medicago polymorpha and the exotic insect herbivore Hypera brunneipennis. Despite differences in selection regimes between invaded and uninvaded environments and the presence of genetic variation for traits relevant to the novel competitive and plant-herbivore interactions, these experiments failed to reveal evidence that Lotus has responded evolutionarily to the double invasion of Medicago followed by H. brunneipennis. However, when herbivory from H. brunneipennis was experimentally reduced, Lotus plants from source populations invaded by Medicago outperformed plants from uninvaded source populations when transplanted into heavily invaded destination environments. Therefore, Lotus showed evidence of adaptation to Medicago invasion but not to the newer invasion of an exotic shared herbivore. The presence of this exotic insect herbivore alters the outcome of evolutionary responses in this system and counteracts adaptation by the native Lotus to invasion by the exotic plant Medicago. This result has broad implications for the conservation of native communities. While native species may be able to adapt to the presence of one or a few exotics, a multitude of invasions may limit the ability of natives to respond evolutionarily to the novel and frequently changing selection pressures that arise with subsequent invasions.

Rapid responses of soil microorganisms improve plant fitness in novel environments

“…For example, the catastrophic effects of global warming on coral reef communities are greatly diminished when corals are colonized by particular clades of thermal-tolerant zooxanthellae symbionts (22). Second, tradeoffs between traits mediating biotic interactions and traits underlying adaptation to global change may hinder (or in some cases facilitate) evolutionary responses (23,24). For example, insect herbivores appear to inhibit adaptive responses of native plants to biological invasions, likely because of genetic tradeoffs between traits mediating interactions with herbivores and exotic plant competitors (23,24).…”

“…Second, tradeoffs between traits mediating biotic interactions and traits underlying adaptation to global change may hinder (or in some cases facilitate) evolutionary responses (23,24). For example, insect herbivores appear to inhibit adaptive responses of native plants to biological invasions, likely because of genetic tradeoffs between traits mediating interactions with herbivores and exotic plant competitors (23,24). These complex species interactions in natural communities can make the evolutionary consequences of global change difficult to predict, but understanding adaptation in a community context is necessary for assessing species' responses to global change and identifying factors that contribute to adaptive responses to novel environments.…”

Community heterogeneity and the evolution of interactions between plants and insect herbivores

“…For example, Chew (1979) speculated that the selective pressures on the Brassicaceous host plants she studied would likely differ following invasion by the exotic crucifer Thlaspi. Several other examples of invasive plants that apparently alter attack on natives have recently emerged (Zimmerman 1960;Thomas et al 1987;Carroll and Boyd 1992;Solarz and Newman 1996;Rand and Louda 2004;Lau and Strauss 2005;Russell and Louda 2005;Lau 2006). We believe that the study of plant-herbivore interactions in both invaded versus non-invaded sites and in introduced versus native habitats are "natural experiments" that provide interesting research opportunities.…”

Test of local adaptation to biotic interactions and soil abiotic conditions in the ant-tended Chamaecrista fasciculata (Fabaceae)

“…Most studies addressing plant local adaptation have focused on the relative importance of gene Xow and natural selection (Slatkin 1973;Linhart and Grant 1996), and on the role of abiotic factors (e.g., wind, elevation, soil) as forces promoting local adaptation (Jain and Bradshaw 1966;Galen et al 1991). Except for a few studies involving competition (McGraw and Chapin 1989;Prati and Schmid 2000) and leaf herbivores (Schemske 1984;Sork et al 1993;Lau 2006), the inXuence of biotic interactions on plant local adaptation generally has been overlooked (although for animals this has not been the case; see Fauth 1998 and references therein for examples on competitive interactions and local adaptation in amphibians).…”