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1 Supplemental Material: Annu. Rev. Entomol : doi: /annurev-ento Evolution of Plant Defenses in Nonindigenous Environments Orians and Ward Trade-offs and Resource Availability Supplemental Material As with defense evolution and expression, resource availability (acquisition) may affect the nature of trade-offs (17). While it is assumed that there should be a trade-off between mechanical and chemical defense (15, 17), Ward & Young (18) found a positive correlation and not a trade-off between spines (mechanical) and tannin (chemical) defenses in Acacia drepanolobium (Fabaceae) in Kenya. If plants differ little in resources acquired and vary considerably in resources allocated to defense, then a trade-off (negative correlation) between defense and growth or different types of defense may occur (Figure 1s a). Contrastingly, if plants vary considerably in the resources acquired but differ little in the amounts allocated to defense (as might occur if there is a certain optimum defense that is required), then a positive correlation may occur (Figure 1s b). One might expect that plants in high resource conditions may invest in several forms of defense. (a) (b) Figure 1s Trade-offs between different defense traits. (a) Expected pattern: Trade-off between tannin concentration and thorn production (indicated in the black bar). The same pattern would be expected if there was a trade-off between growth rate and defense production. (b) Observed pattern: Positive correlation between tannin concentration and thorn production (indicated in the black bar). Clearly, if there were large differences in resource acquisition and in resource allocation, no correlation would result. (modified by 18 from 17)

2 Empty Niche Disturbances that are more frequent or intense than the natural pattern constitute the most obvious case where an empty niche exists, and several studies have demonstrated that the abundance of exotic plant species is often facilitated by these disturbances (4, 16). For example, grazing by introduced sika deer Cervus nippon in Ireland removes competitors and creates safe sites for Rhododendron ponticum (Ericaceae), an exotic perennial that is normally a weak competitor but not palatable to deer (4). Exotic species can also create a new disturbance regime that is detrimental to native species. Cheatgrass Bromus tectorum (Poaceae), for example, increases the frequency and intensity of fires, which facilitates its own survival and expansion (5). Because many of the most successful exotics occupy disturbed sites (1), it implies that exotic species often move into empty niches. Examples in which exotic species appear to have greater access to resources include species such as Centaurea (Asteraceae) and Tamarix (Tamaricaceae), that have unusually deep roots that allow them to exploit, and ultimately change, the hydrological regime (8, 11, 14). In addition, species with life forms that are depauperate of that life form in the non-indigenous range could be considered as occupying an empty niche.

3 Biogeography of Exotics Oceanic islands are the most susceptible to invasion (9, 12). Of the flora of oceanic islands, 43% are exotics (9). We tested for differences between islands and continents in the percentage of exotic species (relative to total species richness), using existing data (Table 2.1 in 11). We found a highly significant difference in the percentage of exotic species (t = 2.39, d.f. = 18, p = 0.014, one-tailed test) on islands (mean = %) as compared to continents (mean = %). Although lower, there is variation among and within continents. Continent-wise, climate-matching appears to have a strong effect. For example, Europe is more likely to get invaders from North America and vice versa, while Australia and Southern Africa share many invaders (Fig. 2.4 in 11). Overall, the continents of Eurasia and Africa have fewer exotics (<10%) than the Americas (>13%)(9). There is also extensive variation within and among regions/biomes in the number of exotics. Exotic species are common in riparian habitats (where disturbance frequency is high), temperate forests and Mediterranean shrublands (1, 9). In contrast, exotic species are uncommon in deserts, wet tropics, salt marshes, sandy and serpentine soils, and montane habitats (1, 11). Whether savannas have fewer exotic species is unclear some reviews have suggested that savannas have remarkably few exotics (e.g. 9), while others have not (10). Myers & Bazely (11) indicate that grasslands have far more exotics (ca. 240) than any other habitat. Elton postulated that species-rich habitats would be more resistant to exotic species ( diversity-invasibility hypothesis ), but in an apparent contradiction, recent analyses indicate that exotic species richness is positively correlated with native species richness (and resource richness) (e.g. 1, 7, 9). Shea & Chesson (13) argue that this positive correction generally obscures a negative correlation at the local scale. Species-rich environments are also expected to have a high abundance of generalist herbivores (2), so release from herbivores may be especially important in these environments. In contrast, if an exotic plant enters a species-poor community, herbivore pressures should be low, unless there is an abundance of closely-related taxa (6).

4 TABLE 1s Select ecological and evolutionary hypotheses that have been tested using exotic species (see also 3, 12) Concept Hypotheses Ecological Enemy Release In the absence of top-down control, invasive species become more competitive. Escape from specialists is more important than escape from generalists in determining population growth (and vice versa). Time since introduction is more important than geographic range in determining the number of herbivore species on plants. Recognition mismatches lead to enemy escape. Biotic Resistance Species-rich communities have more competitors and are more resistant to new species. Local predators and pathogens inhibit invasion by exotics. Failure by exotic species to detect enemies (recognition mismatch) prevents induced resistance and limits spread of exotics. Novel Weapons New weapons (e.g., secondary chemicals) increase the probability of success in a new habitat. [While the emphasis has been on belowground processes (allelopathy) it applies to above ground interactions as well.] Mismatch between plant defense and insect detoxification systems leads to population growth. Biogeography of Invasion Islands are more susceptible to invasion than mainlands. Disturbed sites are more susceptible than undisturbed sites (includes empty niches). Evolutionary Optimal Defense Plant defense allocation depends on the risk of attack. Induced defenses will be favored when the risk of attack is low and the cost of defense is high. Evolution of Increased Competitive Ability Enemy release causes plants to invest less in defense, more in growth and results in greater competitive ability. Genetic Constraints Low genetic variation constrains adaptation and population growth of introduced species. Evolution of Defense Introduction to a new habitat results in rapid evolutionary changes in defense expression. Resource availability alters the strength of evolutionary responses Geographic Mosaics New associations vary among populations and result in specific genotypic changes that can cause phenotypic matching to occur.

5 ~300 ybp ~150 ybp ~150 ybp 2004 Figure 2s Dispersal of populations of parsnip Pastinaca sativa and its specialist herbivore, the webworm Depressaria pastinacella from Europe to North America and New Zealand. The parasitoid Copidosoma sosares is most abundant in Europe but is now found in parts of North America. ybp = years before present. Y-axis legend shows mean population percent departures from overall mean furanocoumarin concentrations among continents. imp = imperatorin; ber = bergapton; iso = isopimpinellin; xan = xanothoxin; sph = sphondin. (Artwork courtesy of Art Zangerl)

6 Literature Cited 1. Alpert P, Bone E, Holzapfel C Invasiveness, invasibility and the role of environmental stress in the spread of non-native plants. Persp. Plant Ecol. Evol. Syst. 3: Blumenthal DM Interactions between resource availability and enemy release in plant invasion. Ecol. Lett. 9: Callaway RM, Maron JL What have exotic plant invasions taught us over the past 20 years? Trends Ecol. Evol. 21: Cross JR The establishment of Rhododendron ponticum in the Killarney oakwoods, S.W. Ireland. J. Ecol. 69: D Antonio C, Vitousek PM Biologial invasions by exotic grasses, the grass/fire cycle, and global change. Annu. Rev. Ecol. Syst. 23: Dalin P, Björkman C Native insects colonizing introduced tree species patterns and potential risks. In Invasive Forest Insects, Introduced Forest Trees, and Altered Ecosystems, ed. TD Paine, pp , Netherlands: Springer 7. Davis MA, Grime JP, Thompson K Fluctuating resources in plant communities: a general theory of invasibility. J. Ecol. 88: Hierro J, Maron JL, Callaway RM A biogeographical approach to plant invasion biology: The importance of studying exotics in their introduced and native range. J. Ecol. 93: Lonsdale WM Global patterns of plant invasions and the concept of invasibility Ecology 80: Macdonald IAW, Kruger FJ, Ferrar AA, ed The Ecology and Management of Biological Invasions in Southern Africa. Cape Town: Oxford University Press. 324 pp. 11. Myers JH, Bazely DR Ecology and Control of Introduced Plants. Cambridge University Press, Cambridge. 313 pp. 12. Sax DF, Stachowicz JJ, Gaines SD, ed Species Invasions: Insights into Ecology, Evolution, and Biogeography. Sunderland, Massachusetts: Sinauer. 495 pp. 13. Shea K, Chesson P Community ecology theory as a framework for biological invasions. Trends Ecol. Evol. 17: Sher AA, Hyatt LA The disturbed resource-flux invasion matrix: a new framework for patterns of plant invasion. Biol. Invas. 1: Steward JL, Keeler KH Are there tradeoffs among antiherbivore defences in Ipomoea (Convolvulaceae)? Oikos 53: Tierney T, Cushman JH Temporal changes in native and exotic vegetation and soil characteristics following disturbances by feral pigs in a California grassland. Biol. Invas. 8: Van Noordwijk AJ, de Jong G Acquisition and allocation of resources: Their influence on variation in life history tactics. Am. Nat. 128: Ward D, Young TP Effects of large mammalian herbivores and ant symbionts on condensed tannins of Acacia drepanolobium in Kenya. J. Chem. Ecol. 28: