Wednesday, August 5, 2009
Exhibit Hall NE & SE, Albuquerque Convention Center
Background/Question/Methods 1.Evolution through natural selection predicts that organisms optimize fitness through the allocation of limited resources to traits. Variation in trait fitness among populations, particularly between native and introduced ranges, can lead to divergent trait expression of populations with potentially large effects on dominance hierarchies within communities.
2.Optimal defense theory predicts that in novel environments with low herbivory, plants allocate
resources away from costly herbivore resistance towards growth. We expect that inducible defenses
are less costly to retain than constitutive defenses, so biogeographic patterns in the native range may better predict trait allocation in introduced ranges than evolutionary changes after establishment.
3.Little is known about population and/or genetic variation in inducible defenses. Comparison of
traits between native and introduced populations and identification of selective pressures leading to specific defenses will help define trade-offs/thresholds for defense syndromes. When trait change co-occurs with changes in competitive dominance, comparisons between native and invasive populations inform community ecology by incorporating evolutionary history.
4.We conducted a greenhouse pot experiment to examine variation in an indirect, inducible defense, extrafloral nectar (EFN) production, among native and invasive genotypes of Chinese tallow tree, Triadica sebifera, after herbivory from a generalist scale insect, a generalist caterpillar, both, or neither.
Results/Conclusions Relative investment rates of EFN production showed a biogeographic pattern of herbivore defense, indicative of little selection pressure against indirect, inducible defense in the introduced range. Absolute EFN production was greatest in invasive genotypes from Texas populations, which may influence tallow tree's dominance within invaded communities now and in the future.
