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Enemy Release Hypothesis

Enemy Release Hypothesis. Invasive Species Seminar 2 September 2004. Overview. Definition of terms Enemy Release Hypothesis (ERH): Evolution of Increased Competitive Ability Hypothesis (EICA) Distinctions made in Colautti et al review Differences in biogeographic versus community effects

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Enemy Release Hypothesis

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  1. Enemy Release Hypothesis Invasive Species Seminar 2 September 2004

  2. Overview • Definition of terms • Enemy Release Hypothesis (ERH): • Evolution of Increased Competitive Ability Hypothesis (EICA) • Distinctions made in Colautti et al review • Differences in biogeographic versus community effects • Cautions regarding interpretation of results

  3. ERH • Enemy release hypothesis (ERH): • Invasive species encounter fewer natural enemies in areas they invade compared to their native areas (they leave behind their enemies)

  4. ERH • Enemy release hypothesis (ERH): • Invasive species encounter fewer natural enemies in areas they invade compared to their native areas (they leave behind their enemies) • Two mechanisms of release: • Regulatory – invader escapes damage (not well defended in home range) • Compensatory – invader reallocates resources from defense to growth (invader well defended in home range)

  5. ERH • Enemy release hypothesis (ERH): • Invasive species encounter fewer natural enemies in areas they invade compared to their native areas (they leave behind their enemies) • Two mechanisms of release: • Regulatory – invader escapes damage (not well defended in home range) • Compensatory – invader reallocates resources from defense to growth (invader well defended in home range)

  6. Compensatory Release • Ecological time - Plasticity • The invader reallocates resources from defense to growth • Moderate time lag

  7. Compensatory Release • Evolutionary time - Evolution of increased competitive ability hypothesis (EICA) (Blossey and Nötzold 1995) • Compared seeds of purple loosestrife (Lythrum salicaria) from native and invading populations, grown together in one location • Plants from invading population were taller and had greater final biomass

  8. Compensatory Release • Evolutionary time - Evolution of increased competitive ability hypothesis (EICA) (Rogers and Siemann 2003, 2004) • Herbivore preferred invasive ecotype over native ecotype of Chinese tallow tree (Sapium sebiferum)

  9. Compensatory Release • Evolutionary time - Evolution of increased competitive ability hypothesis (EICA) (Rogers and Siemann 2003, 2004) • Herbivore preferred invasive ecotype over native ecotype of Chinese tallow tree (Sapium sebiferum) • Invasive ecotype was able to recover from both foliar and root damage, while native ecotype was negatively affected (did not compensate even with fertilizer addition)

  10. Compensatory Release • Evolutionary time - Evolution of increased competitive ability hypothesis (EICA) (Rogers and Siemann 2003, 2004) • Herbivore preferred invasive ecotype over native ecotype of Chinese tallow tree (Sapium sebiferum) • Invasive ecotype was able to recover from both foliar and root damage, while native ecotype was negatively affected (did not compensate even with fertilizer addition) • Recent work of Blossey (TREE, soon)

  11. Colautti et al Review • Difference of scale • Biogeographic level – more support for ERH, but must interpret with caution • Counts or effect? • Intraspecific • Release or exchange? • Community level – less support for ERH

  12. Colautti et al Review • Other factors • Propagule bias – fewer compared to what? • Invasion bottlenecks – invasions are a subsample • Additional hypotheses

  13. Colautti et al Review • Other factors • Propagule bias – fewer compared to what? • Invasion bottlenecks – invasions are a subsample • Additional hypotheses • Increased susceptibility • Enemy inversion • Enemy of my enemies

  14. Discussion • What’s really going on? Can invasiveness be described by a single hypothesis, or does it differ case by case?

  15. Discussion • What’s really going on? Can invasiveness be described by a single hypothesis, or does it differ case by case? • Now what? Should we do more experiments to gather evidence on additional cases, or should we do different experiments to test invasiveness more effectively? If so, how?

  16. Discussion • What’s really going on? Can invasiveness be described by a single hypothesis, or does it differ case by case? • Now what? Should we do more experiments to gather evidence on additional cases, or should we do different experiments to test invasiveness more effectively? If so, how? • Can we anticipate different cases? What if a known invasive arrives at a new location? Will it behave the same way as before? What about other factors that are changing e.g. climate, land use, etc.

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