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Pathogens and Plant Invasion Ecology

Pathogens and Plant Invasion Ecology. What do invasive plants have to do with us?. What do invasive plants have to do with us?. Framework for study of pathogen invasions. What do invasive plants have to do with us?. Framework for study of pathogen invasions Pathogens’ role in plant invasions.

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Pathogens and Plant Invasion Ecology

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  1. Pathogens and Plant Invasion Ecology

  2. What do invasive plants have to do with us?

  3. What do invasive plants have to do with us? • Framework for study of pathogen invasions

  4. What do invasive plants have to do with us? • Framework for study of pathogen invasions • Pathogens’ role in plant invasions

  5. What do invasive plants have to do with us? • Framework for study of pathogen invasions • Pathogens’ role in plant invasions • Mechanism for introduction of pathogens

  6. Invasive species: The second biggest threat to biodiversity today. (Vitousek et al. 1997) Photo: Charles Webber, California Academy of Sciences

  7. Ecosystem Effects • Soil chemistry/nutrient cycling

  8. Ecosystem Effects • Soil chemistry/nutrient cycling • Fire frequency & intensity

  9. Ecosystem Effects • Soil chemistry/nutrient cycling • Fire frequency & intensity • Hydrology & sedimentation

  10. Ecosystem Effects • Soil chemistry/nutrient cycling • Fire frequency & intensity • Hydrology & sedimentation • Erosion

  11. Effects on Biota • Displacement of native species • E.g., ice plant and native shrubs

  12. Effects on Biota • Displacement of native species • E.g., ice plant and native shrubs • Hybridization with native species • E.g., Spartine alterniflora and S. foliosa

  13. Effects on Biota • Displacement of native species • E.g., ice plant and native shrubs • Hybridization with native species • E.g., Spartine alterniflora and S. foliosa • Promote (or introduce) non-native animals & microbes • E.g., Myrica faya in Hawaii

  14. What makes a species invasive? • “The ability to increase when rare.” (Crawley 1997)

  15. What makes a species invasive? • “The ability to increase when rare.” (Crawley 1997) • …Well, duh. So what makes a species likely to be a problem?

  16. A cautionary tale: Baker’s traits and USDA GMO deregulation • Keeler (1989) suggests using Baker’s traits as predictor of weed risk in GM crops • Williamson (1994) proves this method has little/no predictive value • As of 1997, APHIS continues to accept list as only evidence to discount ecological risk in petitions to deregulate crops

  17. Invasible Ecosystems • Disturbed areas • Ports of entry • Community composition/diversity

  18. Pathogens’ Role • Natural Enemies Hypothesis: plants leave enemies behind; are better competitors

  19. Pathogens’ Role • Natural Enemies Hypothesis: plants leave enemies behind; are better competitors • Biotic Resistance Hypothesis: native pathogens prevent new plants from establishing

  20. The Enemy Release Hypothesis

  21. Problems with Empirical Model • Beneficial associations: • Natives • Exotics • Biotic resistance

  22. Gilbert & Parker, UCSC Photos: I.M. Parker, UCSC

  23. California Coastal Clovers • 7 exotic, 9 native • Beneficial association with fungal endophytes in 2 most invasive • Leaf spot (Lesptosphaerulina, Pseudopeziza, Phoma) most severe on exotics (BR) • Leaf necrosis (Stemphylium)slightly more severe on natives (NE) • Damping-off most severe in natives (NE)

  24. Introduced plants can bring their pathogens • Chestnut Blight • Dutch Elm Disease • Phytophthora infestans

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