Pathogens and Plant Invasion Ecology

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Pathogens and Plant Invasion Ecology
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What do invasive plants have to do with us?
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What do invasive plants have to do with us?

• Framework for study of pathogen invasions

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What do invasive plants have to do with us?

• Framework for study of pathogen invasions
• Pathogens role in plant invasions

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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

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• Invasive species The second biggest
• threat to biodiversity today.
• (Vitousek et al. 1997)

Photo Charles Webber, California Academy of
Sciences
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Ecosystem Effects

• Soil chemistry/nutrient cycling

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Ecosystem Effects

• Soil chemistry/nutrient cycling
• Fire frequency intensity

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Ecosystem Effects

• Soil chemistry/nutrient cycling
• Fire frequency intensity
• Hydrology sedimentation

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Ecosystem Effects

• Soil chemistry/nutrient cycling
• Fire frequency intensity
• Hydrology sedimentation
• Erosion

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Effects on Biota

• Displacement of native species
• E.g., ice plant and native shrubs

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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

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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

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What makes a species invasive?

• The ability to increase when rare. (Crawley
  1997)

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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?

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A cautionary tale Bakers traits and USDA GMO
deregulation

• Keeler (1989) suggests using Bakers 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

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Invasible Ecosystems

• Disturbed areas
• Ports of entry
• Community composition/diversity

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Pathogens Role

• Natural Enemies Hypothesis plants leave enemies
  behind are better competitors

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Pathogens Role

• Natural Enemies Hypothesis plants leave enemies
  behind are better competitors
• Biotic Resistance Hypothesis native pathogens
  prevent new plants from establishing

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The Enemy Release Hypothesis
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Problems with Empirical Model

• Beneficial associations
• Natives
• Exotics
• Biotic resistance

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Gilbert Parker, UCSC
Photos I.M. Parker, UCSC
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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)

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Introduced plants can bring their pathogens

• Chestnut Blight
• Dutch Elm Disease
• Phytophthora infestans