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
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
Invasive species: The second biggest threat to biodiversity today.
(Vitousek et al. 1997)
Photo: Charles Webber, California Academy of Sciences
Ecosystem Effects
• Soil chemistry/nutrient cycling
Ecosystem Effects
• Soil chemistry/nutrient cycling
• Fire frequency & intensity
Ecosystem Effects
• Soil chemistry/nutrient cycling
• Fire frequency & intensity
• Hydrology & sedimentation
Ecosystem Effects
• Soil chemistry/nutrient cycling
• Fire frequency & intensity
• Hydrology & sedimentation
• Erosion
Effects on Biota
• Displacement of native species– E.g., ice plant and native shrubs
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
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
What makes a species invasive?
• “The ability to increase when rare.” (Crawley 1997)
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?
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
Invasible Ecosystems
• Disturbed areas
• Ports of entry
• Community composition/diversity
Pathogens’ Role
• Natural Enemies Hypothesis: plants leave enemies behind; are better competitors
Pathogens’ Role
• Natural Enemies Hypothesis: plants leave enemies behind; are better competitors
• Biotic Resistance Hypothesis: native pathogens prevent new plants from establishing
The Enemy Release Hypothesis
Problems with Empirical Model
• Beneficial associations:– Natives– Exotics
• Biotic resistance
Gilbert & Parker, UCSC
Photos: I.M. Parker, UCSC
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)
Introduced plants can bring their pathogens
• Chestnut Blight
• Dutch Elm Disease
• Phytophthora infestans
