Download 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
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