Pathogens and Plant Invasion Ecology

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