3)What makes a species invasive? d) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies

3)What makes a species invasive? d) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species are immigrants to a new area Aliens often arrive as seeds

3)What makes a species invasive? d) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species are immigrants to a new area Aliens often arrive as seeds In other words, they arrive without the grazers, insect pests, diseases, parasites, etc. of their native range – their “enemies”

3)What makes a species invasive? d) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species immigrate without enemies Hence, alien species “escapes” from their enemies and are no longer affected by biotic constraints Thus, alien growth and success is much greater in new range

3)What makes a species invasive? d) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species immigrate without enemies Aliens lack biotic constraints However, alien success will depend on potential enemies in new range: Are potential enemies generalists or specialists?

3)What makes a species invasive? d) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species immigrate without enemies Aliens lack biotic constraints However, alien success will depend on potential enemies in new range: Are potential enemies generalists or specialists? Are population sizes of potential enemies large or small?

3)What makes a species invasive? d) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species immigrate without enemies Aliens lack biotic constraints However, alien success will depend on potential enemies in new range: Are potential enemies generalists or specialists? Are population sizes of potential enemies large or small? Do potential enemies feed on foliage or seeds?

3)What makes a species invasive? d) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species immigrate without enemies Aliens lack biotic constraints However, alien success will depend on potential enemies in new range: Are potential enemies generalists or specialists? Are population sizes of potential enemies large or small? Do potential enemies feed on foliage or seeds? Are there similar hosts for potential enemies in new area?

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mack et al. (2000) Chrysanthemoides native to South Africa but invasive in Australia Acacia native to Australia but invasive in South Africa For both species, few pests in invaded area

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mack et al. (2000) Chrysanthemoides native to South Africa but invasive in Australia Acacia native to Australia but invasive in South Africa For both species, few pests in invaded area Compare performance of each species in native area vs. invaded InvadedNative

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mack et al. (2000) Chrysanthemoides native to South Africa but invasive in Australia Acacia native to Australia but invasive in South Africa For both species, few pests in invaded area When Chrysanthemoides is invader, does much better (sometimes much much much better!!) InvadedNative > > > > > > >

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mack et al. (2000) Chrysanthemoides native to South Africa but invasive in Australia Acacia native to Australia but invasive in South Africa For both species, few pests in invaded area When Acacia is invader, does much much much better InvadedNative < < <

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mack et al. (2000) Chrysanthemoides native to South Africa but invasive in Australia Acacia native to Australia but invasive in South Africa For both species, few pests in invaded area When species is invader, does much (much) better InvadedNative > > > > > > > InvadedNative < < <

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mack et al. (2000) Flip side can also occur: New pest in an area devastates natives Example is American chestnut (Castanea dentata) & chestnut blight (invasive fungus Endothia parasitica)

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mack et al. (2000) Flip side can also occur: New pest in an area Example is American chestnut (Castanea dentata) & chestnut blight (invasive fungus Endothia parasitica) Dramatic ↓ in chestnut after arrival of blight in 1934

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mack et al. (2000) Flip side can also occur: New pest in an area Example is American chestnut (Castanea dentata) & chestnut blight (invasive fungus Endothia parasitica) Dramatic ↓ in chestnut after arrival of blight in 1934 Other trees had ↑

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mack et al. (2000) Flip side can also occur: New pest in an area Example is American chestnut (Castanea dentata) & chestnut blight (invasive fungus Endothia parasitica) Dramatic ↓ in chestnut after arrival of blight in 1934 Other trees had ↑, or small changes

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Wolfe (2002) American Naturalist 160: Silene latifolia native to Europe but invasive in North America Surveyed populations in both Europe and North America for generalist and specialist enemies

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Wolfe (2002) American Naturalist 160: Silene latifolia native to Europe but invasive in North America More populations experience damage in native range (Europe) then invaded range (North America)

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Wolfe (2002) American Naturalist 160: Silene latifolia native to Europe but invasive in North America More populations experience damage in native range True for both generalists

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Wolfe (2002) American Naturalist 160: Silene latifolia native to Europe but invasive in North America More populations experience damage in native range True for both generalists and specialist

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Wolfe (2002) American Naturalist 160: Silene latifolia native to Europe but invasive in North America More populations experience damage in native range More individuals within a population are damaged in native range (Europe) then invaded range (North America)

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Wolfe (2002) American Naturalist 160: Silene latifolia native to Europe but invasive in North America More populations experience damage in native range More individuals within a population are damaged in native range True for both generalists

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Wolfe (2002) American Naturalist 160: Silene latifolia native to Europe but invasive in North America More populations experience damage in native range More individuals within a population are damaged in native range True for both generalists and specialists

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Klironomos (2002) Nature 417: Enemies not necessarily insects Tested if soil organisms can affect growth Logic: In native soils, pathogens accumulate rapidly, ultimately reducing growth of natives. For invasives in new soil, pathogens accumulate much slower, and hence do not adversely affect growth of invasives.

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Klironomos (2002) Nature 417: Logic: Pathogens accumulate in soils for natives but not invasives Series of experiments that used 5 invasive & 5 rare species from Canadian meadows From each species, isolated 2 fractions of soil micro-organisms Pathogen / saprobe filtrate = Detrimental AMF (mycorrhizal) spores = Beneficial Grew plants with microbes from their own soil vs. microbes from other species’ soil

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Klironomos (2002) Nature 417: Logic: Pathogens accumulate in soils for natives but not invasives Used 5 invasive & 5 rare species from Canadian meadows From each species, isolated 2 fractions of soil micro-organisms Pathogen / saprobe filtrate = Detrimental AMF (mycorrhizal) spores = Beneficial Grew plants with microbes from their own soil vs. microbes from other species’ soil Predictions: If use sterile soil, should see no affect on growth for both invasives & rare species If use AMF, should see beneficial growth for both If use pathogens, negative effects only for rare species

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Klironomos (2002) Nature 417: Logic: Pathogens accumulate in soils for natives but not invasives Predictions: If use sterile soil, no affect for both invasives & rare species

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Klironomos (2002) Nature 417: Logic: Pathogens accumulate in soils for natives but not invasives Predictions: If use sterile soil, no affect for both invasives & rare species If use AMF, beneficial for both

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Klironomos (2002) Nature 417: Logic: Pathogens accumulate in soils for natives but not invasives Predictions: If use sterile soil, no affect for both invasives & rare species If use AMF, beneficial for both If use pathogens, negative only for rare

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Klironomos (2002) Nature 417: Logic: Pathogens accumulate in soils for natives but not invasives Predictions: If use sterile soil, no affect for both invasives & rare species If use AMF, beneficial for both If use pathogens, negative only for rare Thus, invasives accumulate slower rate because they escape harmful pathogens when invading foreign territory

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mitchell & Power (2003) Nature 421: Additional support that pathogens are important Examined 473 plant species naturalized to North America from Europe Examined occurrence of viruses and various fungal pathogens (rust, smut, powdery mildew) in native and naturalized ranges

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mitchell & Power (2003) Nature 421: Additional support that pathogens are important Compare pathogens on 473 species in native vs. naturalized range Predictions: Fewer pathogens in naturalized range Because viruses are more easily transmitted and have broader host ranges then fungi, expected that ↓ for viruses would be smaller than that for fungi The bigger the escape from pathogens, the more noxious And vice versa: accumulate more pathogens, less noxious

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mitchell & Power (2003) Nature 421: Additional support that pathogens are important Compare pathogens on 473 species in native vs. naturalized range Predictions: Fewer pathogens in naturalized range

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mitchell & Power (2003) Nature 421: Additional support that pathogens are important Compare pathogens on 473 species in native vs. naturalized range Predictions: Fewer pathogens in naturalized range Smaller ↓ for viruses (24%) than for fungi (84%)

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mitchell & Power (2003) Nature 421: Additional support that pathogens are important Compare pathogens on 473 species in native vs. naturalized range Predictions: Fewer pathogens in naturalized range Smaller ↓ for viruses Escape related to noxiousness (a)As ↑ escape, ↑ noxiousness

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Evidence: from Mitchell & Power (2003) Nature 421: Additional support that pathogens are important Compare pathogens on 473 species in native vs. naturalized range Predictions: Fewer pathogens in naturalized range Smaller ↓ for viruses Escape related to noxiousness (a)As ↑ escape, ↑ noxiousness (b)As ↑ pathogens, ↓ noxiousness

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Summary: Escape from biotic constraints hypothesis Intuitively clear Strong evidence in a number of cases Underlying concept for biological control

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Summary: Escape from biotic constraints hypothesis Intuitively clear Strong evidence in a number of cases Underlying concept for biological control But: Assumes: Native specialist enemies are left behind Host switching does not occur Generalist in new range avoid invader

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Summary: Escape from biotic constraints hypothesis Intuitively clear Strong evidence in a number of cases Underlying concept for biological control But: Assumes: Native specialist enemies are left behind Host switching does not occur Generalist in new range avoid invader Need to demonstrate that native enemies limit plant population in native range

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Summary: Escape from biotic constraints hypothesis Intuitively clear Strong evidence in a number of cases Underlying concept for biological control But: Assumes: Native specialist enemies are left behind Host switching does not occur Generalist in new range avoid invader Need to demonstrate that native enemies limit plant population in native range Is the release through ↓ invader mortality OR through adverse affects on natives causing ↓ competition?

3)What makes a species invasive? d) Escape from biotic constraints hypothesis Summary: Escape from biotic constraints hypothesis Intuitively clear Strong evidence in a number of cases Underlying concept for biological control But: Assumes: Native specialist enemies are left behind Host switching does not occur Generalist in new range avoid invader Need to demonstrate that native enemies limit plant population in native range Is the release through ↓ invader mortality OR through adverse affects on natives causing ↓ competition? Long-lived species and species with long-lived seedbanks probably little affected by enemies