Readings, enemy release and biodiversity hypotheses 1.Enemy release hypothesis: Keane, r. Crawley, M Exotic plant invasions and the enemy release hypothesis. TREE 17: Biodiversity hypothesis: Shea K, Chesson P Community ecology theory as a framework for biological invasions. TREE 17:

3)What makes a species invasive? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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? g) 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

3)What makes a species invasive? h) Biodiversity hypothesis Basic concepts: High biodiversity confers high community stability

3)What makes a species invasive? h) Biodiversity hypothesis Basic concepts: High biodiversity → high community stability Stable communities are not easily invaded

3)What makes a species invasive? h) Biodiversity hypothesis Basic concepts: High biodiversity → high community stability Stable communities not invaded Shares features with vacant niche hypothesis NOTE: Biodiversity hypothesis does not require vacant niche

3)What makes a species invasive? h) Biodiversity hypothesis Basic concepts: High biodiversity → high community stability Stable communities not invaded Shares features with vacant niche hypothesis Biodiversity hypothesis does not require vacant niche But uses niche concepts that: Different species have different niches

3)What makes a species invasive? h) Biodiversity hypothesis Basic concepts: High biodiversity → high community stability Stable communities not invaded Shares features with vacant niche hypothesis Biodiversity hypothesis does not require vacant niche But uses niche concepts that: Different species have different niches As ↑ number species, ↑ amount of potential niche space that is filled

3)What makes a species invasive? h) Biodiversity hypothesis Basic concepts: High biodiversity → high community stability Stable communities not invaded Shares features with vacant niche hypothesis Biodiversity hypothesis does not require vacant niche But uses niche concepts that: Different species have different niches As ↑ number species, ↑ filling of niche space Thus highly diverse communities more difficult to invade

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space Thus, as ↑ number species

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space As ↑ number species, availability of resources, on average,

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space As ↑ number species, availability of resources, on average, ↓

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Defined mathematically in A

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Each species has some minimum average resource need = R*

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Each species has some minimum average resource need = R* Corresponds with some minimum species diversity = N*

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Each species has some minimum average resource need = R* Corresponds with some minimum species diversity = N* Above N*, that species cannot invade

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Each species has some minimum average resource need = R* Corresponds with some minimum species diversity = N* Above N*, that species cannot invade

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Each species has some minimum average resource need = R* Corresponds with some minimum species diversity = N* Above N*, that species cannot invade because average community resource level is less then minimum for that species (R*)

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Each species has some minimum average resource need = R* Corresponds with some minimum species diversity = N* Above N*, species cannot invade At or below N*, can invade

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Each species has R* At or below N*, species can invade

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Each species has R* At or below N*, species can invade If do for all species in community, can determine relative invasibility as diversity changes

3)What makes a species invasive? h) Biodiversity hypothesis Theoretical evidence: From Tilman (1999) ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Each species has R* At or below N*, species can invade If do for all species in community, invasibility ↓ as diversity ↑

3)What makes a species invasive? h) Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature 417: Had 147 plots originally seeded with up to 24 natives Observed 13 aliens invaded naturally through time

3)What makes a species invasive? h) Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature 417: Had 147 plots originally seeded with up to 24 natives Observed 13 aliens invaded naturally through time As ↑ native diversity: (a) ↓ invader cover

3)What makes a species invasive? h) Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature 417: Had 147 plots originally seeded with up to 24 natives Observed 13 aliens invaded naturally through time As ↑ native diversity: (a)↓ invader cover (b)↓ invader number

3)What makes a species invasive? h) Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature 417: Had 147 plots originally seeded with up to 24 natives Observed 13 aliens invaded naturally through time As ↑ native diversity: (a)↓ invader cover (b)↓ invader number (c)↓ invader max size

3)What makes a species invasive? h) Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature 417: Had 147 plots originally seeded with up to 24 natives Observed 13 aliens invaded naturally through time As ↑ native diversity: (a)↓ invader cover (b)↓ invader number (c)↓ invader max size (d)NS median size

3)What makes a species invasive? h) Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature 417: Conclude: Invaders do more poorly with ↑ native diversity

3)What makes a species invasive? h) Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature 417: Invaders do more poorly with ↑ native diversity Why? As ↑ native diversity: ↑ number of neighbors

3)What makes a species invasive? h) Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature 417: Invaders do more poorly with ↑ native diversity Why? As ↑ native diversity: ↑ number of neighbors ↑ number of neighboring species

3)What makes a species invasive? h) Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature 417: Invaders do more poorly with ↑ native diversity Why? As ↑ native diversity: ↑ number of neighbors ↑ number of neighboring species ↑ crowding

3)What makes a species invasive? h) Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature 417: Invaders do more poorly with ↑ native diversity Why? With high native diversity, have dense, species rich, crowded neighborhoods

3)What makes a species invasive? h) Biodiversity hypothesis Contrary evidence: Allcock and Hik 2003 Grazed woodland in Australia Habitats included alluvia (rich) grasslands (intermediate) and woodlands (resource poor) Negative relationship between exotic and native diversity Natives –ve relationship to high biomass; exotics +ve relationship.

3)What makes a species invasive? h) Biodiversity hypothesis Contrary evidence: From Levine (2000) Examined riparian communities along South Fork Eel River, CA Dominated by native tussock sedge Carex nudata Each tussock is discrete island (neighborhood) colonized by up to 20 perennial plants & mosses

3)What makes a species invasive? h) Biodiversity hypothesis Contrary evidence: From Levine (2000) Surveyed similarly sized tussocks over 7 km stretch of river Recorded incidence of 3 invaders (Agrostis, Plantago, Cirsium)

3)What makes a species invasive? h) Biodiversity hypothesis Contrary evidence: From Levine (2000) Surveyed similarly sized tussocks 3 invaders (Agrostis, Plantago, Cirsium) All invaders had ↑ occurrence with ↑ diversity, contrary to biodiversity hypothesis

3)What makes a species invasive? h) Biodiversity hypothesis Contrary evidence: From Levine (2000) Surveyed similarly sized tussocks 3 invaders (Agrostis, Plantago, Cirsium) All invaders had ↑ occurrence with ↑ diversity, contrary to biodiversity hypothesis Why? To support high diversity, must have lots of resources

3)What makes a species invasive? h) Biodiversity hypothesis Contrary evidence: From Levine (2000) Surveyed similarly sized tussocks 3 invaders (Agrostis, Plantago, Cirsium) All invaders had ↑ occurrence with ↑ diversity, contrary to biodiversity hypothesis Why? To support high diversity, must have lots of resources Thus, diverse sites are “best” sites

3)What makes a species invasive? h) Biodiversity hypothesis Contrary evidence: From Levine (2000) Surveyed similarly sized tussocks 3 invaders (Agrostis, Plantago, Cirsium) All invaders had ↑ occurrence with ↑ diversity, contrary to biodiversity hypothesis Why? To support high diversity, must have lots of resources Thus, diverse sites are “best” sites Best sites most likely to be invaded

3)What makes a species invasive? h) Biodiversity hypothesis Contrary evidence: From Lonsdale (1999) Ecology 80: Global survey – compiled data from 184 sites around the world Separated into “Island” vs. “Mainland” Within each group, broke down further into nature “reserves” and “non-reserves”

3)What makes a species invasive? h) Biodiversity hypothesis Contrary evidence: From Lonsdale (1999) Ecology 80: Global survey – compiled data from 184 sites around the world Separated into “Island” vs. “Mainland” Within each group, broke down further into nature “reserves” and “non-reserves” As expected, for given diversity, number invaders: Islands > Mainlands

3)What makes a species invasive? h) Biodiversity hypothesis Contrary evidence: From Lonsdale (1999) Ecology 80: Global survey – compiled data from 184 sites around the world Separated into “Island” vs. “Mainland” Within each group, broke down further into nature “reserves” and “non-reserves” As expected, for given diversity, number invaders: Islands > Mainlands Non-reserves > Reserves

3)What makes a species invasive? h) Biodiversity hypothesis Contrary evidence: From Lonsdale (1999) Ecology 80: Global survey – compiled data from 184 sites around the world Separated into “Island” vs. “Mainland” Within each group, broke down further into nature “reserves” and “non-reserves” As expected, for given diversity, number invaders: Islands > Mainlands Non-reserves > Reserves But, for all sites, more invaders with greater diversity

Resolving the conflict: Shea and Chesson 2002 Within ecosystems, more species = less invasable Among ecosystems, more diverse systems (more resources) = more vulnerable

Resolving the conflict: Shea and Chesson 2002 Within ecosystems, more species = less invasable Among ecosystems, more diverse systems (more resources) = more vulnerable Within ‘clusters’ extrinsic factors (e.g. climate) are similar Factors differ across ‘clusters’.

3)What makes a species invasive? h) Biodiversity hypothesis Summary: Logical arguments to support the hypothesis

3)What makes a species invasive? h) Biodiversity hypothesis Summary: Logical arguments to support the hypothesis But logical arguments contrary to hypothesis

3)What makes a species invasive? h) Biodiversity hypothesis Summary: Logical arguments to support the hypothesis But logical arguments contrary to hypothesis Data that support the hypothesis

3)What makes a species invasive? h) Biodiversity hypothesis Summary: Logical arguments to support the hypothesis But logical arguments contrary to hypothesis Data that support the hypothesis But other data contrary to hypothesis

3)What makes a species invasive? h) Biodiversity hypothesis Summary: Logical arguments to support the hypothesis But logical arguments contrary to hypothesis Data that support the hypothesis But other data contrary to hypothesis Thus, biodiversity alone does not account for invasibility Diversity patterns at different scales may explain paradox in part