Readings, enemy release and
biodiversity hypotheses
1. Enemy release hypothesis:
Keane, r. Crawley, M. 2002. Exotic plant invasions
and the enemy release hypothesis. TREE
17:164-170
2. Biodiversity hypothesis:
Shea K, Chesson P. 2002. Community ecology
theory as a framework for biological invasions.
TREE 17:170-176
3) What makes a species invasive?
g) Escape from biotic constraints hypothesis
“Escape from enemy” hypothesis
“Enemy release” hypothesis
Basic concepts:
• Species in their native range are suppressed by natural
enemies
aka
3) What makes a species invasive?
g) Escape from biotic constraints hypothesis
“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
aka
3) What makes a species invasive?
g) Escape from biotic constraints hypothesis
“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”
aka
3) What makes a species invasive?
g) Escape from biotic constraints hypothesis
“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
aka
3) What makes a species invasive?
g) Escape from biotic constraints hypothesis
“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?
aka
3) What makes a species invasive?
g) Escape from biotic constraints hypothesis
“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?
aka
3) What makes a species invasive?
g) Escape from biotic constraints hypothesis
“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?
aka
3) What makes a species invasive?
g) Escape from biotic constraints hypothesis
“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?
aka
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
Invaded
Native
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!!)
Invaded
Native
>
>
>
>
>
>
>
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
Native
Invaded
<
<
<
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
Invaded
Native
Native
Invaded
>
>
>
>
<
>
>
>
<
<
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 160:705-711
• 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 160:705-711
• 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 160:705-711
• 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 160:705-711
• 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 160:705-711
• 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 160:705-711
• 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 160:705-711
• 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: 67-70
• 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: 67-70
• 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: 67-70
• 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: 67-70
• 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: 67-70
• 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: 67-70
• 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: 67-70
• 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 pathogens
@ 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: 625-627
• 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: 625-627
• 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: 625-627
• 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: 625-627
• 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: 625-627
• 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: 625-627
• 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: 636638
• 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: 636638
• 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: 636638
• 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: 636638
• 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: 636638
• 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: 636638
• 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: 636638
• 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: 636638
• 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: 636638
• 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: 636638
• 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: 1522-1536
• 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: 1522-1536
• 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: 1522-1536
• 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: 1522-1536
• 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