Presentation is loading. Please wait.

Presentation is loading. Please wait.

Readings, enemy release and biodiversity hypotheses 1.Enemy release hypothesis: Keane, r. Crawley, M. 2002. Exotic plant invasions and the enemy release.

Similar presentations


Presentation on theme: "Readings, enemy release and biodiversity hypotheses 1.Enemy release hypothesis: Keane, r. Crawley, M. 2002. Exotic plant invasions and the enemy release."— Presentation transcript:

1 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:

2 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 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

4 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”

5 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

6 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?

7 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?

8 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?

9 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?

10 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

11 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

12 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 > > > > > > >

13 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 < < <

14 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 < < <

15 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)

16 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

17 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 ↑

18 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

19 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

20 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)

21 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

22 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

23 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)

24 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

25 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

26 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.

27 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

28 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

29 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

30 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

31 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

32 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

33 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

34 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

35 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

36 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%)

37 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

38 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

39 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

40 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

41 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

42 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?

43 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

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

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

46 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

47 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

48 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

49 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

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

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

52 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,

53 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, ↓

54 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

55 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*

56 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*

57 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

58 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

59 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*)

60 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

61 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

62 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

63 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 ↑

64 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

65 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

66 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

67 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

68 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

69 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

70 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

71 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

72 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

73 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

74 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.

75 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

76 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)

77 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

78 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

79 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

80 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

81 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”

82 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

83 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

84 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

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

86 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’.

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

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

89 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

90 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

91 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


Download ppt "Readings, enemy release and biodiversity hypotheses 1.Enemy release hypothesis: Keane, r. Crawley, M. 2002. Exotic plant invasions and the enemy release."

Similar presentations


Ads by Google