3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Many invasive species have a “ruderal” life history strategy.

“ruderal” = small, very-short lived plants that grow and mature rapidly and that have a large reproductive effort, especially in response to stress

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• These types of species are typically associated with disturbed

types of habitats.

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed habitats• Changes in land use cause changes in the extent and

frequency of disturbance to an ecosystem

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed

habitats• Land use changes affect disturbance

Examples from Hobbs in Mooney & Hobbs (2000)

Change can be abrupt

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed

habitats• Land use changes affect disturbance

Examples from Hobbs in Mooney & Hobbs (2000)

Change can be abrupt or gradual

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed

habitats• Land use changes affect disturbance

Examples from Hobbs in Mooney & Hobbs (2000)

Change can be abrupt or gradualChange can be permanent

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed

habitats• Land use changes affect disturbance

Examples from Hobbs in Mooney & Hobbs (2000)

Change can be abrupt or gradualChange can be permanent or transitory

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed

habitats• Land use changes affect disturbance

Examples from Hobbs in Mooney & Hobbs (2000)

Change can be abrupt or gradualChange can be permanent or transitoryTransition back to original state

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed

habitats• Land use changes affect disturbance

Examples from Hobbs in Mooney & Hobbs (2000)

Change can be abrupt or gradualChange can be permanent or transitoryTransition to original or new state

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed

habitats• Land use changes affect disturbance

Examples from Hobbs in Mooney & Hobbs (2000)

Change can be abrupt or gradualChange can be permanent or transitoryTransition to original or new stateTransition can be natural

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed

habitats• Land use changes affect disturbance

Examples from Hobbs in Mooney & Hobbs (2000)

Change can be abrupt or gradualChange can be permanent or transitoryTransition to original or new stateTransition can be natural or deliberate,

with deliberately different end states

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed habitats• Land use changes affect disturbance• How can disturbance and land use changes enhance

invasions?

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed habitats• Land use changes affect disturbance• Disturbance and land use changes enhance invasions by:

Changing the amount or flow of resources hence inducing a change in resource availability

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed habitats• Land use changes affect disturbance• Disturbance and land use changes enhance invasions by:

Changing the amount or flow of resources hence inducing a change in resource availability

Increases the probability of success for ruderals

3) What makes a species invasive?i) Disturbance and land use hypothesis

Basic concepts:• Invasive species are ruderals• Ruderals associated with disturbed habitats• Land use changes affect disturbance• Disturbance and land use changes enhance invasions by:

Changing the amount or flow of resources hence inducing a change in resource availability

Increases the probability of success for ruderalsBecause of the changes in vegetation states, provides

opportunities for other species to exist

3) What makes a species invasive?i) Disturbance and land use hypothesis

Evidence: D’Antonio & Vitousek (1992)• Without invasive species, typically if disturb woodlands, they

eventually return back to woodlands

DisturbanceRecovery

3) What makes a species invasive?i) Disturbance and land use hypothesis

Evidence: D’Antonio & Vitousek (1992)• Without invasive species, eventually return back to woodlands• But if have invasions of alien grasses during or after land is

cleared, then alien grasses induce a novel disturbance: fire

DisturbanceRecovery

3) What makes a species invasive?i) Disturbance and land use hypothesis

Evidence: D’Antonio & Vitousek (1992)• Without invasive species, eventually return back to woodlands• With alien grass invasion: a novel disturbance = fire• Once have a fire, initiate a series of feedback effects that

virtually preclude the re-establishment of woody plants

DisturbanceRecovery

3) What makes a species invasive?i) Disturbance and land use hypothesis

Evidence: From Kalin Arroyo et al. in Mooney & Hobbs (2000)• Determined number of alien plants in 12 political regions of

ChileTotal of 430 alien weedsAlso 260 alien non-weeds

3) What makes a species invasive?i) Disturbance and land use hypothesis

Evidence: From Kalin Arroyo et al. in Mooney & Hobbs (2000)• Number of alien plants in political regions of Chile• For each political region, also determined density of roads and

how much land area was in agricultural and urban useComputed a “Land Use Index” from these that goes from “low” (1)

to “intensive” (11)

3) What makes a species invasive?i) Disturbance and land use hypothesis

Evidence: From Kalin Arroyo et al. in Mooney & Hobbs (2000)

• Number of alien plants in political regions of Chile

• Corresponding Land Use Index: from “low” (1) to “intensive” (11)

• For alien weeds (A), number increased significantly with index

3) What makes a species invasive?i) Disturbance and land use hypothesis

Evidence: From Kalin Arroyo et al. in Mooney & Hobbs (2000)

• Number of weedy plants in political regions of Chile

• Corresponding Land Use Index: from “low” (1) to “intensive” (11)

• Alien weeds increase with intesity of land use

• Similarly for Total Number of Alien Species (B)

3) What makes a species invasive?i) Disturbance and land use hypothesis

Summary: Disturbance and land use hypothesis• Consistent with ecological theories

3) What makes a species invasive?i) Disturbance and land use hypothesis

Summary: Disturbance and land use hypothesis• Consistent with ecological theories• Evidence from a variety of ecosystems

3) What makes a species invasive?i) Disturbance and land use hypothesis

Summary: Disturbance and land use hypothesis• Consistent with ecological theories• Evidence from a variety of ecosystems• Empirical correlations

3) What makes a species invasive?i) Disturbance and land use hypothesis

Summary: Disturbance and land use hypothesis• Consistent with ecological theories• Evidence from woodland / grasslands• Empirical correlations

But• Is disturbance / land use the factor, or is it something

associated with these?Species traitsResource availabilityChanges in competitive balanceTemporary “vacant” niche

3) What makes a species invasive?i) Disturbance and land use hypothesis

Summary: Disturbance and land use hypothesis• Consistent with ecological theories• Evidence from woodland / grasslands• Empirical correlations

But• Is disturbance / land use the factor? • Plant establishment and invasion occur without disturbance

3) What makes a species invasive?j) Anthropogenic hypothesis

Basic concepts:• Human activities are the cause of invasive species

3) What makes a species invasive?j) Anthropogenic hypothesis

Basic concepts:• Human activities are the cause of invasive species• Humans help invasives overcome barriers; e.g. Richardson et

al. (2000)Humans are the vector for long distance transport

Home range

Introducedarea

Disturbedarea

Naturalarea

Geographic

ReproduceEnvironment

Disperse

3) What makes a species invasive?j) Anthropogenic hypothesis

Basic concepts:• Human activities are the cause of invasive species• Humans help invasives overcome barriers; e.g. Richardson et

al. (2000)Humans overcome geographic barriersHumans alter the environment that allows plants to grow and

reproduce

Home range

Introducedarea

Disturbedarea

Naturalarea

Geographic

ReproduceEnvironment

Disperse

3) What makes a species invasive?j) Anthropogenic hypothesis

Basic concepts:• Human activities are the cause of invasive species• Humans help invasives overcome barriers; e.g. Richardson et

al. (2000)Humans overcome geographic barriersHumans overcome environmental & reproductive barriersHumans help disperse invasives in new range

Home range

Introducedarea

Disturbedarea

Naturalarea

Geographic

ReproduceEnvironment

Disperse

3) What makes a species invasive?j) Anthropogenic hypothesis

Basic concepts:• Human activities are the cause of invasive species• Humans help invasives overcome barriers• Thus, humans and invasive species are interdependent

3) What makes a species invasive?j) Anthropogenic hypothesis

Basic concepts: From Hobbs in Mooney & Hobbs (2000)• Humans and invasive species are interdependent

Direct effects by introducing invading species

3) What makes a species invasive?j) Anthropogenic hypothesis

Basic concepts: From Hobbs in Mooney & Hobbs (2000)• Humans and invasive species are interdependent

Direct effects by introducing invading speciesDirect effects by altering ecosystem properties

3) What makes a species invasive?j) Anthropogenic hypothesis

Basic concepts: From Hobbs in Mooney & Hobbs (2000)• Humans and invasive species are interdependent

Direct effects by introducing invading speciesDirect effects by altering ecosystem propertiesCascading, indirect effects

3) What makes a species invasive?j) Anthropogenic hypothesis

Basic concepts: From Hobbs in Mooney & Hobbs (2000)• Humans and invasive species are interdependent

Direct effects by introducing invading speciesDirect effects by altering ecosystem propertiesCascading, indirect effects, which sets up an invasive cycle

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence:• Humans as vector for introduction?

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence: From Mack et al. (2000)• Humans as vector for introduction

Lantana camara (lantana; shrub verbena) shrub native to tropical New World

Prized for showy flowers and fragrant leaves

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence: From Mack et al. (2000)• Humans as vector for introduction

Lantana camara native to tropical New WorldIntroduced as a horticultural species repeatedly throughout the

world, especially tropics and sub-tropics

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence: From Lonsdale (1999) Ecology 80:1522-1536• Humans as vector for introduction

Asked: Do the number of invasive species increase with number of visitors to natural areas?

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence: From Lonsdale (1999)• Humans as vector for introduction

Do invasives ↑ with visitation?First, control for larger parks

have more natives which draws more visitors (a)

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence: From Lonsdale (1999)• Humans as vector for introduction

Do invasives ↑ with visitation?First, more natives → more visitorsThen look at visitors corrected

for number of natives (= “visitor residuals”)

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence: From Lonsdale (1999)• Humans as vector for introduction

Do invasives ↑ with visitation?First, more natives → more visitorsThen look at visitors corrected for

number of natives (= “visitor residuals”) vs. number of exotics (b)

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence: From Lonsdale (1999)• Humans as vector for introduction

Do invasives ↑ with visitation?First, more natives → more visitorsNumber of exotics significantly

(P<0.001; adj. r2=0.68) with visitors

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence:• Humans as vector for introduction• Human alterations of ecosystem properties

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence:• Humans as vector for introduction• Human alterations of ecosystem properties

Example: Riparian areas in western USOriginally “cottonwood gallery forest”

Cottonwood and willow dominated ecosystemOpen forest with understory of shrubs and herbsUsed by diverse array of animals and birdsRe-establish after spring floods:

Produce abundant wind-dispersed seed in late-springColonize moist, exposed sediments from floodsGrow rapidly (not shade tolerant)

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence:• Humans as vector for introduction• Human alterations of ecosystem properties

Example: Riparian areas in western USOriginally “cottonwood gallery forest”First large impacts came during Spanish settlement

Primarily ranching and irrigated agriculture

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence:• Humans as vector for introduction• Human alterations of ecosystem properties

Example: Riparian areas in western USOriginally “cottonwood gallery forest”Spanish settlement: ranching and irrigated agricultureExpansion of US during mid-1800’s

Trappers removed upstream beavers; resulted in ↑ sediment loads

Large-scale ranching, irrigated agriculture, logging, & mining; resulted in land clearing and extensive disturbance

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence:• Humans as vector for introduction• Human alterations of ecosystem properties

Example: Riparian areas in western USOriginally “cottonwood gallery forest”Spanish settlement: ranching and irrigated agricultureUS expansion (mid-1800’s): sedimentation, clearing, disturbanceEarly 1900’s: Construction of dams, levees, drainage ditches

Prevented spring flood cycleDried fuel and litter accumulated → ↑ fires

3) What makes a species invasive?j) Anthropogenic hypothesis

Evidence:• Humans as vector for introduction• Human alterations of ecosystem properties

Example: Riparian areas in western USOriginally “cottonwood gallery forest”Spanish settlement: ranching and irrigated agricultureUS expansion (mid-1800’s): sedimentation, clearing, disturbanceDam construction (early 1900’s): prevented spring flood; firesSaltcedars & Russian olive introductions (mid-late 1800’s)

Windbreaks, erosion control & stream bank stabilization, ornamentals

Originally encouraged and subsidized by governmentsMore drought tolerant; less exacting on seed dispersal &

establishment requirementsNow dominant species on much of the riparian areas of

western US

3) What makes a species invasive?j) Anthropogenic hypothesis

Summary: Abundant evidence that• Humans are major vector for introduction• Humans greatly alter ecosystem properties

3) What makes a species invasive?j) Anthropogenic hypothesis

Summary: Abundant evidence that• Humans are major vector for introduction• Humans greatly alter ecosystem properties

But:• Invasive species problems are no longer just a natural,

ecological problem

3) What makes a species invasive?

10 hypotheses:1. Vacant niche hypothesis2. Allelopathy hypothesis3. Environmental change hypothesis4. Variable resource availability hypothesis5. Competition hypothesis6. Microevolutionary change hypothesis7. Escape from biotic constraints hypothesis8. Biodiversity hypothesis9. Disturbance and land use hypothesis10.Anthropogenic hypothesis

3) What makes a species invasive?

10 hypotheses:1. Vacant niche hypothesis No support2. Allelopathy hypothesis3. Environmental change hypothesis4. Variable resource availability hypothesis5. Competition hypothesis6. Microevolutionary change hypothesis7. Escape from biotic constraints hypothesis8. Biodiversity hypothesis Conflicting support9. Disturbance and land use hypothesis10.Anthropogenic hypothesis

3) What makes a species invasive?

10 hypotheses:1. Vacant niche hypothesis No support2. Allelopathy hypothesis3. Environmental change hypothesis4. Variable resource availability hypothesis Very limited support5. Competition hypothesis6. Microevolutionary change hypothesis7. Escape from biotic constraints hypothesis8. Biodiversity hypothesis Conflicting support9. Disturbance and land use hypothesis Special case of #1010.Anthropogenic hypothesis

3) What makes a species invasive?

10 hypotheses:1. Vacant niche hypothesis No support2. Allelopathy hypothesis Specific cases, but how many?3. Environmental change hypothesis4. Variable resource availability hypothesis Very limited support5. Competition hypothesis6. Microevolutionary change hypothesis Specific cases ; how many?7. Escape from biotic constraints hypothesis8. Biodiversity hypothesis Conflicting support9. Disturbance and land use hypothesis Special case of #1010.Anthropogenic hypothesis

3) What makes a species invasive?

10 hypotheses:1. Vacant niche hypothesis No support2. Allelopathy hypothesis Specific cases, but how many?3. Environmental change hypothesis Broad support, but exceptions4. Variable resource availability hypothesis Very limited support5. Competition hypothesis Broad support, but exceptions6. Microevolutionary change hypothesis Specific cases ; how many?7. Escape from biotic constraints Broad support;exceptions8. Biodiversity hypothesis Conflicting support9. Disturbance and land use hypothesis Special case of #1010.Anthropogenic hypothesis

3) What makes a species invasive?

10 hypotheses:1. Vacant niche hypothesis No support2. Allelopathy hypothesis Specific cases, but how many?3. Environmental change hypothesis Broad support, but exceptions4. Variable resource availability hypothesis Very limited support5. Competition hypothesis Broad support, but exceptions6. Microevolutionary change hypothesis Specific cases ; how many?7. Escape from biotic constraints Broad support;exceptions8. Biodiversity hypothesis Conflicting support9. Disturbance and land use hypothesis Special case of #1010.Anthropogenic hypothesis Broad support, few exceptions