Plant Invasion and the Structure of Plant Communities

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Plant Invasion and the Structure of Plant
Communities

• Bruce Maxwell
• LRES 543 Agroecology

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Outline

• Biotic Invasions

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Biotic Invasions
Place of Origin
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Planet of the Weeds -D. Quammen

• Are we causing the sixth extinction?
• Nature Abhors a Vacuum or Invasive spp displace
  natives?
• What are the natural background rates of
  speciation/introduction and extinction?
• The River Tweed vs Hawaii

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Immigrant Weed Species Can Fail...

• River Tweed (Wool Manufacturing), U.K.
• 1919 348 alien weed species (most burs)
• 52 from other continents
• - Hayward and Druce, 1919
• 1961 Four species spread beyond woolen mill
  grounds - Salisbury, 1961
• 1987 None of the species were found in the
  region - Crawley, 1987

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Forest Canopy
Open Closed
6 0
10 14
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Biotic Invasions
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Processes Allowing Naturalization and Transition
to Invasive

• Hypotheses that allow naturalization and
  invasion
• Enemy Release
• Highly competitive
• Extra resources
• New niche with little overlap
• Competitive release from generalist predators or
  herbivores
• Disturbance for colonization

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Transformation from immigrant to invader
the lag phase
Opuntia aurantiaca in South Africa
Moran and Zimmerman, 1991
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Transformation from immigrant to invader

• The number, arrangement of infestations and
  frequency of arrival of immigrants.
• Limits on detection of population growth
• Natural selection improving fitness
• Habitat frequency (including alteration)
• The vagaries of environmental hazards (frequency
  and intensity).

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Identifying Future Invaders

• Taxonomic relationships
• Biological traits

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Diagram Illustrating the Relationship of all
Variables Used in Determining Weeds Of National
Significance In Australia
Weeds of National Significance
Invasiveness Criterion
Impacts Criterion
Potential for Spread Criterion
Socioeconomic and Environmental Criterion
Current Distribution
Future Distribution
Social Index
Economic data for Agric. Forestry (current cost
of control)
Environmental Index
Communities Impacted
IBRA Regions Affected
Monoculture Potential
Species Threatened
The Determination of Weeds of National
SignificanceBy John R Thorp Rod LynchISBN 0
642 44913 9
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Reichards Classification SystemReichard, S.H.
and C.W. Hamilton, 1997. Predicting invasion of
woody plants introduced into North America.
Conservation Biol. 11193-203.

• Used a discriminate analysis model to predict
  woody plant invaders 86.2 accurate
• Decision tree results

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Plant Community Vulnerability To Invasion

• Generalized Hypotheses
• Vacant niche
• Community species richness (Elton,1958 vs
  Londsdale, 1999)
• Escape from biotic constraints
• Disturbance before or upon immigration (invaders
  require disturbance or natives cant tolerate
  disturbance)

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Vacant Niche Hypothesis
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Vacant Niche Hypothesis
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Plant Community Vulnerability To Invasion

• Generalized Hypotheses
• Vacant niche
• Escape from biotic constraints
• Community species richness (Elton,1958 vs
  Londsdale, 1999)
• Disturbance before or upon immigration (invaders
  require disturbance or natives cant tolerate
  disturbance)

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Escape from biotic constraint hypothesis
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Plant Community Vulnerability To Invasion

• Generalized Hypotheses
• Vacant niche
• Escape from biotic constraints
• Community species richness (Elton,1958 vs
  Londsdale, 1999)
• Disturbance before or upon immigration (invaders
  require disturbance or natives cant tolerate
  disturbance)

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Community Species Richness Hypothesis
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Plant Community Vulnerability To Invasion

• Generalized Hypotheses
• Vacant niche
• Escape from biotic constraints
• Community species richness (Elton,1958 vs
  Londsdale, 1999)
• Disturbance before or upon immigration (invaders
  require disturbance or natives cant tolerate
  disturbance) (Huston, 1994)

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Disturbance Hypothesis
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Plant Invasion Dependent On

• Available species pool (propagule pressure)
• Predicting new invasions (ornamentals)
• Thresholds of propagules
• Dispersal potential (properties of exotic spp)
• Available habitat (ecosystem properties)
• Abiotic determinants
• Biotic determinants
• Habitat changes over time (nutrient cycling)
• Relative fitness within habitat (exotic native
  spp prop.)
• Adaptive potential of each species (prop. of
  exotic spp)
• Genotypic variability and phenotypic plasticity

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The Crop Field as a Microcosm To Study Invasion
Spp 4
Spp 1
Spp 5
Spp 2
Spp 6
Spp 2
Spp 3
Spp 7
Available Species Pool
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The Crop Field as a Microcosm To Study Invasion
Spp 4
Spp 1
Spp 5
Spp 2
Spp 6
Spp 2
Spp 3
Spp 7
Dispersal Potential of Each Species
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Potential Habitat
Gradient
Emergence Seedling Survival Produce Viable
Offspring Significant Impact On Crop
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The Crop Field as a Microcosm To Study Invasion
Spp 4
No Crop
Spp 1
Spp 5
Spp 2
Spp 6
Spp 2
Spp 3
Spp 7
Habitat Available for Each Species
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Inventory
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Invasive Plant Species Purpose of an Inventory
Plants transported to new, often distant, ranges
where their descendants proliferate, spread and
persist.
Mack et al., 2000

• Seek destroy vs Inventory
• What species are present?
• What is their frequency in the environment?
• Is it correlated with environmental variables?
• What is the full range of habitat?

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Objectives

• Conduct a preliminary study to determine the most
  efficient means to inventory exotic plant species
  in the northern range of YNP
• Computer simulation to determine the most
  efficient sampling scheme for a range of assumed
  weed distributions and infestation sizes
• Conduct field sampling to verify likely weed
  distributions based on first principles

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Random points (11 or 0.55)
Grid (16 or 0.8)
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Random walk (12 or 0.6)
Transects (34 or 1.7)
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Model Simulation Results

• For a range of weed distributions with
  consideration of sampling efficiency transects
  orientated perpendicular to roads trails were
  found to be the most effective methodology for
  creating an inventory of the exotic plant
  species.

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Study area
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Frequency ()
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Distance from roads/trails (m)(Weighted
frequency)
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Vegetation habitat occurrence(Weighted frequency)
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Monitoring
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Marie Jasieniuk
Objective
To identify ecological factors and processes
favoring the invasion of yellow toadflax into
native plant communities of the Rocky Mountains.
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Grid Map of a Yellow Toadflax Patch
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Mapping Plants
1 m2 quadrat divided into 16 0.0625 m2 areas
Individual plants mapped in each 0.0625 m2 area
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Density (no. plants m2)
Northing
Easting
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Tansy Ragwort Viability Analysis
Meghan Trainor

• Objective Quantify the effects of environment
  in the field on tansy ragwort seedling survival,
  mature plant survival, vegetative reproduction,
  seed production, and population spread.
• Adaptive sampling method
• 1 m2 grid overlaid each plot to map individual
  plants

1 m2 sample plot
100 m transect
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Life cycle diagram for tansy ragwort population
projection matrix model to calculate growth rate.

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Preliminary Results
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5
4
?
3
2
1
0
-1
Burned
Burned andSalvage-Logged
Undisturbed Forest
Undisturbed Meadow
Rate of population growth (?) in four different
environments. - Provides a first approximation
comparison to estimate potential of a weed in
different environments
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Monitoring for Impact
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Population and Community Attributes

• Native and exotic species
• density
• survival
• fecundity
• foliar cover
• richness

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Insects on Yellow Toadflax
Flower eating beetle Brachypterolus
pulicarius (Coleoptera Nitidulidae
Seed capsule feeding weevil Gymnetron
antirrhini (Coleoptera Curculionidiae)
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Decision to Manage
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Biotic Invasionsand the Decision To Manage
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Biotic Invasionsand Management
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Biotic Invasions As Agents Of Global Change

• Population level effects
• Community and Ecosystem level effects
• Economic consequences

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Aspen hybridization
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Biotic Invasions As Agents Of Global Change

• Population level effects
• Community and Ecosystem level effects
• Economic consequences

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Do all weeds degrade ecosystems?
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Is the cure worse than the disease?