Impacts of Invasions

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Impacts of Invasions

• Measuring impact is complex
• What should be measured and how?

• For individual plant, individual species, or
  multiple species?

• Over what time frame?

• Lack of comprehensive data

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Ecological Impacts

• Invasive species affect different community
  ecosystem processes

• Disturbance regimes
• Fire

• Resource dynamics
• Nutrients N and C cycling
• Water amount, timing, location

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Ecological Impacts

• Ecosystem engineers species able to physically
  alter habitats (Crooks 2002)

• Alter ecosystem physical processes
  (sedimentation, water availability, N cycling)
• Change habitat structure (more or less
  complexity)
• Effects cascade through community

Jager et al (2009) J of Ecology 971252-1263
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Ecological Impacts

• Impacts on community structure

1. Productivity
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Ecological Impacts

• Impacts on community structure

2. Community dynamics
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Ecological Impacts

• Changes in productivity and community dynamics
  often observed as

1. Direct competition
2. Large scale species displacement
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Ecological Impacts Competition

• Question How is invasion by exotic grasses
  impacting native recruitment in dry forests of
  Hawaii?
• Methods Experimental field studies removing
  invasive grasses

Dodonea viscosa Aalii
Pipturus albidus Mamaki
Sophora chrysophylla Mamane
Acacia koa Koa
Denslow et al. (2006) Oecologia 148 118-128
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Denslow et al. (2006) Oecologia 148 118-128
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Ecological Impacts Replacement
Question How has invasion by Cape ivy affected
3 coastal habitats in SF Bay Area? Methods
Comparative and experimental field studies
Delairea odorata - Cape Ivy
Alvarez Cushman (2002) Ecological Applications
121434-1444
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Alvarez Cushman (2002) Ecological Applications
121434-1444
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Alvarez Cushman (2002) Ecological Applications
121434-1444
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Alvarez Cushman (2002) Ecological Applications
121434-1444
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Alvarez Cushman (2002) Ecological Applications
121434-1444
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Ecological Impacts Mutualisms

• Question How does invasion by Alliaria petiolata
  alter plant composition of NA forests?
• Methods Examined mycorrhizal colonization of
  tree roots from soil cultured with Alliaria

Stinson et al. (2006) PLoS Biology 4 140
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Stinson et al. (2006) PLoS Biology 4 140
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Ecological Impacts

• Species impacts can be by
• Indirect effects on community structure or
  function
• Direct species replacement

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Ecological Impacts
Threatened endangered species 614 animals
and 749 plants are federally listed in US
half of federally listed species are believed
to be associated with invasives (includes plants
plus other organisms)
a quarter of species are believed to be
threatened by direct effects of invasive species
http//www.fws.gov/Endangered/wildlife.htmlSpecie
s
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Ecological Impacts TE Species
Question Is there a relationship between species
invasion and imperiled species in CA? Methods
examined distribution of 834 exotic plants in CA
correlated it to imperiled species using
multivariate analyses (CCA, SEM)
Seabloom et al. (2006) Ecological Applications
16 1338 - 1350
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Seabloom et al. (2006) Ecological Applications
16 1338 - 1350
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Seabloom et al. (2006) Ecological Applications
16 1338 - 1350
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Ecological Impacts Extinctions

• Question How have 8 endangered plants been
  impacted by introduced species?
• Method Literature and field surveys

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• galopagos

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Ecological impacts Extinctions

• How much of a role do invasive species really
  play?

• Extinctions are caused by multiple factors
• Habitat destruction
• Invasive species
• Pollution
• Disease

Most documented extinctions involve speculation
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Ecological impacts Extinctions

• Animals more impacted than plants
• Mainland less impacted than islands

Sax Gains (2008) PNAS 105 11490-11497
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Sax et al. (2002) American Naturalist 160 766-783
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Ecological Impacts

• Do invasions always negatively impact ecosystem
  properties and community structure?

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Positive impacts

• All of the factors that have a negative impact on
  native plants can also be positive under certain
  conditions
• Competitive release
• Facilitation by acting as nurse plants
• Trophic subsidy
• Pollination
• Predatory release

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Ecological Impacts

• Summary
• Ecological impacts typically involve
• (1) nutrients/water flow
• (2) primary production impacts
• (3) alterations of disturbance regimes
• (4) changes in community dynamics

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Ecological Impacts

• Summary
• Ecological impacts typically involve
• (1) nutrients/water flow
• (2) primary production impacts
• (3) alterations of disturbance regimes
• (4) changes in community dynamics

• Ecosystem functions (C sequestration, N cycling,
  water, fire frequency/intensity)

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Ecological Impacts

• Summary
• Ecological impacts typically involve
• (1) nutrients/water flow
• (2) primary production impacts
• (3) alterations of disturbance regimes
• (4) changes in community dynamics

• Ecosystem functions (C sequestration, N cycling,
  water, fire frequency/intensity)

• Effects observed as
• Species replacements (direct/individual or large
  scale)

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Ecological Impacts

• Summary
• Ecological impacts typically involve
• (1) nutrients/water flow
• (2) primary production impacts
• (3) alterations of disturbance regimes
• (4) changes in community dynamics

• Ecosystem functions (C sequestration, N cycling,
  water, fire frequency/intensity)

• Effects observed as
• Species replacements (direct/individual or large
  scale)

• Loss of native species (threatened or endangered
  species)
• Often in conjunction with human-caused habitat
  change
• Especially on islands
• Especially rare/specialized species
• More evidence for population reduction than for
  extinction (e.g. Harrison et al 2006)