Download Ecological Impacts

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
Impacts of Invasions
• Ecology
– Species replacement
– Ecosystem functions
– Threatened & endangered species
• Economic
– Total environmental damage estimates
• Social
– Water quantity and quality
– Human health
Ecological Impacts
Conceptual model:
Walker & Smith in Lukens & Thieret (1997)
• Invasive species affect different community &
ecosystem processes
Ecological Impacts
• Types of impacts (Parker et al. 1999)
– Impacts on ecosystem properties
– Impacts on community structure
– Impacts on individual species
Ecological Impacts
• Impacts on ecosystem properties
1. Disturbance regimes
D’Antonio in Mooney & Hobbs (2002)
Ecological Impacts
• Impacts on ecosystem properties
2. Resource dynamics
Ehrenfeld (2003) Ecosystems 6: 503-523
Ecological Impacts: Nitrogen
Question: How is N cycling affected by exotic grass
invasion?
Method: Examined rates of N mineralization & nitrification,
and characterized soil microbial communities
Hawkes et al. (2005) Ecology Letters 8:976-985
Hawkes et al. (2005) Ecology Letters 8:976-985
Ehrenfeld (2003) Ecosystems 6: 503-523
Ecological Impacts: Carbon
Woody plant invasion into
grasslands is thought to
increase amount of C stored
Ecological Impacts: Carbon
Question: Does woody plant invasion increase C
sequestration?
Method: Examined 6 sites along precipitation gradient
Jackson et al. (2002) Nature 418:623-626
Jackson et al. (2002) Nature 418:623-626
Jackson et al. (2002) Nature 418:623-626
Ehrenfeld (2003) Ecosystems 6: 503-523
Tamarix ramosissima
Ladenburger et al. (2005) J. of Arid Env 65: 111-128.
Ecological Impacts: Water
Kulmatiski et al. (2006) Plant & Soil 288: 271-284
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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
Crooks (2002) OIKOS 97: 153-166
Ecosystem Impacts: Transformers
• Question: What is the long-term
impact of C. pubescence
invasion on Galapagos
vegetation?
• Methods: Monitoring permanent
plots over 7 years
Jager et al (2009) J of Ecology 97:1252-1263
Jager et al (2009) J of Ecology 97:1252-1263
Jager et al (2009) J of Ecology 97:1252-1263
Ecological Impacts
• Impacts on community structure
1. Productivity
Ecological Impacts
• Impacts on community structure
2. Community dynamics
Ecological Impacts
• Changes in productivity and community
dynamics often observed as:
1. Direct competition
2. Large scale species displacement
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
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 12:1434-1444
Alvarez & Cushman (2002) Ecological Applications 12:1434-1444
Alvarez & Cushman (2002) Ecological Applications 12:1434-1444
Alvarez & Cushman (2002) Ecological Applications 12:1434-1444
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
Stinson et al. (2006) PLoS Biology 4: 140
Ecological Impacts
• Species impacts
– Effects can be by:
• Direct species replacement
• Indirect through effects on community structure or
function
Ecological Impacts
Threatened & endangered species
~ 409 animals and 598 plants are federally listed in US
~ 400 of 958 federally listed species (~42%) believed
to be due to invasives (includes plants plus other
organisms)
294 (29%) believed threatened by direct effects
of invasive species
104 records of extinctions directly due to invasives
88 animals (many birds, NZ and HI)
16 plants
Ecological Impacts: T&E 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)
Ecological Impacts: Extinctions
• Question: How have 8 endangered plants been
impacted by introduced species?
• Method: Literature and field surveys
• galopagos
Ecological impacts: Extinctions
How much of a role do invasive species
really play?
Extinctions are caused by multiple factors:
1. Habitat destruction
2. Invasive species
3. Pollution
4. Disease
Most ‘documented’ extinctions involve speculation
Ecological impacts: Extinctions
• Animals more impacted than plants
• Mainland less impacted than islands
Sax & Gains (2008) PNAS 105: 11490-11497
Ecological Impacts
• Do invasions always negatively impact
ecosystem properties and community
structure?
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
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
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
• Effects observed as:
Species replacements (direct/individual or large scale)
Ecological Impacts
•
Ecosystem functions (C sequestration, N fixation, fire
frequency/intensity)
Ecological Impacts
•
Ecosystem functions (C sequestration, N fixation, fire
frequency/intensity)
• 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)