Reading assignments: ecological
impacts
• Invasives and fire:
– D’Antonio and Vitousek 1992. Biological invasions by exotic
grasses, the grass-fire cycle, and global change. Annual review
of Ecology and Sytematics 23:65-87.
– Brooks et al. 2004. Effects of invasive alien plants on fire
regimes. BioScience 54: 677-688.
• Ecosystem changes:
– Crooks 2002. Characterizing ecosystem-level consequences of
biological invasions: the role of ecosystem engineers. Oikos
97:153-166.
3) Impacts
a) Ecological
ii) Ecosystem functions
Ecosystem engineers: What are they?
3) Impacts
a) Ecological
ii) Ecosystem functions
Ecosystem engineers: What are they?
• Alter ecosystem physical processes (water use, N
cycling)
• Change habitat structure (more complexity, less
complexity)
• Effects cascade through community
3) Impacts
a) Ecological
ii) Ecosystem functions
• Overview
• Specific examples: General compilation
From Crooks (2002)
Effects on Nitrogen
N loss
Invasive plants
Fire
Altered composition
Altered litter quality
Altered microbial activity
Altered microclimate
Altered root exudation
Altered microbial community
N fixation
Altered NPP
Altered timing of uptake
N cycling and pools
Modified from D’Antonio and Hobbie in Sax et al. 2005
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Overview
~409 animals and 598 plants are federally listed species in US
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Overview
~409 animals and 598 plants are federally listed species in US
294 (29%) threatened by direct effects of invasive species (IUCN)
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Overview
Effects can be by:
Direct species replacement
Indirect through effects on community structure or function
3) Impacts
a) Ecological
iii) Threatened & endangered species : IUCN database
• Overview
Effects can be by:
Direct species replacement
Indirect through effects on community structure or function
Worldwide
Extinctions: 104 records of extinctions directly due to invasives
88 animals (many birds, NZ and HI)
16 plants
Endangered and vulnerable: 1317 directly due to invasives
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Overview
• Specific examples: King Ranch bluestem
Bothriochloa ischaemum (Caucasian bluestem) brought in to
southern Great Plains (NM, OK, TX) from Russia in 1929
C4 perennial bunchgrass:
establishes readily from seed
long growing season
tolerates heavy grazing
fair forage quality
forms dense sod in mature pastures
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Overview
• Specific examples: King Ranch bluestem
Bothriochloa ischaemum (Caucasian bluestem) brought in to
southern Great Plains (NM, OK, TX) from Russia in 1929
C4 perennial bunchgrass: desirable forage species
Seeded extensively (for example, ~2 million acres in western
OK)
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Overview
• Specific examples: King Ranch bluestem
Bothriochloa ischaemum (Caucasian bluestem) brought in to
southern Great Plains (NM, OK, TX) from Russia in 1929
C4 perennial bunchgrass: desirable forage species
Seeded extensively
But extremely invasive:
Spread along highways into native areas (cemetaries,
native grasslands)
Difficult to control
Threatens federally listed endangered plant Ambrosia
cheiranthefolia (south Texas ambrosia)
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Overview
• Specific examples: Hawaii
80-90 native plant species extinct
270 plant species listed as threatened or endangered
94 noxious weeds, many more alien species
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Overview
• Specific examples: California
• Seabloom et al (2006) examined distribution of 834 exotic plants
in CA. Multivariate analyses (CCA, SEM)
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Overview
• Specific examples: California
• Seabloom et al (2006) examined distribution of 834 exotic plants
in CA. Multivariate analyses (CCA, SEM)
• exotic/invasive species tightly linked to distribution of imperiled
species (regression, CCA)
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Overview
• Specific examples: California
• Seabloom et al (2006) examined distribution of 834 exotic plants
in CA. Multivariate analyses (CCA, SEM)
• exotic/invasive species tightly linked to distribution of imperiled
species (CCA)
• Human activities facilitate initial invasion but exotics spread
ahead of front of human development into areas with high
numbers of threatened plants (SEMs)
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Not a lot of evidence for extinctions (Gurevitch and Padilla
2004)
• But: ‘Winners and Losers’ in anthropogenic biotic
homogenization (McKinney and Lockwood 1999)
• Invasive plants are ‘winners’
• ‘losers’ are species whose numbers/range decline
• Geographically restricted natives with specific habitat
requirements = high extinction rates
3) Impacts
a) Ecological
iii) Threatened & endangered species
• Not a lot of evidence for extinctions (Gurevitch and Padilla
2004)
• But: ‘Winners and Losers’ in anthropogenic biotic
homogenization (McKinney and Lockwood 1999)
• Invasive plants are ‘winners’
• ‘losers’ are species whose numbers/range decline
• Geographically restricted natives with specific habitat
requirements = high extinction rates
Traits of ‘winners’
r selected
Widespread
Rapid dispersal
High variability
Generalist
Human commensalism
Traits of ‘losers’
K selected
Rare
Slow dispersal
Low variability
specialist
Maladapted to humans
3) Impacts
a) Ecological
Summary
• Only a small percentage (0.1%) of introduced plants become a
problem
3) Impacts
a) Ecological
Summary
• Only a small percentage (0.1%) of introduced plants become a
problem
• Ecological impacts typically involve: (1) nutrients/water flow; (2)
primary production impacts; (3) alterations of disturbance
regimes; and (4) changes in community dynamics
3) Impacts
a) Ecological
Summary
• Only a small percentage (0.1%) of introduced plants become a
problem
• Ecological impacts typically involve: (1) nutrients/water flow; (2)
primary production impacts; (3) alterations of disturbance regimes;
and (4) changes in community dynamics
• Effects observed as:
Species replacements (direct/individual or large scale, w/ or
w/o interactions with other factors such as fire)
3) Impacts
a) Ecological
Summary
• Only a small percentage (0.1%) of introduced plants become a
problem
• Ecological impacts typically involve: (1) nutrients/water flow; (2)
primary production impacts; (3) alterations of disturbance regimes;
and (4) changes in community dynamics
• Effects observed as:
Species replacements (direct/individual or large scale, w/ or w/o
interactions with other factors such as fire)
Ecosystem functions (C sequestration, N fixation, fire
frequency/intensity)
3) Impacts
a) Ecological
Summary
• Only a small percentage (0.1%) of introduced plants become a
problem
• Ecological impacts typically involve: (1) nutrients/water flow; (2)
primary production impacts; (3) alterations of disturbance regimes;
and (4) changes in community dynamics
• Effects observed as:
Species replacements (direct/individual or large scale, w/ or w/o
interactions with other factors such as fire)
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
3) Impacts
a) Ecological
Summary
• Only a small percentage (0.1%) of introduced plants become a
problem
• Ecological impacts typically involve: (1) nutrients/water flow; (2)
primary production impacts; (3) alterations of disturbance regimes;
and (4) changes in community dynamics
• Effects observed as:
Species replacements (direct/individual or large scale, w/ or w/o
interactions with other factors such as fire)
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)