Reading assignments: ecological impacts Invasives and fire: –D’Antonio and Vitousek 1992. Biological invasions by exotic grasses, the grass-fire cycle,

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) Impactsa) Ecological

ii) Ecosystem functionsEcosystem engineers: What are they?


ii) Ecosystem functionsEcosystem engineers: What are they?

• Alter ecosystem physical processes (water use, N cycling)

• Change habitat structure (more complexity, less complexity)

• Effects cascade through community


ii) Ecosystem functions• Overview• Specific examples: General compilation

From Crooks (2002)

Modified from D’Antonio and Hobbie in Sax et al. 2005

Invasive plants

Altered litter quality

Altered microbial activity

Altered root exudation

N fixation

Altered microclimate

Altered microbial community

Altered NPP

Altered timing of uptake

N loss

Fire

Altered composition

N cycling and pools

Effects on Nitrogen


iii) Threatened & endangered species• Overview

~409 animals and 598 plants are federally listed species in US


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)


iii) Threatened & endangered species • Overview

Effects can be by:Direct species replacementIndirect through effects on community structure or function


iii) Threatened & endangered species : IUCN database • Overview

Effects can be by:Direct species replacementIndirect through effects on community structure or function

WorldwideExtinctions: 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


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 seedlong growing seasontolerates heavy grazingfair forage qualityforms dense sod in mature pastures




C4 perennial bunchgrass: desirable forage speciesSeeded extensively (for example, ~2 million acres in western

OK)




C4 perennial bunchgrass: desirable forage speciesSeeded extensivelyBut extremely invasive:

Spread along highways into native areas (cemetaries, native grasslands)

Difficult to controlThreatens federally listed endangered plant Ambrosia

cheiranthefolia (south Texas ambrosia)


iii) Threatened & endangered species• Overview• Specific examples: Hawaii

80-90 native plant species extinct270 plant species listed as threatened or endangered94 noxious weeds, many more alien species


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)




• 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)


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


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 selectedWidespreadRapid dispersalHigh variabilityGeneralistHuman commensalism

Traits of ‘losers’K selectedRareSlow dispersalLow variabilityspecialistMaladapted to humans


Summary• Only a small percentage (0.1%) of introduced plants become a

problem



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)





• 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)







frequency/intensity)Loss of native species (threatened or endangered species)

Often in conjunction with human-caused habitat change







frequency/intensity)Loss of native species (threatened or endangered species)

Often in conjunction with human-caused habitat changeEspecially on islandsEspecially rare/specialized speciesMore evidence for population reduction than for extinction (e.g.

Harrison et al 2006)

Documents

Reading assignments: ecological impacts Invasives and fire: –D’Antonio and Vitousek 1992. Biological invasions by exotic grasses, the grass-fire cycle,