Invasive Species Impacts
Wilcove Quiz 1. Based on your understanding of island biogeography, explain why plants in Hawaii are likely to be more imperiled by non-native species than plants in the continental U.S. 2. How might habitat degradation and disturbance further facilitate non-native species invasion? 3. Wilcove et al. argue that human population growth in the U.S. likely to disproportionately affect endangered species. Why?
Wilcove Quiz 1. Why might the requirements of the Endangered Species Act (ESA) fail to adequately protect endangered species from invasive species? 2. Clavero & Garcia-Berthou argue that invasive species are the leading cause of bird extinctions. What sorts of invaders (e.g., taxonomic groups) do you think might have the greatest impact on birds, and why?
Red-eared slider turtle Trachemys scripta elegans
Invasive species impacts • Competition • Community changes (biotic effects)
• Direct predation • Ecosystem functioning (abiotic effects)
• Importance of impact is in the eye of the beholder
Plant competition experiments
Invasive plants are good competitors Based on a meta-analysis of plant competition experiments: – Competition from native plants reduces invasive plant biomass by ~18% – Competition from invasive plants reduces native plant biomass by ~47%
Vila & Weiner, 2004
Invasive plants are good competitors Competition also affects reproduction With competition Without competition
First year
Inflorescence
Lockwood, 2007
Invasive plants are good competitors
Native plant
Invasive competitor
Impacts of plant competition
Effect size
super
twin
Widespread dominant everywhere (‘transformer’)
Widespread, but not dominant anywhere Locally dominant
selective
Range of local ecosystems Lockwood, 2007
Impacts of plant competition
Effect size
super
Range of local ecosystems
Widespread dominant everywhere (‘transformer’)
Impacts of plant competition
Effect size
super
twin
Widespread dominant everywhere (‘transformer’)
Widespread, but not dominant anywhere Locally dominant
selective
Range of local ecosystems
Most invasive plants Lockwood, 2007
Invasive plant impacts Direct effects of competition
Indirect effects of competition
Vila et al., 2011
Invasive Species as Competitors • Fire ants compete for food with all native ants • Reduced numbers of native ants and local extinction of several species (reduced species richness)
Community change: biotic homogenization
Regional loss of diversity, even though local diversity is maintained Olden, 2006
Diversity & Ecosystem Resilience • How does diversity promote ecosystem resilience?
Diversity & Ecosystem Resilience • How does diversity promote ecosystem resilience? – Not all species are affected by disturbance in the same way – Functional redundancy means that if one species takes a hit, another can step in to take its place
Proportion of seeds remaining
Community change: indirect effects Ants No ants
Field mouse foraging declines when fire ants are present
Community change: indirect effects
- Earthworms may increase N deposition (break down litter faster) increasing resources
- Burrowing may disrupt soil mycorrhizae (symbiots of native plants)
Nuzzo et al., 2009
Community change: indirect effects
Nuzzo et al., 2009
Invasive Species as Predators
Towns et al., 2006
Invasive Species as Predators
Wiles et al., 2003
Ecosystem function (abiotic effects) Invaded
Un-invaded
Mack et al., 2000 after Vitousek & Walker, 1989
Ecosystem function (abiotic effects)
Zavaleta, 2000
Ecosystem function (abiotic effects) Buffelgrass (Pennisetum ciliare)
Cogongrass (Imperata cylindrica)
D’Antonio & Vitousek, 1992
Positive impacts
Sogge et al., 2005
Economic consequences
$35 Billion annually in invasive plant damage & control Pimentel et al., 2005
Economic consequences
$20 Billion annually in invasive insect damage & control Pimentel et al., 2005
Economic consequences
$47 Billion for pathogens
Pimentel et al., 2005
Economic consequences
$45 Billion for vertebrates
Pimentel et al., 2005
Species of the day: Cheatgrass (Bromus tectorum) Cheatgrass dominates at least 40,000 km2 (Massachusetts is 27,000 km2) Annual grass, takes advantage of periodic spring water availability
Wet
Dry
Invasive grass-fire cycle
Invasive grass-fire cycle
During the 2000s, cheatgrass was at least twice as likely to burn as any other vegetation type
Invasive grass-fire cycle
Cheatgrass growth and subsequent fires are highly correlated to El Nino rainfall events (taking advantage of temporal variability in resources)
Invasive grass-fire cycle
Large fires that burn multiple vegetation types are more likely to have started in cheatgrass grassland
Impacts Discussion
