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Invasive SpeciesInvasive Species
Geography 444
Adopted from Dr. Deborah Kennard
Weeds, Exotics or Invasives?
• What is a weed?
• Invasive species?
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Weeds, Exotics or Invasives?
• Exotic or non-native:
• “Non-native invasive pest plant”
http://dnr.metrokc.gov/wlr/lands/weeds/photos/kudzu_impact.jpg
Where do our non-native invasives plants come from?
• From a different ? • From a similar ?
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What are biotic provinces?• Areas on the earth that have
evolutionarily relatedorganisms because of geographic isolation
• Animals are more related to other animals in their biotic province than to animals that fill the same niche in a different province– Large mammal herbivores:
Bi d h• Bison and pronghorn antelope in North America
• giraffes and antelopes in Africa
• large rodents like capybara in S. America
• kangaroo in Australia
• In each major biome, certain animal or plant families dominate.
Si il f t l• Similar features evolve because of similar environments– Thorns on some plants are
modified leaves, on other plants thorns are modified branches
– Stem succulence in cacti (Americas) and euphorbias (Africa)
– “Convergent evolution”
– “ecological equivalents”
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• Species introductions bring species that have not evolved and adapted in the presence of the native species.
• Why is this significant?
• “Competitive exclusion principle”: Two species that havespecies that have exactly the same requirements (niches) cannot coexist in the same habitat.
• Native species have adapted to this through niche partitioning.
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Do all species introductions lead to invasive species?
Biomes• A group of similar
ecosystems– Desert, tropical rain , p
forest, grassland
• Determined by physical factors– precipitation– temperature– sunlight & seasons
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• Similar environments lead to the evolution of organisms similar in form and functionform and function (but not necessarily genetic heritage)
• Similar biomes generally share g ysame physiognomy (shape of vegetation) or vegetation characteristics
“Convergent evolution”
Moving Species Around
• Local moves are less harmful than• Local moves are less harmful than global moves.
• Less likely to be harmful if you move a species within its biotic province
• Moving a species into the same biomeo g a spec es o e sa e b o ein a different biotic province is likely to be harmful.
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What makes a species more likelyto be invasive?
• perennial
• germination in wide range of physical conditions• germination in wide range of physical conditions
• grows quickly
• flowers early
• self-compatible
• produces many seeds which disperse widely
• reproduces vegetativelyreproduces vegetatively
• good competitor
Few species will have ALL of these characteristics
Having these characteristics does not mean a species is a successful invader
• If it has high native species richness
What makes a place more likelyto be invaded?
• Islands have more than mainlands
• Temperate agricultural areas and urbanareas
• Nature reserves had less than non-reserves
• The larger the area, the more invasives
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Effects• Economic cost
– $97 billion/year cost to the U.S. economy
• crop losses, reduced grazing potential, weed control costs
• Leafy spurge (Euphorbia esula)– introduced in Minnesota with
t hi toats shipment
– currently ~ 2.5 million acres infested in Canada & U.S.
– invades rangelands
– forage yield reductions of 10-100%
Effects• Decreases Diversity
– decreases species richness by out-competing natives
• Miconia (Miconia calvescens)
– spread in Tahiti from Papeari Botanical Gardens, 1937,
• now invaded 70% Tahitian forests, with 25% dense monospecific stands
• 70-100 plant species threatened (35-45 endemics)
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Invasive species and
diversity
Brown tree snake
• Extinctions and loss of species diversity from Guam
• Safety and health of Pacific Island residents and tourists
• Economic damages from the Brown Treesnake
• Impacts on military from the Brown Treesnake
Effects• Ecosystem function
– may change primary production, nutrient cycling, water consumption
• Myrica Faya– Invasive in Hawaii– N fixing tree alters N
dynamics– N inputs mostly from Myrica in
some communities since volcanic soils are N-poor
– Hawaii the “exotic invasive capital of the world”
– species more susceptible to invasives:
• 1200 species, 90% endemic• humans have added ~4600
species
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Effects• Altered fire regimes
– Can either promote fire or suppress firesuppress fire
• Cheatgrass (Bromus
tectorum)– Provides fine flashy fuels
in arid ecosystem it invades
– Fires ignite and carry wellg y
– Comes back VERY well after fire
– Increases the frequency of fires
Saltcedar (Tamarix spp.)
• From Eurasia
• sold in 1850’s for erosion control on stream bankscontrol on stream banks
• 1 million acres in U.S. southwest
• outcompetes native riparian cottonwood-willow forests
• decreases diversity of birds, small mammals, invertebrates
• Changes the functioning of riparian zones
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Invasives in California
http://www.cal-ipc.org/
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