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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/