Invasive Species. Outline. What are invasive species? How are they spread? Are they all bad? How does a species become invasive? What impacts do they have on biodiversity? How can their impacts be mitigated?. What are invasive species?. Invasive Terminology. Exotic Introduced
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Outline • What are invasive species? • How are they spread? • Are they all bad? • How does a species become invasive? • What impacts do they have on biodiversity? • How can their impacts be mitigated?
Invasive Terminology • Exotic • Introduced • Non-native • Non-indigenous • Alien • #@$%
“Invasive species are exotic or native species that displace, destroy, or out-compete native species for food, space, and water or otherwise fundamentally alter ecological processes, thus threatening intact ecosystems.”
How do they spread? As you can probably guess… HUMANS!!! Introduced either intentionally or accidently
European Starling “When he lies asleep,And in his ear I’ll holla ‘Mortimer!’Nay,I’ll have a starling shall be taught to speakNothing but ‘Mortimer,’ and give it him,To keep his anger still in motion.”[1st Henry IV – I, 3]
Pump house and water control structure for green-tree impoundment at Montezuma National Wildlife Refuge in central New York, 18 June 1968 versus 10 years later
Wet Loamy SoilsTWF005 1Kg The mixture contains 20% wild flowers Betony, Black Knapweed, Common Fleabane, Devils Bit Scabious, Greater Birds-foot Trefoil, Hemp Abrimony, Marsh Woundwort, Meadow Buttercup, Meadow Rue, Meadow Sweet, Ox-eye Daisy, Pepper Saxifrage, Purple Loosestrife, Ragged Robin, Sneezewort, Square stem St John's Wort, Yellow Flag Iris and Yellow RattleGrasses 80%Browntop Bentgrass, Chewings Fescue, Common Sedge, Crested Dogstail, Meadow Barley, Meadow Foxtail, Pendulas Sedge, Sheep's Fescue, Smooth Meadowgrass, Sweet Vernal and Tufted Hairgrass.
Historical versus Current Rates of Colonization • Hawaiian Islands: • flowering plants colonized at a rate of 1/100,000 years before 1778 • since 1778 (European arrival) at a rate of 4/year • Galapagos Islands • 1/10,000 unaided • 1/2 years since European arrival in 1535
Frequency of Finding Weeds (%) Distance from Road or Trail Rew and coworkers, 2002
Role of Roads in Dispersal Alien Species in Chile Chapter 16 in Invasive Species in a Changing World, H.A. Mooney & R. J. Hobbs, eds.
Are they all bad? • Most exotic species are not invasive (Mooney and Hobb 2000) • 50,000 exotic species have been introduced to U.S. (Pimentel et al. 2005) • Provide 98% of U.S. food ($800 billion per year) (USBC 2001) • Actual data supporting invasive species-caused extinctions lacking (Gurevitch and Padilla 2004) • Only about 15% are considered "harmful" (U.S. Office of Technology Assessment 1993) • Xenophobia
The problem species… • But the harmful 15 % have become invaders, causing widespread problems that can prove serious and exceedingly costly • World’s Top 100 most invasive species (http://www.issg.org/database/species/ ) • From 1906 to 1991, a scant 79 exotic species exacted about $97 billion in economic damages • Today damages are estimated at $120 billion per year (Pimentel et al. 2005)
Exotics and Endangered Species • Of the 632 species and subspecies recently officially listed as "endangered" under the Endangered Species Act • 45 are primarily threatened by competition from introduced species. • About 100 species are threatened by introduced species that prey or feed on them. • 5 are threatened chiefly by exotic diseases carried by introduced species. • For 3, a contributing threat is hybridization with introduced plants or animals.
Nile Perch Devastation • Before the introduction of the Nile perch approximately • 400 haplochromine cichlid species • 40 non-cichlid species • Most endemic • Today Haplochromines nearly vanished -- at least half the fauna feared extinct • Important “table fish” disappeared
How does a species become invasive? Three main mechanisms • Ecological disturbance • Escape from predators • Lack of competitors (fill a niche)
Deer Devour Wild Ginseng (McGraw and Furedi 2005) • If not checked, the white-tailed deer will drive wild American ginseng -- one of the most widely harvested medicinal plants in the United States -- to extinction. • Monitored seven populations of wild ginseng in West Virginia forests • Checked every 3 weeks during the spring and summer. • Cameras confirmed deer as the culprits. • Populations declined by 2.7% per year on average. • Deer grazing rates would have to be cut by half to ensure the survival of those populations.
What impacts do they have on biodiversity? • Competition • Ecosystem engineers • Introduce and/or spread pathogens • Predation • Hybridization
The Vine that ate the South • Kudzu (Pueraria lobata)an ornamental plant introduced from Japan • Planting encouraged by US gov’t • Naturalized over 20-30,000 km² in the South • Costs $500 million annually in lost cropland
Ecological Impacts • In Great Smokey Mountains National Park hogs have: • reduced plant cover by as much as 80% • increase bare ground by 88% • reduced the depth of the forest litter by 65% • reduced the weight of leaf litter by 59% • exposed 1,400 - 2,800 tree roots/ha • accelerated decomposition and loss of nutrients from the forest floor • altered the nitrogen transformation process in watersheds, with nitrate-nitrogen in stream water double their usual levels
Effects • In less than 50 years had spread over 225 million acres of the eastern U.S., destroying virtually every chestnut tree (probably one billion) • Chestnut had comprised a quarter or more of the canopy of tall trees in many forests • Staggering ecosystem effects – passenger pigeons? • More subtle ones, too: several insect species that live only on the chestnut are now extinct or endangered
Christmas Island Rat (Rattus macleari) • Wyatt et al. 2008 • Extinction of endemic rat coincides with introduction of disease brought by introduced by black rats
Chytrid Fungus • Blamed for massive frog die-offs worldwide (infamous example: Golden toad) • Spread in C. America estimated at 28-100 km/year • In cool, moist environments 50% of species and 80% of individuals disappear in 1 year • Amphibian Ark- Atlanta Zoo • How did it spread?
Impacts Between 1960 and the 1980s, the following birds became extinct on Guam: • Guam Flycatcher • Rufus Fantail • Brindled White-eye • White-throated Ground Dove • Cardinal Honey-eater • Marianas Fruit-Dove The following became extinct in the wild, but have been maintained in captivity: • Guam Rail • Micronesian Kingfisher
The Culprit • The spread of the snake since the 1950’s closely parallels the extinction of the birds -- birds disappear within a year or so of the snake's arrival. • The snake is known to feed on birds in its native range • Very good at climbing - even onto thin branches. • Tethered and captive birds are, in 85% of cases, eaten within one night.
Question • What mammal is responsible for annually killing 38 million songbirds, four million cottontail rabbits and 100 million small mammals just in Wisconsin?(A) Skunk (B) Fox (C) Raccoon (D) Pine Marten (E) All of the above (F) None of the above
Subsidized Predators • In the United States, domestic cats (>60 million in U.S. homes and perhaps 30 to 40 million more feral) are estimated to kill: • Over a billion native small mammals • And, conservatively, 200 million birds annually • Domestic cats have been implicated, to varying degrees, in: • The endangerment of at least six species of North American birds and small mammals, • The extinction of more than 20 animal species in Australia.
New Zealand Gray Duck Gillespie 1985
Stopping the Spread • Prevent colonization • Eradicate initial populations • Control established populations
Prevent colonization • Planned imports and releases should by regulated by a “clean-list” • Very different from a a “dirty list” approach • Similarly, need a policy of "guilty until proven innocent," rather than assuming that a species will be harmless • No chances should be taken on some imports - e.g., Siberian timber
Unscrambling the Egg • When governments fund an introduction, they should also fund the studies to determine the ecological impacts of the introduction • Particularly important internationally in the context of development assistance projects • Governments should adopt general policies favoring native species