Lecture 23: Eradication Flashcards
What is eradication?
- removal of every potentially reproducing individual of a species OR the reduction of their population density below sustainable levels
- *if you get for ex invasive weeds lower in abundance, it can increase native crab abundance i.e. don’t always have to remove ALL to see benefits
- –> just get them to a low enough level that they are doomed after it
Removal of a bioengineer?
- eradication of intertidal weeds like eel gras, increases native crab populations
Rat eradication in Norway?
- increases native shrew population
Issue using chemical eradication method?
- needs to be specialist
- if not it will harm natives as well
ex: S. american fire ant
L> first pesticide use caused cattle deaths and areas were recolonized by fire ants before native species recovered
**Vietnam of entomology
When is eradication feasible ?
- invader is detectable early
- occurs in a restricted area
- methods can be applied quickly
Eradication of S.African polychaete worm in Cali?
- worms cannot swim, worms crawl in search of gastropod host.
- reduce population of hosts
L> polycheates had no hosts now and were wiped out…snails recovered bc minimal impacts of eradication: snails have pelagic larvae allowing rapid recolonization
Eradication of Stripped mussel in darwin harbour?
- native to Caribbean
- found in marinas
- discovered 6 months into introduction
- marinas were quarantined and treated with chlorine
- wiped them out
Caulerpa taxifolia eradication?
- invaded US via transport for aquariums
- covered lagoon floor with tarp and inject chlorine
What are the requirements for successful eradication ?
- The biology of the target species must make it susceptible to control measures
L> host specificity and poor dispersal ability ex in citrus canker , bacterial disease of citrus trees - resources must be sufficient to compete the project
- The managing agency must have authority and public support to take steps
- Re-invasion must be prevented
- The target species must be detected at low densities
- The community or ecosystem must be restored following removal of the target species
Asian citrus black fly eradication
-2 invasions
- 1st took three years to remove via soap, paraffin oil and water
L> insularity of the site was crucial to reduce human traffic preventing dispersal during eradication
- 2nd invasion fort lauderdale BUT eradication was unsuccessful
How do we declare a successful eradication
- post hoc or based on intuition
BUT we need a reliable method for recognizing a successful wipe out
What can go wrong with eradication?
- without sufficient planning eradication’s can have secondary effects:
1. unexpected impacts on native species and ecosystem services
2. increased susceptibility to invasion - these effects are more likely if:
A. many other invaders are present OR
B. an invader replaces a keystone native species
- Predator-prey interactions
- Apparent competition and prey switching
- introduced generalist predator
- feeds both on exotic prey and native prey
- so say you remove the exotic prey, and it feed on it more it will now harm the native more
- *apparent competition: being less vulnerable to a common predator bc it is focusing on another prey
- Predator-prey interactions
- Apparent competition and prey switching
ex: Stoat in NZ
- feeds on rats and opossums more so and native birds less so
- opossums and rats are introduced
- knocked out them
- started feeding on birds
- Predator-prey interactions
- Apparent competition and prey switching
- compare to Hyperpredation??
- Brown tree snake ex
- it preyed heavily on native species like birds and bats
- other introduced sp = lizards for ex
- as native sp (bats and birds go down) so would the snakes abundance IF it only fed on the native sp but it can subsidize itself with the exotic sp like lizards
- *can drive prey down while not experiencing a negative feedback
- Predator-prey interactions : Meso-predator release
- ex: Kakapo in NZ
- endemic
- flightless parrot
- nocturnal
- naive to mamalian predators
- threaten by introduced cats and rats
- Cats feed on introduced rats mostly and less so on the native parrot
- introduced rats feed on the parrot only
- if cat is removed first-rate is released from the top predator and can designate parrot
- if the rat is removed first the cat will switch to the parrot
- *need to remove both together
- Predator-prey interactions : Meso-predator release
ex: Marion island
- removed exotic cats
- which fed on exotic mice
- they were released from predation and fed more on the native flightless moth which was important to nutrient cycling
**bad bc island species are usually not redundant (so removal = loss of an ecosystem service)
- Predator-prey interactions : Meso-predator release
ex: Macqaurie island
- eradication of exotic cats
- rabbits increased
- vegetation change cursed bc of rabbits being released from predation
- Plant-herbivore interactions
- apparent comp?
- if you remove the exotic herbivore it could increase competition between native plant and exotic plant species , where the exotic might outcompete the native
- Plant-herbivore interactions
- Mascarene Islands: herbivore replacement
- giant tortoises endemic to the islands browsed on native plants but they were hunted to extinction
- introduction of goats replaced the tortoises
L> feeds on both exotic plants and native plants
L> when the goat was eradicated , exotic plants flourished which then reduced native plants
- Plant-herbivore interactions
ex: Pigs and Goats on Sarigan Island
- eradication was followed by the explosion of an undetected exotic vine
- Native species dependence on exotic species
- example
- endangered bird species using saltcedar
Eradication must be followed by?
-restoration
ex: Ice plant
L> removes salt from soil
L> when it dies off the soil gets hyper saturated with salt
L. SO IF YOU REMOVE THE PLANT, THE SOIL NEEDS TO BE REMOVED AS WELL
IF RESTORATION OF THE HABITAT IS THE GOAL
Summary?
-eradication is possible only under certain conditions
- eradication must be followed by vector control
- eradication will usually have negative impacts on non target species
L> these increase with numbers of interacting invaders (interconnectedness)
