Invasive Species Case Study 3*:

California Poisons Lake, Targeting Invasive Pike


California's Department of Fish and Game has begun poisoning Lake Davis, near the small Sierra Nevada community of Portola. The move targets the northern pike, an invasive species — but the gallons of poison will kill many other fish, as well.  In some parts of the country, the northern pike is a popular game fish. A bit bony and toothy, the fish puts up a good fight, which fishermen find rewarding.  No one knows exactly how the northern pike got from its native waters to Lake Davis, but most people figure they were brought in by someone from Minnesota or a local resident who missed fishing for the feisty pike. But in California, the fish are an unwelcome invader.


"They're a voracious fast-growing predator. We don't want them around," said Peter Moyle, a fish biologist at UC-Davis who specializes in invasive species.  Pike can get quite large and devour fish up to half their size — sometimes even waterfowl and small mammals.


The California Department of Fish and Game say they want to prevent the pike from working down the water system, getting into the delta and killing endangered salmon. The state tried to eradicate the pike a decade ago by setting off explosions in the lake, electro-fishing and poisoning. It was highly controversial — and the pike came back.  The Fish and Game officials tried to poison the pike out of the lake in 1997, but like the plot of a horror movie — 18 months later they were back with a vengeance. Since then, the state has tried electro-fishing, netting, even explosives. And now they're back to poison.  Two dozen boats were used on Lake Davis pumping thousands of gallons of a fish-killing poison called rotenone into the water.  The poison will also be fed into miles of tributaries and ponds around the lake. Ed Pert, who is leading the pike eradication project, says the rotenone should knock out everything with gills: pike, trout, catfish, including aquatic bugs.


The pike takeover has been nothing but trouble for the town of Portola just south of Lake Davis. The lake used to be Portola's drinking water source — until the first time the state tried to kill the pike with rotenone. Back then, hundreds of residents protested and the mayor even chained himself to a buoy to try and stop the poisoning. This time the opposition is muted and most have come to see it as necessary.  A local store owner says she hasn't opened for business in three years. She says the pike ate up Lake Davis's trophy-sized trout and drove away her customers. She can't wait until the pike are gone and the state restocks the lake with trout.  It will take a couple of years to know whether the operation was a success. One leading biologist describes it as a crapshoot. And if the pike do return, they're likely here to stay.  Fish and Game officials say this is their last best effort to eradicate the pike in Lake Davis, and in California.


General: all groups have the same questions:

1. Compare the terms ecosystem, community, species, and population as they relate to ecology.
2. What is the difference between exponential and logistic growth? What are some density-dependent factors that keep populations from growing exponentially indefinitely? What are some density-independent factors?
3. What is an ecological niche? What happens when two species have identical niches? How does the fundamental niche differ from the realized niche?
4. Explain an example of resource partitioning, and explain how natural selection can lead to character displacement.
5. Describe an example of each of the three types of symbiosis discussed in your text.
6. Explain how energy moves through the living components of an ecosystem (starting with primary productivity and including a discussion of food webs and ecological pyramids).
7. Explain how water, carbon, and nitrogen cycle through ecosystems, and give at least one example for each of how human activities can alter the cycle.
8. Seven different biomes are described in your textbook. If you were in charge of global ecosystem conservation but were told you had to focus all of your resources on preserving two of the seven types of biospheres, which would you choose, and why?


Specific to this case study


1. Describe a typical Sierra Nevada freshwater lake ecosystem and community structure.

2. What is meant by the term “biodiversity”?  Defend or dispute the statement "Exotics increase the biodiversity of an area." 

3. Describe the effect of invasive species on community structure with the lake ecosystem.

4. Poisoning of the lake ecosystem seems drastic.  Who and how should this decision be made?

5. Describe other possible mechanisms that could be used to control and/or eradicate the Pike from Lake Davis.  How successful have “biological controls” been elsewhere in controlling invasive species? Discuss.

6. Discuss the economic impacts the discovery of the Pike has had on Lake Davis and the surrounding towns. If the Pike cannot be eradicated, discuss how the community will be impacted both good and bad.


* based on a report by Tamara Keith, NPR, September 25, 2007 Š