Hitchhiker Snails: A type of small snail is very widespread in Japan, and colonies of the snails that are genetically similar have been found very far apart. Scientists wondered how the snails could travel such long distances. A recent study provides the answer. Biologist Shinichiro Wada fed live snails to birds and found that some of the snails were excreted alive out the other end. The snails apparently are able to seal their shells shut to keep the digestive fluids from getting in. What is the best estimate for the proportion of all snails of this type to live after being eaten by a bird?
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Hitchhiker Snails A type of small snail is very widespread in Japan, and colonies of the snails that are genetically similar have been found very far apart. Scientists wondered how the snails could travel such long distances. A recent study $^{41}$ provides the answer. Biologist Shinichiro Wada fed 174 live snails to birds and found that 26 of the snails were excreted live out the other end. The snails apparently are able to seal their shells shut to keep the digestive fluids from getting in. (a) What is the best estimate for the proportion of all snails of this type to live after being eaten by a bird? (b) Figure 3.19 shows a bootstrap distribution based on this sample. Estimate the standard error. (c) Use the standard error from part (b) to find and interpret a $95 \%$ confidence interval for the proportion of all snails of this type to live after being eaten by a bird. (d) Using your answer to part (c), is it plausible that $20 \%$ of all snails of this type live after being eaten by a bird?
Confidence Intervals
Constructing Bootstrap Confidence Intervals
A population of snails is preyed on by birds that break the snails open on rocks, eat the soft bodies, and leave the shells. The snails occur in both striped and unstriped forms. In one area, researchers counted both live snails and broken shells. Their data are summarized below: Which snail form seems better adapted to this environment? Why? Predict how the frequencies of striped and unstriped snails might change in the future.
The snail parasite Leucochloridium is a worm that eats the internal organs of snails, but it must complete its life cycle by breeding in the intestines of birds. Snails that are infected crawl out on leaves during the day, and the parasite pulses in their eye stalks in a way that resembles a caterpillar moving. Birds attack and try to eat the caterpillar. This bizarre adaptation likely evolved through selection to reduce the number of worms in an individual snail, increase the probability that infected snails will be removed from the host population, reduce the virulence of the parasite which can sometimes castrate the host, increase the transmission rate among host snails, and reduce the density of the host population below the threshold value necessary for the parasite to spread.
Marisa A.
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