A behavioral ecologist was interested in testing the hypothesis that larval sala

Question

A behavioral ecologist was interested in testing the hypothesis that larval salamanders (basically tadpoles) respond to the presence of chemical cues in the water from their predators (in this case, adult newts) by altering their activity. The idea is that smaller larvae can be more easily consumed by the predatory newts and reducing movement makes the larvae less apparent to the newt predators. Therefore, smaller larvae should reduce their movement more than larger larvae when exposed to the chemical cues of newt presence. To test this the ecologist took 20 randomly selected larvae and measured their lengths. Then she placed each tadpole in a container with fresh water and measured their baseline activity (the number of seconds of continuous movement or feeding). Then she added 1 mL of water from a container with an adult newt in it. This water contained the chemical cues of the newt’s presence. She measured the number of seconds of continuous movement or feeding after exposure to the cue. Change in activity is the number of seconds active after exposure to the cue minus the number of seconds active before exposure to the cue. Larvae that reduce activity due to the cue should have negative scores, while larvae that don’t change activity should get a score around 0, and larvae that increase activity should have positive values.

Which best represents the null hypothesis? Which best represents the alternative hypothesis?

A. µ1 = µ2,

B. µ1 µ2

C. µ1 > µ2

D. µ1 < µ2

E. µ1 µ2

F. µ1 µ2

G. 1 = 2

H. 1 2

I. 1 > 2

J. 1 < 2

K. 1 2

L. 1 2

M. = 0

N. 0

O. = 0

P. 0

Q. These data are consistent with a normal distribution.

R. These data are not consistent with a normal distribution.

S. The variances of the variables are approximately equal.

T. The variances of the variables are not equal.

Explanation / Answer

Alternate hypothesis is

d) mu1 < mu2

Because the reduced activtiy of small larvae is tested against the high movement of large larvae.

That means mu1 the actitity of small larvae should be lesser than high movement of larger larvae

Null hypothesis is the default, which says there is no difference between small and larger larvae.

a) mu1 = mu2.

The variables have to consistent with a normal distribution to test using t-test or z-test for comparing the means.

The variances of the variables are approximately equal to carry out the default t-test or z-test, otherwise some advanced tests have to be performed.

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