Testing Hypotheses in Animal Behavior II (5)

Includes issue with comparative, independent contrasts (continuous and discrete), female swellings (indepedent contrasts), and adaptive significance of behavior

What is the t test? What does it assume? How is it calculated?

1. The t-test tells you whether the difference between two populations is statistically significant or if its due to chance.

2. The test assumes that the data points are independent because it’s the only way the standard deviation of the sample is accurate compared to the standard deviation of the population.

3. t = mean 1 - mean 2 / (sd(1/n - 1/n)^(1/2))

What things can go wrong in a t test? What can it be used to calculate?

1. If all in the same family, then sd decreases, t increases, and there’s an increased chance of a type 1 error (alt. hypothesis).

2. It can be used to calculate the time period at which there were zero differences between groups (knowing mutation rate and number of differences in DNA)

What is an independent contrast? An example?

1. Is the idea that one species evolves independently after diverging, so diverges between sets of related taxa can give independent changes for analysis.

2. Simple versus complex warbler calls and relative size of higher vocal center.

What is a discrete trait? What can they along with independent contrasts be used for?

1. Countable, such as mating system, diet, territoriality

2. Can use these to ask what came first? Swellings or multimale grouping? Flocking or diet?

What are some details on the swelling example? When was it lost and why? How does this relate to independent contrasts?

1. Female primate swell when ready to mate, let males know. It was thought to be a continuous gradient so subordinate males would mate before ovulation and prime males during.

2. It was lost twice. The first time it was because the group went back to single male mating. The second time was because there was an increase in seasonality of breeding (females all ready at once, so competition wasn’t needed and therefore swelling wasn’t needed).

3. The swelling example shows that independent contrasts can be used to answer what came first and why it would be lost.

What does adaptation focus on? What is an example of adaptation? What is the limit of this example?

1. Cost/benefit analysis

2. Black-headed gulls

   1. Remove shells of eggs to reduce predation, but they wait one hour to do it so that way chicks can dry off (not waiting increases chances of cannibalism)

   2. BUT! Oystercatchers live alone so they don’t wait (remove immediately)

3. Limit is that this doesn’t explain why ½ an hour doesn’t work.