AP Biology · Unit 8 · Topic 8.1
A response is not a feeling and not a decision. It is a change in behavior or physiology that follows a cue, and the ones that persist are the ones that left more offspring.
Learning objective 8.1.A Explain how the behavioral and physiological response of an organism is related to changes in internal or external environment, and 8.1.B explain how the behavioral responses of organisms affect their overall fitness and may contribute to the success of a population.
Every animal here starts somewhere random and takes four hundred steps. The three groups differ only in what their steps are allowed to depend on. Watch where they end up — and then watch the last number in the readout, which is the one that actually tells you what kind of response you are looking at.
A kinesis has one dial: how much to slow down when conditions are good. If the amount of clustering were what defined the mechanism, then turning that dial far enough ought to make kinesis indistinguishable from taxis. Here is what happens when you turn it.
| Slowing strength | Ends near the optimum | Approach steps up-gradient |
|---|
The course framework attaches an exclusion statement to this objective: the specific mechanisms are not examinable. What is examinable is the classification and the link to fitness, so that is what this table is for.
| Response | Behavioral or physiological? | Cue | What triggers it | Why it helps |
|---|
There are four things an organism could do and only one of them is right, and which one is right keeps changing. An innate responder does whatever it was born doing — free, but only correct while the world happens to match. A learned responder figures it out during its lifetime — almost always correct, but it pays for the time and the risk. Change how fast the world moves and watch which one wins.
| Environment changes every | Innate fitness | Learned fitness | Winner |
|---|
Notice which column moves. The learner's fitness is identical in every row, because it works the answer out fresh each generation and does not care what the answer was last time. It is paying a fixed price to become indifferent to how fast the world changes. That is only a good deal when the world changes fast — which is exactly why both strategies exist, and why neither is the more advanced one.
Most behaviors are easy to explain: the animal does better. Helping is not, and an alarm call is the hard case — it makes the caller more conspicuous to the predator and makes everyone else safer. A behavior like that should be selected against, and it is not. The resolution is to stop counting individuals and start counting copies of the allele.
| Relative | Relatedness, r | Benefit needed to repay one unit of cost |
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| Signal | Channel | What it is for | Worth noticing |
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Answer these in your own words before you open the answers.
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