Short on time? This page is the recap. For explanations, figures and worked examples, use the full study guide.
Recap
- Organisms detect changes outside (light, night length, temperature, predators) and inside (hunger, water loss, hormones) and respond.
- Behavioural responses are actions (moving, calling, hiding). Physiological responses are internal changes (heart rate, flowering, defensive chemicals).
- Taxis: movement directed toward (+) or away from (−) a stimulus. Kinesis: speed or turning rate changes with stimulus strength; no direction.
- Innate behaviour is inherited and correct first time. Learned behaviour changes with experience (imprinting, song learning, habituation). Selection favours both when they raise fitness.
- Organisms exchange information through visual, audible, tactile, electrical and chemical signals: to warn, to show dominance, to find food, to hold territory and to attract mates.
- Cooperation (pack hunting, herds and flocks, insect colonies, helping relatives) tends to raise individual fitness and population survival.
- Specific mechanisms of behaviour and communication are not examined. Link stimulus, response and fitness.
Key relationships
| Idea | Link to fitness |
|---|---|
| response matches a reliable cue (night length, season) | reproduction timed for best conditions |
| warning colour, alarm call | fewer attacks; others escape |
| song, display, scent mark | more mates or a better territory → more offspring |
| cooperative hunting or defence | more food and safer young per individual |
| kin selection | shared alleles passed on through relatives |
| Statistic | Use |
|---|---|
| χ² = Σ (o − e)² ÷ e | o = observed count, e = expected count under “no preference” |
| df = categories − 1 | χ² above the critical value → reject the null hypothesis |
Assumptions behind experiments
- Animals act independently (each is one count) and each is counted once.
- The control differs from the experiment only in the factor tested (for example, both halves dark to check for side bias).
- One trial supports a conclusion for those conditions; it does not prove it.
Mistakes to avoid
- Calling an end-point count “taxis” without path data.
- Saying animals behave “for the good of the species”.
- Using number of animals − 1 as degrees of freedom.
- Choosing a control that changes two things at once.
- Writing that rejecting the null hypothesis “proves” the hypothesis.
- Describing a mechanism instead of the fitness consequence.
Quick self-check
- A fictional soil insect moves more slowly and turns more often in damp air than in dry air, with no consistent direction. Taxis or kinesis? (Kinesis: the change is in speed and turning, not direction.)
- 50 insects in a two-sided chamber: 33 on one side, 17 on the other. Reject “no preference”? (Expected 25 each; χ² = 64/25 + 64/25 = 5.12; df = 1; 5.12 > 3.84, so reject.)
- Why can a risky alarm call be favoured? (If listeners are relatives, the caller’s shared alleles survive in them: kin selection.)
Next: practice questions.