In Group Behavior animals worked together. Here we look at how single organisms respond to cues in their surroundings, and at the signals they send each other. The responses are adaptations: they help an organism find food, avoid danger and survive.
| Response | What it is | Example |
|---|---|---|
| Tropism (plants) | Growth toward or away from a stimulus | Shoots bend toward light (phototropism) |
| Photoperiodism (plants) | A response to the length of night | Some plants flower only when nights are long, others only when nights are short |
| Kinesis (animals) | A change in how fast or how often an animal moves or turns, with no set direction | Pill bugs move more in dry places and slow down in damp ones, so they end up gathering where it is damp |
| Taxis (animals) | Movement directly toward or away from a stimulus | Many moths fly toward light; trout swim to face the current |
| Communication | Signals that change another's behavior | The honeybee waggle dance; alarm calls; ant scent trails |
Key idea
Why it works
In the waggle dance, studied by Karl von Frisch, a forager returning to the dark hive dances a figure eight on the comb. The angle of the straight "waggle run" from vertical shows the direction of the food relative to the sun, and the length of the waggle run shows the distance.
Worked examples
Worked example: Taxis or kinesis?
- The pill bugs do not head straight for the water.
- They change how fast and how much they move depending on humidity.
- They gather where they move least.
Answer: Kinesis.
Worked example: Testing the result
- $\chi^2 = \frac{(30-20)^2}{20} + \frac{(10-20)^2}{20} = 5 + 5 = 10$.
- One degree of freedom: the critical value is 3.84.
- 10 > 3.84.
Answer: Reject the null hypothesis of no preference: the pill bugs prefer the wet side. (A chi-square test again.)
Common mistake