Visual signals

1. Visual signals Biological Science 3 2011

2. What is vision? • Light signals are detected by photoreceptors in the eye (in mammals, located on the retina at the back of the eye) • Electrical signals are transmitted to the brain via nerves • The brain processes these signals to form a ‘picture’

3. Light forms part of the electromagnetic spectrum • The electromagnetic spectrum describes the spectrum of energy waves of different wavelengths

4. What do animals use vision for? • Avoiding predators • Looking for resources/food/water/prey • Communication within groups • Establishing dominance • Avoiding conflict • Mating rituals • Co-operation in hunting or other tasks

5. Few animals have good colour vision. Most animals either see no colours, or only see the world as shades of blue and yellows. • Squirrels and some primates can see red and green. • Why do many organisms not require colour vision? What do they use instead? • What is the significance of the colour yellow in biology?

6. Ultra-violet • Some birds not only see more hues than we can, but they can also see ultraviolet colours, too. • Insects can also see the ultra-violet part of the spectrum as well as yellow and blue light- so flowers often have markings in these wavelengths.

7. Infra-red • Nocturnal animals have no colour vision but some of them are able to ‘see’ the part of the spectrum called the infra-red. These animals can ‘see’ a picture of warm objects. • Snakes detect infra-red via special sense organs- small pits located on the head

8. Vision & behaviour within groups • Communication • Showing dominance/submission • Communicating within group • Courtship behaviour (plumage, changes in colour)

9. Why are some organisms brightly coloured, while others are not? • Reasons for dull colourations • Camouflage, either as predators or prey • Reasons for bright colourations: • To attract members of the opposite sex • To show poisonous taste • Batesian or Mullerian mimicry

10. Visual signals as a defence • Camouflage • Passive (permanent) • Active- changes colours • Illusions • Disruptive patterning • Appearing larger/threatening

11. Camouflage- predators • Give 2 other examples of predators using camouflage.

12. Camouflage- prey • Structural changes

13. Camouflage • Also called cryptic colouration • May be passive or active

14. Many fish have different colourings on their dorsal and ventral (top & bottom) sides, so that they are camouflaged when seen from below or above, as do penguins • Prey species have paler bellies to give the appearance of being thinner

15. Disruptive patterning • Zebras- predators (e.g. lions) are unable to distinguish individuals in the large group

16. Some organisms make themselves appear larger & more threatening. Many mammals erect their hairs to appear larger and more dangerous. e.g. Frill necked lizards display their frill to intimidate predators (it also helps with temperature regulation) • Porcupines make their quills stand up when threatened to draw attention to them.

17. Visual display- mating rituals • Male birds develop bright plumage and perform mating displays to attract females. • Why are the females of the species generally less brightly coloured? • Female baboons indicate oestrus with changes in colour/swelling • Male fireflies send out flashes of light while in flight as a signal to the female fireflies. Different species of firefly use different flashing codes!

18. Some fish which live in deep water with very little light have light-producing organs on the sides of their bodies. The light is used to attract prey or scare away predators. • Jellyfish use their transparency to avoid predators. Many jellyfish are also bioluminescent.