Migration
Definition The seasonal movement of a whole population to a more suitable environment. This is good for reproduction success as it often has a good food supply and optimum temperature. For example: the monarch butterflies migrate many kilometers to the north of New Zealand for winter where they spend their time hanging in masses in certain trees where they are protected by cold winds but are open to the sun.
Reasons for Migration There is more food for the species in the new environment and it allows them to raise their young. They migrate because it is beneficial to their reproductive and survival success. It has been shown that for the same species animals that are allowed to migrate become bigger and/or leave more offspring. e.g. salmon that do not migrate only grow to about 20cm where the ones that do migrate can grow to 100cm and will produce 125 times the number of eggs.
Triggers to Migration Some animals migrate upon maturation so when their sex organs mature and there is a need or desire to reproduce e.g. eels or salmon. Most animals migrate just before winter when the temperature is dropping and the days are shortened. In migratory birds for example changes in day length is sensed directly through skin and feathers by the pineal gland.
Advantages of Migration Animals remain in a favourable temperature. They grow larger. They leave more offspring. They have a constant food supply. May lead to the colonisation of a new area. Reduces predation/parasitism disease. Greater genetic mixing. Better breading conditions.
Disadvantages of Migration They may get lost or caught in a storm. May get eaten by a predator. May use too much energy in migration which leads to exhaustion. It is a huge investment in energy. They may starve.
Methods of Migration There are different ways that a population navigates to migrate to the place they are going. Such as piloting, compass orientation, navigation, visual clues, solar navigation, magnetic fields, star navigation, chemical navigation and sound used as sonar.