How does global climate change affect ecological systems that rely upon migration?
Some organisms' lives need migration in order to survive.
For example, if there were some birds that went South from Canada to Mexico every year, then they would do the same. However, if the climate in Mexico changes, then so do the patterns of birds. So, if the birds can't survive, then they die. If they die, then animals have less food to eat for those who feed on the birds. If those animals die, then they can't leave food for others, and it continues to go on.