Describe the process of natural selection and how it affects hummingbird populations.

Natural selection has 4 processes.

Individuals looks different and have different characteristics from another within their own species (genetic variation). Some characteristics suits better for the environment, which has to be passed on from one generation to the next. The humming birds with long bills will mate with those that have that too so they'll produce offspring with long bills. 

The second process is over production of offspring. The humming birds produces lots of offspring but only a few survives. 

Another factor of natural selection is struggle for existence, which leads to differential survival and reproduction. There are environmental pressures, like not having enough space or food, for example, humming birds compete fiercely for resources like nectar. Natural selection will favor individuals that are more efficient at getting nectar and natural selection will result in changes in wing shape which can allow them to fly longer distance and affect the length and shape of bill for them to drink nectar. Little changes may affect how well they feed and survive. Those who are the fittest survives and are most likely to reproduce and pass on their advantageous genes to their offspring. If the long bills are more advantageous and can survive better in a particular environment, then overtime, those with short bills will disappear because they can't survive and the entire population would have long bills.