What purposes do Fleas and Ticks serve to nature?

Question

What purposes do Fleas and Ticks serve to nature?

Answer 1

Why do we assume that each and every species has a purpose?

One can speculate as follows:

In the food chain fleas and ticks are dietary staples for some birds.

In evolution these parasites might weaken an animal of lower stamina so that it dies before reproducing.

In religion they provide reminders to "higher animals" that they are not possessed of immunity, and thus not THE highest animal.

One must also mention that they provide transport for many different and usually nasty microbes.