How do you ecologists measure the population density

They use the method of marking and recapture.

Explanation:

The method of marking and recapture is the most common way that ecologists use to measure population density. To carry out this method, scientists must remove some members of the population and mark them in some way, so that they can be identified later. After correctly marking them, the members return to their original population, where they will mix with the other members of the population for a period of time determined by the ecologist. The important thing is that this time is enough for the marked members to mix with the rest of the population. While waiting for that time to pass, ecologists continue to capture and mark other members of the population until the recapture of the first marked members takes place. In this way, the size of the population will be estimated through the proportion of catches.

Ecologists measure the population density by using the Quadrat method and the Mark and Recapture method.