Final answer:
The use of quadrats is false for measuring density in mobile animal populations; they are used for immobile organisms, whereas mark and recapture is used for mobile species.
Step-by-step explanation:
The statement that quadrats are usually used to measure density in mobile populations of animals is false. Quadrats are typically employed to estimate population size and density in immobile organisms such as plants, or for very small and slow-moving organisms.
For mobile organisms such as mammals, birds, or fish, scientists often use a technique known as mark and recapture. This involves marking a subset of the population and later recapturing some to estimate the total population size and density.