Population density, or the size of a population, is crucial for understanding various ecological processes, such as competition, predation, and the effects of human activities. Measuring population density can be challenging and may not always be best represented by simple counts. In some cases, alternative measures like percent cover or biomass are more meaningful, especially when organisms vary significantly in size and impact on their habitat. For large or difficult-to-count populations, indirect methods or relative measures, such as the number of fish caught per trap, are used. Many times, populations are estimated through indirect evidence, such as the use of pug marks and fecal pellets in tiger censuses.