Final answer:
Population density is the measure of the number of people per unit area (option C). It is applied to human populations as well as animals and plants, and affects various aspects of the population's health and behavior. Density can influence competition for resources, disease spread, and social interactions.
Step-by-step explanation:
Population density is the measure of the number of individuals per unit area or volume. In the context of your question, the correct answer is C: Population density is the measure of the number of people per unit area. This concept applies to both human populations in cities, countries, etc., as well as populations of animals or plants in ecological studies. For example, if we consider a population of 100 insects living in a 100 square meter area, the density would be 1 insect per square meter. However, if the same population is found within an area of just 1 square meter, then its density dramatically increases to 100 insects per square meter, indicating a much more crowded situation.
This measure helps us understand and analyze how crowded a population is, which can impact its health and other aspects of its survival and behavior. For instance, higher density could lead to increased competition for resources, spread of diseases, or challenges in finding mates. Conversely, very low densities might suggest difficulties in forming social groups or finding partners for reproduction. It's a crucial metric in ecology that relates to the overall study of populations, their size, and distribution.
Understanding population density helps ecologists predict and explain patterns of resource use, social interactions, and viability of a population over time. The concept is essential in the field of demography, which uses mathematical tools to describe population characteristics and their changes over time.