Final answer:
The comparative study of opossum numbers, their reproduction, and life-spans in different areas of Miami-Dade is considered population ecology.
Step-by-step explanation:
The comparative study of opossum numbers, their reproduction, and life-spans in urban, suburban, and natural areas of Miami-Dade would be considered b) Population ecology. Population ecology focuses on the number of individuals of one species in an area and how and why that number changes over time. In this study, ecologists would be interested in examining the opossum population in each area, understanding its dynamics, and identifying factors that may affect population size.