Final answer:
A population refers to all individuals of a single species living in a specific area. The number of ticks on a dog (option D) represents a population because it consists of individual organisms of the same species in a defined living space.
Step-by-step explanation:
What is a Population?
Within the field of ecology, a population is defined as all the individual organisms of the same species that live and interact in the same area. When looking at examples of a population, we consider a specific species within a defined area. For instance, the entirety of angelfish in a coral reef may constitute the population of angelfish in that reef. Considering the options provided in the question, The fish in the ocean is too broad as it does not specify a particular species. The desert is an ecosystem, not a population. Option C, All the birds in a forest, includes multiple species, therefore, it does not fit the definition of a population. Lastly, The number of ticks on a dog does specify a single species in a defined area, thus representing a population.
When we think about a population, aspects such as population size, density, and birth and death rates are studied to understand the dynamics within a population. Population size refers to the number of individuals within a specific population. This size can be a critical factor in determining the survival or risk of extinction for a species.
In the context of the options given in the question, the correct answer would be: Option D, The number of ticks on a dog, as it represents all individuals of a single species (ticks) living in close association with each other on a specific host (the dog)