The correct answer is B. Adaptability.
Adaptability is the ability of an organism to adjust to changes in its environment. It is a key factor in the success of any animal population, as it allows the population to survive and thrive in changing conditions.
Natality is the rate at which new individuals are born into a population. It is an important factor in the success of a population, but it is not the only factor. A population with a high birth rate can still decline if it is not able to adapt to changes in its environment.
Unlimited food is not a realistic assumption for any animal population. All populations face limitations on the amount of food that is available to them. If a population has unlimited food, it will eventually reach a carrying capacity, which is the maximum number of individuals that can be supported by the environment.
Interspecies activity is the interaction between different species. It can be a positive or negative factor for the success of a population. For example, predation can reduce the size of a population, but mutualism can increase the size of a population.
In conclusion, adaptability is the most important factor for the success of an animal population. It allows the population to survive and thrive in changing conditions.