In an open population, what factors determine the changes in size and density?

The correct answer identifies key factors influencing the dynamics of an open population, which is defined by the potential for individuals to enter and exit the population. Natality refers to the birth rate within the population, which contributes to its growth. Mortality pertains to the death rate, which decreases population size. Immigration is the arrival of individuals from outside populations, increasing size, while emigration is the departure of individuals to other populations, decreasing size.

Together, these factors create a comprehensive understanding of how population size and density fluctuate over time. For instance, high natality and low mortality can lead to population growth, while high rates of immigration can also augment population size. Conversely, high mortality or emigration rates can reduce overall numbers.

Other choices focus on more limited aspects of population dynamics, such as competition and gene flow, which are relevant but do not alone encompass the full range of factors affecting population changes in an open environment.