Population growth is influenced by a range of factors. These are broadly categorised into factors that increase population size (such as birth rate and immigration) and factors that decrease it (such as death rate, emigration, predation, disease, and competition for resources like food).
Predators reduce a population by killing and consuming members of the prey species. Food shortage limits population growth because organisms cannot survive and reproduce without adequate nutrition. Disease causes mortality, directly reducing numbers. All three are environmental resistance factors that check population growth.
Natality refers to the birth rate of a population. It is not a factor that acts on population growth from outside; rather, it is a component of population growth itself. Natality describes how many new individuals are added to a population per unit time. While it influences population size, it is a demographic parameter rather than an environmental or ecological limiting factor.
In ecology, when we refer to "factors affecting population growth," we typically mean the environmental resistance factors (biotic and abiotic) that regulate population size, such as predation, disease, food availability, and competition. Natality is part of the population's intrinsic growth rate, not an external regulatory factor.