what condition could change the density of any of the population

There are several conditions that could change the density of any population. These include climate change, habitat reduction, increasing population, decrease of food and basic needs, diseases, and social interactions among individuals in the population. Density-dependent limiting factors, such as competition for limited food among members of a population, can also cause a populations per capita growth rate to change, typically to drop, with increasing population density. Density-independent factors, such as natural disasters like forest fires, can affect per capita growth rate independent of population density. In general, density-dependent limiting factors affect the per capita growth rate of a population differently depending on how dense the population already is, and most density-dependent factors make the per capita growth rate go down as the population increases.