High population density can high population density can decrease biodiversity within a species decrease competition increase the incidence of disease transmission and food scarcity decrease the use of resources hinder organisms from finding mates

It can increase the incidence of disease transmission and food scarcity.   Population density is the number of individuals in a population per unit area. Density-dependent factors have a greater impact at higher population densities. Birth rate and death rate are the major factors that determine a population's growth rate.

the answer is yes, they are born/created, then they grow to their limit then produce offspring, then die.

trachea, alveoli, lung capillaries, arteries