The red blood cells will shrink in size due to osmotic-like pressure differences until it reaches a "favorable" size. Check here: https://socratic.org/questions/what-would-happen-to-your-red-blood-cells-if-they-were-placed-in-salt...
As population size approaches the carrying capacity of the environment, the intensity of density-dependent factors increases. For example, competition for resources, predation, and rates of infection increase with population density and can eventually limit population size