Many bacteria and archaea are similar in appearance. Most archaea and all bacteria possess cell walls. Both lack nuclei and are unicellular.
One of the major differences between the two kingdoms is the environments in which they thrive: Archaea thrive in more extreme environments, while bacteria do not. Bacteria and archaea also have cell walls made out of different material.
To a certain extent, population numbers are self-regulating because deaths increase when a population exceeds its carrying capacity. Disease, competition, predator-prey interaction, resource use and the number of populations in an ecosystem all affect carrying capacity.
