Weather can act in a density dependent way Differences between two populations in density can be caused by variation in either density dependent or density independent per capita birth rate and death rate . The relation between density and the rate of increase is linear.
All individuals reproduce equally.
There is no emigration or immigration. Whether these assumptions hold seems to depend strongly upon the types of organisms. Many things influence rate of population growth but only density dependent factors whose effect varies in relation to crowding can possibly bring the population under control.