Age structure: the number of individuals in each age category birthrate: the number of individual organisms born into a population in a given year death rate: the number of individual organisms that die in a population in a given year density-dependent limiting factor: a limiting factor that depends on the size of the population density-independent limiting factor: a limiting factor that affects all populations the same, regardless of population size emigration: the movement of individuals out of a population immigration: the movement of individuals into a population limiting factors: the elements in an ecosystem that restrict the growth of a population population density: the number of individuals in a population per unit area population distribution: the pattern in which individuals in a population are dispersed in an area population size: the number of individuals in a population