Excess of population births over deaths divided by .
Per capita rate of increase (r) is of population size (N) over some span of time (t). It can be approximated by the number of births per parent (particularly per female parent) that to (though less than this if the parents don't also persist).
In other words, the larger r, N, or t, then the larger a population will be at the end of that interval, t. This increase, for small t, approximates rNt. Over longer intervals the approximation is less accurate due to the compoudnding nature of exponential growth.
For example, each generation there will be an increase in the population size of rN. If r is 2 and N is 5, then after one generation there will be an increase in the population size of 10.
Compare to K (i.e., carrying capacity) as well as .