In the exponential growth equation, N_t = N₀e^rt, intrinsic rate of natural increase is represented by

Intrinsic rate of natural increase is indicated by ‘r’. i.e. (b – d). It helps in assessing impacts of any biotic or abiotic factor on population growth.

N_t = N₀ e^rt 

where 
N_t = Population density after time t 
N₀ = Population density at time zero 
r = intrinsic rate of natural increase 
e = the base of natural logarithms (2.71828)