Table 4.

Model equations describing different decline-curve shapes

Model	Curve-shape distinction	Formula	Parameters
Linear	No concavity	Ni = m1Ti + c	Nwe represents population size at time i, Twe represents year i, c represents the model intercept at Twe = 0, m1 represents the model slope.
Quadratic	Can be concave or convex. Quadratic concave curves can be distinguished from exponential concave curves as their rate of decline continues to decrease in a constant manner, leading to a right-hand side vertical asymptote.		Nwe represents population size at time i, Twe represents year i, c represents the model intercept at Twe = 0, m1 and m2 represent different model slopes.
Exponential	In exponential concave declines, decline rate slows as the population reduces in size, leading to a right-hand side horizontal asymptote.		Nwe represents population size at time i, Asym represents the horizontal asymptote of the model, RO represents the intercept at Twe = 0, lrc represents the model constant (i.e., decay rate).