option tstart = 0.0, tstop = 300, outstep = .1, device="aqt"

param P = 10.0 label="Product of max. fecundity and juvenile survival."
param tau = 12.0 label="Development time."
param delta = 0.25 label="Per capita death rate"
param A0 = 300 label="Fecundity decay constant."
param N0 = 100.0 label="Initial population."

var A = N0 delay scale=0.0
aux Alag

Alag = A(t - tau)
A'= P*Alag*exp(-Alag/A0) - delta*A

// plot t, A
// print t, A, A(t - tau)