  First, we systemize ealier results the uniform persistence for discrete model
$A_{n+1}=A_nF(A_{n-m})$ of population growth, where $F:(0,\infty)\to(0,\infty)$
is continuous and strictly decreasing. Second, we investigation the effect of
delay $m$ when $F$ is not monotone. We are mainly using $\omega$-limit set of
persistent solution, which is discussed in more general by P. Walters, 1982.
