© X. Li and W. Yang 2009
Received: 4 March 2009
Accepted: 3 September 2009
Published: 27 September 2009
In 1974, Schoener  proposed the following competition model:
May  suggested the following set of equations to describe a pair of mutualists:
Both of the above-mentioned works are considered the continuous cases. However, many authors [3–5] have argued that the discrete time models governed by difference equations are more appropriate than the continuous ones when the populations have nonoverlapping generations. Bai et al.  argued that the discrete case of cooperative system is more appropriate, and they proposed the following system:
On the other hand, as was pointed out by Huo and Li , ecosystem in the real world is continuously disturbed by unpredictable forces which can result in changes in the biological parameters such as survival rates. Practical interest in ecology is the question of whether or not an ecosystem can withstand those unpredictable disturbances which persist for a finite period of time. In the language of control variables, we call the disturbance functions as control variables. During the last decade, many scholars did excellent works on the feedback control ecosystems (see [8–11] and the references cited therein).
Chen  considered the permanence of the following nonautonomous discrete N-species cooperation system with time delays and feedback controls of the form
where is the density of cooperation species , is the control variable ( and the references cited therein).
Throughout this paper, we assume the following.
The aim of this paper is, by applying the comparison theorem of difference equation, to obtain a set of sufficient conditions which guarantee the permanence of the system (1.5).
In this section, we establish a permanence result for system (1.5).
Now, let us consider the first-order difference equation
where are positive constants. Following Lemma is a direct corollary of Theorem of L. Wang and M. Q. Wang [12, page 125].
Following comparison theorem of difference equation is Theorem of [12, page 241].
Now let us consider the following single species discrete model:
where and are strictly positive sequences of real numbers defined for and . Similarly to the proof of Propositions and , we can obtain the following.
This completes the proof of Proposition 2.5.
Now we are in the position of stating the permanence of system (1.5).
then system (1.5) is permanent.
This ends the proof of Theorem 2.6.
then system (2.44) is permanent.
This work is supported by the Foundation of Education, Department of Fujian Province (JA05204), and the Foundation of Science and Technology, Department of Fujian Province (2005K027).
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