Summary
We consider an integro-differential equation for the densityn of a single species population where the birth rate is constant and the death rate depends on the values ofn in an interval of length τ — 1 > 0. We prove the existence of a non-constant periodic solution under the conditions birth rate b > π/2 and τ- 1 small enough. The basic idea of proof (due to R. D. Nussbaum) is to employ a theorem about non-ejective fixed points for a translation operator associated with the solutions of the equation.
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References
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A proof of existence was also announced by G. Dunkel in [1].
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Walther, HO. Existence of a non-constant periodic solution of a non-linear autonomous functional differential equation representing the growth of a single species population. J. Math. Biology 1, 227–240 (1975). https://doi.org/10.1007/BF01273745
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DOI: https://doi.org/10.1007/BF01273745