and Applied Analysis 3 aij , bij , cik, γik : R → 0, ∞ are all continuous functions bounded above and below by positive constants, and τik t ≥ 0 are bounded continuous functions, ri max1≤j≤l{supt∈Rτij t } > 0, and i, j 1, 2, . . . , n, k 1, 2, . . . , l. Furthermore, in the case Dij t,N aij t − bij t e−N , to guarantee the meaning of mortality terms we assume that aij t > bij t for t ∈ R and i,...