We construct a Lyapunov function for tridiagonal competitive-cooperative sy
stems. The same function is a Lyapunov function for Kolmogorov tridiagonal
systems, which are defined on a closed positive orthant in R-n. We show tha
t all bounded orbits converge to the set of equilibria. Moreover, we show t
hat there can be no heteroclinic cycles on the boundary of the first orthan
t, extending the results of H. I. Freedman and H. L. Smith [Differential Eq
uations Dynam. Systems, 3 (1995), pp. 367-382].