  In this paper we present our study on the critical behavior of a stochastic
anisotropic Bak-Sneppen (saBS) model, in which a parameter $\alpha$ is
introduced to describe the interaction strength among nearest species. We
estimate the threshold fitness $f_c$ and the critical exponent $\tau_r$ by
numerically integrating a master equation for the distribution of avalanche
spatial sizes. Other critical exponents are then evaluated from previously
known scaling relations. The numerical results are in good agreement with the
counterparts yielded by the Monte Carlo simulations. Our results indicate that
all saBS models with nonzero interaction strength exhibit self-organized
criticality, and fall into the same universality class, by sharing the
universal critical exponents.
