Before revision:  Methods: We consider the geometric position of individuals of species, and base on that  we find the probability of observing at least one individual of the species , then we apply a translation of the well-studied problem of mixed salt-water in a tank to describe the formula of SAR. -
After revision:  Methods: We consider the geometric position of individuals of species, and base on that , we find the probability of observing at least one individual of the species , then we apply a translation of the well-studied problem of mixed salt-water in a tank to describe the formula of SAR. -