Figure 2: Relative density of cooperators in dependence on the occupation fraction for different values of when and (see legend). Irrespective of the value of , the relative density of cooperators decreases from around 0.485 with the increase of , and then the curves for different values of depart around . Still further, there are three interesting cases: the first interesting case occurs if = 1.0, where the relative density of cooperators increases monotonically with the increase of until approaching a unity; the second interesting case occurs if is in the region, , where the relative density of cooperators increases monotonically with the increase of until reaching its maximum value and then sharp decreases; the third interesting case appears if is in the region , for example, , where the relative density of cooperators decreases monotonically with the increase of until approaching zero.