Boundary spatiotemporal correlations in a self-organized critical model of punctuated equilibrium

In a semi-infinite geometry, a one-dimensional, M-component model of biological evolution realizes microscopically an inhomogeneous branching process for M-->∞. This implies a size distribution exponent τ'=7/4 for avalanches starting at a free, ``dissipative'' end of the evolutionary chain. A bulklike behavior with τ'=3/2 is restored by ``conservative'' boundary conditions. These are such as to strictly fix to its critical, bulk value the average number of species directly involved in an evolutionary avalanche by the mutating species located at the chain end. A two-site correlation function exponent τ'_R=4 is also calculated exactly in the ``dissipative'' case, when one of the points is at the border. Together with accurate numerical determinations of the time recurrence exponent τ'_first, these results show also that, no matter whether dissipation is present or not, boundary avalanches have the same space and time fractal dimensions as those in the bulk, and their distribution exponents obey the basic scaling laws holding there.