TY  - JOUR
VL  - 76
Y1  - 1996/06//
JF  - Physical Review Letters
IS  - 26
A1  - Caldarelli, Guido
A1  - Tebaldi, Claudio
A1  - Stella, Attilio
PB  - American Physical Society
SP  - 4983
N1  - © 1996 American Physical Society
ID  - eprints1182
EP  - 4986
TI  - Branching processes and evolution at the ends of a food chain
AV  - public
KW  - PACS: 87.10.+e
KW  -  02.50.-r
KW  -  05.40.+j
KW  -  64.60.Lx

UR  - http://dx.doi.org/10.1103/PhysRevLett.76.4983
SN  - 0031-9007
N2  - In a critically self-organized model of punctuated equilibrium, boundaries determine peculiar scaling of the size distribution of evolutionary avalanches. This is derived by an inhomogeneous generalization of standard branching processes, extending previous mean field descriptions and yielding ? = 1/2 together with ?? = 7/4, as distribution exponent of avalanches starting from species at the ends of a food chain. For the nearest neighbor chain one obtains numerically ?? = 1.25±0.01, and ?first? = 1.35±0.01 for the first return times of activity, again distinct from bulk exponents.
ER  -