1934 Howard Berg: Random walks in biology. Princeton UP 1983.

G. Lawler/V. Limic: Random walk. Cambridge UP 2010, 360p.

Okubo: Diffusion and ecological problems. 
Springer 1980, 250p. 3-540-09620-5. DM 114.

K. Taira: Diffusion processes and partial differential equations.
Academic Press 1988, 420p. £ 48.