  We propose here a motivation for a mixed local/nonlocal problem with a new
type of Neumann condition.
  Our description is based on formal expansions and approximations. In a
nutshell, a biological species is supposed to diffuse either by a random walk
or by a jump process, according to prescribed probabilities. If the process
makes an individual exit the niche, it must come to the niche right away, by
selecting the return point according to the underlying stochastic process. More
precisely, if the random particle exits the domain, it is forced to immediately
reenter the domain, and the new point in the domain is chosen randomly by
following a bouncing process with the same distribution as the original one.
  By a suitable definition outside the niche, the density of the population
ends up solving a mixed local/nonlocal equation, in which the dispersion is
given by the superposition of the classical and the fractional Laplacian. This
density function satisfies two types of Neumann conditions, namely the
classical Neumann condition on the boundary of the niche, and a nonlocal
Neumann condition in the exterior of the niche.
