  It is known that a species dies out in the long run for small initial data if
its evolution obeys a reaction of bistable nonlinearity. Such a phenomenon,
which is termed as the strong Allee effect, is well supported by numerous
evidence from ecosystems, mainly due to the environmental pollution as well as
unregulated harvesting and hunting. To save an endangered species, in this
paper we introduce a protection zone that is governed by a Fisher-KPP
nonlinearity, and examine the dynamics of a reaction-diffusion model with
strong Allee effect and protection zone. We show the existence of two critical
values $0<L_*\leq L^*$, and prove that a vanishing-transition-spreading
trichotomy result holds when the length of protection zone is smaller than
$L_*$; a transition-spreading dichotomy result holds when the length of
protection zone is between $L_*$ and $L^*$; only spreading happens when the
length of protection zone is larger than $L^*$. This suggests that the
protection zone works when its length is larger than the critical value $L_*$.
Furthermore, we compare two types of protection zone with the same length: a
connected one and a separate one, and our results reveal that the former is
better for species spreading than the latter.
