The graph provided shows the mating seasons of several species of frogs. Peeper frogs mate during early spring, whereas leopard frogs mate in late spring or early summer. The slightly different mating seasons of these two frog species may not necessarily be a complete barrier to reproduction, as there could be other factors that prevent interbreeding.
One possible barrier to reproduction could be geographic isolation. If the habitats of the two frog species do not overlap or are separated by a physical barrier, such as a river or mountain range, then the frogs may not have the opportunity to mate and produce offspring.
Another possible barrier could be behavioral isolation. If the mating calls of the two frog species differ significantly, then the frogs may not recognize each other as potential mates and therefore not mate.
Lastly, genetic incompatibility may also act as a barrier to reproduction. Even if the two species were to mate and produce offspring, the resulting hybrid offspring may not be viable or fertile, which would prevent any gene flow between the two species.
Overall, the slightly different mating seasons between the peeper frog and the leopard frog may be an important factor in preventing interbreeding, but other barriers such as geographic isolation, behavioral isolation, and genetic incompatibility may also be in operation.