Final answer:
The biological species concept defines a species as individuals that can interbreed and produce fertile offspring, leading to reproductive compatibility within a species.
Step-by-step explanation:
According to the biological species concept, individuals belonging to the same species share the characteristic that they can interbreed and produce fertile offspring. This concept applies primarily to sexually reproducing organisms and is used to distinguish one species from another based on reproductive compatibility. Individuals of the same species are capable of producing offspring that can also reproduce, whereas individuals of different species typically cannot produce fertile offspring when mated.
The biological species concept does not necessarily require phenotypic uniformity, geographic co-occurrence, or breeding under natural conditions for individuals to be considered part of the same species. Therefore, the characteristics that individuals belonging to the same species share according to this concept are the ability to produce fertile offspring and to breed under natural conditions, which is why the correct answers to the question asked are options (a) and (d).