Black rhinos are one of two African rhino species, and they are the smaller of the two species. Their population numbers have drastically declined since the beginning of the twentieth century. Horrifically, in the 35 years between 1960 and 1995, the black rhino population fell to less than 2,500 individuals—a population drop of about 98%. Since then, number of black rhinos in existence has rebounded to somewhere between 5,000 and 5,500. However, the species is still critically endangered due to low overall numbers. Another challenge black rhinos face is the fact that their horns are widely desired, so poaching is a present threat.
Low population numbers threaten black rhinos for genetic reasons as well. With so few individuals, the gene pool is limited in size. There is only so much genetic diversity available with so few rhinos. Genetic diversity is a key component to the overall genetic health of any species and population. Low numbers can force a species to begin inbreeding. While some genetic diversity can be gained through inbreeding, there are many consequences as well. Genetic mutations tend to arise, and they are more likely to be passed on from individual to individual. The Florida panther is a good example of this phenomenon. Many of them now have kinked tails as a consequence of low population numbers and inbreeding.