Let's say there are only 1,000 white rhinos in existence - would you rather these 1,000 individuals die, or 1,000 humans? On a one-for-one basis, could you justify claiming that human lives are more important than those of the rhino's? Rhino population: 1,000 - 1,000 = extinction. Human population: 6,500,000,000 - 1,000 = 6,499,999,000.
On the other hand, if this group of 1,000 humans was comprised of my family and friends, the decision would be a lot harder.