Population
Early inhabitants of Christmas Island rarely mentioned these crabs. It is possible that their large population size was caused by the extinction of the endemic Maclear's Rat, Rattus macleari in 1903, which may have limited the crab's population. Surveys have found a density 0.09–0.57 adult red crabs per square metre, equalling an estimated total population of 43.7 million on Christmas Island. Others have estimated that about 120 million are found on this island, but the basis for that claim is unclear.
An exploding population of the yellow crazy ant, an invasive species accidentally introduced to Christmas Island and Australia from Africa, is believed to have killed 10–15 million red crabs (one-quarter to one-third of the total population) in recent years. In total (including killed), the ants are believed to have displaced 15–20 million red crabs on Christmas Island.
Read more about this topic: Christmas Island Red Crab
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