 Prehistoric Polynesian habitation on Nihoa may have initially led to a decrease in the plant population of A. brownii . Major threats to the plant include invasive species , fire , and hybridization with other Amaranthus species . Inbreeding is a serious threat , as the small plant population must reproduce within its own circle resulting in genetic defects . A. brownii is also forced to compete with the non @-@ native weed ( Portulaca oleracea ) , the plant 's main alien species threat . In 2002 and 2004 , the invasive gray bird grasshopper ( Schistocerca nitens ) presented an even larger threat to A. brownii . First recorded on the island in 1977 , the increasing population density of gray bird grasshoppers led to massive defoliation on the island , leaving A. brownii at greater risk of predation . In 2004 alone , an estimated 400 @,@ 000 gray bird grasshoppers destroyed almost 90 % of the vegetation on Nihoa . 
