ecosystem. It may include some specialized plants and animals. The lowland dry ecosystem includes shrublands and forests generally below 3,300 ft (1,000 m) elevation. This system receives less than 50 in (130 cm) annual rainfall, with mostly dry substrate. On O'ahu, this ecosystem is typically found on the leeward side of the Wai'anae Mountains, and the leeward southern coast, including Diamond Head Crater. Biological diversity is low to moderate in this ecosystem. Range Bidens amplectens is native to O'ahu. Plant growth occurs on windward cliffs and crests along the northern portion of the Waianae Mountains on the island. The species is present in the coastal and lowland dry ecosystems, at elevations between 300 and 1,400 ft (90 and 430 m). Bidens amplectens is involved in hybrid swarms near Kaena Point to Makua Valley with Bidens torta. The entirety of the species is restricted to the island of O'ahu. Conservation Population size There are currently 10 populations of Bidens amplectens totaling fewer than 500 individuals. Historically, this species was fairly common. In 2003, the widespread population was estimated to total fewer than 1,000 individuals. Last recorded, there are about 10 populations of Bidens amplectens. Seven of these populations in similar locations have numbers ranging from 10 individuals to more than 100 individuals. Three populations were observed elsewhere, numbered between 25 and 56 individuals. Past and current geographical distribution Historically Bidens amplectens ranged from Puʻupueo to Makaleha along the northwestern side of the Waiʻanae mountains on Oʻahu. Currently, there are about 10 populations at slightly higher elevations on the windward slopes. Bidens amplectens hybridizes and intergrades with Bidens torta from near Kaʻena Point to the head of Mākua Valley on the summit ridges of the Waiʻanae mountains. Pure Bidens amplectens is restricted to the windward cliffs and crests. Major threats Habitat modification and destruction by invasive introduced plants negatively affects Bidens amplectens at all locations in the Waiʻanae mountains. Fire is noted as a threat to Bidens amplectens, as well as its vulnerability to climate change. Predation and herbivory by feral pigs, goats, and rodents were reported to be a threat to Bidens amplectens. The additional threat hybridization with Bidens torta can result in loss of species diversity, local adaptations, and genetic representation. Fire Fire kills Bidens amplectens plants and seeds. Fires also have the potential to allow nonnative species to become established. The nonnative species that invade after fires tend to