Hawaiʻi's geographical isolation strongly influences its ecology. Remote islands like Hawaiʻi have a large number of species that are found nowhere else (see Endemism in the Hawaiian Islands). The remoteness resulted in evolutionary lines distinct from those elsewhere and isolated these endemic species from external biotic influence, and also makes them especially vulnerable to extinction and the effects of invasive species. In addition the ecosystems of Hawaiʻi are under threat from human development including the clearing of land for agriculture; an estimated third of the island's endemic species have already been wiped out. Because of its elevation, Mauna Kea has the greatest diversity of biotic ecosystems anywhere in the Hawaiian archipelago. Ecosystems on the mountain form concentric rings along its slopes due to changes in temperature and precipitation with elevation. These ecosystems can be roughly divided into three sections by elevation: alpine-subalpine, montane, and basal forest.