DIVERSITY & ENDEMISM
Impressive plant endemism in Southwest Australia is attributed to millions of years of isolation from the rest of Australia by the country's vast central deserts. Extreme climate shifts and poor soils also promoted specialization of the region's flora.
Of more than 5,570 species of vascular plants found here, nearly 2,950 are endemic (about 53 percent). A significant number of genera are also endemic: 87 of 697 genera (12.5 percent) are found nowhere else in the world. Additionally, four families are endemic: Ecdeiocoleaceae, Emblingiaceae, Eremosynaceae and the monotypic Cephalotaceae, which is represented by the pitcher plant (Cephalotus follicularis, VU), a carnivorous plant that traps insects in its modified leaves.
The ten largest families in the hotspot (including the Myrtaceae with 785 species, of which 92 percent are endemic, and Proteaceae with 684 species, 96 percent endemic) comprise 61 percent of the flora. The number of species per genus averages eight, although the ten largest genera (including Acacia with 397 species, 51 percent endemic, and Eucalyptus with 246 species, 52 percent endemic) far exceed this figure.
The Banksia plants of the family Proteaceae are among the most distinctive found in this hotspot. These brilliant flowering plants range from trees to small prostrate plants, one of which even has underground stems. Kangaroo paws (Anigozanthos spp.) are another brightly colored flower from the region; their long stems are thought to resemble their namesakes.
The region's flagship tree species include three eucalyptus: jarrah (Eucalyptus marginata), marri (E. calophylla), and karri (E. diversicolor). While jarrah and marri grow to only about 20-30 meters in height, some karri forests have canopies up to 70 meters high, and individual trees may grow as high as 80 meters, ranking this endemic species as one of the tallest trees on earth.
Over 280 native bird species occur in the region, 12 of which are endemic. The level of endemism is slightly higher than in other Mediterranean-type hotspots, and the region is considered an Endemic Bird Area (EBA) by BirdLife International.
The region is home to 22 parrot species (three endemics), including Carnaby's black-cockatoo (Calyptorhynchus latirostris, EN). The noisy scrub-bird (Atrichornis clamosus, VU), which earned its name because of the loud vocalizations of its males, was presumed extinct until a small population was rediscovered in 1961. Several other bird species are near threatened or rapidly declining in the face of habitat loss, modification and fragmentation or inappropriate fire regimes.
This hotspot has roughly 60 native mammal species occurring, of which 12 are endemic, including the mouse-sized, nectarivorous honey possum (Tarsipes rostratus), the only representative of the family Tarsipedidae, which lives only in the coastal plain heaths of Southwest Australia. Another interesting endemic is the quokka (Setonix brachyurus, VU), a small, furry wallaby confined to the mainland, where it has been declining in numbers, and two small offshore islands (Rottnest Island and Bald Island).
Some mammal species have become de facto endemics to Southwest Australia because they are extinct in the rest of their natural ranges. The numbat (Myrmecobius fasciatus, VU), for example, a squirrel-sized marsupial anteater, is the only member of the family Myrmecobiidae, and has become the mammalian symbol of Western Australia. Besides the numbat, four other threatened mammals are endemic to the hotspot, including the most threatened species in the hotspot, Gilbert’s potoroo (Potorous gilberti, CR), which today occurs only in the Two People's Bay Nature Reserve.
As might be expected in a country that leads the world in reptile diversity, there are a wide variety of reptile species in Southwest Australia. Nearly 30 of more than 175 species (15 percent) are endemic to the hotspot. The endemic western swamp turtle (Pseudemydura umbrina, CR), a monotypic genus, is the most threatened reptile in Australia and is among the 25 most threatened freshwater turtle in the world. The wild population of less than 100 is now only found in one or two swamps near Perth.
Other threatened reptiles include the Yinnietharra rock dragon (Ctenophorus yinnietharra, VU), an understudied lizard species that is apparently specialized to two granitic rock outcrops in the region and does not inhabit outcrops of different origins, and the Lake Cronin snake (Echiopsis atriceps, VU) whose very limited range includes unprotected private lands.
There are more than 30 species of amphibian found in this hotspot, nearly two-thirds of which are endemic, including four species that represent endemic genera: the turtle frog (Myobatrachus gouldii), Nicholl's toadlet (Metacrinia nichollsi), Sandhill frog (Arenophryne rotunda), and the harlequin frog (Spicospina flammocaerulea, VU). Besides the last-mentioned species, which was only described in 1997 and is known to have a limited area of occurrence, two other frog species are considered threatened, one of which, the yellow-bellied frog (Geocrinia vitellina, VU), is represented by six populations confined to a 6.3 km² area east of the Leeuwin-Naturaliste Ridge.
The Southwest Australia hotspot has very little freshwater habitat and thus only about 20 native species of freshwater fish. However, about half of these species and three genera are endemic, the most remarkable being the salamanderfish (Lepidogalaxias salamandroides), which is the only member of the hotspot's single endemic family (Lepidogalaxiidae).