KWONGAN: HISTORY OF A GLOBAL BIODIVERSITY HOTSPOT

As a biologist from nan Neotropics, nan lure of exotic bushlands and creatures drew maine to ‘the onshore down under’.

I was peculiarly excited to spot marsupials different from our opossums and nan deadly creatures Australia is world-renowned for.

When I arrived successful WA, I had nary thought I was successful for specified a treat. I soon learned astir autochthonal plants and animals that only hap present – for illustration kangaroo paws, numbats and Carnaby’s achromatic cockatoos, to sanction conscionable a few.

Thus began a bucket database of plants and animals that grows longer pinch each time I walk here.

But really did these type originate? Why do they only hap successful WA and obscurity other connected Earth – aliases moreover Australia? And what makes WA’s animals and plants distinctive?

A PLACE LIKE NO OTHER

Biodiversity refers to each nan lifeforms recovered successful a spot – plants, animals, fungi, microorganisms and familial diversity included.

Biodiversity hotspots are locations pinch a ample number of type recovered obscurity other successful nan world, which are experiencing accelerated residence loss.  

Australia has two internationally recognised biodiversity hotspots: nan coastal forests of Eastern Australia and nan Southwest Ecological Region (or Kwongan).

Caption: Map of nan Southwest Ecological Region
Credit: Nemetsy via Wikimedia Commons

This hotspot extends much than 356,000km² from Shark Bay to Esperance. It contains immoderate of Australia’s rarest and astir endangered species. 

While nan biodiversity numbers successful nan region are striking, much fascinating are nan type recovered exclusively here. They are a testament to really unsocial this spot is and a reminder of really captious it is to sphere it.

DIVERSITY AGAINST ALL ODDS

To understand why WA’s biodiversity is truthful unique, we request to commencement astatine nan very opening – nan land. 

WA’s scenery is mostly flat, pinch nutrient-poor soils and a Mediterranean climate. This intends hot, barren summers and winters (and autumns) pinch frequent, dense rainfall.

These geological and climatic conditions person shaped nan unsocial habitats successful WA. This includes nan mesic biome successful southwestern WA, characterised by sclerophyllous vegetation – plants pinch difficult leaves adapted to nan power and agelong periods of drought.

Studying nan mesic biome helps america to understand nan root and improvement of Australia’s biodiversity. 

For instance, respective plant families, arsenic good arsenic immoderate lineages of Australian birds (particularly songbirds) and marsupials originated nether mesic conditions astir 30 cardinal years ago.

This includes type recovered exclusively successful WA.

A MATTER OF ENDEMISM

Endemism is an important constituent of biodiversity hotspots.

Endemic species are native to a spot and person a limited distribution because they only hap people successful that location. 

In WA, around 52% of nan 8,000 works type successful southwestern WA are endemic to nan state. This includes 62 banksia species, 11 kangaroo paw type and nan jarrah and marri eucalyptus trees.

Caption: Helena and Aurora Range, Great Western Woodlands
Credit: Keren Gila (CC BY-SA 4.0)

The Kwongan is besides location to 12 endemic mammal species, including nan chromatic possum, nan quokka and nan numbat, arsenic good arsenic 15 endemic vertebrate species.

The database doesn’t extremity here. Some of Australia’s rarest type unrecorded successful WA’s southwest, including its most endangered reptile (the occidental swamp tortoise) and marsupial (Gilbert’s potoroo).

Endemism makes WA unique, and we person highly precocious rates of it. 

REMAINS OF A SUPERCONTINENT

To understand WA’s precocious level of endemism, we request to spell backmost successful clip 250 cardinal years. The 7 continents we cognize coming do not beryllium – only nan supercontinent Pangea. 

What we now cognize arsenic Australia is still embedded successful Gondwana, nan confederate information of Pangea.

Now accelerated guardant 96 cardinal years. Gondwana is starting to break up and Australia becomes isolated from nan supercontinent. Yet its southwest remains stable contempt nan geological changes occurring astatine nan time.

This intends type successful nan southwest person evolved without awesome extinctions and have prevailed aliases diverged successful nan unchangeable conditions of nan region.

It besides implies that southwestern WA is an assortment of aged and caller groups of species.

Some of nan older endemic genera see nan endemic mite harvestmen, which originated during nan Mesozoic era (between 252 and 66 cardinal years ago), and nan western swamp tortoise.

Caption: Mite harvestmen (Cyphophthalmi)
Credit: Gonzalo Giribet via iNaturalist (CC BY-NC 4.0)

Caption: Western swamp tortoise (Pseudemydura umbrina)
Credit: Bahudhara (CC BY-SA 3.0)

Some of nan ‘younger’ species see nan red-capped parrot, nan chromatic possum and nan keeled legless lizard, which originated during nan mid-Oligocene (around 33 to 23 cardinal years ago).

IS THERE ANYBODY OUT THERE?

Many type successful southwestern WA knowledgeable divergent evolution. This is erstwhile related populations create different traits from 1 different arsenic they commencement occupying different habitats.

For example, nan red-capped parrot diverged from nan mulga parrot and became a different type astir 11 cardinal years agone when its territory started to barren up.

The mulga parrot is considered endemic to South Australia, while nan red-capped parrot is endemic to WA. 

(Images 5 and 6, broadside by side)

Caption: Red-capped parrot (Purpureicephalus spurius)
Credit: Jean and Fred Hort (CC BY-SA 3.0)

Caption: Mulga parrot (Purpureicephalus spurius)
Credit: David Cook (CC BY-NC 2.0)

The aridification of confederate Australia led to nan statement of nan Nullarbor Plain, a limestone plateau that extends 750 kilometres between cardinal Australia and nan southbound coast.

The Nullarbor Plain became a obstruction that isolated southwestern from southeastern Australia during nan Miocene. 

This separation caused various cases of allopatric speciation, nan statement of type caused by a geographical barrier.

Geographic barriers restrict cistron flow betwixt places, and type tin germinate independently from 1 different – moreover into caller type aliases subspecies.

Another illustration of allopatric speciation by nan Nullarbor Plain is nan heath mouse, a rodent recovered successful southwestern WA, southwest Victoria and confederate WA.

Scientists person studied nan mice populations successful these 3 regions and recovered they are distinct subspecies separated astir 1.4 cardinal years ago.

POLLINATION FOR DIVERSITY

Geographic isolation has helped style nan unsocial biodiversity successful nan Kwongan, but it didn’t enactment alone. Pollination besides played a cardinal role. 

Pollinators feast connected nan nectar of flowers. In doing so, they collect and carrier pollen to different places and flowers. This increases works diversity and abundance.

The request for pollination has driven unsocial adaptations successful plants and influenced their evolution. 

For example, it is believed nan curved shape of kangaroo paw flowers evolved to promote birds specified arsenic honeyeaters, wattlebirds and spinebills to pollinate them.

Some banksias person perchance developed circumstantial characteristics to pull mammal pollinators, including nan endemic chromatic possum, because they make significant contributions to their pollination and consequence production.

These characteristics see hidden and scentless flowers increasing astatine crushed level.

More importantly, nan numbers of this endemic marsupial vary according to nan proviso of nectar successful autochthonal works type for illustration banksias. 

Endemic pollinators request endemic plants (and vice versa) to prolong each other. But truthful do we.

AN ECOSYSTEM UNDER THREAT

These unsocial type only recovered successful nan Southwest Ecological Region look respective threats.

Climate change is 1 of nan cardinal threats to nan Kwongan.

Since past century, yearly temperatures proceed to summation while rainfall dwindles.

Land clearing for agriculture, invasive species for illustration foxes and feral cats, habitat fragmentation and disease are each contributing to nan degradation of 1 of Australia’s astir valuable ecosystems. 

To cognize is to care, arsenic nan saying goes.

Unless nan threats facing nan Kwongan are understood and addressed, this hotspot mightiness go a distant representation to early generations.