The internet thinks quokkas are the happiest animals in the world.

When photographed they often look like they're beaming enthusiastically at the camera — and Rottnest Island, off Fremantle in Western Australia, has used that to its benefit.

Even a cursory search of the web will pull up hundreds of media articles on the quokka's photogeneity and thousands of social media pictures, including "quokka selfies".

About 500,000 tourists a year visit the island, and that number is set to grow to more than 600,000 by the end of 2016.

The presence of tourists on the island has changed quokka behaviours. ( ABC RN: Ann Jones )

But like all good stories, there's more to the "good times with the Rottnest Island quokka" narrative than meets the eye.

The research of University of WA PhD candidate Veronica Phillips delves into the complex story behind Australia's smallest wallaby species.

"At the moment there'll be a lot of quokka skulls just on the ground, because a lot of quokkas will have died in the past month or so," she says, picking up a tiny delicate skull with large teeth at the front — the same teeth you see see poking through furry lips in the selfies.

You can't tell exactly how the quokkas have died, but it's likely to have happened as a part of a year-long cycle of births and deaths driven by resource availability.

"The young is born 27 days after mating," she says.

"The young comes out very, very tiny. They're tiny, they're pink, they're naked, they look like a little pink jelly bean.

"They've got really well-developed forearms and their hind limbs aren't developed at all. They use the forearms to pull themselves up into the pouch."

They will stay in the pouch for six months unless something goes wrong, but even if that joey is lost, the quokka has a back-up system.

"The quokkas undergo what's known as embryonic diapause, so what happens is they'll have a fertilised ovum stored at the blastocyst stage," says Ms Phillips.

"It's sort of like arrested development in the quokka.

"If the joey she has in her pouch is removed from her pouch or dies then the blastocyst will start developing and she'll have another young 27 days later," she says.

"It's like an insurance policy if the young dies at an early stage."

The yearly cycle of life and death is tangible on Rottnest Island. ( ABC RN: Ann Jones )

Reproductive patterns a symptom of Island life

Rottnest Island quokkas have an "anestrous" period, during which they cannot breed.

This runs from November to January, the driest period of the year.

Water is one of the main limiting biological factors on the limestone island.

Quokkas sleep with their head between their legs, normally under the cover of shrubs. ( ABC RN: Ann Jones )

"We've got salt lakes on the island which are hypersaline, so they're three times saltier than seawater, and that salt used to be mined," says Cassyanna Thomas, a conservation officer from the Rottnest Island Authority.

"There's not a lot of fresh water on the island. We do have freshwater seeps and some brackish swamps."

According to Ms Phillips, quokkas do have a fairly high water requirements.

"On the mainland they generally only live in the areas that have 600mls of rain or more a year," she says.

"But this is also tied to the amount of vegetation that is available; quokkas can get water from the vegetation they eat.

"On Rottnest Island there is a period at the end of summer and the beginning of autumn where a lot of the quokkas die from lack of water and nutrition," Ms Phillips says.

No quokkas are allowed inside the shops. ( ABC RN: Ann Jones )

Man-made environment contributes to quokka population

It's not known exactly what the Rottnest Island ecosystem was like prior to European settlement.

More specifically, it's a mystery how much woodland and how many quokkas there were.

"The clearing that occurred threw the balance out in terms of the feeding sites for quokkas," Ms Thomas says.

"There was a very big boom in the quokka population because there was a lot of that low heath that replaced the woodland areas," she says.

Some quokkas on the Island associate humans with food. ( ABC RN: Ann Jones )

"That's why we've got between 8,000 and 12,000 quokkas on the island."

It's likely that you'll see a few of those thousands of quokkas if you visit Rottnest Island.

If you sit down in certain spots with a muesli bar, you might even be mobbed by them.

And if you look around underneath the dry, scrubby heath, you might see a quokka skull, teeth bared in a smile, even in death.