No Plants No Animals

A two-metre-tall dinosaur bird roams the rainforests of north-east Queensland looking for its next meal to swallow whole. A meal that keeps itself, rainforests, and us alive.

Meet the ancient rainforest gardener 

With its vivid blue neck, tall helmet and jet-black feathers - the Southern Cassowary is a striking bird and takes the phrase ‘you are what you eat’ to whole new level of importance. Its remarkable ability to swallow fruit as large as a mango whole (do not try this at home) plays an important role in maintaining the diversity and survival of rainforest trees.

Rainforests are considered the lungs of the planet, they stabilise our climate and are home to world’s five to ten million plant and animal species. Cassowaries have been recorded eating over 238 species of plants! While we all wish we could be revered for our consumption abilities, they get the title of ‘rainforest gardener’ or ‘keystone species,’ because their food intake maintains the balance of its rainforest home.

Explore the connection between plant and animal survival with Senior Principal Research Scientist, Dr Maurizio Rossetto and Birdkeeper from Taronga Zoo Sydney, Corinne Symons in the third episode of our new Branch Out podcast, No Plants No Animals. Hungry for more? Scroll down and keep reading about this topic below.

Size matters: food for thought and our future

Millions of years ago, our rugged land was covered in lush, rich and dense rainforest. Now, only tiny ecosystem pockets remain and in the World Heritage listed Nightcap National Park in northern NSW, several native trees face extinction because they can no longer spread their seeds.

Many Australian rainforest trees produce large fleshy fruits, which drop to the floor when they’re ripe and ready to be eaten by animals. However, in the rainforest - size matters. Only a few native rainforest animals that can ingest fruits larger than 3cm in diameter remain, and unfortunately in NSW, we don't have the Cassowary to do the job.

Dr Rossetto said past ice ages have resulted in the repeated reduction and fragmentation of rainforests in Australia and while some plant species have survived this, many large-fruit dispersers were lost in the process.

"The animals that can feed on the big rainforest fruits and move their seed around are fairly limited in Australia compared to South America, Asia, and Africa, which have rhinoceroses, monkeys, squirrels and all sorts of birds to do this,” Dr Rossetto said.

“While we don't have the Cassowary in NSW, we still have animals such as the wampoo fruit dove and bats, which are capable of eating and dispersing the smaller fruits such as figs and lilly pillies,” Dr Rossetto said.

Many rainforest species in Queensland, such as the larger fruited trees from the same family as the avocado (sometimes known as native walnuts), are now solely reliant on the Southern Cassowary to spread their seeds.

“They scoop up the big fleshy fruits that rainforest trees have dropped beneath them, swallow them in one gulp, digest the pulp and pass out the seeds unharmed all over the rainforest in large piles of poop,” Dr Rossetto said.

“It’s starting to become a ‘chicken and egg’ situation. As the rainforest disappears, so does a vital resource of food, protection and habitat for a huge percentage of Australia’s wildlife,” Dr Rossetto said.

Even plants need to move out of home!

Just as there comes a time for children to grow up and leave the family home, so too must plants. If a plant can’t disperse its seeds - its seedlings will grow very close to the parent plant, and this results in a competition for resources.

Dr Rossetto and his colleagues looked at the distribution of over 1000 species of fleshy-fruited rainforest trees and vines across Australia to study their ecology and evolution.

“If a plant were to drop all its seeds right below itself, the seedlings don’t stand a chance competing for sunlight, water and soil nutrients,” Dr Rossetto said.

“By dispersing seeds over a large area, a parent plant gives the seeds a greater chance at finding space, untapped resources and it allows a species to begin colonizing a new area,” Dr Rossetto said.
 
But it’s not just about being able to settle down and grow up, as plants become increasingly restricted to fewer habitats it means they are more vulnerable to threats such as clearing, climate change, fire and disease.

The zombie apocalypse of plants

Dispersal also leads to the exchange of genetic material and this is so important because it gives plants the ability to produce fit and viable seeds, and to cope with changes in the environment.

The hairy quandong (Elaeocarpus williamsianus) is a small rainforest tree which produces a gorgeous shiny blue fruit. However, after years of not being able to reproduce with unrelated mates (yes, plants have sex), the hairy quandong in the Nightcap National Park no longer produces viable seeds.
 
Dr Rossetto said that some hairy quandong trees have up to 300 sprouting trunks, but because they are all clones (part of the same genetic individual) it’s the zombie equivalent of plants.

"It’s like the living dead, they’re there, but they’re not there,” Dr Rossetto said.

“The survival of species such as the hairy quandong, may rely on human-assistant transplantation to establish new, genetically mixed populations, or even possibly, introduction of animals such as cassowaries to help ensure their dispersal,” Dr Rossetto said.

Branch Out and subscribe to our podcast 

Explore the connection between plant and animal survival with a trip to Taronga Zoo in Sydney in the third episode of our new Branch Out podcast: No Plants No Animals.

You can subscribe to Branch Out on the Apple podcast app or Android podcast app. If you like the show, please leave a rating, review and share it with your followers on social media. 

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