Invasive species are re-structuring our world – yet another consequence of human success

Round this time each year, the red land crabs of Christmas Island are patiently waiting for it to rain, telling them it’s the start of the wet season and to begin their long march to the coast for a reproducing good time! The annual breeding migration of these native crabs is a real spectacle of nature that in the past has captured the attention of Sir David Attenborough, and for a very long time, was conducted completely uninfluenced by humans and their actions.

However, when the crabs leave their burrows again this year, many will be marching through rainforest that looks distinctly different from what it did only decades before. And this is not because of human settlement and mining of the island – although that obviously has had an impact. This is because of the success and influence of some high-impact invasive species. Aliens that at some point hitched a ride on human transportation, and are now wreaking havoc!


Of the remaining 74% of rainforest on Christmas Island, around 2-thirds has been impacted to some extent by the invasion of the Yellow Crazy Ant (Anoplolepis gracilipes). These little, formic acid – spraying guys form your classic ant-scale mutualism with some exotic, honeydew-producing sap-sucking bugs on the island, and while ‘hopped-up’ on this never ending sugar resource, go about forming high density ‘supercolonies’ that actively predate and cause local extinctions of the native red land crab.


Now, when crabs are free to simply go about their business, they are highly influential drivers of rainforest dynamics on Christmas Island. In natural high densities of nearly one crab per square metre, these crabs are responsible for consuming almost all leaf litter and new seedling germinates, so that rainforest on the island is quite interesting and unique – structurally simple and open, and the ground free of leaf litter for much of the year.


As you can imagine, the local extinction of these ‘keystone’ crabs at the hands of the crazy ants indirectly causes massive structural changes to the rainforest community. Leaf litter builds up and persists throughout the year and seedlings recruit en masse creating a structurally complex understory. The red crab is also omnivorous and a potential predator of small vertebrate and invertebrate species so aside from significant habitat augmentation, there is also the creation of enemy-free space.


The properties of the recipient community have changed. We are left with an altered rainforest with a new structure and species assemblage. We have what some call a ‘novel ecosystem’. Something new. Something different. As a result of the impacts of invasive species. As a result of human success.

Now, this is just one example of highly invasive species significantly altering communities but there are many many many more. Humans are travelling all over the planet more frequently and faster than ever before, and we are witnessing an unprecedented amount species moved beyond the limits of their native ranges into areas they do not naturally occur. This is now so pervasive that essentially no ecosystem is free of exotic species.

The aim of my Ph.D research has been to determine how previously unsuccessful exotic species have responded to these altered ecosystem properties on Christmas Island. By untangling complex species interactions, we can begin to better understand the impacts of successful invaders and their potential indirect role in facilitating the invasion success of others, a process called ‘secondary invasion’.

As it looks like human movement around the globe is not going to slow anytime soon, it is inevitable that more situations like that on Christmas Island will crop up. Understanding novel species interactions in altered communities is highly important for our conservation effort and maybe someday soon the red crabs of Christmas Island will again migrate down to the coast without worrying whether or not they are going to run into some crazy ants!

For more information listen to the ‘bit’ I did recently for The Science Show on Radio National about how ‘Exotic ants tip the balance on Christmas Island’.


This blog was written with reference to the tips and advice presented by Ian Lunt in ‘Never blog in your PJs, and other tips for science and ecology bloggers’.

In the past, my blog page has served no audience and existed almost solely for my own musings. However, as this project comes to an end and papers are beginning to be published, I realise that I might have something worth saying and there may indeed be an interested audience out there. An audience I actually should be writing for.

Even important blogs promoting my recent publications or conference talk managed to tick almost none of the key criteria that Ian suggests makes an engaging and well-read entry. As such, future blog endeavours will not be making these mistakes (I hope).

I recommend any ecologist reading this to check out Ian’s blog because as he states, ‘This generation of researchers has to do the lot. Every early career researcher is encouraged to publicize their work on blogs and social media‘. You may also be interested in assessing my post in reference to Ian’s criteria:

  1. Always write for a broad audience. Never write for your close friends or lab mates.
  2. Make a great first impression. Lead with an informative title, engaging paragraph and attractive photograph.
  3. Recognize that good stories have a different structure to scientific papers. Use a successful story-telling structure, like those suggested above.
  4. And chuck out all the big words. They repel more readers than they impress.

Let me know how I faired. Cheers


2 responses to “Invasive species are re-structuring our world – yet another consequence of human success

  1. Pingback: Littlest exotic species provide evidence for big invasion concept | Luke O'Loughlin's PhD Research

  2. Pingback: Juiced-up ants hit ‘da club’ and snails approve! | KAPOW! ECOLOGY

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