Littlest exotic species provide evidence for big invasion concept [reprise]

A couple of years ago I published an observational study on invasive ants facilitating exotic snails by killing native crabs. That’s the specifics that may be of limited interest, but the interactions (invader-facilitated invasion success) are broadly relevant to anyone studying the dynamics of multi-invaded complex systems. The overall conclusion is that we need to better recognise influential invasive species as intrinsic properties of recipient communities. You can quickly skim the paper by watching the video below, then I highly recommend reading the rest of this short blog that summarises the whole thing:

Humans have been really good at moving species all over the world, and in turn, exotic species have been really good at becoming abundant and influential in their new environments. However, sometimes the conditions in a new environment wont allow an exotic species to get their foot in the door and become invasive. For that to happen, conditions need to change – and who better placed to drive that change than other, previously successful, exotic species.


It is well established that the impacts of invasive species can seriously alter ecosystem properties. For example, the invasion of a highly-flammable grass will increase fire intensity and frequency in that environment. What is less established is how these altered ecosystems can now be invaded by other, previously unsuccessful, exotic species – in short, exactly how one exotic species will indirectly help another.

The concept being described here is that of ‘secondary invasion’. Most people will have an implicit understanding of the idea based on the more everyday notion of ‘secondary inflections’. A body contracts some pathogen (successful primary invader) making the body ill (altering the conditions of the environment) which leads to the body contracting other infections it otherwise wouldn’t have caught (previously unsuccessful secondary invader).

In ecological research, secondary invasion is a key part of the ‘invasional meltdown hypothesis’ (two invaders working together that amplifies impacts and accelerates more invasions) but was not explicitly defined as such by the authors. Actually, the concept itself remains undefined in the scientific literature and in desperate need of some dedicated investigation and empirical evidence.

A heavily invaded rainforest ecosystem on Christmas Island has long provided some of the strongest evidence in support of the ‘invasional meltdown hypothesis’, and is now also lending key support to this concept of secondary invasion.

The highly abundant red land crab dominates Christmas Island (natural densities of around 1 crab every square meter) and is responsible for the unique open structure and sparse ground layer typical of the rainforest ecosystem on the island (see below). Enter the invasive yellow crazy ant, that when fueled by the sugar of exotic honeydew-producing scale insects, cause local extinctions of the red land crab. The deletion of this ecosystem-engineer causes a pulse recruitment of seedlings and the build-up and persistence of leaf litter. The influence of the crab as a predator is also removed. The end result is an environment with a completely different set of conditions that other invasive species will respond to.


The rainforest community on Christmas Island has quite different characteristics before and after the impacts of primary invaders.

These changes were recognised early on as a great benefit to the exotic giant African land snail, which had been hanging-out on the island since WWII but had never been able to enter the rainforest without being quickly eaten by abundant red land crabs. The yellow crazy ant (primary invader) had indirectly caused the invasion success of the giant African land snail (secondary invader) by deleting the red land crab and creating enemy-free space (altering the conditions of the environment).

However, the giant African land snail is just one of many land snail species on Christmas Island – most of which are exotic and all of which are very small (20 – 1 mm in length). In a study published earlier this year in Biological Invasions, Pete Green and myself investigated whether the invasion success of these snails also depended on the yellow crazy ants altering the environment.

We found that in rainforest where the yellow crazy ant had removed the red land crab these smaller snails were an order of magnitude more abundant – the difference of only a few individuals compared to hundreds for every sample of leaf litter. When comparing intact to impacted rainforest there was no difference in total number of species (~20) or species composition as calculated from presence absence data, meaning all species were essentially at all sites.


The key results shortened from O’Loughlin & Green (2015) Biological Invasions 17, 2659 – 2674. Data is from quadrats during one wet across four forest states; Intact (abundant red crabs, native control), Supercolony (abundant yellow crazy ant, no red crabs), Ghosted (no red crabs, no yellow crazy ants), Recovered (previously a supercolony that was managed and had red crabs return).

This pattern of success was markedly different from what had been initially observed for the giant African land snail. These smaller species were able to enter the rainforest where crabs were present without issue. Yet they still responded positively (increased abundance) when the invasive ants deleted the native crabs. So how does this help inform our concept of secondary invasion?

When considering what determines invasion success, we need to establish when a species goes from simply being ‘exotic’ to ‘invasive’. It is generally considered that ‘invasive’ be reserved for those species that are well established in highly abundant populations, with the capacity to quickly spread and potential to impact the environment. That means the conditions limiting a species could be at any of the earliest points on the invasion pathway – either at the transport, entry or establishment stage.

What we have here on Christmas Island – with our investigation of the entire land snail fauna – is evidence for two distinct pathways of secondary invasion. A true-entry model (the giant African land snail that could not get into the rainforest at all) and a population-release model (the other smaller exotic species that could enter the rainforest but only persist at very low abundances). Both were indirectly facilitated by primary invaders to establish high abundant populations – by definition, ‘invasive’ – but from different starting points.

Often the focus of research is at a global scale, with big data, attempting to make the broadest generalization on the nature of something (which is of course important). The results and implications of this publication demonstrates that the intricate details of specific phenomena will continue to be understood through dedicated small-scale investigations, on literally some of the littlest species.

Christmas (Island) special

I’ve been busy this back half of 2016, doing the field work for the well-monitored experimental release of the new biocontrol agent on Christmas Island, and haven’t gotten around to updating my pages with either a research blog or a comic….. Now I don’t have to because Matteo Farinella has nailed it. Great Christmas present…..

Matteo Farinella Blog

Christmas is upon us and I realised that I have been so busy this year (between my new research project and my new books) that I didn’t have time to draw any short stories, which have always been my favourite format. So, when I learnt about the troubles of Christmas Island on the new Planet Earth (and later discovered that the story is even more complicated) I decided that it was time for a little personal project. This short comic is the result, it’s inspired by science – because of course it is – but I hope it can also be read as fiction and enjoyed regardless of the science. However, if you do want to know more of the biology here is all all the info you need. Happy holidays!


View original post

Volunteer opportunities – Connell Rainforest Research Plot Network

Are you interested in contributing to one of the world’s longest running, plot-based study of rainforest community dynamics?

In 1963, Professor Joseph H. Connell (University of California, Santa Barbara) initiated two research plots in Queensland to improve our understanding of the mechanisms that maintain high diversity in complex, species rich tropical and subtropical rainforests.

At these plots, stand and demographic data for rainforest trees, saplings and seedlings have been collected at 1-6 year intervals for 50 years! These data have been instrumental in informing long-held assumptions as to how rainforests can maintain such high diversity, rather than becoming dominated by only a few common species.

Putting a team together 

It is time again to conduct another re-census of both plots and we’re looking to put together a team of keen volunteers to do this with us! What we need is a group of 8-10 people, for roughly 10-12 workdays for each plot, to get all the work done. Exact dates are currently being finalised, but the very likely times are as follows:

Monday 7th November – Sunday 20th November (two weeks) Davies Creek Plot, Dinden National Park (25 km southwest of Cairns) Tropical rainforest

Monday 21st November – Sunday 4th December (two weeks) O’Reilly’s Plot, Lamington National Park (84 km south of Brisbane) Subtropical rainforest 

The work itself involves regular length days out on the plots, relocating and recording data for all plants tagged and mapped (up to 2,000 trees and over 10,000 seedlings). Volunteers will need to be field hardy and have the capacity to collect high-quality scientific data.

Who are we looking for? 

We are looking for any person with a strong interest in ecological research, and the scientific rigour to work hard and efficiently in the field. These positions would suit science undergrads or recent graduates that want to get some more practical field experience, or anyone else with a strong interested in botany, being out in a rainforest, or contributing to important long-term research.

We take care of all flights, accommodation, transportation, and food expenses for the field trips.

We will likely preference applicants that are able to do both trips (4 week commitment), but we would definitely still like to hear from you if you are only available for re-census of one plot or the other (2 week commitment).

Getting in contact

If you think you’re the right person for this work, send your expressions of interest to Dr Luke O’Loughlin ( Please include in your email information about yourself that addresses how you would be a great asset to the team (e.g. skills, past experience, plays well with others, etc) and attach a current CV (that includes your contact details). Use the subject heading “Connell plots volunteer” in your correspondence.

Over the next 3-4 weeks, I’ll be taking names and getting in contact with people with more details and lock-in plans after we finalise logistics (probably the first week of August). I will endeavour to reply to received emails but I am currently away in the field with only occasional access to email. If you don’t hear from me, rest assured that your name is on the list and I will be giving you a call in a few weeks. Thanks

More information

For a detailed account of site history and what a re-census entails, see this glossy-science-magazine story about the last survey effort;  READ IT HERE

To see a little bit more of the site and what others have thought of the experience, see what a few of us have posted on Twitter; SEE IT HERE


Dept. Ecology, Environment and Evolution, La Trobe University // The Long Term Ecological Research Network (LTERN) // Terrestrial Ecosystem Research Network (TERN // National Collaborative Research Infrastructure Strategy

The invasional meltdown hypothesis and an oceanic island

The following is the introduction chapter (Chapter 1) from my Ph.D thesis Invader-invader mutualism facilitates secondary invasions in rainforest on Christmas Island.


The intact rainforest of Christmas Island is characterised by abundant red land crabs, a patchy distribution of leaf litter and a structurally simple understory.

Biological invasions

Biological invasions are a major and increasing element of global change (Mack et al. 2000, Wonham and Pachepsky 2006, Pyšek and Richardson 2010). The impact of species invasions poses a significant threat to biodiversity through species loss and altered ecosystem function (Mack et al. 2000, Crooks 2002, Ricciardi 2007) as well as having significant economic consequences (Luque et al. 2014). These costs are associated with, i) the loss of primary production (Wilby and Thomas 2002), ii) loss of biodiversity and other impacts on natural ecosystems (Vilà et al. 2011, Simberloff et al. 2013), iii) the effort and resources required to reduce the entry and spread of new invasive species and the eradication of those already established (Eiswerth and Johnson 2002, Pyšek and Richardson 2010). So extensive is the problem that the research discipline of invasion biology (Elton 1958, Simberloff and Vitule 2013) has developed over the past few decades to examine important questions related to the spread and impacts of invasive species. Along with climate change and habitat loss, biological invasions, and their impacts, are considered a main driver of global environmental change (Didham et al. 2005, Tylianakis et al. 2008). Understanding the determinants of invasion success continues to be intensely studied (Catford et al. 2009, Lockwood et al. 2009, Blackburn et al. 2011) in order to better predict which species will become invasive and what the impacts of these successful species are likely to be.   Continue reading

How to collect that wild swarm of bees

**DISCLAIMER** This is not in anyway my area of expertise and I was merely an observer of the action. Step 1 is most important – if you have your own swarm of bees – call somebody who knows something about that stuff!

WELCOME TO  FUN WITH BEES: a step-by-step guide to collecting that wild swarm of European honey bees (Apis mellifera) that turned up in your garden that one time……


Continue reading

Littlest exotic species provide evidence for big invasion concept

Humans have been really good at moving species all over the world, and in turn, exotic species have been really good at becoming abundant and influential in their new environments. However, sometimes the conditions in a new environment wont allow an exotic species to get their foot in the door and become invasive. For that to happen, conditions need to change – and who better placed to drive that change than other, previously successful, exotic species.


It is well established that the impacts of invasive species can seriously alter ecosystem properties. For example, the invasion of a highly-flammable grass will increase fire intensity and frequency in that environment. What is less established is how these altered ecosystems can now be invaded by other, previously unsuccessful, exotic species – in short, exactly how one exotic species will indirectly help another. Continue reading

The slides and the script: ATBC presentation from Honolulu 2015

The following post features the slides and (roughly) what I said when presenting part of my research at the Association for Tropical Biology and Conservation annual conference held in Honolulu, Hawai’i the other week (12 – 16 July 2015). I was presenting in the ‘invasive species’ session on the Thursday afternoon (last session of the last day!) which included many interesting talks. I present this here for anyone who happened to miss the talk but was otherwise interested in some of the content. Throughout the post the relevant text comes after the slide:

Invasive Giant African Land Snails (Achatina fulica) have little to impact in rainforest


Aloha, today I’m going to tell you about some research I’ve conducted as part of my PhD research, where we looked for any impacts of invasive Giant African Land Snails, when in high-abundance, in a natural – rainforest – setting. And I have obviously given away the answer in the title of this talk – we determined that this potentially damaging invader was nothing more than an aesthetic atrocity – in the context of this study. So how did we come to this conclusion… Continue reading

Ph.D Thesis Submitted!!



Come back soon to see a series of blog posts wrapping this whole thing up. Not now though. Now I’m off to the pub. Then Hawaii.



The end of this PhD research is near…..

To Dear engaged reader of my PhD research blog,

My PhD research is moving towards completion. Papers are in review and edits are being made on those final manuscripts. There is no time for blog-related procrastination now as I move swiftly towards formatting all those chapters into a Thesis which will be “enjoyed” by 4-5 ish people.

I call upon the internet community to ensure I have everything together for a submission date somewhere between mid-April and the end of May. If June rolls around and there is not a post here that simply reads ‘SUBMITTED’, it will be your job to call me out!

In the mean time, please scroll through  and enjoy other posts describing invasive species dynamics on Christmas Island, as well the updated project description on the Hermon Slade Foundation webpage detailing the major findings of the research


Luke O’Loughlin

'The light at the end of the tunnel'

‘The light at the end of the tunnel’

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. Continue reading