Secondary Invasion Part 2 – Getting into ‘da’ Christmas Island Club is not an easy task for some. The bouncer says something about it being Shorty’s Birthday… or something. Either way, that rainforest is a pumpin’ crab party! Invaders can come a-knocking, but those crabs just keep a-rockin’….
Christmas Island rainforest isn’t a great place for many invaders anyway. All of those super-abundant omnivorous red land crabs will either just eat you up directly, and/or limit your ability to set up a home through eating up all the leaf litter and seedlings. And these guys are really really abundant (picture one crab every square meter), which makes for one very open and simple rainforest.
But not all invaders are stopped by the bouncer… Enter the notorious yellow crazy ant! These guys get in, find themselves a good sugar-dealer (read: form a mutualism with a number of exotic honeydew-producing scale insects), and turn what was a crab party into an ant party! That’s right, they kill all the red land crabs.
This deletion of a highly-influential species causes some massive changes in the rainforest. A potential predator is removed, you get the build up and persistence of leaf litter, as well as a pulse recruitment of seedlings…. creating a very different looking rainforest. So what about those invaders that were previously excluded? What are they doing now?
That’s exactly what myself and Pete set out to find by looking at a whole community of exotic land snails. As you would expect, these previously unsuccessful invaders were advantaged by the new rainforest community created by the yellow crazy ants but it wasn’t as straight-forward as simply letting them in. There were a whole bunch of very small species that were present in intact rainforest (this whole time!), but 10-fold more abundant once the ants have done their thing.
So this suggests two pathways of facilitation. Primary invaders (ants and scales) will facilitate secondary invaders (snails) to either enter (big species) or establish (small species) – both key steps along the invasion pathway
For the actual science of this story, you definitely read the paper and contact the authors if you have any questions.
O’Loughlin LS & Green PT (2015) Invader-invader mutualism influences land snail community composition and alters invasion success of alien species in tropical rainforest. Biological Invasions 17: 2659-2674.
K!E#15 by Luke S. O’Loughlin
This comic is a direct sequel to Secondary Invasion Part 1 which was published as part of #ESA15comic – the unofficial comic of the 2015 Ecological Society of Australia conference in Adelaide. You can read that 31 page comic HERE. Stay tuned, Secondary Invasion Parts 3, 4 & 5 are all currently in review; comics will follow!