Amphibious invasion plans

I'm in Hawaii to speak at a symposium on invasive species. Invasive species have many characteristics that might tend to make them invasive. Although I don't expect it to come up, seeing how the symposium is on crustaceans, it's worth asking a question that recurs a lot here:

What about the brains?

Normally, we think of invaders as being able to turn out lots of babies, or having defenses that natives don't, or all sorts of other factors. But could invaders be winning because they are smarter?

This has been investigated before, and for birds and mammals, the answer seems to be yes. But will this also hold true for less brainy animals? Animals like frogs, snakes, and salamanders?

Amiel and colleagues decided to test this question by trawling through the literature for cases where reptiles or amphibians had been introduced into new habitats. And they conclude the answer is again, “Yes!”

Sort of.

There’s a question of definition. Is successfully establishing a population in a new habitat necessarily an invasion? I know some of my colleagues will say, “No. An invasive species is not just established, but is outcompeting native species.” The title is wrong.

Amiel and colleagues also parsed out the relationship by geographic area, and found another little twist. Big brains were correlated with successful introductions in Palearctic, the Nearctic, the Neotropics, Indomalaysia, Oceania, and the Afrotropics.

In Australasia, the pattern was reversed. The more successful introductions were correlated with smaller brain sizes, not bigger, Amiel and colleagues speculate that Australia is, on average, more resource poor than other locations, so that energetically efficient smaller brains are favoured.

They authors also make a passing comment that it’s not clear to them if overall brain size in amphibians and reptiles improved cognitive ability. This is a severe problem. How does one compare the learning behaviour of a salamander and a skink?

Now, a real test of this hypothesis would start to come if people measuring invertebrate brains. So many more species to work with! So many more ecologies!

Reference

Amiel JJ, Tingley R, & Shine R (2011). Smart Moves: Effects of Relative Brain Size on Establishment Success of Invasive Amphibians and Reptiles PLoS ONE 6(4): e18277. 10.1371/journal.pone.0018277

Photo from Flickr.