Animals on some islands are famously unafraid of humans (click here to watch an example). In almost every case, this tameness hasn’t lasted long, ending either with the animals become very wary or harvested to extinction.
A new paper by Delibes and colleagues tells a story about the behaviour of an island animal, but it’s too early to tell if this one will have a better ending. Delibes and company were collecting lizards, the orange-throated whiptail (Aspidoscelis hyperythra). As you can seen, these guys are not large, and a bit cryptically coloured.
The research team decided that they could treat themselves as predators, if you will, and would chase lizards until they caught them or the lizard got away. They did this on the Baja Peninsula and on eight islands just off the peninsula.
More than half the lizards on the islands (~58%) got away. But not even 15% of the lizards living on the mainland were able to get away from the scientists.
This is the reverse of the standard “island animals are less concerned by people” story we normally hear.
The authors examine and discard a few hypotheses to explain this unusual pattern. The presence of cats on the islands is considered, but not all of them had cats. They looked at the tails for signs of regeneration from failed predation attempts, but those were about the same on the islands and the mainland (although the authors do say that is tricky to interpret, though).
It seems to come down to the humans. Now, the islands are not inhabited, so one possibility is just that the lizards on the mainland are used to humans and don’t view them as threats. As noted when I started, however, this is rather the opposite of what is often seen.
They think that the lizards have learned to avoid the scientists.
Delibes and colleagues argue that researchers are significant collectors of the island lizards. As you can imagine, this is a fairly difficult thing to prove, and the team has only circumstantial evidence. They note that a couple of papers involved collecting anywhere from 47 to 160 lizards from these small islands. (Some of them are so small, the dot showing the location of the island covers the entire island.) They also have anecdotes from locals, who told them about the “relatively frequent groups of students who rent boats to travel to the various islands”.
The authors discuss whether this is a learned response, or whether it is an evolutionary change. Unfortunately, it’s not easily testable with the data they have. Certainly, however, human harvesting has caused many species to change behaviours. Lobsters, for instance, used to strand themselves in tide pools. They don’t do that anymore, because they kept getting picked up there by hungry humans. What would be unusual is if researchers alone are more or less responsible for this change.
The curiosity about why the lizards are becoming better at escape rather pales next to the possibility that scientists may be chasing these populations, perhaps not to extinction, but down roads that the lizards wouldn’t have otherwise trekked.
The researchers who wanted to study these lizards’ evolution of these lizards might now be the major drivers of it.
Delibes M, Blázquez M, Soriano L, Revilla E, Godoy J. 2011. High antipredatory efficiency of insular lizards: a warning signal of excessive specimen collection? PLoS ONE 6(12): e29312. DOI: 10.1371/journal.pone.0029312
Photo by squamatologist on Flickr; used under a Creative Commons license.