by Matthew Cobb
Look at this map from Wikipedia. It shows the distribution of lagomorphs, which are rabbits and hares (family Leporidae) and pikas (family Ochotonidae). [Etymological titbit #1: The name comes from the greek for hare, lagos, so means hare-shaped.] Pikas are small mammals that tend to live in cold parts of north America and Eurasia.
What does the distribution tell us? In other words, why are the blue bits blue and why are the grey bits grey?
First of all, this distribution is not entirely natural. Not all the lagomorphs noted here are indigenous. That is, there are lots of bits of blue that are down to human activity: moving rabbits and hares around the world for food and fur. The most notorious examples of this are Australia and New Zealand, where rabbits (and to a lesser extent hares) are now pests. The distribution in Australia is intriguing – I imagine it means that either they’ve been eradicated from the northern areas or they never got there.
The domestic rabbit, Oryctolagus cuniculus, originated on the Iberian peninsula, and has since spread across the world as we took it to breed for food and fur. [Etymological titbit #2, slightly NSFW: from the latin cuniculus we get the old English term coney (hence Coney Island, I guess) and, more scurrilously, some common slang words referring to female genitalia, such as con in French and the c-word in English.]
Second, the absence of lagomorphs from some major islands (Madagascar, Cuba, Borneo), but their presence on others (Ireland, Iceland, Sumatra) is intriguing. Greg Mayer, who helped me avoid some egregious misteaks in writing this post, highlighted some points in a mail:
Borneo (and Java) are both on the continental shelf, so the absence of lagomorphs there is a puzzle, unlike Cuba and Madagascar, which are old continental (Madagascar) or perhaps oceanic (maybe Cuba) islands, so they would have to disperse cross water to get to them naturally. The rabbits of Sumatra (also on the continental shelf) are native, not introduced (which is why Borneo and Java are a puzzle– all three were connected to the mainland and to one another recently. It looks like lagomorphs are not good at crossing water, as most or all of the islands they are on continental. (Iceland is interesting. It’s not out of the question that Arctic hares could have gotten there on sea ice, but I’m pretty sure that Arctic fox are the only native mammal there. The rabbits/hares would then have to be introduced.)
What really got me interested in this, however, was a tw**t by @NashTurley, asking why there are no lagomorphs in Patagonia – indeed, according to this map there would appear to be none in Argentina or the southern part of Chile. So: a) is it true? and b) if so, why? The European hare does appear to have been introduced into Chile and indeed, is infected with a form of tuberculosis bacterium. (I’m not sure if those little blue blobs at the top left of the Chile part of the map refer to the hares, or if they are more widely distributed.). While the Chile map may not be quite right, it does appear to be the case that there are no lagomorphs in Patagonia. NB: the Patagonian rabbit has nothing to do with Patagonia, it’s simply the name of a breed of very large domestic rabbit. So why the absence of lagomorphs?
Attempts have been made to introduce rabbits into Argentina, but they have basically failed. Indigenous species such as the Tapeti (Sylvilagus brasiliensis), a rabbit, are found in Mexico, through Brazil, extending down to northern Argentina, but they don’t make it further south. These animals crossed the Panamanian land bridge around 3 million years ago. Here’s a fine picture of an alert Tapeti, by Jorge La Grotteria, from here.
The Patagonian mara (Dolichotis patagonum) might represent some kind of competitor. This is actually a rodent related to the guinea pig, but which looks remarkably lagomorphic. Photo from Wikipedia:
Darwin was struck by these beasts, and called them ‘Patagonian hares’ because they are about the same size, and seem to occupy the same niche.
Is this, then, the answer? Are rabbits outcompeted by mara? But how would this explain the apparent lack of lagomorphs on the other side of the Andes, in southern Chile? Is it just too cold? Myxomatosis – a nasty lethal viral disease deliberately introduced into Australia and France in an attempt to control the domestic rabbit (it doesn’t affect hares), with unintended consequences for some predators which lost their prey species – originates from the southern cone, and may be involved, too.
Biogeography – the distribution of species around the planet – can often give us insights into both the present and past ecology of species, and their evolution. In this case, however, it provides us with a conundrum. Why are there no lagomorphs in Patagonia?
Thanks to Nash Turley and Greg Mayer.