Little big giants – 06/10/2023 – Reinaldo José Lopes

As dreaming doesn’t cost anything nor does it violate the laws of physics, I confess that every now and then I update a list of times (and places) that I would like to visit perched in a time machine. I’m dying to go to Sicily half a million years ago, for example, just to scratch the ears of a Palaeoloxodon falconeri. It is one of the smallest elephants of all time, anatomically very similar to its relatives today – but measuring only 1 m in height (or about 80 cm, in the case of females). What a cute thing.

The tiny P. falconeri amazes me, above all, because it is far from an isolated case. The Mediterranean of the Pleistocene (the Ice Age) was full of different species of dwarf elephants, which spread across islands such as Malta, Sardinia, Cyprus, Crete and the Greek archipelagos of the Dodecanese and the Cyclades.

It turns out that it doesn’t end at the Mediterranean, nor is it restricted to elephants. Life on islands is capable of operating two seemingly opposite —but actually complementary— tricks in the evolutionary process of mammals and other animals. We know of many, many cases of island dwarfism, but also of island gigantism, with animals becoming both much smaller and much larger than we would expect for members of their lineage.

Both phenomena are, at heart, slightly different responses to the same environmental constraints and opportunities that only an island provides. On the one hand, islands tend to be much, much smaller than a continent, which corresponds, other things being equal, to a lower availability of food resources, among other things.

On the other hand, as the islands generally harbor a lower diversity of species than the mainland, in addition to being surrounded by a barrier that is difficult to cross —a thing called “sea”, you know—, it is not uncommon for a newly-born species to Arriving at the island environment is presented with an almost complete absence of competitors and predators. Suddenly, that little world is hers alone.

The result is that, in many cases, small animals can become much larger than they would normally be on continental soil (hence the fact that there are several giant rodents on islands, for example). At the same time, large animals can miniaturize themselves because 1) they don’t have to remain so huge, since there are no predators, and 2) that way they don’t need as much food in the limited environment of islands —which explains the evolutionary pace of ours. little elephants.

The problem, of course, is what happens when the insulation is broken. As a recent study in the journal Science, signed by Roberto Rozzi, from the Martin Luther University of Halle-Wittenberg, in Germany, shows, midgets and island giants are especially vulnerable to the arrival of invaders.

After all, three-quarters of the extinctions of terrestrial species that have occurred since 1500 have occurred on islands. What Rozzi and his colleagues showed is that this risk is especially high in the most extreme cases, when mammals have reached the highest levels of gigantism or dwarfism.

And things got even worse when humans started to colonize these islands — with a more than tenfold increase in normal extinction rates. This makes the biodiversity that survives in these environments even more precious and worthy of care, even if it doesn’t seem as magical as a pocket elephant.

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