Category Archives: Toads

Toads, Saint Patrick, and biogeography

Warm the soil, add an inch or two of rain. The result: toads. Defrosted and ready to grasp springtime’s possibilities.

toads_amplexusAs I write, I hear one trilling in the pond outside. Hopefully the next weeks will bring dozens more. Toad song after a long, long winter is melodious glory.

Thanks to St Patrick (on whose feast day I’m posting this), the Irish don’t get to delight in the sounds of Bufo bufo, the common European toad. Apparently Patrick kicked them out along with the snakes. It is a herpeto-theological mystery why the saint chose not to preemptively bar more pestiferous species — biting flies, fungal blights, or the English — instead of the humble toad. His work was incomplete, though: the rarer natterjack toad has a toe-hold in a few parts of Ireland.

These tales of missing species from islands point at an important area of study in biology, namely the curious fauna and flora of isolated land masses. The technical term is “disharmonious.” Islands have communities that contain some, but not all, of the species of nearby continents (the islands are therefore out of “harmony”). The more distant the island, the more peculiar the biological community, all a result of the unlikelihood of colonization. Ireland is missing just a few European species. In contrast, the Galapagos islands sit far out to sea and are missing most of the species of mainland South America. Indeed, so few colonists have made it to these outposts that in situ evolution has provided much of the local diversity. The same is true of the Hawaiian islands and other oceanic isolates.

This disharmony is hard to explain from a creationist perspective, so it is no accident that islands feature prominently in the thinking and writing of the originators of the theory of natural biological evolution, Darwin and Wallace. To them, the idea that the distribution of animals and plants is explained by the particularities of historical accident seemed a more fruitful hypothesis than de novo creation.

Now of course, we’re erasing all this isolation with our planes and ships. Our mobility is undoing St Patrick’s work, homogenizing the world, sometimes with regrettable consequences: here is a list of the non-native species currently threatening Ireland’s biodiversity. More saints needed?