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?

16 thoughts on “Toads, Saint Patrick, and biogeography

  1. Joe Mehling

    David – thank you for this wonderful piece of writing- it’ll surely bring a warm smile to everyone, especially those of us in unusually cold northern latitudes. best//joe
    [ps: note typo at the end “we’re erasing all this isolation with out planes”]

  2. Anonymous

    Must be nice to live in warm enough places for toads already! Here in PA. we still feel winter’s iron grip.

  3. pwimberger

    Nice St. Pat’s post! And I loved the picture/pun. For a much longer and also fascinating read on the history of biogeography and the vicariance/dispersalist debate, I highly recommend our former grad student buddy , Alan deQueiroz’s “The Monkey’s Voyage.”

  4. Fountainpen

    Did your mother explain carefully to you when a child that you must not hold that toad!!!! Toads cause warts!!??!!

    I smiled as I saw the delightful picture
    And your words. I picked up a lot of
    Toads and frogs and worms. Got no
    Warts at least I don’t remember the warts only the constant warning from
    My good mother!!

  5. Uncomely and Broken

    Then one hot day when fields were rank
    With cowdung in the grass the angry frogs
    Invaded the flax-dam; I ducked through hedges
    To a coarse croaking that I had not heard
    Before. The air was thick with a bass chorus.
    Right down the dam gross-bellied frogs were cocked
    On sods; their loose necks pulsed like sails. Some hopped:
    The slap and plop were obscene threats. Some sat
    Poised like mud grenades, their blunt heads farting.

    From Seamus Heaney’s Death of a Naturalist

  6. Anonymous

    I also enjoyed your essay very much but it is a bit dispiriting to see the photo given the glacial pace of warming here in coastal Maine. Excuse my memory but where exactly are you – Tennessee? I’m trying to roughly guess on the progress of spring. The back of my house is mere yards from a vernal pool but I fear we are months, not weeks, from the normal arrival of the amphibian racket. If Pennsylvania is in the “iron grip of winter”, I’m not sure of the appropriate equivalent here in the Northeast where it is currently 20 degrees at high noon.

    Dale Dorr


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