This entry was posted on Tuesday, October 10th, 2006 @ 12:54 pm on the category camelids.
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On the other hand there was the recent report of archaeologists finding evidence of a prehistoric miniature elephant, about the size of a Shetland pony [sorry, I didn’t keep the reference].
You are quite right Chris. Many islands have had pygmy elephants or mammoths or similar, from California’s Channel Islands and Siberia’s Wrangel Island to Komodo and Flores in Indonesia – Jared Diamond wrote a famous paper suggesting Komodo dragons had evolved to prey on pygmy elephants.
On the general rule you are also right: it is known as Foster’s Rule. When I was a biologist at Oxford my friends (Catz biologists were a strange bunch) and I came up with Biblical forms for three of the empirical rules of biogeography, which I’ve just dug out on my computer, as follows.
BOOK OF RAPOPORT
1. Verily, I returned, and saw under the sun, that the kingdoms of the frozen lands do stretch for many leagues; yea from Gog even unto Magog do they stretch.
2. Whereas the kingdoms of the lands blessed with abundant sun are smaller than the vineyards of the House of David.
BOOK OF ARRHENIUS
1. And the Lord said â€œBehold, for isles that are small I bless not with manifold creatures, but starve of divers groups.
2. â€œYet, as the isles grow larger – greater, even, than the kingdoms of Judaea and Samaria – then shall they be blessed.
3. â€œFor unto these lands are given many species, and the number of the species shall grow greater not just as they grow in extent, but even more so: for to those isles that have shall yet more be given, yea, even unto the fourth and fifth multiple of the lands of Israel.â€
BOOK OF FOSTER
1. And it came to pass that the Lord saw that the creatures of the land of Israel were of many sizes, yea, and that among those that gave suckle to their children they stretched from the tiny mouse even unto the lion and the mighty elephant, that strike terror into the hearts of men.
2. And he spoke, and said â€œIn the islands beyond the sea, where nought but my hand availeth you, shall you find that the mice are great, and strike terror even into the hearts of men.
3. â€œWhereas the elephants grow but little and scare not a woman, even that she be foolish and fearful in the sight of elephants.â€
By way of explanation of the other two:
Rapoport’s Rule is that range size is greater for animals of equal size at higher latitudes;
Arrhenius provided the first proper account of the species-area relation ship and gave the explanatory equation S =cA^z where S is species, A is area, and c and z are fitted constants. The value of z tends to be higher in specific clades and areas of the earth: a more rigorous, if more wrong, explanation is given by Hubbell in the Unified Neutral Theory of Biodiversity and Biogeography (princeton, 2001), where the key parameter is theta.
I didn’t, but bats in Britain frequently have lyssavirus. Unless you are an insect that feeds over water you are unlikely to be at risk from a Daubenton’s Bat. You can sometimes see them at dusk from the arched bridge over the Thames on the path across Port Meadow from Jericho to Binsey. Lovely creatures.
It is interesting that there were a variety of large mammalian species even as recently as 10.000 years ago, but that almost all are now extince. It seems likely that the spread of homo not-so-sapiens was responsible for this. We’ve been into the extinction business for rather a while.