Thursday, 23 February 2012

Paleobiogeography- quite a mouthful!

It has been a while since my last post, apologies!

To gain a full understanding of a certain behaviour, ecological process or species distribution it is essential to view them from different aspects. For instance, to understand the distribution of a species a Butterfly one would need to investigate metapopulation dynamics, abiotic factors, community ecology and biogeography.

Biogeography is the study of organisms or ecosystems through space and time; Paleobiogeography goes one step further and looks at the effects of plate tectonics as well. Paleobiogeography helps us understand why certain groups have their distributions-

Why are marsupials distributed in Australasia and the Americas?
Because South America, Australia and Antarctica were joined together in one continent and as the continents split, marsupials were left on each landmass though those on Antarctica died out as the continent headed southwards.

Mexican Mouse Opossum Marmosa mexicana- an American Marsupial.

Why is there relatively high endemism in the North Pacific compared to similar latitudes?
Because of Beringia, a refuge of tundra amongst the ice sheets and glaciers during the last ice age which allowed many species to survive whilst surrounding latitudes were uninhabitable.

Mckay's Bunting Plectrophenax hyperboreus- endemic to the Aleutian Islands.

Paleobiogeography can also explain some strange behaviours such as the migration of the Bar-headed Goose Anser indicus which is famous for its high altitude migration over the Himalayas between its wintering grounds on the Indian Subcontinent and the Steppes of Northern Asia. On the face of it, it appears strange and counter productive for a bird to risk the high altitude route over the mountains when many other birds travelling in the same direction choose to fly around the range. Bar-headed Geese have amazing adaptations to cope with the stress of the journey such as modified haemoglobin and breathing rates and a larger wing to weight ratio. 

Bar-headed Geese Anser indicus.

But these adaptations only explain how they overcome the Himalayas, not why. The answer could well lie with paleobiogeography. The Himalayas are a relatively new mountain range formed when the Indian Subcontinent ploughed into the rest of Asia about 70 mya. It is quite possible that the ancestors of the Geese wintered in the low-lying land in the area and slowly, as India crumpled the land upwards the Geese had to fly higher and higher each year until they reached the levels that they regularly migrate at now (around 21,600 ft).

This is just one extreme example of the benefits of understanding paleobiogeography. Hopefully over the next few weeks I'll get round to writing up two other examples of the importance of biogeography in the understanding of species distributions.