With the aid of examples, discuss the biogeographical consequences of previously separated continents merging.

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With the aid of examples, discuss the biogeographical consequences of previously separated continents merging.

According to the theory of plate tectonics or previously named continental drift first proposed by Alfred Wegener in 1912, the continents of the world are constantly moving and re-arranging themselves by the action of great convection currents in the Earth’s mantle.  This causes large landmasses to split into smaller pieces, slide past each other and merge together.  There are many consequences to these events; more importantly to this essay, there are massive biogeographical implications.

There are three main types of environmental barriers that inhibit species spreading by causing major environmental discontinuities.  These include oceans and seas, mountain ranges and large deserts.  Australia is completely surrounded by water and therefore is biogeographically isolated from other landmasses.  The extensive deserts of North Africa and the Middle East effectively separate Africa from Europe and Asia; in a similar way the high Tibetan plateau of which the Himalayas are the southern fringe separates South East Asia and India from the rest of Asia.  (Cox and Moore 1993).  The Americas are independent from the rest of the world by the surrounding oceans however are to some extent currently biogeographically separate from each other.  However when the Panama Isthmus first united them there was a great interchange of species, which will be discussed later.

Although the plates move very slowly, only about 5 - 10 cm a year (Cox and Moore 1993), over geologic time, life would be greatly affected.  At one point in geologic history all the continents were united as one super-continent known as Pangaea about 260 million years ago.  This came from the uniting of Euramerica, Siberia, Gondwana and two portions of what is now China.  At this point all land flora and fauna were joined by land and could potentially colonise the entire world causing the spread of certain species and extinction of other species by competition.  However there would have be a massive dry area inland of the super-continent with extremes of weather that may have experienced annual temperature changes of 50-60oC, which no reptile could sustain and very difficult for other species to survive (Cox and Moore 1993).  This would be the last time all the land in the world would be joined.  After this, the continents have moved and split and slowly formed the world today.

The continents of today are separated to an extent that they can be classified and scientists have split it up into zoogeographical realms.  The first to do this was Alfred Russell Wallace in 1876 who organised them as follows; Nearctic (North America); Neotropical (South America); Palearctic (Europe and Asia); Ethiopian, sometimes described as Africotropical (African); Australasian (Australia) (J.C. Briggs 1987).  This is of course a generalisation as there are highly endemic large islands to be considered like New Zealand, Madagascar and Hawaii.

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Some of the continents that have recently merged include Africa with Eurasia, North America with South America and India with Asia.  The joining of the Americas was very recent, just over 5 million years ago either in the late Miocene or early Pliocene.  It occurred as South America had been independent and was moving west towards the great oceanic trench of the South Pacific; as it reached the trench, it moved over the zone where oceanic crust was being drawn down into the earlier crust.  This then caused a lot of volcanic activity forming the Andean mountain chain.  More ...

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