Saturday, 19 May 2012

The changing ecology of Britain - Part 1

Hand axe from Boxgrove
Since the end of the last glaciation around 10,000 years ago, the environment of Britain has been transformed repeatedly by both natural and man-made alterations. New species have colonised, thrived, and become extinct, sometimes repeatedly, as alterations in climate, especially summer temperatures and rainfall, have made the British Isles suitable for one species and less so for others. Human predation has removed some species, especially large carnivores, but farming and forestry has also created new kinds of habitats which some species have exploited with great success. This series will cover some of those changes, and both the losers and the gainers in the changing face of Britain.

The first humans to live in the British Isles go back a very long way. Boxgrove man dates to around half a million years ago, and has been classed as Homo heidelbergensis. This ancient hominid was probably the ancestor of both the Neanderthals and anatomically modern humans, and from sites on the continent is known to have used fire to make hardened tips to their wooden spears. Although the brain size was on average less than modern humans, it overlapped with the lower end of the modern human range. Even then however, the human presence was already ancient – in 2010 flint tools dated at 800,000 years old were found in Norfolk.

Skull and model of straight-tusked elephant
At the time of Boxgrove, the British climate was warm, and animals were a strange mixture of animals we now think of as typically European, such as horse, red deer and wolf, and more southerly animals such as rhinos, lions, and elephants. How the humans interacted with them or affected their environment is not clear, but humans were already skilled hunters by this point and may have had significant impacts on the populations of favoured prey.

reconstruction of Neanderthals
The more famous Neanderthals were the next major species to occur in Britain. Britain during the glaciations was always a pretty inhospitable place however, and the number of Neanderthals at any one time in Britain was probably always low, even during warm interglacials. The last glaciation was particularly savage, and it was probably this, rather than direct competition with modern humans, which was the cause of their extinction. Although describing Neanderthals as extinct is itself something of a matter of semantics – it is now known that all human populations outside Africa carry some Neanderthal genes as a result of interbreeding in the Middle East with anatomically modern humans from Africa, so in a sense they are still with us – in fact they are us. All the Neanderthal DNA appears to have originated from male Neanderthal x female modern human offspring, as no mitochondrial DNA (passed down through the female line) of Neanderthal origins has been detected. This makes me wonder if the conventional portrayal of Neanderthals as being regarded as inferior beings by the modern humans they encountered is more a result of early 20th century racial theorising than anything that went on at the time – maybe modern humans regarded a Neanderthal son-in-law as a “catch”!

Whatever went on between the two forms of human, at almost the same time as the last Neanderthals were leaving the stage in Spain around 30,000 years ago, the first modern humans known from Britain were already living in Wales. These first pioneers however probably did not survive the peak of the Last Glacial Maximum around 20,000 years ago, and modern human settlement began with people who survived in Spain and southern France and then migrated north as the climate warmed.

At its peak, the ice front in Britain extended as far south as Gloucester, only a few miles north of Bristol, and most of the area from Bristol down far to the south would have been tundra, populated by Reindeer, Horse, Mammoth, and the associated carnivores – Wolf and Polar Bear in particular.

no prizes for guessing what this is
Britain and Ireland would have formed a single landmass as a result of the lower sea level, but where the English Channel now is would have been an icy Arctic river, choked with icebergs, and forming an important barrier to movement for mammals and amphibians. Mammoths survived in North West Europe until around 14,000 years ago, but the warming climate encouraged the conversion of grassland to forest, eliminating their habitat.
The same environmental changes probably caused the extinction of other cold-adapted animals in Britain.. In much later Medieval sagas, Vikings living in Orkney are described as hunting Reindeer in Caithness, but even if the story is true they were long gone by the 1950’s when a small group were introduced to the Cairngorms. Today there are around 150 in the mountains, and the population is controlled to avoid overgrazing. For more on the Cairngorm Reindeer, visit here:

The birds of course were just as affected. Some, like Ptarmigan and Snow Bunting, survived by retreating to mountain tops, but others relocated further North, visiting Britain only as wintering birds and breeding further north. In cold periods however some would spread further south again, and even today Snowy Owls winter in some years in the UK. Between 1967 and 1975, one pair even bred in Shetland.

Snowy owl
Next week, the post-glacial warming, and some unexpected birds.
 (images from wkipedia)

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