Turtles and other non-natives?
A turtle shouldn't really be in the lake at UEA, but here they are, I saw one by the little chicken wire island in the middle, I had been told they were there, and only saw it once, and only actually saw its head and front of carapace and one front leg, through binoculars and from some distance away. Taking a picture from that distance would have been pointless so here is a stock photo of a red eared slider turtle Trachemys scripta elegans,
apparently there are two of these turtles in the UEA lake, a big one and a small one, but I was so far away and as I only saw one, and had nothing to compare it with, hence I have no idea if this was the big one or the small one?
They are native to the USA and popular in the pet trade, cute when little but when they get bigger they can get a bit bad tempered and 'bitey', not really a child friendly pet, so people tend to dump them in lakes. I imagine that's how these two got here.
They are not our only non-native species in the UK, we have thousands of them. These poor turtles cannot breed here, it's too cold, and I don't even know if these two are a pair or same sex?
But non natives can be probelmatic, displacing native species, like grey squirrels Sciurus carolinensis out competeing native reds Sciurus vulgaris.
Species that come from abroad and can reproduce are generally called naturalised, the general rule seems to be if a species was in Britain before the land bridge to mainland europe was covered by sea around 10,000 bc then it's Native, if introduced since and been here for hundreds of years it's called Naturalised. After this point it all gets a bit wishy washy, rabbits Oryctolagus cuniculus are regarded as Naturalised, as are Sweet Chestnut Castanea sativa and Horse Radish Amoricacia rusticana.
But Rhododendron which is naturalised is also considered an invasive species, hence you can see where it gets confusing, you can be a naturalised species and an invasive species too if you create a problem for native species or the environment, and eradicated... much like the coypu Myocastor coypus.
Escaped Porcupine Hystrix hodgsonii hadn't been breeding in Devon and Wiltshire very long at all (15 years or so) and were - for a short while - talked of as naturalised, then later invasive, a short time after that, recaptured and banged up back in a zoo for their escapalogical feats.
So who makes the rules? Er difficult to say, certainly not the species being debated, but as a general rule it seems to be by consensus of interested humans, if a non-native species such as horse raddish, little owl, rainbow trout or Walnut goes about its business without the local humans objecting to it for many years, it gets to be called naturalised non-native.
However if enough people don't like it, like the poor old coypu or grey squirrel it gets on the invasive species list, and if the species affects farmers you often end up on a wanted poster and then eradicated like the coypu, so as long as grey squirrels only affect red squirrels and don't develop a taste for sugar beet they should be fine.
My question is, if a non-native species turned up on an island and started wiping out native species on a grand scale, surely they should be called an invasive species?
Apparently the rule does not apply to Polynesians settlers in New Zealand, Vikings in Iceland, Africans and Indonesians turning up in Madagascar, or any human in Galapagos or Antarctica for that matter, but I'm not sure why?
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