Sunday, 28 April 2013

Caprines: Lands of the Ibex

Alpine ibex
The Ice Ages were, on the whole, not a bad time for goats. True, they had to leave the vertiginous cliffs of their mountain homes when they became too cold and barren to support life - and, in many cases, were swathed in vast glaciers. But, as the world grew colder, the vegetation also moved down the mountain slopes, so that, down in the lowlands, goats found plenty of food they had been used to. Indeed, they were better suited to it than most other animals, which had to move to southern climes, rather than merely heading downhill.

Since there are rather more lowland areas than there are mountains, goats could spread much further than they could during warmer times. When the Ice Ages ended, and the hot weather returned, they simply headed back up the mountains. But not, necessarily, the same mountains that they had previously come down from.

As a result, we now have quite a range of goat species across Asia, and, to some extent, Africa. After all, between (and after) the Ice Ages, each population was isolated from those in other ranges, and could develop on its own. Taking, at least for today, our definition of 'goat' to be "any species from the genus Capra", there are probably at least seven, and maybe eight or nine, wild species of goat. The wild goat itself is one, and the markhor, with its bizarre corkscrew horns, is another. Most of the others are collectively known as "ibexes".

Sunday, 21 April 2013

Pleistocene (Pt 8): Mammoths v. Mastodons

American mastodons
The arrival of the first mammoths in North America was a significant turning point in the development of the local wildlife. It's so important that this date, 1.9 million years ago, marks the beginning of the first of just two 'land mammal stages' that define North American wildlife during the Ice Ages. It used to also mark the beginning of the Pleistocene itself, but for various reasons, that's now been shifted a little further back.

The mammoths in question arrived from Asia, crossing over the Bering land bridge, the recurring appearance and disappearance of which greatly influenced North American wildlife during this time. They were southern mammoths (Mammuthus meridionalis), the dominant species of mammoth in Asia at the time, but they quickly evolved into a home-grown American animal: the Columbian mammoth (Mammuthus columbi).

It used to be thought that, even ignoring any late-surviving southern mammoths, there were at least two different species of mammoth living in North America in the early to mid Pleistocene. We're now pretty confident that they're all just examples of Columbian mammoth. Nonetheless, you will often see references to the "Imperial mammoth" (Mammuthus imperator). Perhaps the biggest elephant that has ever lived - they were about thirteen feet tall at the shoulder - these were probably just really big Columbian mammoths. Not that that's anything to sneeze at, mind you.

Sunday, 14 April 2013

Freedom to Dive

Mediterranean water shrew
There are well over 5,000 different species of mammal in the world. From a human perspective, a great many of them are very similar - at least a thousand of them can reasonably be described as either 'mice' or 'rats'. Where they live in different continents or unconnected parts of the same continent, that's not really an issue: European beavers don't care what the American sort are up to. It's a different matter when they live together.

But, of course, they often do. For example, there are fifteen different species of insect-eating bat in Britain alone. But if you have two different kinds of animal living in the same place, in the same way, eating the same thing, they have no choice but to compete. Inevitably, one of them will be slightly better at it than the other, and, given enough time, one of them has to either die out or change what it's up to. So how come there are so many similar animals?

Generally speaking, the answer is that they're not all doing exactly the same thing: there's some subtle difference in what they're up to. In some way or another, they're partitioning the available resources. One simple possibility, for instance, is that they aren't eating the same thing after all. If (to pick a rather unlikely hypothetical example) one of you eats only raspberries and the other eats only blackberries, there's plenty for both, and you don't have to fight over who gets to eat what.

Sunday, 7 April 2013

Life in Ngorongoro

The Ngorongoro Crater
There are a great many species of mammal (and, indeed, other animals) that are endangered, or at least have their continued survival threatened to some extent. If we're at all interested in conservation, we obviously need to know which ones those are, and a good starting point is seeing how much their populations have declined recently. However, we need to do more than just that. We also need to why they're declining, how unusual such a decline is, and so on. Without that information, we'll have no idea how to fix the problem, or even whether the decline is anything much to worry about in the first place.

Long-term population studies are one way to achieve this. If we can look at a population of animals over the course of several generations, we can map declines and rises against the times that various events occurred, to see which are most important, and how easy it was for them to recover from temporary problems. If we study several species at the same time, we can also see whether some events that were good for one species were bad for another - a vital piece of information if we want to protect both of them.