Sunday, 4 October 2015

How Not to be Eaten

This picture is far less cute if you're a mouse
Animals, on the whole, want to avoid being eaten. There are a number of ways of achieving this, including being well armed or armoured, or just being too large for most predators to bother with. For relatively small and inoffensive animals, however, we're left with being difficult to find, and being good at escaping when you are detected.

But even this can cover a range of different strategies, or combinations of strategies, not least because there are a lot of different predators out there, and what may be good for escaping from one may be less effective against another. Moreover, if every animal evolved to avoid, say, the open grasslands in favour of forest cover, then there'd be an awful lot of potential food out there going begging. Inevitably, something would evolve to take that risk. There's always a pay-off involved.

It's as a result of things like this that there are so many species of small mammal, with subtle differences between them that are not always obvious to the casual observer. To understand the predator-prey dynamics of a particular habitat, we really need to look at a whole range of creatures. So many, perhaps, that it's beyond our ability to easily analyse in its entirety, but we can at least take a stab at a manageable group of species in one particular place, trying to see what makes them different, and why what works for some does not always work for another.

Saturday, 26 September 2015

The Dog Family: The Marks of Zorros

When North and South America collided towards the end of the Pliocene epoch a little over two million years ago, dogs were, for the first time, able to cross to the southern continent, a place that had previously been somewhat lacking in large mammalian carnivores. The dogs that crossed over all seem to have been related to wolves, rather than foxes. However, the fox body plan and lifestyle, with its high adaptability, proved so useful that most of the living descendants of these animals look just like foxes.

However, they are not "true" foxes, but rather, wolf-like animals that evolved into creatures that happened to closely resemble the members of the much older lineage that we find on the other continents (red foxes, Arctic foxes, the various kinds that we find in Africa, and so on). Recognising the distinction surprisingly early, some nineteenth century naturalists called them "fox-tailed wolves", and there has been a (largely unsuccessful) move to call the animals "zorros" in English, to distinguish them from the true foxes. That this didn't take off is perhaps due to the fact that "zorro" simply means "fox" in Spanish, and most of the researchers studying the animals are likely to be Spanish speakers... so it's not really a lot of help.

Sunday, 20 September 2015

Pliocene (Pt 7): Home, Home on the Steppe

The beginning of the Pliocene epoch in North America was not marked by any great cataclysmic event, such as happened in Europe at that time. Nonetheless, while we're not far enough back that North America is unrecognisable, or in a different place, or anything like that, there would have been clear differences if we could see it from space.

Perhaps the most obvious difference would be that the Great Lakes didn't exist yet, since they were carved out by the advancing glaciers of the Ice Ages - which have yet to happen. With sea levels higher, Florida (then, as now, not a place known for its mountain ranges) is largely underwater, and there were probably many other changes around the coast, too.

Arguably the most important difference, however, is further south. Mexico is not so different, at least in its general outline, but beyond that things start to change. Depending on the exact point within the Pliocene we're talking about, you could perhaps have walked as far as Nicaragua without getting your feet wet. Beyond that, however, the Central American peninsula tapers to a point, and where Costa Rica and Panama should be, there is nothing but a chain of tropical islands, a southern counterpoint to the much larger chain of the Caribbean further north.

Sunday, 13 September 2015

A Forest Fit for Sloths

One of the main problems facing the continued survival of wild animal species across the world is loss of habitat. (Naturally, this goes for all kinds of animals, and plants, too, even if we're mainly interested in mammals here). As humans expand in numbers and push into the wilderness, we turn a lot of it into farmland to feed ourselves, use it for logging or mining, or simply build roads across it. The animals that are least concerned about this are those that we have domesticated, whether as pets or as livestock, with supremely adaptable generalists such as rats and pigeons following not far behind.

At the opposite extreme, of course, are the specialists, those that require one very specific sort of land to live in. In between there are a great spectrum of other animals, that can cope with some change, but not too much, that find orchards and plantations a reasonable substitute for forest, and so on. If we're interested in conserving particular animals, one of the first things we need to understand is just what their requirements are.

Even then, it's not enough to know that a particular animal "likes forests". What kind of forests? Do they really have to be primeval and untouched, or are there are at least some viable alternatives? Are there, perhaps, particular parts of the forest that they like more than others? In the grand scheme of things, just leaving stuff alone is probably the best answer from a conservation perspective, but, since human numbers aren't going to start falling any time soon, compromise is often inevitable. So the question then becomes: on what can we compromise?

Sunday, 6 September 2015

A History of the Strange-Jointed Beasts

All living species of mammal fall into one of three major groups, representing the lowest branches of the mammalian family tree: the placental mammals, the marsupials, and the bizarre, egg-laying, monotremes. Well over 90% of identified living species fall into the first of those groups, which prompts the interesting question of how we divide those up - what, in short, are the next branches on the tree?

In the strict, old-style, system of classification, the next major level down is that of the "order", groups of broadly similar creatures that are in turn, divided into more than one hundred "families". Primates, for instance, are an order.

What the orders are, and how many of them there might be, has varied a little down the years, but nineteen or twenty would be a good, modern estimate. But, of course, the orders themselves are entirely arbitrary, and, even if they weren't, it isn't as if they all sprang simultaneously from the same stock. In evolutionary terms, there must have been some early branches in the placental family tree from which the "orders" that we know today descended.

The question of how to group the orders together into some higher level pattern is one that mammalogists have been been pondering for well over a hundred years. The problem is that the orders are pretty distinctive - is a moose more like a wolf than it is a monkey? When all you have to go in is physical anatomy, these are not the simplest questions to answer, and it's not surprising that people have come up with different answers.

Sunday, 30 August 2015

The Dog Family: Arctic and Grey Foxes

Arctic fox
The same generalist habits and adaptability that have allowed foxes to colonise the deserts have also allowed them to evolve to suit one of the other great barren ecosystems: the Arctic tundra. Here, where even wolves are not particularly common, we find what else but the Arctic fox (Alopex lagopus)?

Arctic foxes are truly creatures of cold and desolate habitats. In Europe, they are found only in Norway, Iceland, and the coasts of the White and Barent's seas in northern Russia. Indeed, it is one of only two species of land-dwelling mammal native to Iceland - the other is the wood mouse, although there are some human-introduced animals there as well. Elsewhere Arctic foxes are found right round the coasts of the Arctic Ocean, in northern Siberia, in northern and western Alaska, northern Canada and its islands, and even in Greenland. Despite this wide, multi-continental, distribution, most belong to just one subspecies, although those living in Iceland, Greenland, and Svalbard form one or two distinct subspecies between them, and there are also distinct subspecies on the isolated Pribilof and Commander Islands in the Bering Sea.

Sunday, 23 August 2015

Tuskless Walruses of Japan

There are a number of mammal "families" that contain just one living species. Of course, what constitutes a "family" of animals is an arbitrary distinction, rather like the one that says Pluto isn't a planet. So, really, all we're saying is that there are some mammal species that, in our subjective and pro-mammalian opinion, are do distinct and unusual that we feel they ought to be placed in a group all of their own. If they were insects, or snails, or something like that, we'd probably feel differently. But they're mammals, like us, so we don't.

One such family is the walrus family, containing - you've guessed it - the walrus (Odobenus rosmarus). Walruses are pinnipeds, which is to say, they are related to seals and sea lions. Just by looking at them, we can tell that walruses can walk on all fours like sea lions and fur seals, but unlike "true" seals, yet lack the external ears that sea lions and fur seals have and true seals don't. When you get to the interior structure of the skeleton, and so on, there are a number of technical differences that tell us that, no, this isn't just our imagination, they really are a bit different from all the others. And, there's, you know... the tusks.