With a Little Help from My Friends

There are a number of disadvantages to living in groups. Some of the more obvious are that the group will be, collectively, easier for predators to spot, and that they will all have to compete for the same resources. Other problems, which might be less obvious, include the fact that infections and parasites are more likely to spread amongst a group of similar animals that remain in close contact. All of these are good reasons for solitary living, as seen in a great many mammal species.

Despite which, of course, there are many mammals that do live communally. For these animals, whatever costs there may be are obviously outweighed by the benefits, of which there are several. While a large group of animals may be easier to see, it's also easier for them to keep a lookout, since not everyone needs to be actively scanning the horizon (or whatever) all of the time. They can also share in communal tasks, such as child-rearing, putting less strain on the individuals. Predators that hunt in packs can take down prey far too large for any one of them to kill on their own. Even huddling together against the cold can be a worthwhile benefit.

Small British Mammals: Rats!

Brown rat

The term "rat", as commonly used, has no defined biological meaning. A "rat" is simply any rodent that looks at least somewhat like a mouse, but is larger. Animals fitting this description have evolved multiple times, so that rats do not form a single evolutionary group, and not all of them are even members of the mouse family.

Nonetheless, there is a biological group that we can call, for lack of a better term, the "true rats" (technically the "Rattini") which includes the animals that most people likely think of when the term "rat" is used without further qualification. There are two species of this kind of animal in Britain, not least because both of them are found just about everywhere else as well.

Miocene (Pt 13): The Time of No Cats

Aelurodon

Today, there are a number of native cat species in America. The North has its bobcats, lynxes, and puma/cougar/mountain lions while, further south, there are even more species (ocelots and jaguars being merely the most obvious). At the dawn of the Miocene, 23 million years ago, however, it was a somewhat different story.

While there was nothing similar in the south, there had been plenty of cat-like animals on the northern continent before. True, they had not literally been cats, but rather nimravids, a group of remarkably cat-like animals that lived long before actual cats existed. The climatic changes of the Early Miocene seem not have suited them, however, and almost died out as the new epoch dawned. It's possible that one, Dinictis, a bobcat-sized sabretooth, did manage to struggle on for a few million years, but even that is debatable. But, otherwise, while their relatives, the barbourofelids, continued on in Europe, to eventually be replaced by actual cats, in North America... there was nothing.

The Spikiness of Tenrecs

Being a small mammal (or, indeed, any other kind of animal) can be tough; there's always something out there that wants to try and eat you. There are a whole host of adaptations that animals use to try and avoid this fate. Running fast and being good at hiding or camouflage are, perhaps, the most obvious and widespread defensive methods. Another approach is to live somewhere that it's really difficult for most predators to find you, such as spending your entire life in an underground burrow.

Fighting back, as larger horned animals might do, generally isn't so effective, although skunks (for example) have certainly found a way of doing that. But there is also the option of body armour. It's something we see quite a lot in reptiles and, in living mammals, it's perhaps best developed in armadillos. But body armour doesn't have to be a bony or keratinous shell, for something that wants to avoid being eaten, spines can also be an effective deterrent.