Sunday, 19 May 2019

Small British Mammals: Common and Field Voles

Field vole
In many respects, voles are extremely similar to mice. In many languages, the local word for 'mouse' also describes voles, and this was even the case in English prior to around the 19th century, when the term "vole-mouse" was borrowed from a now-extinct Scandinavian tongue, and shortly thereafter abbreviated to simply "vole". In its original language, it literally meant "field", and a similar etymology can be seen in languages such as German (Feldmaus) and French (campagnol) among many others.

Scientifically, voles have also been mixed in with the mice at different times. While they have recognised as a distinct group with their own scientific name since 1821, for much of the 20th century they were considered a subgroup within the wider mouse family. That's really only changed in the last 20 years or so, as genetic and biochemical evidence has shown that the two groups, while related, have distinct evolutionary histories.

Sunday, 12 May 2019

The Big African Not-a-Lion

Spot the real lion
When it comes to fossil animals, there can be little doubt that the ones most popular with the general public are the large ones. There's a reason that dinosaurs seem to hold the most enduring fascination, and that even popular science books about the whole range of prehistoric life are almost bound to have them as part of their title. (And, while some dinosaurs were small, most of the ones we know about weren't, perhaps partly because it's easier to preserve large solid bones than small fragile ones).

It's not really any different with prehistoric mammals, with mammoths, mastodons, and sabretooth cats being the ones that most people would instantly recognise and be familiar with. Even dire wolves, which weren't really all that big, are surely better known than, say, extinct foxes or weasels of the same age. Which brings up a second point: even if an animal isn't as large as an elephant or Diplodocus, being unusually large for a carnivore will still help its public profile enormously.

Sunday, 5 May 2019

Lots of Little Deer Mice

If a sexually reproducing animal is to preserve its species without population loss, each pair of parents has to produce, on average, two offspring that will themselves live long enough to reproduce. This is just basic arithmetic, but there are at least three different ways that an animal can achieve this result and which one is used varies from species to species.

One approach is to maximise the chances of each of your offspring surviving. This is called the K-selection strategy, and results in the population being as close to the maximum capacity of the local habitat as possible. (The 'K' stands for 'capacity'... in German). Such animals don't need to reproduce very often, or produce very many offspring when they do, but they have to invest a lot of resources in their survival. They tend to be relatively large animals, with few predators... elephants, primates, and whales are all good examples among mammals. Humans are a particularly extreme example, given how long it takes us to raise our children, and, as with other strong K-selectors, twins are rare in our species.

Sunday, 28 April 2019

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.

Sunday, 21 April 2019

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 with 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.

Sunday, 14 April 2019

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.

Sunday, 7 April 2019

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.