Saturday, 17 March 2018

Miocene (Pt 6): The Coming of the Mice

The Early and Mid parts of the Miocene epoch were, for the most part, times when the world was much warmer than it is today. It wasn't a steady pattern, however, and I've already described how the fluctuations in climate, over the course of many millions of years, affected the rodents of Europe. It was a time when the most common small mammals in Europe were not mice and voles, but dormice, accompanied by early hamsters, squirrels, and the gliding eomyids.

By 10 million years ago, however, the colder, drier climate had become locked in for the long term. We know that the forests of Europe changed dramatically at this time, the old subtropical trees, such as figs and palms, being replaced by oak, alder, and elm. Likely as a result of this change in the available food supply, most of the dormice died out, leaving only a few close relatives of the relatively small number of species we have today.

Sunday, 11 March 2018

The Crusty Forearms of Male Bats

Bats, of course, are not blind. There eyesight is, in fact, pretty good in the majority of species. Which makes sense for an animal that has to fly around at night when the light is dim but not entirely absent. It's only for animals like moles, which live underground, where the light can't penetrate at all, that vision becomes an expensive and unnecessary luxury.

Having said that, many species of bat do spend a lot of time in caves, and, in there it really is too dark to see anything, no matter how good your night vision might be. As a result, the other senses of bats are often highly tuned. Hearing is the obvious one, since bats rely on that for their sonar abilities, but many species also have well-developed senses of smell. In particular, since bats also tend to be highly social, scent often forms a crucial part of their ability to communicate with one another - as it does for many other mammal species.

Sunday, 4 March 2018

Silence of the Pacas

Whether or not a given species of animal lives in groups is something of a trade-off. Several different factors are involved, but just one example is that you will simultaneously be more visible to predators and be protected from them by "safety in numbers". For many animals, the benefits outweigh the downsides, although a lot depends on the individual environments and lifestyles of those creatures.

But living in groups also brings its own requirements, perhaps most notably the need to communicate with other members of your herd or pack. Safety in numbers, after all, is of limited utility if one member of the group can't warn others of something dangerous it's just seen. And this isn't simply a yes/no situation; the more complex the group structure, it is argued, the more sophisticated the communication needs to be.

Sunday, 25 February 2018

The Pig Family: Wild Boar and the Domestication of Pigs

European wild boar
Generally speaking, the wild ancestors of agricultural animals have not fared particularly well. Wild goats are a threatened species, wild horses are an endangered one, camels are doing even worse, and wild cattle have been extinct for centuries. Wild sheep haven't done quite so badly, although they're hardly widespread, but, in general, one of the main problems facing such animals is that the sort of places they like to live are exactly the ones we want to turn into agricultural land to raise their domesticated kin.

Indeed, only two wild ancestors of widely domesticated herbivore are doing well: chickens and pigs. (This may, of course, depend on your definition of "widely"; I'm ignoring, say, rabbits). Indeed, the wild ancestor of the domestic pig is not only reasonably common, it's the single most widespread of any species of wild pig.

Sunday, 18 February 2018

Early Whales of the North Pacific

The majority of living cetacean species belong to a group called the odontocetes, or "toothed whales". Most of them aren't really what we think of as "whales" at all, since the group includes all of the dolphins and porpoises. The group does, however, include a number of much larger species - some of them just really big dolphins, such as the killer whales, but others being less closely related, such as sperm whales, beaked whales, and narwhals.

The odontocetes as a whole stretch back far into the fossil record, with the oldest known examples dating back to around the dawn of the Oligocene epoch 34 million years ago. They rapidly spread across the globe, unhindered by the geographical barriers that often affect more land-based mammals. (The continents were all separate at the time, which would have helped, since it was possible to swim right around the globe without leaving the mid-latitudes).

Sunday, 11 February 2018

Jackals on the Motorway

Mammals tend to have a particular area in which they live most of their lives and conduct their various activities. This is known as the animal's "home range", and it's not quite the same thing as a "territory". That's because the latter is an actively defended bit of land, that the animal strives to keep clear of rivals, perhaps marking it with scent as a warning, and using aggression against intruders if they have to. The majority of mammal species don't bother to defend territories, but that doesn't mean that they don't have a home range - after all, they have to live somewhere.

One key difference between a territory and a home range is that the former, by definition, is not shared with any neighbours. Of course, the animal might be social, living in herds, packs or other kinds of band, so that all members of the group share a single territory, but, again, it's not shared with outsiders. A home range, on the other hand, almost always overlaps with at least some others used by members of the same species, especially if they happen to be of the opposite sex. Breeding would be problematic if they didn't.

Sunday, 4 February 2018

How Mothers Stop Their Daughters from Sleeping Around

Northern mole-vole (E. talpinus)
Generally speaking, mammals are equally likely to be born as either males or females. The exact proportion may vary a little, and it doesn't follow that both sexes form 50% of the adult population, because one or the other may be more likely to die young. It's even less the case that all males, or all females, are equally likely to pair up and have offspring of their own.

This disparity is known as reproductive skew, and it varies considerably between species, and sometimes even between populations of the same species. At one extreme, it's essentially zero. This happens if the species is basically monogamous, usually because child rearing is a sufficiently draining exercise that being able to share the duties between two individuals is really helpful. It can also happen for what might be regarded as the exact opposite reason - if the species is highly promiscuous so that the females will mate with absolutely anyone, once again, everyone's chances of reproducing are the same. There's just less of that courtship stuff to worry about, off-set by having a single-parent family once you're done.