Pinnipeds: Grey and Harp Seals

Grey seal

There are four different species of seal that live off the coasts of northern continental Europe. Perhaps the best known is the harbour seal, or "common seal", which is also the most widespread of all seal species, being found across both the North Atlantic and the North Pacific. When the scientific naming of species was introduced in 1758, it was the only such species recognised from the area, but it only took a few decades for proper scientific descriptions of the others to follow, recognising that they were distinct from their "common" cousin.

The last of the four to be split off was the animal we now know as the grey seal (Halichoerus grypus), in 1791. While that's still fairly early as such things go, the fact that it was the last of the local seals to be formally identified as something different from the regular sort is likely down to the fact that it does look very similar to the harbour seal. Although, in fairness, it was first named by an entomologist, so clearly you don't have to be a mammal specialist to tell them apart.

The Giant Chinese Badger-Otter

Otters and badgers are both members of the weasel family, the Mustelidae. As a result, while they are visibly quite different, they have a number of anatomical similarities, reflecting their shared ancestry. Indeed, some of the similarities, such as those in the precise shape of their teeth, are rather greater than one might expect simply from them belonging to the same family. On the basis of this, it was being suggested as recently as the 1990s that otters were essentially aquatic badgers - descendants of early badger species that had entered the water, developing webbed feet, a long muscular tail, and so on, in the process.

We now know, from various genetic and molecular studies, that this isn't so. The closest living relatives of otters are probably the weasels themselves and/or the zorillas and their kin, with badgers representing a rather earlier branch in the mustelid family tree. Given this, the apparent strong similarities between the two are either a case of parallel evolution, perhaps due to the fact that, by the standards of weasels, they're both fairly large animals, or, perhaps more likely, that they are ancient features of the group that happen to have been lost in their other relatives.

A Side Order of Flies

Most species of bat eat insects, whether caught on the wing or plucked from leaves or other surfaces. But this is by no means true of all species, with the second most common diet - perhaps representing around a quarter of known species - being one based on fruit. Indeed, fruit-eating had evolved more than once among bats, with the giant fruit bats of the Old World not being especially close relatives of the much smaller ones found in the Americas.

While a great many herbivorous and omnivorous mammals include fruit as part of their diet, one estimate is that only around 10% of mammalian species rely on it as their primary source of food - most of them bats or primates. While that's not exactly a tiny proportion, given the number of mammalian herbivores in general, it isn't a huge one either. This, it has been suggested, is because, while fruit are great as a source of calories, they tend not to be high in protein, and a healthy animal needs a supply of both.

In the case of humans, eating plenty of fruit is well known to be a good thing, but trying to eat nothing but fruit for any extended period of time is likely to be a problem. Not only are you likely to suffer from lack of protein in your diet, but you will also suffer deficiencies in certain minerals and vitamins. That one of the main vitamins you would be short of is vitamin D, which promotes calcium absorption in the gut, is a particular problem, bearing in mind that there isn't much calcium in fruit to start with. For this reason, fruit-only diets can be a real problem for children, who need that calcium to grow their bones.

By the Light of the Silvery Moon

Why bother being nocturnal? Being active only at night makes it much harder to see what you're doing, and while it's possible to develop good night vision to minimise the problem, this is evolutionary costly. Well, if you're a herbivore, the advantage of being active at night is that it's much easier to hide from predators, since, they, too, would have to evolve good night vision to find you. And, if you're a predator, the advantage is that at least some of your competitors won't be around at night, allowing you to snack on nocturnal herbivores and not have to share your food supply.

But this, of course, cuts both ways. For example, while darkness hides you from predators, it also makes it more difficult to spot predators coming if they have seen you. As so often, this leads to a balance, and different species taking advantage of different points on the continuum of possible behaviours.

We can see some of the effects of this in how animals respond to different levels of darkness. Not all nights are equal, after all. The most predictable change is in the amount of moonlight, with the night of a full moon being considerably brighter than a night without a visible moon. Somewhat less predictably, of course, there's the weather, unless, perhaps, you live in a desert where overcast skies are fairly unlikely. So, if you're a nocturnal herbivore, should you be more active on the night of a full moon, or less?