Saturday, 23 February 2013

Pleistocene (Pt 7): Meanwhile, Across the Atlantic...

Columbian mammoth
(It's likely that the real animal was hairier than the one in
this reconstruction, but it shows the tusks effectively)
Over the last five parts of this series I have described the history of Pleistocene Europe, describing some of the ways that the animal life of the continent changed over those thousands of millennia, and looking at a few particular animals in more detail. But one doesn't need a degree in zoology to notice that today, the wildlife of North America, for example, is different to that of Europe. North America has coyotes, raccoons, cougars, armadillos, and pronghorn antelope, to name just a few animals that are simply absent in Europe. (Or, in the case of raccoons, were absent until somebody made the mistake of releasing some of the furry nuisances in 1930s Germany).

It's hardly surprising that that continent also had different wildlife during the Pleistocene. One notable difference, for instance, is that we humans weren't there. Obviously, neither Columbus nor Leif Ericsson were genuinely the first person to discover America. But even whichever long-lost group of Native Americans was actually the first to discover the great western continent, they did so long, long, after the first Europeans discovered Europe. While Europe had at least some species of human inhabiting it for about two-thirds of the Pleistocene, nobody reached America until the epoch was all but over.

Sunday, 17 February 2013

Tuco-tucos on the Edge

Flamarion's tuco-tuco (C. flamarioni)
There are a great number of endangered animal species in the world, and, as of the time of writing, 644 of them are mammals. These include, of course, such dramatic and visible animals as rhinos and pandas. But they also include many smaller, less glamorous animals. For example, over 200 species of rodent are endangered worldwide, and while that's not actually very many out of the total number of rodent species that exist, it's still quite high in absolute terms.

I realise, of course, that it's unrealistic to expect the public to get as concerned about obscure rodent species as they are about, say, endangered cats. Because, you know, snow leopards. But, in the semi-random style of this blog, inspired largely by whatever I happen to have seen in the literature recently, I want to talk about the social tuco-tuco (Ctenomys sociabilis).

For those who've not heard of them, tuco-tucos are a family of burrowing rodents native to South America. They look rather like voles, but are somewhat larger, at around 20 cm (8 inches) long, if you include the tail. They're good at digging, but they don't live underground in the same sense that moles or mole-rats do, since they leave their burrows during the day to feed on things like grass seeds. In fact, they've been described as the South American equivalent of gophers, although the two groups aren't really that closely related as rodents go. One of their distinctive features is their loose, wrinkly, skin, which apparently allows them to turn round easily in their narrow burrows.

Sunday, 10 February 2013

Do Monkeys Get Divorced?

Panamanian night monkeys (Aotus lemurinus)
Probably the most common reproductive strategy in mammals is that of polygyny. That is, any given reproductive group consists of a small number of reproductive males - often only one - and a much larger number of females. There are various different ways this can be arranged. For example, males may leave the pack or herd when they reach maturity, wandering about on their own, or in very small groups, until they find a new pack that they can take over, getting all the females for themselves. Alternatively, there may be no long-lasting partnerships, with males and females living in separate groups for most of the year, and then males staking out patches of ground to attract a number of females to them for the duration of the breeding season.

Both of these situations lead to an inevitable conflict between males. If each male mates with several females, but females stay loyal to a single male (even if only for the season), a lot of males won't get a look in. There are strategies for some smaller males to get round this problem, but, in general, fighting is your best bet. And that means that male mammals are often larger than females, and with larger teeth, horns, antlers, or whatever else it may be that they do their fighting with.

But there are alternatives to polygyny. If females mate with lots of males, then male competition needs to work in a different way, whether by getting in first, or by producing more, and higher quality, sperm than your rivals. And then, of course, there's monogamy.

Sunday, 3 February 2013

Caprines: Telling the Sheep from the Goats

Transcaspian urials
(Note that the rams of this species/subspecies have
particularly argali-like horns)
To most people, especially in the West, the most familiar member of the goat subfamily is probably... the sheep. Worldwide, domestic sheep are more common than goats, although not necessarily by as much as you might think. Goats are more popular than sheep as farm animals in places like India and Africa, but overall, sheep have the edge in numbers. That's probably no great surprise to those of you in most parts of Europe or America, and even less so if you're in Australia or New Zealand.

But perhaps I should back up there. Did I really just say that sheep are a kind of goat?

Well, yes I did. Kind of. Sheep are members of the goat subfamily, but really, they're goats only in the sense that ferrets are a kind of weasel. But why is it that way round at all?

The goat subfamily, or Caprinae, was given its name by the great Victorian zoologist John Edward Gray, quite early in his career, in 1821. From a scientific standpoint, there was absolutely no reason why he couldn't have named it the sheep subfamily, but instead, he chose goats as the best example of the group. I don't know his actual reasoning, but it certainly makes sense: far more members of the group resemble goats than resemble sheep. And so, from this, admittedly arbitrary, standpoint sheep are an odd kind of goat, and not the other way round.