Saturday, 25 November 2017

Miocene (Pt 4): Bear-Dogs and Dog-Bears

Many of the animals we would see in Early Miocene Europe, were we able to visit, would be of broadly recognisable types: deer, pigs, antelopes, rhinos, and elephant-like mastodons. True, many of these are nor animals we would expect to find in Europe today, and the individual species were, of course, different from the modern sort, and in some cases quite dramatically so. But they at least have identifiable relatives today.

But all of the animals I've just mentioned are herbivores. Yet, when it comes to the larger predators of the day, we instead find that most of them were rather different, lacking close modern relatives. While more recognisable carnivores did, in fact, turn up as the Miocene progressed, at least in the beginning, the majority were survivors from an even earlier time, before many modern kinds of animal had arisen.

Sunday, 19 November 2017

The Barcoded Droppings of French Water Moles

How do you know what a given species of animal eats in the wild? The question is of more than merely academic interest. In addition to its obvious relevance to zookeepers, it can also help us to understand how a particular ecology works and what sort of harm we might do it by changing something. In the case of endangered species, it can also be important for conservation, since it's no good protecting the animal if you don't also protect its food supply.

The simplest way to answer the question is probably just to follow the animal around at a suitable distance and watch what it does. In the case of large, visible animals such as lions or moose, this is likely an effective, if somewhat time consuming, method. But it works rather less well with something small or difficult to observe, especially since small mammals spend most of their time eating. (They have to, to maintain their body temperature, since small objects lose heat more rapidly, and they need, proportionally speaking, a lot of calories).

Sunday, 12 November 2017

Sex in the Slow Lane

There are many different mating systems in use across the animal kingdom, but the one that is most common among mammals is polygyny. In this system, one male mates with multiple females, typically because he won't let other males anywhere near them. From an evolutionary perspective this makes sense, since a male can sire offspring with multiple partners simultaneously, while females are limited by the size of their litters, and the effort required to look after the resulting young (which is more of a consideration for mammals than it is, for example, for most fish).

In fact, it has been estimated that something like 90% of all mammal species practice polygyny to at least some degree. There are, of course, other options. For example, where it takes a particularly large amount of effort to look after young, it may really help if the male assists in doing that, something that naturally tends to favour monogamy. This is the case among humans, where childcare is both lengthy and arduous, so that two parents are better than one, where this can be managed. However, it has been observed that not all male humans are 100% loyal to their spouses (I hope this isn't too big a shock) so that monogamy isn't the absolute rule that it might be.

The same thing happens with other mammal species. The species as a whole might be polygynous (or whatever), but that doesn't mean that every single individual always follows the usual pattern.

Sunday, 5 November 2017

Pinnipeds: The Evolution of Seals

There are seventeen species of "true" seal alive today. Most of them are reasonably widespread and numerous animals, and, despite the effects of seal hunters, are not under any particular threat. Populations of hooded seals are in a steady decline, but, although they are still hunted in places, a 1985 ban on the use of seal fur across most of Europe has hugely reduced the demand for the animals; the main reason for the current population decline seems to be the loss of their icy breeding habitats. The two species of living monk seal, and the Caspian seal, have not been so lucky, and are all considered endangered species. And an eighteenth species, the Caribbean monk seal, went extinct in the 1950s.

Early attempts to deduce how these various species relate to one another identified a number of different sub-groups among the seals, based largely on anatomical resemblances. On this basis, it was thought for a while that the Arctic and Antarctic seals were each others' closest relatives, with the more temperate species representing older, and perhaps more ancestral, forms. But this picture began to change in the 1990s, and its replacement has subsequently been confirmed by a number of different genetic analyses. While the exact details have still not been fully settled, we do now know the broad pattern of what happened, and I've provided one consensus family tree below. Using estimated rates of evolutionary change, calibrated with the age of known fossils, we can also get a rough idea of when some of the key events in this history unfolded.