Sunday 26 February 2012

Why Forest Fires Are Good For You (if you're a big brown bat)

Big brown bats

Forest fires are both destructive and spectacular. Not quite up there with volcanoes or tsunamis, perhaps, but nonetheless pretty dramatic, wreaking havoc on the local environment. Human-caused fires, when they get out of control, can be very damaging to the ecosystem, which may take years to recover. Yet forest fires have been around since long before humans, and, for at least some forests, they are just a natural part of the cycle of life. Indeed, there are some plants whose seeds germinate specifically after a local wildfire. But how does this affect animal communities?

One such environment is that of sandhill forests. Sandhills are so named because of their sandy, well-drained soils, often dominated by ash, but (unlike the much more barren sand dunes) they support significant plant communities. In the southeast USA, between Virginia and eastern Texas, the dominant tree in these forests is the longleaf pine. Frequent fires are essential for this species to do well, and, left without fire for too long, the nature of the forests change dramatically, in this case being replaced by denser oak woodland.

Sunday 19 February 2012

Weasels up Trees: Pine and Beech Martens

Pine marten
In my survey of the weasel family, I have so far looked at the mustelines; those members of the family that are most closely related to the weasels themselves. Aside from the numerous kinds of "true" weasel, this has included stoats, polecats, and mink, but, of course, the mustelines are not the only members of the weasel family. It is now time to turn to a second grouping within the family, the marten-like animals.

The oldest fossil martens date from the Pliocene; the epoch immediately before the great Pleistocene Ice Ages. By this time, they had already begun to develop some of their distinctive features. Martens are much larger than true weasels, and within, or slightly above, the size range of the largest mustelines, the European polecats. Where mustelines have evolved narrow bodies for chasing prey down into their burrows, the martens have never needed to do so, and while they have the short legs typical of most members of the family, their bodies are noticeably more compact. They are generally brown in colour, and most species have a highly visible 'bib' of paler - usually yellowish - fur on their chest.

The most distinctive feature of the martens is that they spend much of their lives in the trees, quite a different habitat from other members of the family. By heading up into the trees, they have been able to find a source of food quite away from their ground-dwelling kin, and over much of their range (although by no means all), they are the only small carnivores that hunt among the branches.

Sunday 12 February 2012

The Lonely Koala

The koala (Phascolarctos cinereus) is, by many standards, a fairly odd animal. Like most medium to large Australian marsupials, it is herbivorous, but it goes further than that by eating nothing but eucalypt leaves, which are not only low in nutrients, but actually poisonous. Presumably, they do this simply because nothing else does, which means that food should always be available, and they deals with the low nutrient content by spending around two thirds of their life snoozing, and with the poison with unusually efficient detoxifying liver enzymes. Like horses, they are hind-gut fermenters, which also helps them to extract what nutrition they can from food that, frankly, isn't very good.

Koalas have no close living relatives. There is only one living species (with no subspecies), and its considered different enough from everything else to be given its own family - one of a number of mammalian "families" that contain just one species. It's now agreed that the closest relatives koalas do have are the wombats, and even a brief glance at the respective animals tells you that they can't be that close.

So the only opportunity we have for really unravelling the history of koalas comes from examining fossils. For, while koalas are the only member of their family alive today, there were, of course, others in the past. But, still, not terribly many. Some other single-species families, such as that of the pronghorn antelope, represent the last surviving member of a group that was one much larger. Once, there were lots of species of North American antelope, many of them pretty weird to modern eyes, but now only the pronghorn remain, a solitary reminder of a once more diverse group.

Sunday 5 February 2012

What Fur Seals do at Sea

I seem to have done quite a few posts on cetaceans over the last few months, and have discussed, among other things, the difficulty of finding out what they're up to, compared with land animals. But, of course, whales and dolphins are not the only fully marine mammals. There are, in fact, four groups of such mammals, with the second largest, after the cetaceans, being the pinnipeds - seals and their relatives.

Seals differ from whales and dolphins in that, while they spend almost their entire lives at sea, they still have to come onshore to breed and give birth. Mammals have an advantage over birds, and most reptiles, in that they don't lay eggs, which would drown if you tried to lay them underwater, but it's still quite difficult for newborn, air-breathing, young to immediately take to swimming. Whales and dolphins have mastered this evolutionary trick (as have sea snakes, for that matter), but seals have yet to do so. Give them a few more million years, perhaps.