Saturday, August 27, 2011
Tuesday, August 16, 2011
I am working on another big funding application. This one is a lot more work than the previous applications, as the required research statement, the largest of several sections, is 25 pages. I can't really complain. If I was going to give someone enough money to run a research group for five years, I too would want to know in some detail what they would do with the money. Further, sitting down and trying to put my plans into a single document makes me systematically consider how my various plans fit together, always a useful exercise. My only complaint really is that I should have done much more on this much earlier. Trying to finish everything up at the same time that my wife is preparing to deliver a baby and my family is visiting is an less than an optimal solution.
Thursday, August 04, 2011
One should be cautious in naming a taxonomic group for their ecological habits.
I offer you these examples:
1. Most turtles are amphibious; all are reptiles, not amphibians. Turtles have scales, lay hard leathery eggs, have the physiological and genetic makeup of reptiles. I often see phrases such as, "turtles and other Amphibians" in writing about biology by non-scientists. The taxonomic term 'amphibians' is not helpful in getting across to people that turtles are reptiles.
2. Consider the Carnivora. Most Carnivora are carnivores, but some, such as the giant panda, eat largely plants. Further, many carnivorous mammals are not Carnivora in the taxonomic sense. Unnecessarily confusing.
3. Pity the poor Insectivora. It turns out things are worse than just dietary nonconformity (not all the Insectivora ate insects, and not all insectivorous mammals were called Insectivora). The group called Insectivora no longer exists! Biologists had assumed that similarities in diet and morphology among the moles, shrews, tree shrews, golden moles, hedgehogs, moonrats, solenodons, tenrecs, elephant shrews and colugos were the result of common descent (they all had these traits because they were all closely related to each other). It is now clear that Insectivora was an ecological rather than taxonomic grouping. This is because modern molecular genetic and phylogenetic methods make clear that most of these Insectivores are not any more closely related to each other than they are to you, or to an elephant. Specifically, the moles, shrews, solodons, hedgehogs and moonrats form one group, whose closest relatives include the carnivores and hoofed mammals. The tree shrews and culogos (of southeast Asia) are more closely related to the primates. The golden moles, tenrecs and elephant shrews (all African groups) are related to larger mammals found in Africa such as the aardvarks and elephants.
4. The Caprimulgidae (Latin for goat suckers), do not suck goats. They were named for a feeding behavior falsely attributed to them. They are in fact insectivores.
Wednesday, August 03, 2011
This is all a roundabout way of getting to the question of who is a demographer. Ask a demographer what is the largest annual scientific meeting for demographers, and she will probably say The Population Association of America (PAA). I consider myself a demographer as well as a biologist, but I think most PAA members would say the stuff I do isn't demography. This is for the simple reason that I mostly study non-human populations, and the PAA defines demography as the study of human population processes. Studying the same processes in non-humans is, by this definition, not demography. Last year they had a session on evolutionary demography, but all the accepted papers were on humans. This year they don't even have such a session. I think that inserting the word 'human' into the definition of demography is roughly akin to saying that anyone who doesn't follow the teachings of a particular Rabii isn't really Jewish, so I call myself a demographer.
I was recently surprised to find myself in a conversation in which the tables were turned. A colleague was arguing that most PAA members are not really demographers, but sociologists. His argument was that many human-focused hard-core demographers feel out of place at the PAA. After their meetings this spring several colleagues complained that most talks at PAA meetings are really quantitative sociology rather than demography. The distinction is a fine one, but basically classical demography has a core set of questions and methods, and these have certainly been supplanted to a considerable degree by questions coming out of sociology, mostly approached with methods that don't require the quantitative machinery of formal demography. My colleague told me, "All the talks are full of regression tables, and most of the regressions aren't even done well."
So is it fair to say that my colleagues and I, who apply classical demographic methods to non-humans are more demographery than the quantitative sociologists at the PAA? I'm afraid not. We can no more revoke their demographer label than they can revoke ours. However, since the social demographers who control the PAA aren't interested in evolutionary demography, and most of their presentations frankly aren't that interesting to us (there really are a ridiculous number of regression tables, mostly demonstrating the relationship between fertility and female education for yet another population), I'm going to let my membership lapse. I'm thinking I'll join the British Ecological Society instead. They have lots of evolutionary demography at their meetings. I don't even feel the need to call myself an ecologist.
Monday, August 01, 2011
There are five independent lineages of extant (extant is the opposite of extinct) marine mammals:
1. The Cetaceans (whales, porpoises and dolphins), relatives of pigs and hippos.
2. The Sirenians (manatees and dugongs), mildly related to elephants and hyraxes.
3/4. The Pinnepeds (walrus, seals and sea lions), descended from a dog-like carnivore.
3/4. The sea otter, an otter, which is an aquatic weasel.
5. The polar bear, bear.
I have ordered these in the degree to which they have become fully aquatic. The Cetaceans neither need to, nor safely can, leave the water. This is true of Sirenians also, but they tend to feed and birth in shallow water near shorelines, where whales wander the open oceans and dive to amazing depths. The Pinnepeds aren't so good on land, but they do haul up to breed and pup. The sea otter is in some ways more fully marine than the Pinnepeds, mating and usually giving birth at sea. But again, otters are more tied to the land than are Pinnepeds the rest of the year, living and feeding in coastal kelp forests and being capable of fast and efficient movement on land. The polar bear is marine in that it swims long distances, hunts at sea, and has structures that specifically help it do these things. But it still prefers to walk rather than swim, brings its food onto solid ground to feed, breeds and pups out of the water and so forth.
There are more independent groups of sea birds, even if you don't consider each transition from freshwater to saltwater. Penguins are perhaps the most fully marine, flying only in water, feeding entirely on seafood, having special mechanisms for dealing with high levels of salt. The Procellariiformes (albatrosses and petrels) are not far behind, spending about as much time at sea (although over rather than in) as penguins do. The Phaethontiformes (tropicbirds) spend most of their lives at sea, as do many of the Pelicaniformes (pelicans, frigatebirds, boobies, gannets, cormorants and shags). While many gulls live far from the sea, many Charadriiformes (gulls, terns, skuas, plovers, puffins, auks etc.) are extremely marine. Many Anseriformes (ducks, swans and geese), particularly the Merginae (sea ducks) are, well, sea ducks. It was recently discovered that gyrfalcons spend long periods hunting on and around sea-ice, although they probably don't actually swim. I'm sure I've forgotten other examples.
Why so many birds moving out to sea, but so few mammals?
The obvious first hypothesis is that the ability to fly is very useful at sea, while the ability to walk/run/hop etc. is not. The falcons are a pretty terrestrial group, but with few changes beyond the behavioral, gyrfalcons can spend extended periods at sea. Ospreys and eagles, relatives of falcons, use talons that evolved grabbing terrestrial prey to scoop fish. Even hummingbirds and warblers that can't forage or land at sea regularly spend long periods migrating over open ocean. Birds may have an easier entree than do mammals.
Given this, it may be surprising that the most fully marine descendent of terrestrial vertebrates are not birds. All birds lay eggs, and none have figured out how to make that work at sea, so all need to maintain the ability to be land animals. Almost all mammals give live birth, and three groups (Cetaceans, Sirineans and sea otters) can do that without ever leaving the water. The birds may have an easier time getting started down evolutionary paths that lead to a marine life, but they seem to have an inescapable constraint that keeps them from finishing that path: shelled eggs.
The marine reptiles show an interesting parallel to this. Marine iguanas, saltwater crocs and sea turtles all lay eggs, and all do so on land. Sea snakes, excepting one genus, birth live young, and do so at sea. That one genus lays eggs on land.
If some snakes have evolved the ability to have their eggs hatch internally and their hatchlings ready to swim the moment they emerge from the mother, why can't some bird do the same? Imagine how much better off an emperor penguin would be if instead of spending the Antarctic winter fasting in the cold, it could spend that time feasting in the ocean with it's chick developing internally.
Any answer I could offer would be pure speculation. One class of question that evolutionary biology is very bad at answering is "why didn't X evolve." Why hasn't any bird evolved live birth? Maybe it is something about their egg shells. Maybe they are in a habitat where that just doesn't work. Probably it just never happened.