Isegoria

Carl Zimmer examines the complex and pathogen-laden world of ticks:

Foxes were originally very abundant in the eastern United States, where they feasted on small mammals like white-footed mice. But the past few decades have not been good to them. “Fox harvests in the Northeast have declined substantially,” says Levi.

A number of studies suggest that coyotes have been responsible for the decline. Originally, foxes coexisted with wolves in the eastern and midwestern United States. Once wolves were eradicated, coyotes expanded from the Midwest to take their place. Coyotes kill foxes or scare them out of range.

Levi and his colleagues built a mathematical model of how these changes can affect rates of Lyme disease. When foxes disappear, the model suggests, numbers of small mammals like white-footed mice boom, feeding a growing population of ticks and their pathogens. For evidence, Levi points to historical records from sites across the Midwest and eastern United States. In some places, Lyme disease rates have gone up even though the deer population has not. But the rates in those places match up nicely with a decline in fox numbers.

Groups — swarms, flocks, herds, mobs — produce complex behaviors from simple rules:

Golden Shiners

Behavior: Seek darkness

Presumably for protection, shiners search out dark waters. But they can’t actually perceive changes in light levels that might guide their way. Instead, they follow one simple directive: When light disappears, slow down. As a result, the fish in a school pile up in dark pools and stay put.

Ants

Behavior: Work in rhythm

When ants of a certain species get crowded enough to bump into each other, coordinated waves of activity pulse through every 20 minutes.

Humans

Behavior: Be a follower

Absent normal communication, humans can be as impressionable as a flock of sheep. If one member of a walking group is instructed to move toward a target, though other members may not know the target—or even that there is a target—the whole group will eventually be shepherded in its direction.

Locusts

Behavior: Cannibalism

When enough locusts squeeze together, bites from behind send individuals fleeing to safety. Eventually they organize into conga-line-like clusters to avoid being eaten. They also emit pheromones to attract even more locusts, resulting in a swarm.

Starlings

Behavior: Do what the neighbors do

These birds coordinate their speed and direction with just a half dozen of their closest murmuration-mates, regardless of how packed the flock gets. Those interactions are enough to steer the entire group in the same direction.

Honeybees

Behavior: Head-butting

When honeybees return from searching for a new nest, they waggle in a dance that identifies the location. But if multiple sites exist, a bee can advocate for its choice by ramming its head into other waggling bees. A bee that gets butted enough times stops dancing, ultimately leaving the hive with one option.

Thanks to a highway-widening project in California’s Laguna Canyon, scientists have identified several new species of early toothed baleen whales:

“In California, you need a paleontologist and an archaeologist on-site” during such projects, Rivin says. That was fortuitous: The Laguna Canyon outcrop, excavated between 2000 and 2005, turned out to be a treasure trove containing hundreds of marine mammals that lived 17 million to 19 million years ago. It included 30 cetacean skulls as well as an abundance of other ocean dwellers such as sharks, says Rivin, who studies the fossil record of toothed baleen whales. Among those finds, she says, were four newly identified species of toothed baleen whale—a type of whale that scientists thought had gone extinct 5 million years earlier.

The earliest baleen whales still had teeth.

Neanderthal hunters were redlining near the maximum sustainable risk per calorie, Gregory Cochran suggests:

If the average member of the species incurs too much risk, more than that sustainable maximum, the species goes extinct. The Neanderthals must have come closer to that red line than anatomically modern humans in Africa, judging from their beat-up skeletons, which resemble those of rodeo riders. They were almost entirely carnivorous, judging from isotopic studies, and that helps us understand all those fractures: they apparently had limited access to edible plants, which entail far lower risks. Tubers and berries seldom break your ribs.

In Africa, most calories probably came from plant foods back in the Middle Stone Age, as they do in African hunter-gatherers today, and that fits too: early African hunters seem to have mainly gone after relatively safe prey like eland, avoiding really dangerous animals like cape buffalo. This is not to say that they did not hunt, or that hunting was unimportant, but they had alternatives.

Risk per calorie was particularly high among the Neanderthals because they seem to have had no way of storing meat – they had no drying racks or storage pits in frozen ground like those used by their successors. Think of it this way: storage allow more complete usage of a large carcass such as a bison, that might weigh over a thousand pounds – it wouldn’t be easy to eat all of that before it went bad. Higher utilization – using all of the buffalo – drops the risk per calorie.

You might think that they could have chased rabbits or whatever, but that is relatively unrewarding. It works a lot better if you can use nets or snares, but no evidence of such devices has been found among the Neanderthals.

It looks as if the Neanderthals had health insurance: surely someone else fed them while they were recovering from being hurt. You see the same pattern, to a degree, in lions, and it probably existed in sabertooths as well, since they often exhibit significant healed injuries.

By the way, why were mammoths rapidly wiped out in the Americas while elephants survived in Africa and south Asia?

First, North American mammoths had no evolved behavioral defenses against man, while Old World elephants had had time to acquire such adaptations. That may have made hunting old world elephants far more dangerous, and therefore less attractive.

Second, there are areas in Africa that are almost uninhabitable, due to the tsetse fly. They may have acted as natural game preserves, and there are no equivalents in the Americas.

Third, the Babel effect: in the early days, paleoIndians likely had not yet split into different ethnic groups with different languages: with less fighting among the early Indians, animals would not have had relatively border regions acting as refugia. Also, with fewer human-caused casualties, paleoindians could have taken more risks in hunting.

Dave Chamberlain adds a story about elephant-hunting:

I read a story of a herd of african elephants that were such a nuisance to the local farmers that hunters were employed to kill them. The elephants quickly changed their habits before all of them could be shot. They hid in the dense jungle during the day and came out to feed at night. The hunters became the hunted, several of them going into the jungle where the elephants were hiding were trampled. The hunters quit and the diminished elephant herd still exists, and — wouldn’t you know it? — they haven’t forgotten; they still have a reputation as some of the meanest and most dangerous elephants in Africa. African animals had a million years to adapt to the slowly increasing hunting skills of man.

When competent human hunters encountered naive fauna, the biggest animals,  things like mammoths and toxodons and diprotodons, all went extinct — which leads Gregory Cochran to make some larger points:

It is not hard to see why this occurred. Large animals are more worth hunting than rabbits, and easier to catch, while having a far lower reproductive rate. Moreover, humans are not naturally narrow specialists on any one species, so are not limited by the abundance of that species in the way that the lynx population depends on the hare population. Being omnivores, they could manage even when the megafauna as a whole were becoming rare.

There were subtle factors at work as well: the first human colonists in a new land probably didn’t develop ethnic/language splits for some time, which meant that the no-mans-land zones between tribes that can act as natural game preserves didn’t exist in that crucial early period. Such game preserves might have allowed the megafauna to evolve better defenses against humans – but they never got the chance.

It happened in the Americas, in Australia, in New Zealand, in Madagascar, and in sundry islands. There is no reason to think that climate had much to do with it, except in the sense that climatic change may sometimes have helped open up a path to those virgin lands in which the hand of man had never set foot, via melting glaciers or low sea level.

I don’t know the numbers, but certainly a large fraction of archeologists and paleontologists, perhaps a majority, don’t believe that human hunters were responsible, or believe that hunting was only one of several factors. Donald Grayson and David Meltzer, for example. Why do they think this? In part I think it is an aversion to simple explanations, a reversal of Ockham’s razor, which is common in these fields. Of course then I have to explain why they would do such a silly thing, and I can’t. Probably some with these opinions are specialists in a particular geographic area, and do not appreciate the power of looking at multiple extinction events: it’s pretty hard to argue that the climate just happened to change whenever people showed when it happens five or six times.

It might be that belief in specialization is even more of a problem than specialization itself. Lots of time you have to gather insights and information from several fields to make progress on a puzzle. It seems to me that many researchers aren’t willing to learn much outside their field, even when it’s the only route to the answer. But then, maybe they can’t. I remember an anthropologist who could believe in humans rapidly filling up New Zealand, which is about the size of Colorado, but just couldn’t see how they could have managed to fill up a whole continent in a couple of thousand years. Evidently she didn’t understand geometric growth. She is not alone.

Should you ever be desperate and in need of game, Jehu adds, take a copy of the hunting regulations for your state:

Look up all the hunting methods and tactics that are banned. Those are the ones that your lower-tech ancestors would have used. They’re banned precisely because of their effectiveness and efficiency.

Dave Chamberlin continues in that vein:

Fish are damned tasty and also damned stupid; they have never learned that swimming up to a bright light during night time frequently gets them caught on the end of a spear. Fisherman are pissed off that American Indians are still allowed to go fishing this way because it is so easy and so effective.

Sharpening a stick with a knife (or a piece of flint if you want to be historically accurate) it is really easy to incomplete a cut that leaves a perfect barb near the point that would keep a fish from sliding off the spear.

Fire made food far more digestable, but it also kept us warm, protected us at night, and made fish so easy to catch it’s now considered cheating. No wonder Homo erectus spread out far beyond Africa.

Jared Diamond, in discussing animal domestication, claims that the local availability of species with the right qualities for domestication was key, Gregory Cochran notes, rather than anything special about the biology or culture of the humans living there:

In some cases that may be true: there aren’t many large mammals left in Australia, and they’re all marsupials anyway. Stupid marsupials. He claims that since Africans and Amerindians were happy to adopt Eurasian domesticated animals when they became available, it must be that that suitable local animals just didn’t exist. But that’s a non sequitur: making use of an already-domesticated species is not at all the same thing as the original act of domestication. That’s like equating using a cell phone with inventing one. He also says that people have had only mixed success in recent domestication attempts — but the big problem there is that a newly domesticated species doesn’t just have to be good, it has to be better than already-existing domestic animals.

Indian elephants, although not truly domesticated, are routinely tamed and used for work in Southern Asia. The locals in Sub-Saharan Africa seem never to have done this with African elephants — but it is possible. The Belgians, in the Congo, hired Indian mahouts to tame African elephants, with success. It’s still done in the Congo, on a very limited scale, and elephants have recently been tamed in other parts of sub-Saharan Africa, such as the Okavango delta. Elephants have long generations, which makes true domestication difficult, but people have made domestication attempts with eland, African buffalo, and oryx. They’re all tameable, and eland have actually been domesticated to some extent. If a species is tameable, economically useful upon taming, and has a reasonable reproductive schedule, domestication is possible: selection for even a few generations can change their behavior enough to make dealing with them a lot easier.

As for the Americas — have you ever had a deer eating out of your hand? Bison seem too wild and scary to have ever been domesticated, but then I’m sure you would have said the same thing about the aurochs, the wild ancestor of cattle.

In fact, in my mind the real question is not why various peoples didn’t domesticate animals that we know were domesticable, but rather how anyone ever managed to domesticate the aurochs. At least twice. Imagine a longhorn on roids: they were big and aggressive, favorites in the Roman arena.

Speaking of deer eating out of your hand:

I remember some biology grad students telling the tale of some other students’ field research, where they snared birds to later tag them — only to find them being eaten by deer.

Deer don’t dislike meat; they’re just terrible hunters.

Dolphins don’t believe in Open Source:

Observing wild dolphins in Shark Bay, Australia, researchers from Georgetown University used hunting tools as a marker of dolphin societal habits.

Noticing some dolphins in the area used a sponge to protect their beaks while hunting, they attempted to discover why the practice had not spread.

They found the useful tool had first been used by a single dolphin nicknamed “Sponging Eve”, after she scrape her nose while foraging for food in rough sand.

To solve the problem, she broke off a piece of sea sponge to protect her, going on to teach the behaviour to her offsping.

But two decades later, knowledge of the tool had not spread among the whole dolphin population in the area.

Scientists observed 36 spongers and 69 non-spongers in the area over a 22 year period, taking careful note of their relationships.

They found: “Spongers were more cliquish, had more sponger associates and stronger bonds with each other than with non-spongers.

“Like humans who preferentially associate with others who share their subculture, tool-using dolphins prefer others like themselves, strongly suggesting that sponge tool-use is a cultural behaviour.”

This tendency to associate with those most like themselves is, scientists believe, a “critical role in human (sub)cultures”, and “may be true for dolphin society as well”.

(Hat tip to the perfidious Buckethead.)

The bubonic plague hasn’t completely disappeared, even from the US, where seven cases are diagnosed in an average year, primarily in the southwest.

I don’t know why an Oregon man would try to take a dead rodent from the mouth of a stray cat, but he did, the cat bit him, and now he’s been diagnosed with plague:

The plague bacteria cycles through rodent populations without killing them off; in urban areas, it’s transmitted back and forth from rats to fleas. There’s even a name for it, the “enzootic cycle.”

The bacteria thrive in forests, semi-arid areas and grasslands, which plague-carrying rodents from wood rats to rock squirrels call home.

Once a coin flip with death, the plague is now easier to handle for humans in the U.S. The national mortality rate stood at 66 percent before World War II, but advances in antibiotics dropped that rate to its present 16 percent.

Central Oregon health officials don’t blame the cat.

“The reality is that, in rural areas, part of the role of cats is to keep the rodent population controlled around our homes and barns” said Karen Yeargain of the Crook County Health Department.

The Prineville man, who is in his 50s, remained in critical condition Friday at a Bend hospital. His illness marks the fifth case of plague in Oregon since 1995.

State public health veterinarian Dr. Emilio DeBess said the man was infected when he was bitten by the stray his family befriended. The cat died and its body is being sent to the CDC for testing.

Humans resemble juvenile apes, and this neoteny may explain how our species diverged from the other apes and became so successful.

Now it looks like birds may also have neoteny — or paedomorphosis — to thank for their outliving the (other) dinosaurs:

Bhullar and Abzhanov reached this conclusion by comparing the skulls of birds and dinosaurs across phylogenies, or related groups, and at different developmental stages. To quantitatively compare cranial geometries, they scanned the skulls of theropod dinosaurs (which are thought to be birds’ ancestors), crocodiles and alligators (dinosaurs’ cousins), early transitional birds such as Archaeopteryx, and modern birds. Then they created digitized versions of each skull and mapped out cranial landmarks, such as nostril tips, eye socket dimensions and places where bones meet.

Their measurements showed that whereas a typical non-avian dinosaur began life with a round head, large eyes and a big brain (relative to the rest of the body) then later developed an elongated snout and smaller relative brain size, birds kept their baby faces.

If birds did evolve by paedomorphosis, they join species such as axolotls. These salamanders evolved to retain tadpolelike gills and fins and, unlike most other amphibians, remain aquatic into adulthood. This feature appears to be due to a hormone disruption. By adding thyroid hormone into their water, researchers have caused axolotls to metamorphose into terrestrial salamanders.

But why would it be advantageous for adult animals to look like kids? Greg Erickson, who studies evolutionary morphology at The Florida State University and was not involved in the study, says that paedomorphosis can help a species to develop new adaptations and exploit new niches. In particular, he suggests that paedomorphosis may have enabled birds to develop larger eyes, which aid in spatial assessment during flight as well as a high brain-to-body-mass ratio, which may contribute to intelligence.

An even simpler explanation is that kids are small and, in times of environmental stress, small is good. Bhullar cites an example of Temnospondyli — large primitive amphibians that were common before 120 million years ago. Catastrophic events killed off most of the temnospondyli, except for a few paedomorphic species. “The interesting thing to me is that [after the catastrophe] these little paedomorphic animals were at the base of a giant radiation,” Bhullar says. He suggests that a similar phenomenon may have occurred during the catastrophic events that killed the dinosaurs — being small may have been an advantage, because smaller animals require less food and can more easily hide. “Everything that lived on land and weighed more than one kilogram perished,” Bhullar says. “The only dinosaurs that survived were the paedomorphic ones.” And after many of those larger species went extinct, the little dino may have been better placed to exploit the new niches that opened up.

Larger animals tend to have larger eyes, but faster animals tend to have larger eyes too:

“If you can think of mammals that are fast like a cheetah or horse, you can almost guarantee they’ve got really big eyes,” says Kirk. “This gives them better vision to avoid colliding with obstacles in their environment when they’re moving very quickly.”

Kirk and physical anthropology doctoral student Amber Heard-Booth are the first to apply Leuckart’s Law — a hypothesis that was developed specifically for birds and speed of flight — to 50 species of mammals. The paper is forthcoming in the journal Anatomical Record. Heard-Booth presented the findings at the 2011 American Association of Physical Anthropology Meeting, where she was awarded the Mildred Trotter Prize for exceptional graduate research in evolutionary morphology.

Previously it was thought that the time of day that an animal is active (nocturnal or diurnal) would be the main factor driving the evolution of mammalian eye size. However, comparative research on the anatomy of the eye has shown that although nocturnal and diurnal species differ in eye shape, they often have similar eye sizes. Although nocturnal species may appear to have bigger eyes because more of the cornea is exposed to let in more light, activity pattern only has a modest effect on eye size.
By comparison, body mass plus maximum running speed together can explain 89 percent of the variation in eye size among mammals.

The researchers controlled for body size and evolutionary relationships, and found that the relationship between eye diameter and maximum running speed is stronger than the relationship between body mass and running speed.