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Lobsters–and Territory

 

If you are like most people, you don’t often think about lobsters[5]–unless you’re eating one. However, these interesting and delicious crustaceans are very much worth considering. Their nervous systems are comparatively simple, with large, easily observable neurons, the magic cells of the brain. Because of this, scientists have been able to map the neural circuitry of lobsters very accurately. This has helped us understand the structure and function of the brain and behaviour of more complex animals, including human beings. Lobsters have more in common with you than you might think (particularly when you are feeling crabby–ha ha).

Lobsters live on the ocean floor. They need a home base down there, a range within which they hunt for prey and scavenge around for stray edible bits and pieces of whatever rains down from the continual chaos of carnage and death far above. They want somewhere secure, where the hunting and the gathering is good. They want a home.

This can present a problem, since there are many lobsters. What if two of them occupy the same territory, at the bottom of the ocean, at the same time, and both want to live there? What if there are hundreds of lobsters, all trying to make a living and raise a family, in the same crowded patch of sand and refuse?

Other creatures have this problem, too. When songbirds come north in the spring, for example, they engage in ferocious territorial disputes. The songs they sing, so peaceful and beautiful to human ears, are siren calls and cries of domination. A brilliantly musical bird is a small warrior proclaiming his sovereignty. Take the wren, for example, a small, feisty, insect‑eating songbird common in North America. A newly arrived wren wants a sheltered place to build a nest, away from the wind and rain. He wants it close to food, and attractive to potential mates. He also wants to convince competitors for that space to keep their distance.

 

Birds–and Territory

 

My dad and I designed a house for a wren family when I was ten years old. It looked like a Conestoga wagon, and had a front entrance about the size of a quarter. This made it a good house for wrens, who are tiny, and not so good for other, larger birds, who couldn’t get in. My elderly neighbour had a birdhouse, too, which we built for her at the same time, from an old rubber boot. It had an opening large enough for a bird the size of a robin. She was looking forward to the day it was occupied.

A wren soon discovered our birdhouse, and made himself at home there. We could hear his lengthy, trilling song, repeated over and over, during the early spring. Once he’d built his nest in the covered wagon, however, our new avian tenant started carrying small sticks to our neighbour’s nearby boot. He packed it so full that no other bird, large or small, could possibly get in. Our neighbour was not pleased by this pre‑emptive strike, but there was nothing to be done about it. “If we take it down,” said my dad, “clean it up, and put it back in the tree, the wren will just pack it full of sticks again.” Wrens are small, and they’re cute, but they’re merciless.

I had broken my leg skiing the previous winter–first time down the hill–and had received some money from a school insurance policy designed to reward unfortunate, clumsy children. I purchased a cassette recorder (a high‑tech novelty at the time) with the proceeds. My dad suggested that I sit on the back lawn, record the wren’s song, play it back, and watch what happened. So, I went out into the bright spring sunlight and taped a few minutes of the wren laying furious claim to his territory with song. Then I let him hear his own voice. That little bird, one‑third the size of a sparrow, began to dive‑bomb me and my cassette recorder, swooping back and forth, inches from the speaker. We saw a lot of that sort of behaviour, even in the absence of the tape recorder. If a larger bird ever dared to sit and rest in any of the trees near our birdhouse there was a good chance he would get knocked off his perch by a kamikaze wren.

Now, wrens and lobsters are very different. Lobsters do not fly, sing or perch in trees. Wrens have feathers, not hard shells. Wrens can’t breathe underwater, and are seldom served with butter. However, they are also similar in important ways. Both are obsessed with status and position, for example, like a great many creatures. The Norwegian zoologist and comparative psychologist Thorlief Schjelderup‑Ebbe observed (back in 1921) that even common barnyard chickens establish a “pecking order.”[6]

The determination of Who’s Who in the chicken world has important implications for each individual bird’s survival, particularly in times of scarcity. The birds that always have priority access to whatever food is sprinkled out in the yard in the morning are the celebrity chickens. After them come the second‑stringers, the hangers‑on and wannabes. Then the third‑rate chickens have their turn, and so on, down to the bedraggled, partially‑feathered and badly‑pecked wretches who occupy the lowest, untouchable stratum of the chicken hierarchy.

Chickens, like suburbanites, live communally. Songbirds, such as wrens, do not, but they still inhabit a dominance hierarchy. It’s just spread out over more territory. The wiliest, strongest, healthiest and most fortunate birds occupy prime territory, and defend it. Because of this, they are more likely to attract high‑quality mates, and to hatch chicks who survive and thrive. Protection from wind, rain and predators, as well as easy access to superior food, makes for a much less stressed existence. Territory matters, and there is little difference between territorial rights and social status. It is often a matter of life and death.

If a contagious avian disease sweeps through a neighbourhood of well‑stratified songbirds, it is the least dominant and most stressed birds, occupying the lowest rungs of the bird world, who are most likely to sicken and die.[7] This is equally true of human neighbourhoods, when bird flu viruses and other illnesses sweep across the planet. The poor and stressed always die first, and in greater numbers. They are also much more susceptible to non‑infectious diseases, such as cancer, diabetes and heart disease. When the aristocracy catches a cold, as it is said, the working class dies of pneumonia.

Because territory matters, and because the best locales are always in short supply, territory‑seeking among animals produces conflict. Conflict, in turn, produces another problem: how to win or lose without the disagreeing parties incurring too great a cost. This latter point is particularly important. Imagine that two birds engage in a squabble about a desirable nesting area. The interaction can easily degenerate into outright physical combat. Under such circumstances, one bird, usually the largest, will eventually win–but even the victor may be hurt by the fight. That means a third bird, an undamaged, canny bystander, can move in, opportunistically, and defeat the now‑crippled victor. That is not at all a good deal for the first two birds.

 

Conflict–and Territory

 

Over the millennia, animals who must co‑habit with others in the same territories have in consequence learned many tricks to establish dominance, while risking the least amount of possible damage. A defeated wolf, for example, will roll over on its back, exposing its throat to the victor, who will not then deign to tear it out. The now‑dominant wolf may still require a future hunting partner, after all, even one as pathetic as his now‑defeated foe. Bearded dragons, remarkable social lizards, wave their front legs peaceably at one another to indicate their wish for continued social harmony. Dolphins produce specialized sound pulses while hunting and during other times of high excitement to reduce potential conflict among dominant and subordinate group members. Such behavior is endemic in the community of living things.

Lobsters, scuttling around on the ocean floor, are no exception.[8] If you catch a few dozen, and transport them to a new location, you can observe their status‑forming rituals and techniques. Each lobster will first begin to explore the new territory, partly to map its details, and partly to find a good place for shelter. Lobsters learn a lot about where they live, and they remember what they learn. If you startle one near its nest, it will quickly zip back and hide there. If you startle it some distance away, however, it will immediately dart towards the nearest suitable shelter, previously identified and now remembered.

A lobster needs a safe hiding place to rest, free from predators and the forces of nature. Furthermore, as lobsters grow, they moult, or shed their shells, which leaves them soft and vulnerable for extended periods of time. A burrow under a rock makes a good lobster home, particularly if it is located where shells and other detritus can be dragged into place to cover the entrance, once the lobster is snugly ensconced inside. However, there may be only a small number of high‑quality shelters or hiding places in each new territory. They are scarce and valuable. Other lobsters continually seek them out.

This means that lobsters often encounter one another when out exploring. Researchers have demonstrated that even a lobster raised in isolation knows what to do when such a thing happens.[9] It has complex defensive and aggressive behaviours built right into its nervous system. It begins to dance around, like a boxer, opening and raising its claws, moving backward, forward, and side to side, mirroring its opponent, waving its opened claws back and forth. At the same time, it employs special jets under its eyes to direct streams of liquid at its opponent. The liquid spray contains a mix of chemicals that tell the other lobster about its size, sex, health, and mood.

Sometimes one lobster can tell immediately from the display of claw size that it is much smaller than its opponent, and will back down without a fight. The chemical information exchanged in the spray can have the same effect, convincing a less healthy or less aggressive lobster to retreat. That’s dispute resolution Level 1.[10] If the two lobsters are very close in size and apparent ability, however, or if the exchange of liquid has been insufficiently informative, they will proceed to dispute resolution Level 2. With antennae whipping madly and claws folded downward, one will advance, and the other retreat. Then the defender will advance, and the aggressor retreat. After a couple of rounds of this behaviour, the more nervous of the lobsters may feel that continuing is not in his best interest. He will flick his tail reflexively, dart backwards, and vanish, to try his luck elsewhere. If neither blinks, however, the lobsters move to Level 3, which involves genuine combat.

This time, the now enraged lobsters come at each other viciously, with their claws extended, to grapple. Each tries to flip the other on its back. A successfully flipped lobster will conclude that its opponent is capable of inflicting serious damage. It generally gives up and leaves (although it harbours intense resentment and gossips endlessly about the victor behind its back). If neither can overturn the other–or if one will not quit despite being flipped–the lobsters move to Level 4. Doing so involves extreme risk, and is not something to be engaged in without forethought: one or both lobsters will emerge damaged from the ensuing fray, perhaps fatally.

The animals advance on each other, with increasing speed. Their claws are open, so they can grab a leg, or antenna, or an eye‑stalk, or anything else exposed and vulnerable. Once a body part has been successfully grabbed, the grabber will tail‑flick backwards, sharply, with claw clamped firmly shut, and try to tear it off. Disputes that have escalated to this point typically create a clear winner and loser. The loser is unlikely to survive, particularly if he or she remains in the territory occupied by the winner, now a mortal enemy.

In the aftermath of a losing battle, regardless of how aggressively a lobster has behaved, it becomes unwilling to fight further, even against another, previously defeated opponent. A vanquished competitor loses confidence, sometimes for days. Sometimes the defeat can have even more severe consequences. If a dominant lobster is badly defeated, its brain basically dissolves. Then it grows a new, subordinate’s brain–one more appropriate to its new, lowly position.[11] Its original brain just isn’t sophisticated to manage the transformation from king to bottom dog without virtually complete dissolution and regrowth. Anyone who has experienced a painful transformation after a serious defeat in romance or career may feel some sense of kinship with the once successful crustacean.

 

Дата: 2018-09-13, просмотров: 618.