Throughout The Beak of the Finch, author Jonathan Weiner shows how deeply entwined the fates of living things that share the same spaces truly are. By highlighting how the subtlest changes in weather to more extreme changes like the introduction of a new species into an environment can throw an ecosystem into chaos, the book makes clear the intricate and far-reaching impact of this interconnectedness.
The book examines how natural disasters and weather phenomena—floods, droughts, and extreme singular weather events—can change a species’ development significantly. After an alternating period of a serious drought followed by a torrential flood on the Galápagos island of Daphne Major at the end of 1982, researcher Lisle Gibbs was stunned to find that the finches of Daphne were evolving before his eyes: “[Lisle] checked and rechecked. It was true. Natural selection had swung around against the birds from the other side. Big birds with big beaks were dying. Small birds with small beaks were flourishing. Selection had flipped.” This rapid “flip” of natural selection—from prioritizing the traits of big birds with big beaks who weathered droughts well to small birds with small beaks who could thrive in a wetter, rainier environment—illustrates that a species’ development depends on its ecosystem. By highlighting the rapidity of this “flip”—and how over the course of just a couple of extreme-weather seasons, an entire species changed—the book shows that the development of any given species is directly tied to the environmental pressures its ecosystem exerts upon it.
Weather and other natural phenomena can also impact species in less obvious—but equally meaningful—ways. During the heavy rainy season in the Galápagos in 1982 and 1983, adult finches on the island of Genovesa would abandon their nests—or their newly-hatched young—when the weather got too cold or intolerable for them. In an attempt to preserve themselves in the face of an environment in flux, these adult finches sacrificed their offspring—or, in some cases, lost them accidentally when heavy winds and rains snapped the tree branches where they made their homes. To hammer home this point, the book turns to an example from the extremely rainy season in the Galápagos in 1982 and 1983. As El Niño wreaked havoc on the area, local mockingbird populations on the island of Genovesa became sick with pox. The pox didn’t spread to many finches—but because the disease wiped out so many of the mockingbirds’ elders, the juveniles who normally stayed close to their tight-knit family groups were suddenly left to roam and wander. While migrating between different parts of the island in newfound patterns, the mockingbirds began attacking and eating the finches who were their neighbors (as well as those finches’ young.) This episode illustrates how external changes within a given ecosystem can have ripple effects within that ecosystem. Not only were the mockingbirds’ social groups more or less destroyed—but many members of an entirely new generation of finches, too, were wiped out, impacting the finches’ population counts, social organizations, and future mating patterns.
The book also illustrates how certain things introduced to an environment—new plants, pollinators, or animals—can forever change that environment. As one example, the book uses a thought example that Charles Darwin himself devised: he suggested that introducing more cats into an English village would forever change that village’s ecosystem. The cats would eat the mice. The mice, which often eat the honey and combs of bees, would diminish in numbers, and so the bees would flourish. As the bees grew in number, they’d pollinate more flowers and perhaps even introduce new species of flowers to the area. Ultimately, the village could see a complete change in its landscape through this chain of events, which illustrates the delicate interconnectedness of different species within a single ecosystem. Another example the book brings up is the arrival of polar bears in Iceland via a floating iceberg. Because polar bears weren’t native to the region, the animals who existed there already—deer, foxes, seals, and more—didn’t recognize them as predators, and were thus more vulnerable to them. The bears ate all of these creatures. Fewer deer meant the flourishing of the local plants they deer had previously feasted on—and the proliferation of the insects that fed on the plants, too. Fewer foxes meant more ducks, which meant fewer fish. “What havoc the introduction of any new beast of prey must cause in a country,” Charles Darwin wrote in his Journal of Researches, predicting even in his era the upheaval and change that even a slight change in an ecosystem might create and illustrating the interconnectedness of species and the systems around them.
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The Interconnectedness of Species and Ecosystems Quotes in The Beak of the Finch
The whole family tree of Darwin’s finches is marked by this kind of eccentric specialization, and each species has a beak to go with it. Robert Bowman, an evolutionist who studied the finches before the Grants, once drew a chart comparing the birds' beaks to different kinds of pliers. Cactus finches carry a heavy-duty lineman’s pliers. Other species carry analogues of the high-leverage diagonal pliers, the long chain-nose pliers, the parrot-head gripping pliers, the curved needle-nose pliers, and the straight needle-nose pliers.
According to [Darwin’s] theory, even the slightest idiosyncrasies in the shape of an individual beak can sometimes make a difference in what that particular bird can eat. In this way the variation will matter to the bird its whole life—most of which, when it is not asleep, it spends eating. The shape of its particular beak will either help it live a little longer or cut its life a little shorter, so that, in Darwin's words, "the smallest grain in the balance, in the long run, must tell on which death shall fall, and which shall survive."
Where there are many finches, each mericarp has fewer seeds, but it has longer and more numerous spines. In the steep, rugged, protected place, the mericarps have more seeds and fewer, shorter spines. Peter [Grant] suspects that the caltrop is evolving in response to the finches. Where the struggle for existence is fierce, the caltrop that is likeliest to succeed is the plant that puts more energy into spines and less into seeds; but in the safer, more secluded spot, the fittest plants are the ones that put more energy into making seeds and less energy into protecting them. The finches may be driving the evolution of caltrop while caltrop is driving the evolution of the finches.
Now it became of great significance that variations of body and beak are passed on from one generation to the next with fidelity. As a result, the males' unequal luck in love helped to perpetuate the effects of the drought. The male and female fortis that survived in 1978 were already significantly bigger birds than the average fortis had been before the drought. Of this group the males that became fathers were bigger than the rest. And the young birds that hatched and grew up that year turned out to be big too, and their beaks were deep. The average fortis beak of the new generation was 4 or 5 percent deeper than the beak of their ancestors before the drought.
So the birds were not simply magnified by the drought: they were reformed and revised. They were changed by their dead. Their beaks were carved by their losses.
In most places on this planet, the sight of a dead bird is so rare that it shocks us, even scares us. […]
But on the desert island of Daphne Major, dead birds are commonplace. They are everywhere. […] Each generation lies where it falls, and the next generation builds on the ruins of the one before.
In the dry season, natural selection metaphorically scrutinizes these birds, “daily and hourly,” as they strive to keep body and beak together. Some birds make it, and some don't. In the wet season, which is also the breeding season, the survivors are scrutinized daily and hourly by one another, not metaphorically but literally, as males begin jousting for territory building nests, and singing from the highest cactus in their territories, while females troop by and inspect the males' nests and plots of lava and listen to their songs.
In other words, as soon as nature stops selecting among these birds, the birds start selecting among one another. Again, some make it and some don't.
The answer is that a male guppy has more to do in life than merely survive. It also has to mate. To survive it has to hide among the colored gravel at the bottom of its stream and among the other guppies of its school. But to mate it has to stand out from the gravel and stand out from the school. It has to elude the eyes of the cichlid or the prawn while catching the eyes of the female guppy.
Natural selection had swung around against the birds from the other side. Big birds with big beaks were dying. Small birds with small beaks were flourishing. Selection had flipped.
Both big males and big females were dying, [Gibbs] noticed, but many more males than females—again, the reverse of the drought. Everything the drought had preferred in size large—weight, wingspan, tarsus length, bill length, bill depth, and bill width—the aftermath of the flood favored in size small.
Thus the Grants suspect that the finches here are perpetually being forced slightly apart and drifting back together again. A drought favors groups of one beak length or another. It splits the population and forces it onto two slightly separate adaptive peaks. But because the two peaks are so close together, and there is no room for them to widen farther apart, random mating brings the birds back together again.
These two forces of fission and fusion fight forever among the birds. The force of fission works toward the creation of a whole new line, a lineage that could shoot off into a new species. The force of fusion brings them back together.
So there is a simple trade-off here for a stickleback. If the fish specializes in the muck, it cannot compete in the open water; if it specializes in the open water, it is outclassed down in the muck. The fish is in much the same position as a finch in the Galápagos, where specializing in big seeds unfits you for the small ones, and specializing in the small seeds unfits you for the big ones.
To Dolph all this evidence powerfully suggests that the colonists in these lakes have altered the course of each other's evolution, just as the finches have altered each other's courses in the Galápagos.
These two oscillations are driven by the same events. They are both governed by the same changes in the adaptive landscape. In an adaptive landscape that is wrinkling and rolling as fast as Daphne, a landscape in which the peaks are in geological upheaval, it can pay to be born different, to carry a beak 3, 4, or 5 millimeters away from the tried and true. Since the super-Niño, some of the old peaks have turned into valleys, and some of the old valleys are peaks. Now a hybrid has a chance of coming down on the summit of a new peak. It can luck onto a piece of the new shifting ground.
A “web of complex relations” binds all of the living things in any region, Darwin writes. Adding or subtracting even a single species causes waves of change that race through the web,” onwards in ever-increasing circles of complexity.” The simple act of adding cats to an English village would reduce the number of field mice. Killing mice would benefit the bumblebees, whose nests and honeycombs the mice often devour. Increasing the number of bumblebees would benefit the heartsease and red clover, which are fertilized almost exclusively by bumblebees. So adding cats to the village could end by adding flowers.
The arrival of human beings means a new phase in the evolution of Darwin's finches, and its directions are still unclear. […] Rosemary and Peter do think they see something odd about the finches of Santa Cruz. The birds around the research station, and in the village, seem to be blurring together. The Grants have never made a systematic study of this: but to their eyes the species almost look as though they are fusing. "They just sort of run into each other," says Rosemary. There is no difference between the largest fortis and the smallest magnirostris.
You don't find situations that chaotic under natural conditions, but you do find them in the havoc that human beings bring in their train. […] Thus, our disturbances hybridize both the environment and the species.
We are hybridizing the planet.
A pesticide applies selection pressure as surely as a drought or flood. The poison selects against traits that make a species vulnerable to it, because the individuals that are most vulnerable are the ones that die first. The poison selects for any trait that makes the species less vulnerable, because the least vulnerable are the ones that survive longest and leave the most offspring. In this way the invention of pesticides in the twentieth century has driven waves of evolution in insects all over the planet.
In the world's oceans, Norwegian cod, chinook salmon, Atlantic salmon, red snapper, and red porgy are getting smaller, very likely through the selection pressures of the net. Fishermen are not happy with the trend toward small fish, any more than elephant poachers are pleased with the trend toward tusklessness. But both resistance movements are direct results of Darwinian law.
The black mutants swept up through the mort populations wherever the air was black with the soot of the industrial revolution. Their numbers did not rise in rural parts of Cornwall, Scotland, and Wales. In rural Kent, Darwin's adopted county the black form of the moth was not recorded during his lifetime; but by the middle of this century, nine out of ten Biston betularia were black in Bromley, and seven out of ten in Maidstone.
Manchester, of course, was one of the grimy hubs of the industrial revolution.
They rise, they are discovered by seeds and birds, they support Darwinian chains of action and reaction, and they sink again to the bottom of the sea, while new islands rise in their place. This rise and fall may have gone on here in the middle of the sea for as many as eighty or ninety million years. […] We know [that Daphne Major is] a place that was here before we came and will remain when we are gone. The very island will sink someday, and another will rise when it is drowned.
