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Why aren't there more Ash-Red pigeons?

Why aren't there more Ash-Red pigeons?



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My favorite color pigeon is Ash-Red, but I don't see a lot of them. I figured it must be a recessive phenotype, but when I googled it, I found out it's dominant. So why aren't there more Ash-Red pigeons around?

Edit: I'm in North America.

Edit 2: This website from the University of Utah is where I learned that Ash-Red is the dominant phenotype.


Welcome to Biology.SE

Assumption

I will assume it is true that the allele causing a ash-red plumage is dominant over all other alleles. Note however that you should cite your reference when making such claim in your post.

Dominance and allele frequency

Phenotypes associated to a dominant alleleAaren't necessarily more common than the phenotype of the recessive allelea. It all depends on the allele frequency. If the dominant allele is at low frequency then bothAAandAa(both displaying the dominant phenotype) are at low frequency (esp.AAindividuals) and most individuals areaaand show the recessive phenotype.

Learn more

You might want to read about Hardy-Weinberg rule with this post for example.


City birds are smarter than country birds

Birds living in urban environments are smarter than birds from rural environments.

But, why do city birds have the edge over their country friends? They adapted to their urban environments enabling them to exploit new resources more favorably than their rural counterparts, say a team of all-McGill University researchers.

In a first-ever study to find clear cognitive differences in birds from urbanized compared to rural areas, the researchers report key differences in problem-solving abilities such as opening drawers to access food, and temperament (bolder) among city birds versus country.

The team tested the two groups of birds using not only associative learning tasks, but innovative problem-solving tasks. Innovativeness is considered to be useful in the “real life” of animals in the wild, more so than associative learning.

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“We found that not only were birds from urbanized areas better at innovative problem-solving tasks than bullfinches from rural environments, but that surprisingly urban birds also had a better immunity than rural birds,” says Jean-Nicolas Audet, a Ph.D student in the Department of Biology and first author of the study published in the journal Behavioral Ecology.

“Since urban birds were better at problem-solving, we expected that there would be a trade-off and that the immunity would be lower, just because we assumed that you can’t be good at everything’ (in fact, both traits are costly). It seems that in this case, the urban birds have it all”.

Native birds of Barbados

The work was conducted at the McGill Bellairs facility in Barbados using bullfinches captured from various parts of the Caribbean island. “The island of Barbados shows a strong range of human settlement, there are some very developed areas but also mostly left untouched, thus providing an excellent environment to study the effects of urbanization”, adds Audet.


Why aren't there more Ash-Red pigeons? - Biology

Although all three of these play important roles in reducing natural populations, this section focuses on predation.

Predation can be defined as an event in which one organism kills and consumes another organism or uses its nutrients without killing it. People often think of showy vertebrate predators first, such as lions chasing down a gazelle or birds feeding on butterflies they catch in mid-flight. But smaller invertebrate predators such as insects, spiders, bacteria, and viruses kill many more butterflies in most natural populations than do frogs, lizards, birds, toads, mice, and other vertebrates. Invertebrate predators also include parasites, organisms that take nutrients and resources from other organisms without killing them directly (although parasitism can result in death), and the specialized form of parasites called parasitoids, insects that consume other insects from the inside out.

All butterflies have mechanisms that help protect them from predation. Some species are camouflaged: they either look like something else, such as a leaf or stick, or blend in with their backgrounds. Others have patterns that make them appear to be a bigger animal, such as eyespots on wings. Still other butterflies protect themselves through behavior. Adults can fly off, while larvae can live together in groups or drop to the ground suddenly if a predator approaches. Some butterflies also have mechanical or chemical defenses. Mechanical defenses are things like hairs, spines, or bristles that make it harder for the predator to get a good grasp on the larva, while chemical defenses make the butterfly less appetizing (maybe a noxious smell or a bad taste).

Monarchs have an effective chemical defense. When they eat milkweed, they sequester the poisonous cardenolides (also called cardiac glycosides) in the milkweed. Cardenolides are poisonous to vertebrates (although maybe not to invertebrates, bacteria, and viruses), and most Monarchs face little predation from frogs, lizards, mice, birds, and other species with backbones.

But being poisonous doesn't help the Monarchs after a predator has already killed and tried to eat them. Monarchs need some way to warn off predators before they become lunch. Monarchs do this through their warning coloration, or bright colors (yellow, orange, black, and white). This coloration warns potential predators that the animal contains poisonous chemicals. Warning coloration may work particularly well in adult butterflies because the hard body and wings allows a predator to bite the adult, taste the poison, and release the butterfly without killing it. It is common to see butterflies with beak-sized sections gone from their wings. Large wings help the butterfly escape relatively unharmed. Since Monarch wings contain distasteful cardenolides, one bite may discourage further attack without killing the adult.

Early studies of Monarchs showed that when a blue jay ate a Monarch butterfly, it vomited shortly afterwards due to the cardenolides. That bird also learned to never eat another Monarch butterfly. Like this early study, most research about Monarch predation has focused on bird predation, especially on adults, and researchers have found a few species that eat Monarchs despite the cardenolides. However, invertebrates that eat the larvae are probably more important Monarch predators and thus play a more significant role in controlling Monarch population size. Despite their importance, scientists have done much less research on invertebrate predation of Monarchs. This is an important hole, since the cardenolides Monarchs sequester may not affect invertebrates in the same way. As you read about the studies of vertebrate predation on Monarchs, and about the little information we have on invertebrate predation, think about ways you might investigate the impact of invertebrate predators on Monarch butterfly populations.


Birds of a feather

In the new study, however, researchers reveal vulturine guineafowl to be a "striking exception," according to a statement from the Max Planck Institute of Animal Behavior. The birds organize themselves into highly cohesive social groups, the study's authors report, but without the "signature intergroup aggression" common among other birds that live in groups. And they achieve this with a relatively small brain, which is reportedly small even by avian standards.

"They seemed to have the right elements to form complex social structures, and yet nothing was known about them," says lead author Danai Papageorgiou, a Ph.D. student at the Max Planck Institute of Animal Behavior. Faced with a dearth of research on this species, Papageorgiou and her colleagues began investigating a population of more than 400 adult vulturine guineafowl in Kenya, tracking their social relationships across multiple seasons.

By marking and then observing each bird in the population, the researchers were able to identify 18 distinct social groups, each of which contained 13 to 65 individuals, including multiple breeding pairs plus various solo birds. These groups remained intact throughout the study, even though they regularly overlapped with one or more other groups, both during the day and at their night roosts.

The researchers also wanted to learn if any of the groups were preferentially associating with each other, a hallmark of a multilevel society. To do that, they attached GPS tags to a sample of birds in each group, giving them a continuous record of every group's location throughout the day. This generated data that could reveal how all 18 groups in the population with interacting.

The results showed groups of vulturine guineafowl were associating with each other based on preference, the researchers say, as opposed to random encounters. The study also found that intergroup associations were more likely during specific seasons and around specific locations in the landscape.

"To our knowledge, this is the first time a social structure like this has been described for birds," says Papageorgiou. "It is remarkable to observe hundreds of birds coming out of a roost and splitting up perfectly into completely stable groups every single day. How do they do that? It's obviously not just about being smart."


Why there are so many species at the equator and so few at the poles?

A Spondylus americanus (left) from the Florida Keys, a tropical species with long spines that act as defense against predation and Arctica islandica, sometimes known as the Methuselah clam for its long life, which is found only in cold waters like the Gulf of Maine. Credit: Katie Collins

Earth is teeming with strange life forms—crabs with 12-foot-long legs scuttling off the Japanese coast, mushrooms that glow at night in eastern North America, butterflies that drink the tears of Amazonian turtles.

Among all of the world's natural kingdoms, however, one rule reigns supreme: There are lots of different species at the tropics, but their numbers drop off sharply as you move toward the poles. "This holds true across virtually all kinds of life and in all kinds of environments, but the reasons why are still hotly contested," said Prof. David Jablonski, a leading University of Chicago scientist of extinction and biodiversity. "This is a fundamental question that goes back before Darwin."

Jablonski's goal is to understand biodiversity, and the stakes are big—including how species will adapt to climate change.

Scientists like Jablonski—whose research on mollusks has shaped the field—have traditionally researched either a species' form (the shape of an organism's body) or its function (the way it makes a living). For example, a clam's shell can be spiny or smooth, and it can make a living eating sunken logs off a coast or by filtering plankton in tidal flats. Each way of looking at the animal tells you something different about evolution, niches and the patterns of biodiversity but each is so complex on its own that they're rarely studied in unison. Jablonski believes integrating the two could yield important insights.

Two recent studies from his lab take this approach, combining forces with other specialists to investigate the diversity shift from topics to poles in an innovative way.

In the first study, they worked with bird biologist Prof. Trevor Price to compare Jablonski's mollusk data with Price's bird insights on how species across the world live in different environments.

In tropical birds, some ways to make a living are packed with species—lots that eat insects on tree branches, for example—and others support just a few. This pattern persists midway into the latitudes, but then there's a distinct tipping point and the number of ways to make a living, and the uneven distribution among them, drop off.

The exact same is true for mollusks. "That result knocked our collective socks off," said Jablonski, who is the William R. Kenan Jr. Distinguished Service Professor of Geophysical Sciences.

"For animals, you don't get much different than a bird and a bivalve, but you see this strikingly similar pattern," said Stewart Edie, a postdoctoral researcher and the joint first author of both papers. "That usually suggests we're looking at a higher-order control that's operating on a large scale around the planet, both on land and sea."

The theory is that in the tropics, there's more room for fine-scale specialization among species—not just birds that eat seeds, but birds that eat only one kind of seed, in one part of the environment (branches high in the forest canopy, for example). But with increasing latitude, the climate becomes more seasonal and more difficult to survive in, and it's less viable to be a specialist. "A lot of the ways of life are still present you just have to eat every kind of seed, or live anywhere in the canopy," Jablonski said.

A map of the researchers' study area for the Florida Keys and Gulf of Maine. On the top row are the shells at higher latitudes, which tend to be smoother and plainer than their spiky, colorful counterparts closer to the equator, on bottom row. Credit: Katie Collins

That's something new about how biodiversity works, he said, and it may have implications for how things will play out as climate change progresses. "For example, what's going to happen to parasites that attack crops or plants we care about—species will arrive that can focus on specific hosts as it gets warmer," he said.

The second paper, headed by postdoctoral researcher Katie Collins, turned to technology to analyze how the forms of mollusks change from tropics to poles.

They used a micro CT scanner to scan samples of 95 percent of all the species found in the Florida Keys and the Gulf of Maine, yielding a treasure trove of 3-D images. Most studies just work with shell length and height, "but that's not the whole picture," Collins said. "A third dimension adds a new layer of understanding." "Now we can put hard numbers on shell form where we just had general impressions before," added co-author Rüdiger Bieler, curator of invertebrate zoology at Chicago's Field Museum and member of UChicago's Committee on Evolutionary Biology.

When you go to a beach in the Florida Keys, your eye is drawn to large, brightly colored shells with spines and ridges and knobs. But north of Cape Cod, you don't find those. The shells are all smooth, plain and often small, which at first blush seems to indicate a massive shift in species form.

That's not what scientists found, though. "It turns out there are plain shells everywhere," Collins said."The tropical shells are actually a mix of plain and fancy species the fancy shells just drop out of the mix as you go north. So the individual species aren't transforming to adapt to new conditions whole lineages of fancy things drop out."

"It looks like the high-latitude climate narrows down the range of viable shell forms, and some lineages are just frozen out, so to speak," said Jablonski.

This too has implications for humans as they continue to alter the climate and environment.

"What this suggests is that most animals are more likely to drop out than to adapt to the tougher conditions at high latitude," Collins said. "This could affect humans in a very real way. Bivalves serve a huge role in fisheries, and we don't know if the ones we like to eat most, like oysters or scallops or mussels, are going to disappear, or move out of their accessible fishing grounds, as the climate changes around them."

This study was done on modern species the next step will be to add fossils. (Scientists love mollusks because their shells are easily fossilized.) "For example, we want to know whether the fancy lineages turn over more rapidly over time are more extinction-prone or if they're stable," Collins said.

"Taken together, these new studies show that the different dimensions of biodiversity don't all change together on a global scale, and the mismatches tell us something new about the forces shaping life on earth," said Jablonski.


What’s the difference between race and subspecies?

A long time ago, the words race and subspecies were used to mean the same thing in biology. This was before we knew how much or how little genes could differ between animals. Now we only use subspecies to refer to living things that aren’t human. We only use race when we talk about humans. We often try to group humans by race based on how they look. While humans may look different on the outside, our DNA looks very similar. Because we are so similar, scientists say that we can't use race to sort humans either. Are humans really so alike?

Comparisons of humans, emperor penguins, and chimpanzees. Which of these pairs of animals do you think has the most variation within their species? Taylor Swift and Kanye West by David Shankbone Penguins by Liam Quinn Chimpanzees by Delphine Bruyere.

Take a look at the photos on the left. There are three pairs of two members of the same species. Which pair do you think is more genetically similar? Would you guess Kanye West and Taylor Swift are more alike, or two penguins? What about Kanye and Taylor versus two chimps? It may surprise you to learn that penguins have twice as much genetic variation as humans do. And this subspecies of chimp has more genetic variation than all the humans on earth.


10 Myths About Pigeons

There are plenty of references to pigeons in modern society. People can be pigeon-toed or pigeon-holed, or even act as stool pigeons. If you've ever wondered why pigeon-themed parlance plays such a central role in human culture, look no further than your local playground or shopping center. These birds are everywhere.

Because pigeons thrive in man-made environments, they've become extremely common wherever there are people. In fact, pigeons are abundant in Europe, Asia and Africa, as well as throughout North America. In addition to being the subjects of legend and lore, these creatures are also the focus of a lot of misconceptions. Check out our list of the most common myths about pigeons, and perhaps you'll learn a thing or two about our familiar feathered friends.

10: Pigeons Make Bad Fathers

"Papa was a rolling stone" may be true of many bird species, but not pigeons. These birds tend to mate for life, which means that it's very unusual for a male and female to separate once they've formed a bond. And that's not all -- a male pigeon also contributes to nest-building and incubating eggs. In addition, he defends his family against intruders or anything that threatens their well-being.

Male pigeons also help feed their young. These proud papas actually produce a type of milk called crop milk for their offspring. It's a highly nutritious fluid produced in their crop (a throat pouch where food is stored). So while most male birds fly the coop after mating, pigeons stick around and take good care of their families.

9: Pigeons Explode if You Feed Them Rice

The old wives' tale about pigeons and other birds exploding when they eat uncooked rice is a myth, and one that has modified many wedding day send-offs throughout the world. The false theory is that because birds are unable to digest grains of raw rice, it'll expand in their stomachs and cause the animals' bellies to burst.

Now for the truth. While many smaller birds are unable to digest uncooked rice, pigeons are among those that can, according to the Royal Society for the Protection of Birds.

And don't worry, even those that can't digest raw rice are not known to explode if they eat it. So the next time you're at a wedding, don't hold back. Grab a handful of rice and shower the newlyweds to your heart's content

8: It's Good Luck to Be Pooped on by a Pigeon

OK, this one is tough to prove or disprove with any sort of scientific accuracy, but the consensus is that being defecated on by anyone or anything is a bad thing. For one thing, pigeon poop is smelly. And second, while not toxic in small amounts, it can cause serious, life-threatening fungal infections if inhaled in significant quantities, according to the Illinois Department of Public Health.

If that doesn't convince you, consider that pigeons also carry parasites, which may be transmitted to humans through contact with their droppings. When you counter this with the scarcity of evidence to support claims of post-pigeon poop good fortune, it becomes clear that you should avoid standing below a flock of these birds around mealtime.

7: Pigeons and Doves Are Divine

Again, this myth is difficult to discuss rationally, but we felt we had to include it in the list since pigeons and doves (same family, different species) appear so often in scripture and the writings of the ancient world. Whether serving as sacrifice in Jewish tradition or as Noah's messenger on the ark, pigeons and doves play a central role in the lore of the world's religions.

Pigeons and doves also represent peace, purity, faith and fidelity in numerous cultures around the world. Why the birds hold such a sacred place in human societies is difficult to discern, but pigeons are no more or less likely than other animals to guide us to the hereafter.

Despite sounding like part of a conspiracy theory, this pigeon myth is actually rooted in a measure of truth. Pigeons have been used by governments and militaries around the globe for centuries, and many pigeon activities have proved quite critical in espionage operations. For example, before the widespread use of satellite imagery, pigeons would be fitted with tiny cameras and flown over enemy territory on information-gathering exercises.

They've also been used extensively as messengers -- the birds would carry critical notes between military installations even as late as World War II. That being said, it's extremely unlikely that the pigeons you feed at the local park are working undercover for a foreign government.

There are plenty of references to pigeons in modern society. People can be pigeon-toed or pigeon-holed, or even act as stool pigeons. If you've ever wondered why pigeon-themed parlance plays such a central role in human culture, look no further than your local playground or shopping center. These birds are everywhere.

Because pigeons thrive in man-made environments, they've become extremely common wherever there are people. In fact, pigeons are abundant in Europe, Asia and Africa, as well as throughout North America. In addition to being the subjects of legend and lore, these creatures are also the focus of a lot of misconceptions. Check out our list of the most common myths about pigeons, and perhaps you'll learn a thing or two about our familiar feathered friends.

4: Pigeons All Look Pretty Much Alike

This is definitely a misconception about these ubiquitous birds. Pigeons are common in so many places around the world that they tend to blend into the scenery. But take a closer look and you'll see a huge variety of colors and patterns among pigeons. In fact, there are dozens of distinct color variations, including red, white, blue-black and gray, according to the Cornell Laboratory of Ornithology.

Much of the variation in pigeon coloring is due to selective breeding throughout history by people who have collected pigeons for their feathers. This should come as no surprise since these animals have been cohabitating with humans for 5,000 to 10,000 years, often as pets, messengers or human sustenance.

3: Pigeons Can Fly Thousands of Miles Per Day

Based on the incredible flying abilities of pigeons, stories about their winged performance have been greatly inflated over the years. For example, pigeons have a remarkable ability to find their way home, but not from halfway around the world -- as legend would have it. The truth is still impressive. Pigeons are able to navigate home across hundreds of miles using the sun, the Earth's magnetic field and landmarks such as tall buildings.

There are also many tall tales about pigeons traveling more than a thousand miles in one day -- sometimes many thousands. This is an exaggeration. The truth is that racing pigeons fly between 40 and 50 miles (64 and 80 kilometers) per hour, with the top performers covering a maximum of about 600 miles (966 kilometers) in a single day, according to the Solar Center at Stanford University. So while these stats are remarkable, pigeons are not the superheroes that many mythmakers would have you believe.

As wild creatures go, pigeons are not among the most feared. But don't let their mild manner and ability to coexist with humans fool you. Pigeons are known to attack other birds and even humans if threatened, especially when they feel their nest is in danger.

So, what does a pigeon attack look like? Most pigeon aggression is directed toward other members of the flock, which has a strict hierarchy. Pigeons may also attack people if provoked. This may involve coming together as a flock to peck at a target, who can usually manage to get away without injury. The bottom line is that while feeding pigeons is OK, try not to make them angry. They may be small, but they probably outnumber you by at least a 20-1 ratio.

The notion that pigeons are stupid couldn't be farther from the truth. These animals have been the subject of countless scientific studies over the past few decades and are widely considered to be among the smartest creatures on Earth. For example, pigeons can be taught to perform complex actions and remember images for several years. They can even recognize their own image. Now that is something cats, dogs and even infant humans generally can't do.

It's probably because pigeons are so common that people don't give them their due. There is also that unfortunate habit of pooping all over cars, sidewalks and park benches. But pigeons are actually quite smart and well-adapted to their environment. So next time you find yourself face to face with a flock, take a moment to appreciate these beautiful birds. They are among the most interesting -- and misunderstood -- creatures in our world.


Where Are the Birds?

It was a surprise, then, when bird watchers in recent decades reported seeing fewer birds, not more, in areas where cicadas had emerged. Could it be that the din of the cicadas’ mating buzz drowning out the birdsong, so that the bird watchers only thought there were fewer birds?

Cicadas aren't toxic for birds to eat, but could it be something else about the cicadas was driving the birds away? Or is there another explanation? Koenig and Liebhold teamed up to find out. They began by looking in the data from the Breeding Bird Survey, a yearly census of bird populations collected by the U.S. Geological Survey since 1966. During a Breeding Bird Survey, volunteer scientists and expert bird watchers across the country drive their assigned routes during breeding season, stopping at pre-determined locations to look and listen for birds.

The key to Koenig and Liebhold’s research was that in the Brood X emergence years of 1987 and 2004, Breeding Bird Survey volunteers in the brood’s range were asked to gather information about cicadas as well as about birds. At each stop along their routes they were asked to note whether they could hear cicadas calling or not. “That was fabulous,” says Koenig, who is an expert at crunching Breeding Bird Survey data. “It allowed us to test those hypotheses.” Koenig reasoned that if the cicadas were driving the birds away, bird numbers would be lower in areas where cicadas were heard and higher in nearby areas where cicadas couldn’t be heard. If the cicadas were drowning out the birds’ songs, then the number of birds would be lower in areas where cicadas could be heard, but remain the same in nearby areas. If, however, there were actually fewer birds in the area, there would be fewer birds both in areas where cicadas could be heard and in the nearby areas without cicadas. And that’s what the data showed . They also showed the number of birds bouncing back the very next year.

The plot thickened when Koenig looked at the Christmas Bird Count, another annual bird survey. These data showed fewer crows, blue jays and other insect-eating birds in areas of cicada emergence, six months before the emergence happened. The normal bird population had dipped, as if anticipating the insect surge. “There are no cicadas around nobody is thinking of cicadas,” says Koenig. “And there was already a decline. That’s what made me think that maybe I’m not making this up after all.” After proving that there are actually fewer birds in areas with a cicada emergence, the team’s next question was, “Why?” It's a question they're still trying to answer today.


Does This Species Belong Here?

Many common animals, plants and insects are not native to the environments in which they are now found. Take this quiz and learn more about the living things that surround you.

“It’s almost a religious kind of belief, that things were put where they are by God and that that’s where they damn well ought to stay,” said Ken Thompson, an ecologist and retired senior lecturer at the University of Sheffield in England, who wrote the 2014 book “Where Do Camels Belong: Why Invasive Species Aren’t All Bad.”

“We’re actually moving plants and animals around the world all the time,” he said. “We have been for centuries.”

Dr. Thompson and other scientists have called for a more nuanced approach to evaluating whether the presence of a species is harmful or beneficial. Eradicating most invasive species is virtually impossible in an era of globalization, they note. And as climate change pushes more species out of their home ranges and into new areas, the number of so-called invaders is likely to multiply exponentially.

Yet the notion that a species should not be judged on its origins is highly controversial, as Mark Davis, a biology professor at Macalester College in Minnesota, discovered when he and 18 other researchers submitted an article in 2011 saying just that in the journal Nature.

Image

The response was immediate — and signed by 141 scientists, many of them specialists in the field known as invasion biology. Their approach, they said, was already sufficiently “nuanced,” thank you very much.

“Most conservation biologists and ecologists do not oppose nonnative species per se,” wrote Daniel Simberloff, a professor of environmental science at the University of Tennessee, who led the group that wrote the rebuttal. He added that Dr. Davis and his colleagues had vastly played down the severe harm that alien species caused.

But in the five years since that contentious exchange, the idea that invasive species should be assumed guilty until proven innocent has begun to wane, the shift prompted in part, Dr. Davis speculated, by concerns over the use of chemical pesticides and the disruption of landscapes caused by many eradication efforts.

Some alien species are undeniably harmful, a fact that neither Dr. Davis nor others who share his view dispute. The fungus that causes chestnut blight, for example, decimated thousands of trees and changed the American landscape in the early 1900s. The Zika virus is invading new regions, carried by infected mosquitoes that some say are being driven northward by warmer temperatures. The vampirelike lamprey, sneaking into the Great Lakes in the 19th century, gradually champed its way through the fish population.

Islands and mountaintops are especially vulnerable to damage from invaders because their native species often evolved in isolation and lack natural defenses against predators or immunity to exotic diseases. The brown tree snake, accidentally transported to Guam, has virtually eliminated the bird population there.

But, Dr. Davis noted, “all species have negative impacts on something,” and the danger, he said, is often exaggerated.

A study published Feb. 17 in the journal Biology Letters, for example, concluded that alien species “are the second most common threat associated with species that have gone completely extinct” since 1500 A.D.

But the study, Dr. Davis and other experts said, relies on subjective judgments about extinction and does not distinguish between island species — which are far more vulnerable — and land or ocean species.

In some instances, nonnatives offer clear benefits. In California, for example, monarch butterflies prefer to spend their winters in the branches of the eucalyptus, an exotic tree transplanted to the state more than 150 years ago and viewed by some as an invasive fire hazard. In Spain, non-native crayfish serve as prey for migratory wetland birds, including some endangered species.

And some notorious invaders can have positive effects. Western states have spent a fortune trying to eradicate the tamarisk tree, which many experts believe hogs more than its share of water and damages the habitat of native species.

But Julian D. Olden, an associate professor in the School of Aquatic and Fishery Sciences at the University of Washington, said tamarisks had been found to provide shelter for birds like the southwestern willow flycatcher. Some studies have also concluded that the tree’s water use is not significantly different from that of other tree species.

The antipathy to foreign plants and wildlife is relatively recent. While the distinction between native and non-native species dates to the 18th century, the term “invasion” was first used in a 1958 book — “The Ecology of Invasions by Animals and Plants,” by Charles Elton — that drew on the militaristic vocabulary of the post-World War II era.

But the moniker did not achieve its full derogatory weight until the 1990s and early 2000s, when academic interest in the subject peaked and the number of papers on the subject generated by invasion biologists grew proportionately.

To biologists like Dr. Simberloff, taking action to head off alien species early on makes sense, allowing governments to address threats before invaders take firm hold. Non-native species are far more likely to do harm than native plants and animals, he argued, adding that the debate was “a phony controversy.”

Whether a species is viewed as native, however, often depends on when you arrived on the scene. Much of what Americans eat was originally imported: The horse, an icon of the American West, for example, was reintroduced by the Spanish thousands of years after the original North American horse became extinct. Several states list the honeybee as their state insect. But like many other state fish, insects and flowers, the bees are in fact immigrants.

In at least one case, a species that was long extinct in its native range was treated as an interloper when it finally returned home.

Beavers were common in Britain until they were hunted to extinction centuries ago. But when a group of the toothy dam builders took up residence along the River Tay in western Scotland several years ago, local farmers and fishermen greeted the animals with hostility, saying they posed a threat to farmland and salmon runs and were potential carriers of disease.

Scottish Land and Estates, an organization representing landowners, insisted that the beavers’ centuries of absence from Britain nullified their resident status, the Independent reported in 2010.

“It’s just silly,” Dr. Thompson said, of the reaction to the Tay beavers. “I don’t think we would have ended up in this ridiculous situation if we hadn’t been so bombarded by propaganda about invasive species.”

Often, he and others say, “invasion” is just another word for “change.” And the only thing that is certain is that more change is to come. Already, the flora and fauna of countries around the world are more homogeneous than they once were, as globalization has, accidentally or intentionally, moved exotic species from one place to another.

“From birds to plants to fish to mammals, there’s strong evidence that things are becoming more similar,” Dr. Olden said, likening the phenomenon to “the popping up of big-box retailers and the loss of mom-and-pop shops.”

As more species migrate, new quandaries are likely to arise. And as the human population increases, driving more animals and plants toward extinction, a species’ second home may be the only one it has.

In a paper published last month in the journal Conservation Biology, two scientists in California, Michael P. Marchetti and Tag Engstrom, describe the “paradox” of species that are under threat in their native range but are viewed as invasive in other places they have settled.

They include the Monterey pine, endangered in California and Mexico but treated as a pest in Australia and New Zealand, and the Barbary sheep, endangered in Morocco and other countries but running rampant in the Canary Islands and elsewhere.

“This is a challenge,” Dr. Olden said. “If we identify a plant or animal that might not be able to respond to climate change, do we roll the dice and intentionally move that species northward, or up in elevation?”


The Four Seasons

In areas between the polar and tropical regions, daylength, temperature, and rainfall change through the year. These changes give rise to the four seasons of spring, summer, autumn, and winter.

In spring, plants are in bloom and insects are more active. Click to enlarge.

Lengthening days and warming temperatures mark the end of winter. The warmth in the air melts snow, thaws lakes and rivers, and may trigger storms. With this new abundance of warmth and water, plants grow and bloom and insects begin to buzz and swarm. Many animals reproduce during spring because of the increase in greenery and swarming food.

As days continue to grow longer and temperatures grow hotter, spring heats up into the hot, stuffy days of summer. Summer is the time when the sun beams most directly at the earth under your feet. Many animals with breeding seasons will stop mating midsummer so that they can raise the last of their young before the hot summer temperatures fall to cooler autumn days.

Autumn is a season of preparation. As days shorten and temperatures drop, both plants and animals set up for winter. Deciduous trees drop their leaves and squirrels fatten up for hibernation. Cultures around the world celebrate autumn by harvesting their bountiful summer crops before winter comes.

With the surface only receiving indirect sunlight, winters in many temperate plates are characterized by freezing temperatures and very short daylengths. Most plants and animals prefer to avoid winter. Animals hibernate or migrate to warmer climates. Those that stick around avoid the cold by piling on thick layers of fur or fat. Many plants enter dormancy until spring arrives and the ground begins to thaw.

Additional images via Wikimedia Commons. "Acer japonicum Vitifolium JPG1fu" (autumn leaves) by Jean-Pol GRANDMONT.


Watch the video: S Jakubem v přírodě online - Holubářství - Závodní holubi s Miroslavem Ptáčkem (August 2022).