Why do different kinds of environments change the anatomies, appearances, biology and/or physiologies of the wild animals and/or plants after migrating?

Krishna: Different environments exert different selective pressures on populations of animals.

Evolutionary adaptation, or simply adaptation, is the adjustment of organisms to their environment in order to improve their chances at survival in that environment.

Every organism has a unique ecosystem within which it lives. This ecosystem is its natural habitat. This is where the basic needs of the organism to survive are met: food, water, shelter from the weather and place to breed its young. All organisms need to adapt to their habitat to be able to survive. This means adapting to be able to survive the climatic conditions of the ecosystem, predators, and other species that compete for the same food and space. An adaptation is a modification or change in the organism's body or behaviour that helps it to survive.

An animal may adapt to its habitat in different ways. It may be a physical or structural adaptation, just as the limbs of birds have modified into wings or the way the cheetah is shaped for running at a fast speed.

It may be in the way the body works in circulating and respiration, for instance the gills that fish have enable them to breathe in water. Or it may be the way the animal behaves whether it is hunting for food, or running fast to avoid predators or migrating to other places for food or survival.

Animals in the wild can only live in places they are adapted to. They must have the right kind of habitat where they can find the food and space they need.

Let me give an example. Earlier Africans had lots of melanin in their skin. This is to protect from UV rays of the Sun near the equator.

Populations of Homo sapiens migrated to the Levant and to Europe between 130,000 and 115,000 years ago, and possibly in earlier waves as early as 185,000 years ago (1).

When human beings migrated from Africa to northern parts of the globe, they didn’t need so much protection from the sun. Moreover with limited exposure to Sunlight, they couldn’t produce D vitamin naturally. So among scientists studying human evolution, it has been almost universally assumed that the need to make more vitamin D at Northern latitudes drove genetic mutations that reduce production of the pigment melanin, the main determinant of skin tone.

However, dark skin people can produce D vitamin as efficiently as lighter skin people. So the main reason is -

Pigmented skin provides a better skin barrier, which according to new research was critically important for protection against dehydration and infections among ancestral humans living in sub-Saharan Africa. But the need for pigment to provide this extra protection waned as modern human populations migrated northward over the past 60,000 years or so (2). Then why did the skin become light ? Once human populations migrated northward, away from the tropical onslaught of UVB, pigment was gradually lost in service of metabolic conservation. The body will not waste precious energy and proteins to make proteins that it no longer needs.

Various skin tones due to adaptation
(Image source: Shutterstock)

Any number of characteristics can vary among individuals of a given species — some may be larger, hairier, fight off infections better, or have smaller ears. These characteristics are largely determined by their genes, which are passed down from their parents and subsequently passed down to their own offspring.

Some of these characteristics, or traits, provide competitive advantages like speed, strength, or attractiveness necessary for their survival and reproduction. If those traits are particularly helpful, individuals with those traits will produce more offspring than those without. Over generations, the number of individuals with that advantageous trait, or adaptation, will increase until it becomes a general attribute of the species.

Adaptations that develop in response to one challenge in the surroundings sometimes help with or become co-opted for another. Feathers were probably first adaptations for tactile sense or regulating temperature. Later, feathers became longer and stiffer, allowing for gliding and then for flight. Such traits are called exaptations (a feature that performs a function but that was not produced by natural selection for its current use).

Some traits, on the other hand, lose their function when other adaptations become more important or when the environment changes. Evidence of these traits remain in a vestigial form — reduced or functionless. Whales and dolphins have vestigial leg bones, the remains of an adaptation (legs) that their ancestors used to walk.

Adaptations often develop in response to a change in the organisms’ habitat.

Sometimes, an adaptation or set of adaptations develops that splits one species into two. This process is known as speciation.

Organisms sometimes adapt with and to other organisms. This is called coadaptation. Certain flowers produce nectar to appeal to hummingbirds. Hummingbirds, in turn, have adapted long, thin beaks to extract the nectar from certain flowers. When a hummingbird goes to feed, it inadvertently picks up pollen from the anthers of the flowers, which is deposited on the stigma of the next flowers it visits. In this relationship, the hummingbird gets food, while the plant’s pollen is distributed. The coadaptation is beneficial to both organisms.

Did you know that animals camouflage themselves so they can adapt to their environment? Adaptation can protect animals from predators or from harsh weather. Many birds can hide in the tall grass and weeds and insects can change their colour to blend into the surroundings. This makes it difficult for predators to seek them out for food.

Some animals, like the apple snail, can survive in different ecosystems- from swamps, ditches and ponds to lakes and rivers. It has a lung/gills combination that reflects its adaptation to habitats with oxygen poor water. This is often the case in swamps and shallow waters.

Mimicry is another type of coadaptation. In mimicry, one organism has adapted to resemble another. The harmless king snake (sometimes called a milk snake) has adapted a colour pattern that resembles the deadly coral snake. This mimicry keeps predators away from the king snake.

The mimic octopus (Thaumoctopus mimicus) has behavioural as well as structural adaptations. This species of octopus can copy the look and movements of other animals, such as sea snakes, flatfish, jellyfish, and shrimp.

This gives a tremendous advantage to octopus to survive in dangerous situations.

Climate change could be physically altering a variety of species across the planet, as individuals change their shape to suit the fluctuating temperatures across the world.Animals are now 'shapeshifting' as the planet warms, as limbs, ears and beaks change size to adapt to rising temperatures. While these adaptations may alleviate overheating in the short term, these species can't adapt forever especially if the time to adapt is very short and environmental change is very fast like it is happening now.

Features such as tails, legs and ears are changing to provide different levels of heat exchange with the environment (3).

At around the same time that Charles Darwin was publishing On the Origin of Species in 1859, other scientists were also investigating how species varied around the world.

One of these was Carl Bergmann, whose eponymous rule states that within a group of organisms living across a large range, bigger species will be found in cooler environments. This is because by minimising their surface area to volume ratio they reduce heat loss, while the opposite occurs in warmer environments. For instance the largest species of penguin, the emperor penguin, lives in Antarctica, while the smaller Humboldt penguins are found in South America.

Meanwhile, Joel Asaph Allen formulated his own rule, which describes how organisms adapted to warmer environments have larger limbs and other body parts in order to maximise their heat loss by increasing surface area, such as the larger ears on African elephants when compared to Asian elephants.

With temperatures set to rise over the coming century, the researchers behind this review looked at a range of studies to see whether adaptations induced by climate change would follow Allen's rule.

They found that birds in particular are likely to see significant changes as a result of a warming planet. One study found that 58% of all bird species follow Allen's rule when it comes to the size of their bill, which is used to regulate their body temperature.

Australian parrots, for instance, have seen up to a 10% increase in their bill surface area since 1871, with the amount of increase predicted from the average summer temperatures in the years before the specimens were collected.

Aside from birds, evidence from a variety of studies demonstrates that bats change their wing size in response to climate change, while mice, pigs and shrews have longer tails in response to changes in temperature.

While the changes occur across a range of species, they're not universal across every animal considered. These adaptations may be beneficial in the short to medium term, but as the climate continues to change, animals cannot continually adapt. At some point, the trade-off won't be beneficial anymore, which could lead to population declines and even extinction.

So any organism has to adapt to its environment in order to survive, get suitable food, reproduce and flourish, feel comfort, and not waste precious energy and resources. If it is developed to face an environment in the beginning, it has to change when the situation changes like after migrating. If an animal migrates from a warmer environment to a cooler one, it has to adapt to the weather by storing food in their body and protecting themselves from the cold with thick furs. Otherwise it perishes.

Adapt or perish. That is what Nature demands of living beings. And that is exactly what they do!

Footnotes:

1. Early human migrations - Wikipedia
2. In Human Evolution, Changes in Skin’s Barrier Set Northern European...
3. Animals 'shapeshifting' to adapt to rising temperatures

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