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1/12/17
Through natural selection, animals have modified both their behavioral and physical
characteristics to better equip themselves to meet the demands of their environment. An
organisms ability to adapt is key to its survival and may give arise to new species. Through
continual adaptations you may get the formation of new species. This process of species
formation is called speciation. Species are defined as members of populations that actually or
potentially interbreed in nature.
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Species may have adapted to reduce competition for food. Koalas occupy a unique niche in that they consume
eucalyptus leaves which are poisonous to most other animals. Giraffes eat the leaves of the acacia tree that other animals
can not reach. In turn, the acacia avoids being eaten by growing up tall first and then spreading out with its leaves like
an umbrella. The acacia will also exudes a bitter chemical through its leaves as it it eaten. In response, the giraffe
moves on. The tree is not overgrazed and is available as a food source later.
Flamingo’s beaks are adapted for filter feeding. The sharply downward bent bill is held upside down in the water and
swept back and forth. The fleshy tongue pumps water through comb-like filtering structures lining the top half of their
bill, filtering out the minute organisms. The form of the beak allows them to feed without getting the feathers wet.
An adaptation may be a defense response to protect themselves and their young from predators, pests and weather. This
would include things as protective coloration or eyes on the side of the head for prey animals. Having eyes on the side
of their head allow these animals to see everywhere except directly behind them. With ducks and zebras, you may have
individuals facing in both directions to spot predators from all directions. Ducks can have one side of their brain sleep
while the other side remains awake watching for predators.
Animals must be able to move throughout their habitat and have locomotion adaptations. Feet have morphed into fins
for swimming or arms that have evolved into wings for flying, legs have been made longer for jumping or running
faster.
Adaptations may relate to reproduction or the perpetuation of species. Individuals must recognize their own species,
attract a mate and raise young. Cats (excluding lions) are solitary that occupy different but overlapping territories. Both
sexes scent mark their territories. The male constantly checks these scent messages as he roams his territory. When he
encounters an estrous female, he will track her down. A non-estrous female may shun him.
Marsupials, like this koala, lack a true placenta and are born in a minimally developed state. Newborns climb to the
pouch and latch themselves onto a teat and remain while they continue to develop and are ready to come out of the
pouch.
In the kangaroo, the mother mates shortly after giving birth and the fertilized embryo develops into a blastocyst of 85 100 cells, and then becomes dormant. While the female is nursing an offspring (joey) in the pouch, the blastocyst
remains dormant. When the joey stops nursing due to weaning or death the blastocyst resumes development. A female
may have three offspring simultaneously in different stages of development; the blastocyst, the joey in the pouch and a
partially weaned offspring (referred to as young-at-foot). The female produces milk for the joey and a different, richer
one for the young at foot.
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An adaptation may be an external physical feature such as coloration. Color or patterns can be used as camouflage
or for identification. The lighter coloring of the kangaroo may keep it cooler in the heat of day in Australia.
An adaptation of size or shape enables it to reach food such as the long neck of the giraffe allows it to eat leaves on
the taller trees. A larger body size can keep you warmer in a cool environment. Otters and penguins have very
streamlined bodies for their water environments. The male of a species might be larger than the female and the larger
size may help him compete for the right to mate with a certain female.
When you are at the zoo look at the various species and observe their features such as eyes, hands, tongues, ears or
toes. These may serve a special purpose. The feature might give them an advantage when they move or when they
are hunting for prey. It might help them locate food or sense predators or a mate. Be observant out there.
The adaptation might not be something you can see but is beneficial to it’s survival. It may be an internal
physiological adaptation. It might be a four-chambered stomach that the ruminants have adapted to ease digestion
from their herbivorous diet. Giraffes, antelopes and cows have this adaptation. Birds have adapted a light skeleton
for flying, Scimitar-horned Oryx are able tolerate higher body temps and have specialized kidneys to reduce water
loss.
Lastly adaptations can be behavioral. You might see social behaviors of animals living in groups or alone. You
might see animals defending their territory or in the gorilla community where the male is dominant in a social
grouping of females and young. You might see animals resting during the day because they are nocturnal and do their
feeding at night. The zebras and rhinos may roll in the mud to protect their skin from sun and insects.
These are only a few of the many adaptations that animals have. The more you learn about an animal’s adaptations
the more amazing they will become to you and the more you will want to learn about an animal or plant.
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Camouflage is an excellent example of a external physical characteristic. Coloring helps an animal
blend into its environment and avoid detection. A dry, savanna animal will be tan or brown, a wet,
rainforest animal will be glossy green, and so forth. Coloring may also have a physiological benefit;
lighter colors reflect more of the sun’s radiation than a darker one and thus helps them to remain cool.
Other animals use textures and patterns to help them to blend in; the patterns may resemble shadows
and windblown vegetation. Other patterns may appear confusing for predators and make it hard to find
an individual in a group.
Other animals have countershading camouflage where they have dark backs and light underneath.
Many birds and ocean fish have this countershading. The magellanic penguins at the zoo are no
exception. From above the penguin look like the ocean floor and from below, like the sun or bright
water surface. Another example of countershading is seen in koalas, who spend all their time sitting in
a tree and have whitish fur below and darker fur along their backs and head.
Coloring can be a warning signal to predators to stay away (aposematism). In the case of the poison
dart frog, their coloring warns potential predators that they are poisonous to eat.
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After each animal is listed an adaptation. Select if it is a physical or behavioral adaptation.
A giraffe’s 18 inch prehensile tongue is an example of an external physical adaptation for
grabbing leaves from tall trees.
A kangaroo licking its palms is a behavioral adaptation for staying cool.
Rhinos rolling in mud to is another behavioral adaptation to protect their skin from sun and
insects.
Oryx’s ability to increase their body temperatures and decrease their metabolic rate is an internal
physiological adaptation. This ability allows them to suppress sweating and minimize their
panting, thus conserving water. Oryx are able to raise their body temps to 116 degrees Fahrenheit
without sweating.
Producing a shrill alarm cry by a meerkat is a behavioral adaptation that warns the others to seek
the burrows for safety. Another behavioral adaptation is they take turns as sentry while the others
feed.
The bright colors of the peacock versus the dull colors of the peahen is a external physical feature
but the displaying of the colorful tail feathers of the male is a behavioral adaptation to attract a
female.
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In these pictures you can see the three species of Zebra: the plains zebra, the Grévy's zebra and the
mountain zebra. What is the mechanism where different species arise?
Speciation happens when a subset gets isolated from the rest of the population and don’t interbreed any
more. One population may be developing traits in response to environmental characteristics that are
present only for their population, passing on features distinctly different than those of the first population.
This reaches a point where the two populations are different enough that they can no longer reproduce with
each other, and a new species evolves. This was the case of the three species of zebra who occupy
locations in Africa.
This is a slow process which usually involves development of subspecies first. Subspecies may never
progress to full species in some cases.
If one looks at the geographic distribution of related species, one can see evidence of speciation. Islands
and continents separated over time show distinct differences within and among species.
Madagascar is a prime example of having a large number of endemic species that can be found no where
else in the world. The most likely explanation for the existence of Madagascar’s mostly unique biotic
environment is that the life forms have been evolving in isolation from the rest of the world for millions of
years.
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Adaptive Radiation is the evolution from one kind of organism to several divergent forms, each
specialized to fit a distinct and diverse way of life. Examples came be seen in Darwin’s finches or in these
African cichlids. Adaptive radiations often occur as a result of an organism arising in an environment with
unoccupied niches, such as a newly formed lake or isolated island chain. The colonizing population may
diversify rapidly to take advantage of all possible niches.
Another excellent example of adaptive radiation is lemurs in Madagascar. In the absence of competition
from monkeys and apes, many types of lemurs developed with over 40 species still in existence today
despite loss of number due to human hunting, habitat loss, etc.
Adaptive radiations commonly follow mass extinctions. Today there is good evidence that a major
meteorite impact occurred at the end of the Cretaceous Period, leading to the extinction of non-avian
dinosaurs resulting in the rise of mammals. Before this time, mammals were barely existing in the shadow
if the dinosaurs for millions of years. When the dinosaurs went extinct, these mammals blossomed into the
wide diversity of species we see today. Which was good for us as humans.
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Lets discuss some mechanisms that may prevent breeding between two species.
Geographic isolation happens when species occur in different areas, and are often separated by
barriers. Madagascar's lemurs were isolated from evolutionary changes of the rest of the world and
radiated into the large island's many niches without much competition or predation.
Ecological isolation occurs when species occupy different habitats. They do not encounter individuals
of other species with different ecological preferences. The lion and tiger overlapped in India until 150
years ago, but the lion lived in open grassland and the tiger in forest. Consequently, the two species did
not hybridize in nature.
Temporal isolation occurs when species breed at different times. This may be different times of the day
or different seasons. In North America, five frog species of the genus Rana differ in the time of their
peak breeding activity.
Behavioral isolation is when species engage in distinct courtship and mating rituals. Individuals of
different species may meet, but one does not recognize any sexual cues that may be given.
Mechanical isolation occurs when interbreeding is prevented by structural or molecular blockage of the
formation of the zygote. Mechanisms include the inability of the sperm to bind to the egg in animals, or
the female reproductive organ of a plant preventing the wrong pollinator from landing.
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Convergent evolution describes the independent evolution of similar features in unrelated species; through natural
similar traits or adaptations have resulted from species adapting to similar environments or ecological niches. In
this example here, sharks and dolphins have independently developed streamlined bodies allowing for rapid
movement through their water environment. Another example would be a bat’s wing versus a bird wing; both are
different approaches to flight.
Within our own Children’s Zoo the meerkats and prairie dogs both have communal underground lifestyle but
meerkats are carnivorous, from Africa and are in the Family Carnivora, whereas the prairie dogs are herbivorous,
from North America and are in the Family Rodentia.
When you are at the Magellenic Penguin exhibit, also look at the North American River Otters. Here are two
animals with very streamlined bodies for their watery environments but the penguin is a bird covered with feathers
and the otter is a mammal covered by dense fur.
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Coevolution is the evolutionary change of one species triggered by the interaction with another species. How can the
evolution of one species affect the evolution of another? Every form of life on Earth interacts over time with other
organisms, as well as with its physical environment. Predator/prey relationships are a classic example of how two
species influence each other.
Predators and prey are involved in an endless competitive tussle, a “cat-and-mouse” game, which has giving rise to
physical and behavioral adaptations, resulting in coevolution of both the predator and the prey. Predators are under
strong selection to evolve more efficient hunting strategies. In response, the prey is under strong natural selection to
evolve better predator evasion techniques. Predators and prey are constantly adapting, evolving, and proliferating not
merely to gain reproductive advantage, but also simply to survive while pitted against ever-evolving opposing
organisms in an ever-changing environment.
In general, when we look for examples of adaptation that have evolved between predators and prey, we tend to find
there's a wider or more diverse range of prey adaptations to escape capture than there are predator adaptations to
enhance capture. If a predator doesn’t adapt to a changing prey, they just lose a meal, whereas, if the prey doesn’t adapt
they die. Predator’s typically eat a wide range of prey items; evolving a specific response that improves the capture
over one prey type, might compromise its ability to capture another prey type. Prey typically have shorter generation
times allowing them to adapt more quickly to better hunting strategies of the predators.
Prey defense mechanisms might include sheltering in safe havens (i.e. burrows), better camouflage, prevent
recognition through mimicry, cryptic and warning coloration, early detection of predator, or active defense (i.e spines,
toxins). A predators counter adaptations might involve improved prey detection, learning (avoid being tricked),
secretive approach or subduing skills (ie. Meerkat preying on a scorpion) or immunity to toxin. Over evolutionary
time, when a predator and prey are constantly adapting and improving their strategy, the net result might not be an
improved success for either predator or prey. This is due to the constant shifting nature of their relationship.
One such predator-prey relationship exists between between wolves and caribou. Wolves hunt caribou, chasing them
down to capture them. The slower caribou are more likely to be preyed upon, leaving the faster individuals to
reproduce. The resulting faster offspring will be even more difficult for the wolves to catch, and only the fastest wolves
(or perhaps the wolves who are genetically capable of devising strategies to hunt very fast prey) will get enough food
to survive.
Can you think of another example of relationship among our zoo animals? Perhaps an animal from Australia that
consumes only eucalyptus. (Answer: Koala eat only eucalyptus that are toxic to most animals)
As we will see later in our plants and animal module, co-evolution is especially seen among plants and their
pollinators. A number of species of flowering plants have coevolved with specific pollinators (i.e. insects, bats, birds).
The pollinator gets a reward such as nectar for pollinating the plant.
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The English Peppered Moth is typically a mottled white with black making them well-camouflaged against
lichens on tree trunks. Occasionally a very few moths have a genetic mutation which causes them to be all
black. Black moths resting on light-colored, speckled lichens are not very well camouflaged, and so are easy
prey for any moth-eating birds.
With the Industrial Revolution, many factories and homes started burning coal. This created a lot of black soot
and pollution which killed the lichens and settled out everywhere, turning the city tree trunks black. With the
settling of the soot, the population of peppered moths was found to contain more black moths. This is an
example of:
A. Extinction
B. Adaptive Radiation
C. Natural Selection
D. Convergent Evolution
The correct answer if C. Natural Selection
The black soot on the trees enabled the occasional black moths living in the cities to be well-camouflaged so
they could live long enough to reproduce, while the normal speckled moths were now more visible and they
were gobbled up. The English Peppered Moth adapted to its new environment.
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Definitions:
Species: an individual belonging to a group of organisms having common characteristics and are capable of mating
with one another to produce fertile offspring.
Speciation: the process of species formation. The isolation of populations results in development of different gene
pools and resultant different traits. Islands and continents separated over time show distinct differences within and
among species as a result. Shift of continents over time results in distinctly different types of animals/plants on
various continents and islands. Reasons two species will not breed can be geographical, ecological, temporal,
behavioral or mechanical.
Adaptive radiation: process in which organisms diversify rapidly into a multitude of new forms, particularly when a
change in the environment makes new resources available, creates new challenges and opens environmental niches
Convergent evolution: unrelated species can develop similar traits as the process of natural selection results in the
same solution to a similar problem.
Coevolution: The process of reciprocal evolutionary change that occurs between pairs of species or among groups of
species as they interact with one another; two (or more) species reciprocally affect each other's evolution; the
evolutionary change of one species triggered by interaction with another species.
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