Adaptive radiation

Adaptive radiation
evolution

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ASSIGNMENT
SUBMITTED TO:
SIR ARSHAD
SUBMITTED BY:
HAFIZ M WASEEM
ROLL NO.
MCF1901171

PROGRAMME:
MSC ZOOLOGY
SHIFT:

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EVENING
SEMESTER:
2
ND

UNIVERSITY OF EDUCATION LAHORE

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Contents
1 Adaptive Radiation Definition: .....................................................................................................4
2 What is Adaptive Radiation? ........................................................................................................4
3 Adaptive Radiation Examples: ......................................................................................................5
4 Characteristic features of an adaptive radiation ............................................................................6
4.1 Common ancestry: ...............................................................................................................6
4.2 Phenotype-environment correlation: ....................................................................................7
4.3 Trait utility:..........................................................................................................................7
4.4 Rapid speciation: .................................................................................................................7
5 Types of Adaptive Radiation:........................................................................................................8
5.1 General adaptation: .............................................................................................................8
5.2 Environmental change: ........................................................................................................8
5.3 Archipelagoes. .....................................................................................................................8
6 Role of genetic drift: ....................................................................................................................9
7 Adaptive radiation favor increased complexity: .............................................................................9
8 Triggering adaptive radiation: ......................................................................................................9
8.1 The evolution of a key adaptation: ........................................................................................9
8.2 Release from competition/vacated niches: .......................................................................... 10
8.3 Specialization: ................................................................................................................... 10

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ADAPTIVE RADIATION
1 Adaptive Radiation Definition:
“Adaptive Radiation refers to the adaptation of an organism that enables them to spread successfully or
radiate into other environments.”
2 What is Adaptive Radiation?
According to Darwin’s Theory of Evolution, living organisms change their physical and anatomical
structures over a long period of time for better adaptations to the changing environment. The initiation
of the point of evolution was when organisms wanted to exploit a niche and they were not able to do so
with their existing body design or structural component. Organisms started to split and adapt various
versions for better survival. Adaptive radiation is the evolutionary process by which many species
originate from one species in an area and radiate to different species. The phenomenon of adaptive
radiation was first observed by Darwin when he travelled to a place called Galapagos Island. There he
observed that there were finches with different types of beaks. So, he concluded that all of these inches
radiated on the same island from a single ancestor Finch. All of these finches developed beaks according
to the kind of food available to them. Hence, they evolved from the conventional seed-eating finches to
vegetarian and insectivorous finches. They later came to be known as Darwin’s finches.

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3 Adaptive Radiation Examples:
Adaptive radiation explains the reason for biodiversity. The concept of adaptive radiation could be
simplified through the following example.
 Consider a family consisting of four children. They have the same parents and origin, grew under
the same circumstances and moved to different regions for a better opportunity. Now each one
of them has their own adaptation according to their lifestyle and place they stay. Here the
lineage splits and radiates different characteristics.

Adaptive Radiation
 Another example of adaptive radiation is the development of different Australian Marsupials
from a single ancestral stock in the Australian subcontinent. This explains divergent evolution
for the ancestral stock from which a number of species arise. But, if in a given geographical area,
several adaptive radiations take place for various species, it gives rise to convergent evolution.
 Marsupials are one of the most common examples of adaptive radiation. The marsupials have
diverged into different orders and species. Each order diversified from its order
Euaustralidelphia

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 Adaptive radiation refers to the evolution of ecological and morphological disparity within a
rapidly diversifying lineage. It is the diversification of an ancestral species into an array of new
species that occupy various ECOLOGICAL NICHES and that differ in traits used to exploit those
niches. Adaptive radiation includes the origination of both new species (speciation) and
phenotypic disparity. Archetypal examples of adaptive radiations include Darwin’s finches on the
Galápagos archipelago; silvers word plants on Hawaii; anole lizards on the islands of the
Caribbean; three spine stickleback fish in north temperate waters; and cichlid fishes in the East
Africa Great Lakes and in various tropical crater lakes. Adaptive radiations are also visible in the
FOSSIL record. For example, the CAMBRIAN EXPLOSION is considered an adaptive radiation.


Anoles lizard
4 Characteristic features of an adaptive radiation
An adaptive radiation is defined by four characteristic features, which are also used to detect instances of
adaptive radiations (see Schulte 2000):
4.1 Common ancestry:
Members of an adaptive radiation are characterized by their common ancestry, that is, all species of an
adaptive radiation go back to a single common ancestor. Common ancestry is not the same as monophyly,
as not all descendants of the common ancestor need to be included in the radiation.

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4.2 Phenotype-environment correlation:
In an adaptive radiation, there is a fit between the diverse phenotypes of the descendant species and the
divergent ENVIRONMENTS in which they live. For example, the body and limb size of Anoles lizards
matches the twig diameter in their habitat
4.3 Trait utility:
The morphological and/or physiological traits that differ between the descendant species of an adaptive
radiation are “useful” to exploit the respective ecological niche. For example, the different bills of
Darwin’s finches are useful for a particular food type.
4.4 Rapid speciation:
In an adaptive radiation, speciation is typically rapid. Speciation during adaptive radiation can be
allopatric, but is primarily parapatric or sympatric, as adaptive radiations are, in most cases, confined to a
certain geographic area.

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5 Types of Adaptive Radiation:
5.1 General adaptation:
A new type of adaptation allows a group to explode a new adaptive zone. Bird flight was such an
adaptation. Once the ability to fly was developed, a whole new adaptive zone was opened for exploitation
and radiation into that zone was rapid. The arctic tundra doesn't offer much protection and birds which lay
eggs on the tundra have to expend a lot of energy guarding them and attacking predators. A bird which
lives on a cliff face is protected from predators such as bear and fox. Price points out that there are more
than 1,500 species of bird lice, which "colonized" birds, then became parasitic, and radiated into the
different microhabitats on bird's bodies.
5.2 Environmental change:
There have been several changes in sea level during the Earth's history. During the Cambrian, more than
500 million years ago, the sea level rose, flooding continental shelves. This provided an opportunity for
radiation into this new environment.
5.3 Archipelagoes.
Islands and island groups are isolated habitats - a type of archipelago. (Another type of archipelago would
be a mountain isolated in the center of a barren dessert.) Because they are isolated from other habitats,
movement into them is a rare event. Typical of these environments is a rare colonization event, followed
by rapid divergent evolution. This occurs, because like exploitation of the air by birds, there is a lack of
predators and competing individuals and lots of vacant ecological niches. Radiation into archipelagoes
requires a diverse habitat to provide the ecological niches - It is unlikely that much adaptive radiation
would occur onto a barren island. Examples of adaptive radiation of archipelagoes include Darwin's
finches, Hawaiian honeycreepers and Hawaiian silvers words.
Adaptive radiation in Hawaiian silver words:

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6 Role of genetic drift:
Natural selection, using the raw material provided by mutation, seems to be the fundamental mechanism
driving adaptation to new habitats. However, some cases may involve other mechanisms, including
genetic drift. In particular, movement between islands may involve genetic drift because of the small
number of individuals which can move to a new island. However, radiation into many closely related
species is difficult to explain by genetic drift alone.
7 Adaptive radiation favor increased complexity:
It would seem that organisms become more complex with time. The average amount of complexity
increases. Gould has argued that this does not mean that evolution is directed towards increased
complexity but rather is just the consequence of a simple principle of mathematics: Imagine that one has a
simple organism which then radiates into different niches or adaptive zones. Random variation alone will
produce more complex and less complex organisms. But, since the complexity of the "ancestral"
organism is already very low, there is a limited range of organisms which could exist which would be less
complex. There are many variations which would be more complex! So the average complexity of
descendant increases, even just considering random variation. One does not have to propose some exotic
mechanism involving adaptation to account for increasing average complexity.
8 Triggering adaptive radiation:
An adaptive radiation generally means an event in which a lineage rapidly diversifies, with the newly
formed lineages evolving different adaptations. Different factors may trigger adaptive radiations, but each
is a response to an opportunity.
8.1 The evolution of a key adaptation:
A key adaptation usually means an adaptation that allows the organism to evolve to exploit a new niche or
resource. A key adaptation may open up many new niches to an organism and provide the opportunity for
an adaptive radiation. For example, beetle radiations may have been triggered by adaptations for feeding
on flowering plants.

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8.2 Release from competition/vacated niches:
Lineages that invade islands may give rise to adaptive radiations because the invaders are free from
competition with other species. On the mainland, other species may fill all the possible ecological niches,
making it impossible for a lineage to split into new forms and diversify. On an island, however, these
niches may be empty. Extinctions can also empty ecological niches and make an adaptive radiation
possible. For example, open niches vacated by dinosaur extinctions may have allowed mammals to
radiate into these positions in the terrestrial food web. The extinction of the dinosaurs at the end of the
Cretaceous may have allowed mammal radiation.


8.3 Specialization:
Specialization may subdivide a single niche into many new niches. For example, cichlid fishes have
diversified in East African lakes into more than 600 species. This diversification may have been possible
because different fish lineages evolved to take advantage of different foods (including insects, algae,
mollusks, small fish, large fish, other fishes' scales, and even other fishes' eyes!).
Diverse Cichlid Fishes of Lake Malawi

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Reference: