An-najah national university Master ecology Evolution and biodiversity Dr. Raed al- kawni By Maha...

$: An-najah national university Master ecology Evolution and biodiversity Dr. Raed al- kawni By Maha abdel raof nasir 2014\2015.$
An-najah national universityMaster ecology

Evolution and biodiversityDr. Raed al- kawni

By

Maha abdel raof nasir2014\2015

Introduction to the origion of life

what is Evolution

.

What is evolution

It is the biological model for the history of life on Earth.. Evolution refers to descent with modification. Small modifications occur at the genetic level (in DNA) with each generation, and these genetic changes can affect how the creature interacts with its environment

What is evolution

Over time, accumulation of these genetic changes can alter the characteristics of the whole population, and a new species appears. Major changes in life forms take place by the same mechanism but over even longer periods of time. All life today can be traced back to a common ancestor some 3.85 billion years ago

What is evolution

the modifications fundamentally alter the characteristics of the whole population. When the population accumulates a substantial number of changes and conditions are right, a new species appear

What is evolution

The ability that animals and plants have to develop differently in different conditions is known as plasticity. It’s possible that plasticity opens the door to new paths that evolution can then take. When organisms find themselves in a new environment, they develop in a way that helps them cope with their new surroundings

What is evolution

Evolution as a Game

Biological evolution is so different from other processes that it is worthwhile to spend some

extra time exploring this idea.

There are no simple rules that species must follow to win or to stay in the game of life.

Complexity is a feature of evolution.

State your opinion?

To realise biological diversity it is important most to undersatnd how the diversity has

changed in the past over the earths history.

During most of earths history , evolution seems to have proceeded on average much more slowly.

What is evolution

The ecological theater and the evolutionary play

Ecologist huntchinsone reffered to this interaction in the title of one of his book

“the ecological theater and the evolutionary play”

The ecological theater and the evolutionary play

Here the ecological situation ( the condition of the environment ) is the theater within which natural selection occurs, and natural selection results in a story of evolution played out in that theater over the history of life on earth

How do we know about the history of

evolution?

How do we know about the history of evolution

1 The Fossil RecordThe most direct evidence that evolution has occurred is found in the fossil record. Today we have a far more complete understanding of this record than was available in Darwin’s time. Fossils are the preserved remains of onceliving organisms. Fossils are created when three events occur..


1 The Fossil RecordFirst, the organism must become buried in sediment; then, the calcium in bone or other hard tissue must mineralize; and, finally, the surrounding sediment must eventually harden to form rock. The process of fossilization probably occurs rarely. Usually, animal or plant remains will decay or be scavenged before the process can begin. In addition, many fossils occur in rocks that are inaccessible to scientists.


1 The Fossil RecordWhen they do become available, they are often destroyed by erosion and other natural processes before they can be collected. As a result, only a fraction of the species that have ever existed (estimated by some to be as many as 500 million) are known from fossils. Nonetheless, the fossils that have been discovered are sufficient to provide detailed information on the course of evolution through time

Earliest form of life

the course of evolution through timein part from the study of fossils

1 -microorganisms 3.5 billion years old2 -bacteria for the next 2 billion years

molluscs - 3- eukaryotic cells4 -multicellular life –jellyfish 600 million years

(Camberian period )remained in the oceans5 - Plants evolved to live on land100 years later

((silurian period

the course of evolution through time

6 -invertebrates

7 -insects8 - fishes

9 - birds10 – Amphibia and reptiles 11- mammals

the course of evolution through time

What caused the evolution of multicellular

Organisms؟

Microorganisms and bacteria greatly changed the global environment, specially by altering

the chemistry of the atmosphere

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Repeated glaciations and de-glaciations raised and lowered sea level causing expansion declines of swamps throughout the Carboniferous Period. The expansion of swampy wetlands with their rich plant life extracted vast amounts of CO2 from the atmosphere. amount of carbon was extracted from the atmosphere to form coal deposits in the Carboniferous Period.

carboniferous

Note the expansion of life on land in the carboniferous, including early reptiles and in particular, extensive land plants in swamps.

Also note that the expansion of these life forms occurred following another major extinction even in the middle carboniferous.

Biological evolution and diversity

How did it all come about?

Before modern science, the diversity of life and the adaptation of living things to their environment seemed too amazing to have

come about by chance.

Biodiversity as a result of evolution

Early theories on the origins of life

1 spontaneous generation microorganisms reproduce from non living

materials.

aristotle - Ancient greek BC 384- 322

Early theories on the origins of life 1 spontaneous generation

the hypothetical process by which living organisms develop from nonliving matter to explain the origin of life. According to this theory, pieces of cheese and bread wrapped in rags and left in a dark corner, for example, were thus thought to produce mice.


•By the 18th century it had become obvious that higher organisms could not be produced by nonliving material. The origin of microorganisms such as bacteria, however, was not fully determined until Louis Pasteur proved in the 19th century that there is no spontenous generation .


2 THE contribution of geology

William smith At the end of the eighteenth centuryRelative dating of rocks using fossils Smith, who had little formal education, traveled throughout England as a surveyor and spent six years supervising the digging of the Somerset Canal in southwestern England. Along the way he became well acquainted with the rock through which he cut the canals.


2 THE contribution of geologyHe was surprised to find that the fossils in the layers often were arranged in the same distinctive order from the bottom to the top of the rocks. And as he traveled across England, he discovered the same sequences of fossils in rock

layers .

Early theories on the origins of life2 THE contribution of geology

Early theories on the origins of life2 THE contribution of geology

Each type of animal, he realized, had a widespread existence for a particular span of time, a span that partially overlapped with that of other animals. That made it possible for Smith to recognize the order in which rocks had .been formed throughout

Early theories on the origins of life3 The contribution of Taxonomy

If the taxonomic system is to reflect the totality of similarities and differences among organisms,

it must have an evolutionary foundation.. .


Similarities due to evolutionary parallelism provide some evidence of relationship, because the greater the genetic and phenetic similarity between two groups, the greater the likelihood that they will produce similar mutations, have similar evolutionary potentialities, and undergo .parallel evolutionary change


A workable taxonomic system can provide only a muddy reflection of phylogeny. If the evolutionary diversification of any large taxonomic group were profoundly influenced by the nature of the supply of mutations, if the supply of mutations differed in the various

subgroups----,


If the fixation of many of these mutations did not depend on survival value, and if the evolutionary barriers between different ecologic niches or adaptive zones were in general low, then we might expect that group to show ecological and adaptive correlations most commonly at the lower taxonomic levels such as genera and species

Early theories on the origins of life3 The contribution of Taxonomywhereas the higher taxa would tend to embrace a wide array of ecological types. These ecologically varied higher taxa would tend to be characterized in large part by features of doubtful adaptive significance, and the critical taxonomic characters for many of them would be so beset by exceptions that the recognition, characterization, and definition of the groups

would often be difficult .


•The taxonomic pattern of the angiosperms, especially the dicotyledons, is precisely that which would be expected under the foregoing set of postulates.

The evolution of complex organism


Carl Linnaeus (1707-1778)For Linnaeus, species of organisms were real entities, which could be grouped into higher categories called genera (singular, genus). By itself, this was nothing new; since Aristotle, biologists had used the word genus for a group of similar organisms, and then sought to define the differentio specifica -- the specific difference of each type of organism. But opinion varied on how genera should be

grouped .


Naturalists of the day often used arbitrary criteria to group organisms, placing all domestic animals or all water animals together. Part of Linnaeus' innovation was the grouping of genera into higher taxa that were also based on shared similarities. In Linnaeus's original system, genera were grouped into orders, orders into classes, and classes into

kingdoms ..


Thus the kingdom Animalia contained the class Vertebrata, which contained the order Primates, which contained the genus Homo with the species sapiens -- humanity. Later biologists added additional ranks between these to express additional levels of similarity.

Modern taxonomy

Five-Kingdom Model

American ecologist Robert Whittaker created a five-kingdom model that accounted for prokaryote and eukaryote distinctions. In this schemata, all prokaryotes were placed in the kingdom Monera. The remaining eukaryotes were separated by differences mostly in structure. Plants and animals were easily

separated into their own kingdoms .

Evolution of plants

Modern taxonomy

Five-Kingdom Model

It was decided that because fungi were neither plant nor animal but subsisted by decaying or decomposing once-living matter, they also become their own kingdom. Everything else was clumped into the kingdom Protista.

Modern taxonomy

Five-Kingdom ModelThe protists included all eukaryotes that did not clearly fit into the plant, animals, or fungi kingdoms. With the advent of sophisticated collecting and microscopy techniques, the question arose as to where the “new” types of bacteria belong

Modern taxonomyMain taxonomic ranks

LatinEnglish

regiodomain

regnumkingdom

phylumdivisiophylum (in zoology)division (in botany)

classisclass

ordoorder

familiafamily

genusgenus

speciesspecies

codes.

Eighteenth century theories

BuffonLate in the 18th century, a small number of European

scientists began to quietly suggest that life forms are not fixed. The wealthy French mathematician and naturalist, George Louis Leclerc, Comte de Buffon,

actually said that living things do change through time .


BuffonHe speculated that this was somehow a result of influences from the environment or even chance. He believed that the earth must be much older than 6000 years. In 1774, in fact, he speculated that the earth must be at least 75,000 years old. He also suggested that humans and apes are related.


LamarckLamarck believed that microscopic organisms appear spontaneously from inanimate materials and then transmute, or evolve, gradually and progressively into more complex forms through a constant striving for

perfection .


lamarkThe ultimate product of this goal-oriented evolution was thought by Lamarck to be humans. He believed that evolution was mostly due to the inheritance of acquired characteristics as creatures adapted to their

environments..


lamarkThat is, he believed that evolution occurs when an organism uses a body part in such a way that it is altered during its lifetime and this change is then inherited by its offspring. For example, Lamarck thought that giraffes evolved their long necks by each generation stretching further to get leaves in trees and that this

change in body shape was then inherited .


LamarkLikewise, he believed that wading birds, such as herons and egrets, evolved their long legs by stretching them to remain dry. Lamarck also believed that creatures could develop new organs or change the structure and function of old ones as a result of their use or disuse

Ninteenth century theories

DarwinDarwin came to understand that any population consists of individuals that are all slightly different from one another. Those individuals having a variation that gives them an advantage in staying alive long enough to successfully reproduce are the ones that pass on their traits

more frequently to the next generation .


DarwinSubsequently, their traits become more common and the population evolves. Darwin

called this "descent with modification".


DarwinThe Beaks of Darwin’s Finches

Darwin’s finches are a classic example of evolution by natural selection. Darwin collected 31 specimens of finch from three islands when he visited the Galápagos Islands off the coast of

Ecuador in 1835 .


DarwinDarwin, not an expert on birds, had trouble identifying the specimens, believing by examining their bills that his collection contained wrens, “grossbeaks,” and blackbirds. You can see Darwin’s sketches of four of these birds in the next figure.


Darwinpagos finches provide an excellent example of this process. Among the birds that ended up in arid environments, the ones with beaks better suited for eating cactus got more food. As a

result, they were in better condition to mate .


DarwinSimilarly, those with beak shapes that were better suited to getting nectar from flowers or eating hard seeds in other environments were at an advantage there. In a very real sense, nature selected the best adapted varieties to survive and to reproduce. This process has come to be known as natural selection.


DarwinDarwin did not believe that the environment was producing the variation within the finch populations. He correctly thought that the variation already existed and that nature just selected for the most suitable beak shape and against less

useful ones..


DarwinPeppered Moths and Industrial Melanism When the environment changes, natural selection often may favor new traits in a species. The example of the Darwin’s finches clearly indicates how natural variation can lead to evolutionary change. Humans are greatly altering the environment in many ways; we should not be surprised to see organisms attempting to adapt to these new conditions. One classic example concerns the peppered moth,


DarwinBiston betularia. Until the mid-nineteenth century, almost every individual of this species captured in Great Britain had light-colored wings with black specklings (hence the name “peppered” moth). From that time on, individual with dark-colored wings increased in frequency in the moth populations near industrialized centers until they

made up almost 100% of these populations .


DarwinBlack individuals had a dominant allele that was present but very rare in populations before 1850. Biologists soon noticed that in industrialized regions where the dark moths were common,the tree trunks were darkened almost black by the soot of pollution.


DarwinDark moths were much less conspicuous resting on them than were light moths. In addition, the air pollution that was spreading in the industrialized regions had killed many of the light-colored lichens on tree trunks,

making the trunks darker

Natural selection ".Natural selection acts to preserve and

accumulate minor advantageous genetic mutations. Suppose a member of a species developed a functional advantage (it grew wings and learned to fly). Its offspring would inherit that advantage and pass it on to their offspring. The inferior (disadvantaged) members of the same species would gradually die out, leaving only the superior

(advantaged) members of the species .

Natural selection

Natural selection is the preservation of a functional advantage that enables a species to compete better in the wild. Natural selection is the naturalistic equivalent to domestic breeding. Over the centuries, human breeders have produced dramatic changes in domestic animal populations by selecting individuals to

breed .

Natural selection

Breeders eliminate undesirable traits gradually over time. Similarly, natural selection eliminates inferior species gradually over time.

Darwin's Theory of Evolution - Slowly But Surely...

Darwin's theory

Summary of Darwin's theory

Darwin's theory of evolution is based on key facts and the inferences drawn from them, which biologist Ernst Mayr summarised as

-Every species is fertile enough that if all offspring survived to reproduce the population would grow (fact).

-Despite periodic fluctuations, populations remain roughly the same size (fact).

Darwin's theory

Summary of Darwin's theory - Resources such as food are limited and are

relatively stable over time (fact).

- A struggle for survival exist.

- Individuals in a population vary significantly

from one another (fact) .

- Much of this variation is inheritable (fact).

Darwin's theory

Darwin - Individuals less suited to the environment are

less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their inheritable traits to future generations, which produces the process of natural selection (inference).

Darwin's theory

DarwinThis slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species

(inference) .

Darwin's theory

Biological evolution

refers to-----------------------------------------------------------

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Darwin's theory

The change In inherited charachateristic of a population from generation to generation.

Biological diversity is one of the features that distinguish life from everything else in the universe.

Darwin's theory

Is Evolution a Theory?

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Theory of evolution

Evolution is a scientific theory that was proposed

by Charles Darwin .

Theory of evolution

Theory gives explanations and predictions for naturally occurring phenomena based on observations and experimentations. This type of theory attempts to explain how events seen

in the natural world work .

Theory of evolution

Biological evolution is one way process

Theory of evolution

Once a species is extinct, it is gone forever.

When a new species evolves, it can not evolve

backward into parents.

Theory of evolution

According to the theory of bio evol, new species arise as a result of competition for resourses and the difference among individuals in their

adaptations to environmental conditions.

Since the environment continually changes, which individuals are best adapted changes too.

Processes lead to evolutution

1 Natural selection 2 Mutation 3 Migration

4 Genetic drift

Processes lead to evolutution 1- natural selection

When Darwin published The “Origin of Species” in 1859, he proposed the mechanism by which evolution occurred. That mechanism called

natural selection.


is a description of what happens when variations occur in a population where resources are

limited. When more individuals are born than the environment can support, those with advantageous variations are more likely to survive than those without them. This differential reproduction leads to overall changes in the traits of a population over time


When there is variation within a species, some individuals may be better suited to the

environment than others .

(change is not always for the better)

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Organisms whose biological characteristics make them better able to survive and reproduce in their environment leave more offspring than others. This form a larger proportion of the next generation and are more fit for the

environment .

This process of increasing offsprings is called natural selection.

Natural selection involves four primary factors

1 inheritance of traits from one generation to

the next and some variation in these traits ,

genetic variability.

2 environmental variability3 differential reproduction that varies with the

environment4 influence of the environment on survival and

production

Darwinian Natural Selection

Three conditions necessary for evolution by natural selection

•Natural variability for a trait in a population

•Trait must be heritable

•Trait must lead to differential reproduction

•A heritable trait that enables organisms to survive AND reproduce is called an

“ adaptation”

Genetic variation is added to genotype by mutation.

•Mutations lead to changes in the phenotype .

•Phenotype is acted upon by natural selection .

•Individuals more suited to environment

produce more offspring and contribute more

to total gene pool of population .

Steps of Evolution by Natural Selection

steps of Evolution by Natural Selection

•Population’s gene pool changes over time

•Speciation may occur if geographic and

reproductive isolating mechanisms exist…

Three types of Natural Selection

1 )Directional

•Allele frequencies shift to favor individuals at

. one extreme of the normal range •Only one side of the distribution reproduce .

•Population looks different over time


2 )Stabilizing

•Favors individuals with an average genetic

makeup •Only the middle reproduce

•Population looks more similar over time •Population split into two groups


3 )Disruptive

•Environmental conditions favor individuals at

both ends of the genetic spectrum

Directional Selection

•Directional change in the

range of variation.

•Allele frequencies tend to shift

in response to directional

changes in the environment .

•Shift in allele frequency in a

consistent direction.

Directional Selection

Examples:

•Phenotypic variation in a population of

butterflies

•Pesticide resistance •Pest resurgence

•Antibiotic resistance

Stabilizing Selection

•Selection against or in favor of

extreme phenotypes .

•Intermediate forms of a trait

are favored .

•Alleles that specify extreme

forms are eliminated from a

population. •example: Birth Weight and Clutch Size.

Average remains the same Number of individuals with intermediate coloration increases

eliminates Fringe Individuals.


•Selection Against or in

Favor of Extreme Phenotypes

•Both forms at extreme

ends are favored .

•Intermediate forms are

eliminated .

•Bill size in African finche

Adaptation Limits

•A change in the environment can only lead to

adaptation for traits already present in the gene pool

•Most individuals without trait would have to die in

order for the trait to predominate and be passed on

•

Adaptation Limits

•Reproductive capacity may limit a population’s

ability to adapt .

•If you reproduce quickly (insects, bacteria)

then your population can adapt to changes in

a short time .

•If you reproduce slowly (elephants, tigers ,

corals) then it takes thousands or millions of

years to adapt through natural selection .

Evolution

Evolution is the change in a POPULATION’S genetic material (gene pool) over time.

(successive generations )

•Those with selective advantages (i.e., adaptations) ,

survive and reproduce .

•All species descended from earlier ancestor species

Microevolution

Microevolution

•Small genetic changes in a population such as the spread of a mutation or the change in the

frequency of a single allele due to selection

( changes to gene pool .)

•Not possible without genetic variability in a population …

1 .Mutation (random changes in DNA—ultimate source of new alleles) [stop little]

•Exposure to mutagens or random mistakes in

copying .

•Random/unpredictable relatively rare

Micrevolution MicroevolutionFour Processes cause

Micrevolution MicroevolutionFour Processes cause

2 .Natural Selection (more fit = more offspring)

3 .Gene flow (movement of genes between

populations.)

4 .Genetic drift (change in gene pool due to

random/chance events .)

Macroevolution

Macroevolution

•Long term, large scale evolutionary changes

through which new species are formed and

others are lost through extinction .

Macroevolution•

•Macroevolution is the cumulative result of a

series of microevolutionary events.

•Typically seen in fossil record.

•Nobody around to see the small, gene pool changes over time.

Example of macroevolution

By 55 million years ago, the first members of the horse family, the dog-sized Hyracotherium, were scampering through the forests that covered North America. For more than half their history, most horses remained small, forest browsers. But changing climate conditions allowed grasslands to expand, and about 20 million years ago, many new species rapidly evolved. Some--but not all--became larger and had the familiar hooves and grazing diets that we associate with horses today. Only these species survived to the present, but in the past, small and large species lived side by side.

Example of macroevolution

Coevolution

• Interactions between species can cause

microevolution.

•Changes in the gene pool of one species can

cause changes in the gene pool of the other.

Coevolution

Adaptation follows adaptation in something of a long term “arms race” between interacting

populations of different populations .

Coevolution

The Red Queen Effect: The gist of the idea is that, in tightly coevolved interactions, evolutionary change by one species (e.g., a prey or host) could lead to extinction of other species (e.g. a predator or parasite), and that the probability of such changes might be reasonably

independent of species ageز

Coevolution

Can also be symbiotic coevolution:

•Angiosperms and insects (pollinators)

•Corals and zooxanthellae

•Rhizobium bacteria and legume root nodules

How new species arise?

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coevolution

When natural selection takes place over a long time, a number of characteristic can change. The accumulation of these changes may be so great that the present generation can no longer reproduce with individuals that have the original DNA structure, resulting in a new

species .

What is species

Species is a group of individuals that can

reproduce with each other .

What is species

There are two key ideas within this definition :

First, a species is a population of organisms .

•The human species, Homo sapiens, consists of over 6 billion individuals, whereas the endangered California condor species, Gymnogyps californianus, consists of about 160

individuals .

What is species

•Two or more populations that demonstrate gene flow between them constitute a single

species .

•Conversely, two or more populations that do not demonstrate gene flow between them are

generally considered to be different species .

What is species

Second, the definition involves the ability of individuals within the group to produce fertile

offspring .

•Individuals within the group have potentially

the capability of interbreeding to produce

fertile offspring (gene flow) .

What is species

The biological species concept

•A species is a population or group of populations whose members have the potential to interbreed with each other in nature to produce viable, fertile offspring, but who

cannot produce viable, fertile offspring with members of other species.

• .

What is species

•A biological species is the largest set of populations in which genetic exchange is possible and is genetically isolated from other population.

What is species

humans have considerable diversity, but we belong to the same species

What is species

because of our capacity to interbreed

A closer look to natural selection

Mosquitoes and the malaria parasite

The development of resistance to DDT by mos and to chloroquine by plasmodium is an

example of biological evolution in action today.

Genetic drift

2 -Genetic drift

Occurs when changes in frequency of a gene in a

:population are due not to

mutation ,

Natural selection ,

Migration

but simply to chance.

Genetic drift

Genetic drift is the random (i.e. unpredictable) fluctuations that naturally occur in a population’s gene pool when the population is small.

When genetic drift happens

One way this happens is through the. founder effect It occurs when a small number of individuals are isolated from a larger population , they may have a much smaller genetic variation than the original species and which characteristic the isolated population has will be affected by chance.


Do founder effect and genetic drift

be always better for individuals؟


The individuals may not be better adapted to the environment, in fact , they may be more poorly adapted .genetic drift can occur in any small population and may also present problems when a small group is by chance isolated from

the main populatipon.

A closer look to genetic drift

Bighorn sheep live in the mountains of the southwestern deserts of the united states and mexico. In summer, sheeps feed high up in the mountains , where it is cooler and wetter and

there is more vegetation .

Before high density european settlement of the region, the sheep could move freely and migrated from mountain to another.


With development , populations of bighporn sheep could no longer migrate among mountains and become isolated in very small groups , so chance may play a large role in what inherited characteristics remain in the population


The best adapted individuals do not always survive to reproduce, while poorly adapted individuals don’t always die before passing on their genes. Over time, in small populations, genetic drift can lead to noticeable change.

mutation

3 mutationGenes contained in chromosome within cells are

inherited from one generation to the next.

When cell divides, the DNA is reproduced and

each new cell gets a copy .

But sometimes mutation occurs.

Mutation is

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mutation

Sometimes error in reproduction changes the DNA and therefore changes inherited

characteristic .

mutation

The vast majority of mutations are neutral or harmful and are not preserved, but occasionally beneficial mutations occur that are preferentially passed down through the generations

Effects of mutation

1 In some cases, a cell or offspring with

amutation can not survive .

2 in other cases mutation simply adds variability

to the inherited characteristics .

.

Effects of mutation

3 in still other cases, individuals with mutations are so different from their parents that they can not reproduce with normal offspring of their species, so a new species has been created

Migration and geographic isolation

4 Migration and geographic isolation

Migration has been an important evolutionary

process over geologic time


Some times two populations of the same species become geographically isolated from each other for a long time. During this the two pop may change so much that they can no longer reproduce together even when they are brought back into contact.


In this case tow new species have evolved from the original species. This can happen even if the genetic changes are not more fit but simply different enough to prevent reproduction


in still other cases, individuals with mutations are so different from their parents that they can not reproduce with normal offspring of their species, so a new species has been created

A closer look

Hawaiian island a finchlike ancestor evolved into several species, including fruit and seed eaters, insect eaters, each with a beak adapted for its specific food

Principles of Evolution

1 Perpetual Change :

•All species are in a continuous state of change .

•This continuous diversification of offspring

ensures a “perpetual change” in genetic

composition between generations


Perpetual Change :

•Any organism that reproduces sexually (e.g., plants, animals, algae, fungi) will produce offspring that are genetically distinct from either parent, due to the process (meiosis) by which gametes (eggs and sperm) are produced as well as the randomness of fertilizations.


2 Nature Limiting Factors

The combined influences of physical and biological

limiting factors acting upon an organism .

It is important to understand that natural selection and therefore evolution is not a goal-oriented or anticipatory process, it is governed by the rules of

nature (physical & biological limiting factors) .



Biological limiting factors include any influence of biological origin, that may regulate the welfare of an organism, e.g., predation,

competition, disease .



•Physical limiting factors include any influence of a nonbiological origin that may regulate the welfare of an organism such as drought, flood,

wind, temperature extremes, etc .



.Natural selection is NOT an anticipatory process as selection acts upon the individual in the current environment.

•Natural selection acts upon an organism in its current environment

•It does not “select” for traits that may be favorable or adaptive in future environments.

Types of variation

Genetics is concerned with explaining how some characteristics are passed from

Generation to generation

by inheritance However, it is important to firstly deal with

some background information about them

Types of variation

This may then be tied in with evolution and the development of different species of living organisms

Types of variation

Like most living organisms, humans show variation. If you consider almost any characteristic, you will find differences between various people(or other animals or plants) in a

population..

Forms of variation

Continuous

discontinuous

Forms of variation

continuous variation

Characteristics showing continuous variation vary in a general way, with a broad range, and many intermediate values between the extremes

Forms of variation

continuous variationAs a matter of fact, if you consider a large enough sample from a population, perhaps plotting frequency as a histogram or as a frequency polygon, you will find that most of the values are close to the average (mean), and extreme values are actually rather rare

Forms of variation

continuous variationHeight is an example of a continuously variable characteristic, as long as you consider a consistent sample, for example a large number of people of a particular age and sex.

As you will find out later, it is usually difficult to give a straightforward explanation of the genetic basis for these continuously variable characteristics because they result from a combination of genetic factors as well as environmental influences.

Forms of variation

examples of human characteristics which show continuous variation

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Forms of variation

ContinuousWhen a characteristic or phenotype normally exists in a range or gradient, it varies continuously (like shades of gray, as opposed to black and white). It's easy to think of examples of phenotypes that vary continuously, for example, height and skin color. In between the shortest person in the world and the tallest person in the world, any height is possible, not just 4 feet, 5 feet or 6 feet. And of course, skin comes in all kinds of

shades, not just two or three .

Forms of variation

continuous variationIf you would make a frequency graph of the range of heights or skin colors in a group of people, it would look like a bell curve, with intermediate phenotypes being the most common. This is a good way to recognize continuous variation.

Forms of variation

variation DiscontinuousIn contrast, some phenotypes vary discontinuously. These phenotypes have 'black and white' differences: for example, you can have blood type A, B, AB or O, but there aren't any intermediate blood types in between. Another example is the ability to roll your tongue. Either you can or you can't, so

this phenotype varies discontinuously .

Forms of variation

discontinuous variationCharacteristics showing discontinuous variation fall into a few very distinct classes. The ability to roll the tongue, and blood groups, are examples of discontinuous variation. These characteristics can be explained much more easily by simple rules of genetics and are less

likely to be affected by other factors).

Forms of variation

discontinuous variation

For the tongue-rolling ability, how many classes are there

Forms of variation

classes of blood group

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Genetic variation causes

Gene Mutation is a very rare event indeed mutation in a single inheritable characteristic (gene) is usually less likely than one in a million, but once it has happened, it may be passed on to the next generation, along the same lines as

other inherited characteristics .


Gene MutationHowever, not all individuals carrying mutations survive; most have been found to be harmful, so that the organisms carrying them are at a disadvantage. In the wild, such organisms are unlikely to survive.


Nevertheless, some (beneficial) mutations confer an advantage, and others (neutral?) cause neither advantage nor disadvantage - at least until there is some reason for selection of adapted types to occur. This may be another reason for variation within a

population..


Gene MutationIn fact, the few different forms resulting from mutation which are beneficial can spread through a population by natural selection, and this may have the eventual effect of changing a population so much that it differs from its original form - resulting in the evolution of a new species


Chromosome Mutations may also result in change in the number of chromosomes incorporated into sex cells. A child produced as a result may have, for instance, an extra chromosome, or an extra part of a chromosome attached to the normal set Down's syndrome is caused by having 47chromosomes

instead of the normal ------------------ per cell .

What is the frequency of babies being born with Down's syndrome?


Chromosome Mutations

Mutations as described above may occur "naturally", but in the laboratory it has been shown that they may be caused (more efficiently) by other means. Similarly, various factors in the environment may increase the

chance of mutations occurrin .


Chromosome Mutations

The risks associated with some lifestyle activities are nowadays known, and exposure to many of these are avoidable. For instance, chemicals in tobacco include mutagens, and several types of ionising radiation have mutagenic effects


Phenotypic variation=environmentalPhenotypes are traits or characteristics of an organism that we can observe, for example,

size, color, shape, capabilities, behaviors, etc ..


Phenotypic variation=environmentalNot all phenotypes can actually be seen: for example, blood types are phenotypes that we can only observe using laboratory techniques. Phenotypes can be caused by genes, environmental factors, or a combination of both


Phenotypic variationthen, is the variability in phenotypes that exists in a population. For example, people come in all shapes and sizes: height, weight and body shape are phenotypes that vary. Hair, eye color and the ability to roll your tongue are variable phenotypes, too. What about other

organisms ?


Phenotypic variation=environmentalall organisms can have phenotypic variation. In plants, flower color and leaf shape are examples of variable phenotypes. In bacteria, resistance to antibiotics is a variable phenotype: some bacteria are resistant and survive antibiotic treatment, while others are susceptible and die when antibiotics are

given .

speciation

The evolutionary formation of new biological species, usually by the division of a single species into two or more genetically distinct ones

speciation

The formation of new biological species by the development or branching of one species into two or more genetically distinct ones. The divergence of species is thought to result primarily from the geographic isolation of a population, especially when confronted with environmental conditions that vary from those experienced by the rest of the species, and from the random change in the frequency of certain alleles (known as genetic drift). According to the theory of evolution, all life on Earth has resulted from the speciation of earlier organisms

speciation

Reproductive isolation

•the biological species concept emphasizes

reproductive isolation

•Reproductive barriers can be categorized as

prezygotic or postzygotic, depending on

whether they function before or after the

formation of zygotes.


No single barrier may be completely impenetrable to genetic exchange, but many species are genetically sequestered by multiple barriers.


•Typically, these barriers are intrinsic to the

organisms, not simple geographic separation .

•Reproductive isolation prevents populations

belonging to different species from

interbreeding, even if their ranges overlap .

Reproductive barriers

1 Prezygotic barriePrezygotic barriers impede

mating between species or

hinder fertilization of ova if

members of different

species attempt to mate .


1 Prezygotic barrie

These barriers include :

1 .habitat isolation ,

2 .behavioral isolation ,

3 .temporal isolation ,

4 .mechanical isolation ,5 .gametic isolation.


1 Prezygotic barriers •Habitat isolation: Two organisms that use

different habitats even in the same geographic

area are unlikely to encounter each other to even

attempt mating .


1 Prezygotic barriers

This is exemplified by the two species of garter

snakes, in the genus Thamnophis, that occur in

the same areas but because one lives mainly in

water and the other is primarily terrestrial, they

rarely encounter each other .


1 Prezygotic barriers A Behavioral isolation .

Many species use

elaborate behaviors

unique to a species to

attract mates . .


1 Prezygotic barriers • b Temporal isolation. Two species that breed

during different times of day, different seasons, or

different years cannot mix gametes .

•For example, while the geographic ranges of the

western spotted skunk and the eastern spotted skunk

overlap, they do not interbreed because the former

mates in late summer and the latter in late winter .



c Mechanical isolation. Closely related species

may attempt to mate but fail because they are

anatomically incompatible and transfer of sperm

is not possible .



c Mechanical isolationTo illustrate, mechanical barriers contribute to the reproductive isolation of flowering plants

that are pollinated by insects or other animals .

•With many insects the male and female copulatory organs of closely related species do not fit together, preventing sperm transfer.


1 Prezygotic barriers •D Gametic isolation : occurs when gametes of two

species do not form a zygote because of

incompatibilities preventing fusion or other

mechanisms . •In species with internal fertilization, the environment

of the female reproductive tract may not be conducive to the survival of sperm from other species•

Reproductive barriers •D Gametic isolation

For species with external fertilization, gamete

recognition may rely on the presence of specific molecules on the egg’s coat, which adhere only to specific molecules on sperm cells of the

same species .

•A similar molecular recognition mechanism enables a flower to discriminate between pollen of the same species and pollen of a different species.


D Gametic isolation

•If a sperm from one species

does fertilize the ovum of

another, postzygotic

barriers prevent the hybrid

zygote from developing into

a viable, fertile adult. These

barriers include : .


2 Postzygotic barriers

•reduced hybrid viability ,

•reduced hybrid fertility ,

•and hybrid breakdown


2 Postzygotic barriers •a Reduced hybrid viability. Genetic incompatibility

between the two species may abort the development of the hybrid at some embryonic stage or produce

frail offspring .

•This is true for the occasional hybrids between frogs in the genus Rana, which do not complete

development and those that do are frail .•


2 Postzygotic barriers •b Reduced hybrid fertility. Even if the hybrid

offspring are vigorous, the hybrids may be

infertile and the hybrid cannot backbreed with

either parental species .

•This infertility may be due to problems in meiosis

because of differences in chromosome number or

structure .

•


2 Postzygotic barriers •b Reduced hybrid fertility

For example, while a mule, the hybrid product of mating between a horse and donkey, is a robust organism, it cannot mate (except very rarely) with either horses or

donkeys.


2 Postzygotic barriers •c Hybrid breakdown. In some cases, first

generation hybrids are viable and fertile .

•However, when they mate with either parent species or with each other, the next generation are feeble or

Sterile.


2 Postzygotic barriers •c Hybrid breakdown

To illustrate this, we know that different cotton species can produce fertile hybrids, but breakdown occurs in the next generation when offspring of hybrids die as seeds or grow into weak and defective plants

Modes of Speciation

Two general modes of speciation are distinguished

by the mechanism by which gene flow among

populations is initially interrupted .

1 .Allopatric speciation :

•Geographic barriers can lead to the origin of species

•Geographic separation of populations restricts gene flow

Modes of Speciation

.2 Sympatric speciation :

•A new species can originate in the geographic midst of the parent species .

•speciation occurs in geographically overlapping populations.

when biological factors, such as chromosomal changes and nonrandom mating, reduce gene flow.

Modes of Speciation

1 Allopatric speciation occurs when a physical boundary like a mountain or a river separates a species. It's the scientific name for the geographic isolation that can cause a species to split. For example, 3 million years ago, the Isthmus of Panama formed, closing off the land between North America and Central

America .

Modes of Speciation

1 Allopatric speciation Researchers from the Smithsonian Tropical Research Institute in Panama have studied how this change in geology affected the region's snapping shrimp population. Shrimp on either side of the isthmus were nearly identical, but when researchers tried to mate them, the shrimp wanted nothing to do with one another. In fact, the shrimp lived up to their names and snapped at their neighbors.

Modes of Speciation

1 Allopatric Speciation

•Geographic barriers can lead to the origin of species

•Several geological processes can fragment a population

into two or more isolated populations .

•Mountain ranges, glaciers, land bridges, or splintering of lakes may

divide one population into isolated groups. .

Modes of Speciation

1 Allopatric Speciation •Alternatively, some individuals may colonize a

new, geographically remote area and become isolated from the parent population .

•For example, mainland organisms that colonized the Galapagos Islands were isolated from mainland populations.

Modes of Speciation

1 Allopatric Speciation How significant a barrier must be to limit gene exchange. This depends on the ability of organisms

to move about .

•A geological feature that is only a minor hindrance to one species may be an impassible barrier to another .

•i.e. The valley of the Grand Canyon is a significant barrier for ground squirrels which have speciated on

opposite sides, but birds which can move freely haveno barrier .

Modes of Speciation

1 Allopatric Speciation •The likelihood of allopatric speciation increases

when a population is both small and isolated. A

small, isolated population is more likely to have

its gene pool changed substantially by genetic

drift and natural selection . .

Modes of Speciation

1 Allopatric Speciation •However, very few small, isolated populations

will develop into new species; most will simply perish in their new environment .

•A question about allopatric speciation is whether the separated populations have become different enough that they can no longer interbreed and produce fertile offspring when they come back in contact

Modes of Speciation

•At the northern end of the ring, the coastal and inland populations interbreed and produce viable offspring. In this area they appear to be a single biological

•At the southern end of the ring, the coastal and inland populations do not

interbreed even when they overlap. In this area they appear to be two separate

species.

1 Allopatric Speciation

Modes of Speciation

1 Allopatric Speciation- Summary

•In summary, in allopatric speciation, new species

form when geographically isolated populations

evolve reproductive barriers as a byproduct of

genetic drift and natural selection to its new

environment .

.

Modes of Speciation

1 Allopatric Speciation- Summary

•These barriers prevent interbreeding even if populations come back into contact.

•These barriers include prezygotic barriers that reduce the likelihood of fertilization and postzygotic barriers that reduce the fitness of hybrids

Modes of Speciation

2 Sympatric Speciation- Polyploidy

•In sympatric speciation, new species arise within

the range of the parent populations .

•Here reproductive barriers must evolve between sympatric populations .• .

Modes of Speciation

2 Sympatric Speciation- a PolyploidyIn plants, sympatric speciation can result from

accidents during cell division that result in extra sets of chromosomes, a mutant condition

known as polyploidy .

In animals, it may result from gene-based shifts in habitat or mate preference

Modes of Speciation

•2 Sympatric Speciation- a PolyploidyPolyploidy is a condition in which there are more than two complete sets of chromosomes in an organism

•Polyploidy is much rarer in animals. It is found in some insects, fishes, amphibians, and reptiles. Until recently, no polyploid mammal was known. However, the 23 September 1999 issue of Nature reports that a polyploid

(tetraploid; 4n= 102 )rat has been found in Argentina

•2 Sympatric Speciation- a Polyploidy

Modes of Speciation

•2 Sympatric Speciation- a PolyploidyPolyploidy in plants

•Polyploidy is very common in plants, especially in

angiosperms. From 30% to 70% of today's angiosperms

are thought to be polyploid .

.

Modes of Speciation

•2 Sympatric Speciation- a Polyploidy Species of coffee plant with 22, 44, 66, and 88

chromosomes are known. This suggests that the ancestral condition was a plant with a haploid (n) number of 11 and a diploid (2n) number of 22, from

which evolved the different polyploid descendants .

•In fact, the chromosome content of most plant groups suggests that the basic angiosperm genome

consists of the genes on 7–11 chromosomes .

Modes of Speciation

2 Sympatric Speciation- a PolyploidyDomestic wheat, with its 42 chromosomes, is probably hexaploid (6n), where n (the ancestral haploid

number) was 7 .

•Polyploid plants not only have larger cells but the plants themselves are often larger .

•This has led to the deliberate creation of polyploid varieties of such plants as watermelons, and snapdragons

Modes of Speciation

2 Sympatric Speciation- a PolyploidyAllopolyploidy

•Another mechanism of producing polyploid

individuals occurs when individuals are produced

by the mating of two different species, an allopolyploid .

•While the hybrids are usually sterile, they may be quite vigorous and propagate asexually .

•

2 Sympatric Speciation- a PolyploidyAllopolyploidyVarious mechanisms can transform a sterile

hybrid into a fertile polyploid .

•These polyploid hybrids are fertile with each other but cannot interbreed with either parent species

Modes of Speciation

Sympatric Speciation . b Autopolyploid

•An individual can have more that two sets of

chromosomes from a single species if a failure in meiosis results in a tetraploid (4n) individual .

Modes of Speciation


•This autopolyploid mutant can reproduce with itself (self-pollination) or with other

tetraploids .

•It cannot mate with diploids from the original

population, because of abnormal meiosis

by the triploid hybrids

Modes of SpeciationSympatric Spciation . b Autopolyploid

Modes of Speciation

Sympatric Speciation . b Autopolyploid - Alterations of chromosome number or

structure cause some genetic disorders .

- Large-scale chromosomal alterations often lead to

spontaneous abortions or cause a variety of

developmental disorders.

Modes of Speciation


-Abnormal Chromosome Number when nondisjunction occurs

•Pairs of homologous chromosomes do not separate normally during meiosis

•Gametes contain two copies or no copies of a particular chromosome

Modes of Speciation

2 Sympatric Speciation d Aneuploidy

•Results from the fertilization of gametes in which nondisjunction occurred

•Is a condition in which offspring have an abnormal number of a particular chromosome .

•If a zygote is trisomic it has three copies of a particular chromosome

•If a zygote is monosomic it has only one copy of a

particular chromosome

Modes of Speciation

Sympatric Speciation- c Allopolyploid •One mechanism for allopolyploid speciation in plants

involves several cross-pollination events between two

species of their offspring and perhaps a failure of meiotic

disjunction to a viable fertile hybrid whose chromosome

number is the sum of the chromosomes in the two parent

Sympatric Speciation

Modes of Speciation

•Sympatric Speciation- c Allopolyploid

•Many plants important for agriculture are the products of

polyploidy .

•For example, oats, cotton, potatoes, tobacco, and wheat are

polyploid .

•Plant geneticists now hybridize plants and use chemicals that

induce meiotic and mitotic errors to create new polyploids with

special qualities .

•Example: artificial hybrids combine the high yield of wheat with the ability of rye to resist disease .

Modes of Speciation

Modes of Speciation

Sympatric Speciation- in Animals

•While polyploid speciation does occur in animals, other mechanisms also contribute to sympatric speciation in

animals .

•Sympatric speciation can result when genetic factors cause individuals to be fixed on resources not used by

the parent .

•These may include genetic switches from one breeding habitat to another or that produce different mate

preferences .•

Modes of Speciation

Sympatric Speciation- c Allopolyploid

•Sympatric speciation is one mechanism that has been proposed for the explosive adaptive radiation of almost 200 species of cichlid fishes in Lake Victoria, Africa.

•While these species clearly are specialized for exploiting different food resources and other resources, non-random mating in which females select males based on a certain appearance has

probably contributed too .

Modes of Speciation

2 Sympatric Speciation- Summary •Sympatric speciation requires the emergence of some

reproductive barrier that isolates a subset of the population without geographic separation from the parent

population .

•In plants, the most common mechanism is hybridization between species or errors in cell division that lead to

polyploid individuals . •In animals, sympatric speciation may occur when a subset of

the population is reproductively isolated by a switch in resources or mating preferences.

Concepts Of Species

Evolutionary Biologists Have Proposed

Several Alternative Concepts Of Species

•The ecological species concept: defines a

species in terms of its ecological niche, the set of

environmental resources that a species uses and

its role in a biological community .

•As an example, a species that is a parasite may be defined in part by its adaptations to a specific organism.

•

Concepts Of Species

Niches

•A species functional role in an ecosystem

•Involves everything that affects its survival and

reproduction

•Includes range of tolerance of all abiotic factors •Trophic characteristics

•How it interacts with biotic and abiotic factors

•Role it plays in energy flow and matter cycling

Biodiversity

The variety of life is biological diversity Use of the term “biological diversity” in its current sense began in 1980 Biodiversity = biological diversity Coined in 1985 for a conference, the proceedings of which were published as the book “Biodiversity” edited by E. O. Wilson Biodiversity is the variability among living organisms from all sources including terrestrial and aquatic systems and the ecological complexes of

which they are a part ;

Biodiversity

biodiversity

It is the diversity within species, among species, and of ecosystems; interactions at all levels

among organisms

Types of diversity

1 Genetic diversityGenetic diversity encompasses the genetic coding that structures of organism

neocleotides, genes, chromosomes )

Biodiversity

.2 Organismal diversityOrganismal diversity encompasses the full taxonomic hierarchy and its components, from individuals upwards to populations, subspecies andspecies, genera, families,

phyla, and beyond tokingdoms and domains .

.2 Organismal diversityMeasures of organismaldiversity thus include some of the most familiar expressions of biodiversity, such as the numbers of species (i.e. species richness). Others should bebetter studied and more routinely employed than they have been thus far.

Biodiversity

3 Ecological diversityThe third group of elements of biodiversity encompasses the scales of ecological differencesfrom populations, through habitats, to ecosystems, ecoregions, provinces, and on up to biomesand biogeographic realms (Table 2.1). This is an

Ecological diversity

Elements of biodiversity

• Ecological diversity

•Biogeographic

•Biomes

•Provinces

•Ecoregions

•Ecosystems •Habitats

•Population

Biodiversity

1 Organismal diversity

•Domains or Kingdoms

•Phyla

•Families

•Genera

•Species •Subspecies

•Populations

•Individuals •

•

Biodiversity

2 Genetic diversity

•Populations

•Individuals

•Chromosomes •Genes

•Nucleotides

Three Levels of Biodiversity

• •1 Genetic – the variety of genotypes .

•Genetic variation, responsible for different traits of individuals, interacts with local environmental conditions to determine the extent to which population can adapt to environmental changes

and survive exposure to new diseases .

•Genetic variation is extremely important to the survival of populations. Isolated populations (e.g., on a small island) tend to have less genetic variations, therefore,

are more susceptible to extinction .•

Biodiversity•

••2 Organismal diversity

•Species– Groups of actually or potentially interbreeding natural populations genetically isolated from other such groups by one or more reproductive isolating mechanisms

Biodiversity• •3 Ecological diversity

•Ecosystem – Genes determine the traits of individuals

that form populations of a species .

•Populations and their environments (e.g., water or minerals) interact dynamically to form an ecosystem

•Loss of genetic or species diversity will affect the performance of ecosystems

Why Biodiversity is important?

•Biodiversity is the nature •Loss of biodiversity is a cutoff of our connection to

nature and to history •Inspiration and cultural heritages: Species inspire

songs, stories, dances, poetry, myths, arts, cuisine, rituals, festivals… Nature is an unsurpassed source of relaxation, wonderment, rejuvenation, beauty

and peace .


Diversity has provided humanity with the wide variety of products :

•Crops, domestic animals, medicines, etc.). 90% of the calories consumed by human beings come from 80 plant species. An estimated

4.5 billion people (~80% of the world population) use plants as their primary source of medicine .


•Biodiversity providing free ecosystem services :

•Microorganisms, plants, and animals play a critical role in balancing ecosystem

The dynamics of taxonomic diversity

The dynamics of taxonomic diversity on Earth is :determined by two processes

1 .Speciation

•Organisms make mistakes in reproduction

•Many mistakes are harmful (deleterious) but some mistakes are

favored and are fixed by selection •Mutation + Selection = Speciation

The dynamics of taxonomic diversity

2 .Extinction

•Bad Gene or Bad Luck ?

•Demographic disturbance •Environmental disturbance

•Catastrophes

Factors contributing to the loss of biodiversity

1 .Accelerating growth of human population

2 .Land-use changes (habitat destruction, fragmentation leading to inbreeding, loss of genetic diversity and local extinction)

3 .Increase of atmospheric carbon dioxide (global warming, raising sea level, changes in climate patterns, prolonged droughts)


•4 .Invasive species (outcompete native species, 35-45% of endangered or threatened

species in US is caused by invasive species)

•5 .Pollution (oil spill, acid precipitation, toxic chemicals in fertilizers and pesticides, urban sewage runoff, etc.)

•


6 .Overuse of resources (populations cannot sustain if exploitation rate is greater than growth rates. Nine of world’s major ocean fisheries are declining because of over fishing

as well as water pollution and habitat destruction).

extinction

In biology and ecology, extinction is the end of an organism or of a group of organisms

normally a species .

The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been

lost before this point .

extinction

Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "re-appears" (typically in the fossil record) after a period of apparent absence.

Causes of extinction

geological transformation of the Earth's crust and major climatic oscillations

species interactions

activities of humans


Of humans; further acceleration of extinction rates began approximately 1600 AD, with the onset of accelerated human population growth and expanded scope of agriculture. Natural causes of extinction are regarded as being an irrelevantly small fraction of present extinction events, but are important to understand for historical context. Darwin was the first to fully articulate the concepts of speciation and extinction as applied to natural succession, although he never used the terms evolution or extinction. (Darwin. 1859) The primary cause of

Causes of extinctionhuman-induced extinction events is simply human overpopulation of planet Earth. The most important causal activities are habitat destruction,

pollution .Habitat destruction elements include agricultural land

conversion, deforestation, overgrazing and urbanization ;

within these activities the process of habitat fragmentation is a sometimes hidden cause of major

biodiversity loss .hunting or fishing threatened fauna and killing of

threatened fauna for herbal or cultural extracts .


Pollution impacts include buildup of toxic atmospheric substances, discharge of water pollutants into natural water reserves, chemical contamination of soils and noise pollution.

Introduction of species is usually an unintended activity where seeds, fauna aboard and other viably reproducing biota are transported by man to a new environment which has insufficient resident predators (or predators unfamiliar with, and therefore naive to the new prey) to control the invading taxon, or exotic predators inadvertently (or intentionally) introduced to a new region, where the native fauna are often unable to recognise the invading organism as a threat.

References

conservation biology for All 2011. NavijotS. Sodhi . Paul R. EhrlichHarverd university, Stanford university

Daniel B. Botkin & Edward A. Keller. 2011.

Environment science : earth as a living planet.

8th edition.

Daniel B. Botkin & Edward A. Keller. 2010.

environment science : earth as a living planet7th edition. John Wiley & sons Pet Ltd

Daniel B. Botkin & Edward A. Keller. 2003Environment science : earth as a living planet.

4th edition. John Wiley & sons, INC .

Evolution’s Baby Stepsby Carl Zimmer

National geography

http://biologos.org/questions/what-is-evolution

Charles lyell http://evolution.berkeley.edu/evolibrary/article/history_12

http://www.jstor.org/discover/10.2307/1218675?uid=2&uid=4&sid=21104103402761taxonomy

http://biology.about.com/od/evolution/a/aa092304a.htm\

http://www.biotopics.co.uk/genes/varn.html

http://education-portal.com/academy/lesson/phenotypic-variation-definition-lesson-quiz.html#lesson

http://curiosity.discovery.com/question/how-does-speciation-occur

http://science.nationalgeographic.com/scienc

e/prehistoric-world/cambrian

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