Final Task of Zoogeografi Subject

8/9/2019 Final Task of Zoogeografi Subject

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Nuni Rismayanti Nurkalbi071 404 193

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1. Factor that leading the appearance of new species!a. Natural selection, is the process by which certain heritable traitsthose that

make it more likely for an organism to survive and successfully reproduce

become more common in a population over successive generations. It is a key

mechanism of evolution. It is the differences in survival and reproduction

among individuals in a population because of their interaction with the

environment. In other words, some individuals possess alleles (genotypes) that

generate traits (phenotypes) that enable them to cope more successfully in

their environment than other individuals. The more successful individuals

produce more offspring. Superior traits are adaptations to the environment

and increase an individuals fitness, or relative ability to survive and leave

offspring. When the environment favors a trait, that is, when a trait increases

the survival of its bearer, selection is said to act for that trait. In contrast,

selection is said to act against unfavorable traits. Favorable traits are adaptive,

while unfavorable traits are maladaptive.

b.Polyploidy is the possession of more than the normal two sets ofchromosomes found in diploid (2n) cells. Polyploidy often occurs in plants

(and occasionally animals) where triploid (3n), tetraploid (4n), and higher

ploidy chromosome numbers are found.A quite different method by which

new species can appear is by polyploidy- the doubling of the whole set of

chromosomes in the nucleus of the developing egg or seed, so that each

chromosome automatically has an identical partner. Polyploidy species are

often larger than the original parent type, and also more hardy and vigorous;

many weeds are polyploidy. Only a few animals groups fall into this category

(e.g. turbellarians, lumbricid eartworms, and weevils). This new species,

formed by natural polyploidy, has been extremely successful and has spread

around the world, often creating problems for shipping by forming mats of

vegetation within which sediments are deposited, and so contributing to the

silting up to estuaries. Polyploidy occurs because of nondisjunction of all


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chromosomes during meiosis, producing two viable diploid gametes and two

sterile gametes with no chromosomes. A tetraploid zygote can be established

when a diploid sperm fertilizes a diploid egg. Since normal meiosis in the

tetraploid individual will continue to produce diploid gametes, reproductive

isolation with other individuals in the population (and thus speciation) occurs

immediately in a single generation.

c. Speciation (isolation), a species is usually defined as a group of individualscapable of interbreeding. Speciation, the formation of new species, occurs by

the following processes,

a) Allopatric speciation begins when a geographic barrier divides apopulation so that interbreeding between the two resulting populations is

prevented. Common barriers include mountain ranges or rivers, but any

region that excludes vital resources, such as a region devoid of water, a

burned area devoid of food, or an area covered with volcanic lava, can act

as a barrier because individuals cannot survive its crossing. Once

reproductively isolated by the barrier, gene frequencies in the two


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populations can diverge due to natural selection (the environments may be

slightly different), mutation, or genetic drift. If the gene pools sufficiently

diverge, then interbreeding between the populations will not occur if the

barrier is removed. As a result, new species have formed. For example, a

German shepherd dog and a greyhound that appear just as different from

one another but both are members of same species. The essential

difference is that under normal conditions in the wild, they will mate

together (due to artificial selection by human). Biologist commonly define

the species as consisting of a group of populations whose members can all

breed together to produce offspring that are fully fertile, but that in the

wild do not do so with other such groups.

b) Sympatric speciation is the formation of new species without the presence of a geographic barrier. For example, two different species of

lacewing insect are found in the cold temperate and boreal of North

America. Chrysopa carnea, is found in grasslands, meadows, and on

deciduous trees, but only rarely on conifer trees; it is light green in color.

C. downesi is found only on conifer trees, and is a very dark green. Apart

from their different color, the two species are nearly indistinguishable

morphologically and, although they will interbreed in the laboratory, they

do not in nature. It was originally suggested that the common ancestor of

these two living species lived in both habitats. A simple genetic mutation

could then have led to the appearance of the dark green coloration in some

individuals. This coloration advantage for individuals in the coniferous

habitats and disadvantage in the grassland/meadow/ deciduous tree

habitat.It has subsequently been shown that the two species also differ in

their complex mating calls, and it has been suggested that this, rather than

their coloration, was the original basis for the separation of the two species

c) Adaptive radiation (mutation) is the relatively rapid evolution of manyspecies from a single ancestor. It occurs when the ancestral species


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colonizes an area where diverse geographic or ecological conditions are

available for colonization. Variants of the ancestral species diverge as

populations specialize for each set of conditions.

2. Explain the evolution process without discuss about the fossil!Until recently, it was thought that evolution took place too slowly for it to

be detectable over the timescale of scientific studies of living organisms, so that

it could only be detected in the fossil record. However, it is now clear that this

perception was wrong. For many years, British workers Peter and Rosmary Grant

have studied the finches on the tiny Galapagos island called Daphne Major, only

34 ha (84 acres) in area and 8 km (5 miles) from the nearest large island. The

finches, which belong to the genus Geospiza, live in a variety of environments

and use a number of sources of food. Some, with narrow bills, live on the ground

and feed on insects, snails, etc. some, with strong, heavy bills, live in the cactus

thickets and feed on the cactus seeds, flowers and pollen. However, most live in

the bushes and trees and feed on the seeds, nuts and fruits of some dozen species

of plant.

G. magnirostris, have large bills; G. fuliginosa, have small bills; G. fortis,

have bills of intermediate size. When food is plentiful, all these three species

prefer to eat the softest types of seed. In drier seasons, there are fewer of these

favorite seeds, because smaller plants, which tend to wither and die during a

drought, produce them. As a result, each species has then to become more


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specialized, spending more of its time feeding on those seed to which its beak

size is be adapted. G. magnirostris whit their biggest and strongest beak (best for

cracking the hardest seeds) can gathering food faster than G. fortis for feed on

same seed, but not all ofG. fortis can eat that seed while, G. fuliginosa has to

feed on smaller, softer seeds. This provides a very precise example of the nature

and results of the correlation between morphology (beak size) and ecology

(availability of different types of food).

Two of the extreme years in the century- both the driest year, 1977, and

the wettest year, 1983 had immense effects on the finches of the island. The

drought of 1977, make the plants failed to flower and set seed so that it make

shortage for finches food. The first effected to the new generation of finches,

make fledglings of 1977 died before they were 3 months old. But the drought

also hit the adults and the death hit harder at the finches that cold only eat softer

seeds, number ofG. fortis dropped by 85% from 1200 birds down to 180 but

suffered worst to G. fuliginosa, it number from a dozen to only a single bird.

Finally, the drought had been kindest to birds with big beaks The average

size of the G. fortis birds that survived was 5.6% greater than the average size of

the 1976 population, and their beaks were correspondingly longer (and stronger)-

11,07 mm long and 9,96 mm deep, compared with 1976 averages of 10,68 and

9,42 mm.

In 1983 years, that was the years of the strongest 20th century El Nino

event; the rainfall was ten times the previously known maximum, and as result,

the plants grew rampantly. That time, small seeds predominated-they formed

up to 80% of the total mass of seeds. That was partly because the smaller plants

grew luxuriously so they can produced many more seeds, while the growth of

Tribulus had been hampered by smothering vines. The availability of seed (small

seed), make number ofG. fortis having increased by more than four times. Now

it was selecting smaller birds, with smaller beaks, more suited to eating the


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plentiful smaller seeds. The main information from that is the conditions and

selection, can oscillate violently.

A total reversal of the selection pressures within 6 years-a time span

that would have been totally invisible in the fossil record, had there been

one. Therefore, the fluctuation in relative numbers of finches that the Grants

have observed in response to the changes in the availability of food of different

types, have not been between different, independent species. This records show

precisely what Darwins explanation had predicted, and what biologist have long

accepted. Each population is adapted to its existing rnvironment, withing a

pattern of the availability of food and of competition with other populations. But

that adaptation is not immutable: it cannot afford to be, for the environment itself

is fluid and changeable. Therefore, as from year to year, the environment

makes new demands and provides new opportunities, and it will change in

harmony with those demands and opportunities. Adaptation by evolution is

never far behind our efforts to control the biological world.

Darwin yang berasumsi bahwa evolusi merambat selambat gletser dan

hanya dapat diamati dalam catatan fosil. Pada 1973, Peter dan Rosemary Grant,

sekarang di Princeton University, memulai pengamatan tahunan terhadap

populasi pipit di pulau kecil Daphne Major di Galpagos. Mereka segera

menemukan bahwa pada kenyataannya pipit berevolusi dari tahun ke

tahun, saat kondisi pulau itu beralih dari basah ke kering dan basah

kembali. Misalnya, Daphne Major awalnya mengamati hanya dua burung pipit

tanah yang berbiak secara teratur, salah satunya adalah burung pipit tanah sedang

(G. fortis) yang makan bebijian kecil. Ketika kemarau parah melanda pulau itu

pada 1977 dan bebijian kecil menjadi langka, burung pipit sedang terpaksa

beralih memakan bebijian yang lebih besar dan lebih keras. Burung yang

berparuh lebih besar lebih mampu mencari makan dan dapat bertahan hidup

untuk menurunkan sifat bawaan itu kepada anaknya. Perubahan lain terjadi

setelah pesaing tiba pada 1982: burung pipit tanah besar (G. magnirostris) yang


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juga makan bebijian besar yang keras. Selama bertahun-tahun, kedua spesies itu

hidup berdampingan dan pada 2002, kedua jenis menjadi sangat berlimpah. Lalu

kemarau tiba dan pada 2005 tinggal 13 pipit tanah besar dan 83 pipit tanah

sedang yang masih hidup. Yang luar biasa, alih-alih menyesuaikan diri

terhadap kemarau dengan makan bebijian yang lebih besar seperti yang

dilakukan 28 tahun sebelumnya, pipit sedang yang menyintas mengalami

pengecilan ukuran paruh yang mencolok karena saat bersaing dengan

sepupu mereka yang lebih besar, pipit sedang berjuang mencari ceruk

hidup dengan makan bebijian yang sangat kecil. Burung pipit yang berparuh

lebih kecil bukanlah spesies pipit yang baru, tetapi Peter Grant menduga hanya

diperlukan beberapa episode semacam itu sampai terbentuk spesies baru yang

tidak mau bereproduksi dengan spesies asalnya.

3. Why there are many variations in a species!In order for natural selection to operate, there must be variation among

individuals in a population. Indeed, considerable variation exists in nearly all

populations. The variation arises from or is maintained by the following

mechanisms:

1. Mutationsprovide the raw material for new variation. All other contributionsto variation, listed below, occur by rearranging existing alleles into new

combinations. Mutations, however, can invent alleles that never before existed

in the gene pool.

2. Sexual reproduction creates individuals with new combinations of alleles.These rearrangements, orgenetic recombination, originate from three events

during the sexual reproductive process, as follows.

y Crossing over, or exchanges of DNA between nonsister chromatids ofhomologous chromosomes, occurs during prophase I of meiosis.


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y Independent assortment of homologues during metaphase I createsdaughter cells with random combinations of maternal and paternal

chromosomes.

y Random joining of gametes during fertilization contributes to thediversity of gene combinations in the zygote.

3. Diploidy is the presence of two copies of each chromosome in a cell. In theheterozygous condition (when two different alleles for a single gene locus are

present), the recessive allele is hidden from natural selection. As a result,

more variation is maintained in the gene pool.

4. Outbreeding, or mating with unrelated partners, increases the possibility ofmixing different alleles and creating new allele combinations.

5. Balanced polymorphism is the maintenance of different phenotypes in a population. Often, a single phenotype provides the best adaptation, while

other phenotypes are less advantageous. In these cases, the alleles for the

advantageous trait increase in frequency, while the remaining alleles decrease.

However, examples of polymorphism (two or more different phenotypes) are

observed in many populations.4. Explain the controversy of evolutionary theory!

There is now a vast amount of evidence for Darwins explanation of

evolution by natural selection. Nevertheless, controversy still exists about some

details of the circumstances in which new species evolve or the rate at which this

happens.

1. Some biologists believe that evolutionary change normally takes place at asteady, gradual rate. Others instead believe that, even if genetic alterations

gradually accumulate within a population, this may not be reflected in

detectable morphological or physiological changes until they are so

numerous as to shift the balance ofthe whole genotype. Example: the finches


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were evolution from year to year, when the condition of Galapagos island

change from wet to dry and become wet again.

2. It is also difficult to isolate such underlying patterns from the more directeffects of the environment. For example: a study of the fossil shells of

gastropod mollusks that lived in northern Kenya over the last few million

years shows long periods during which their structure and size remain

unchanged, interrupted by shorter periods (5000-50.000 years) during which

they changed rapidly. This was interpreted as an example of punctuated

equilibrium.

3. Darwins suggests that it is the fittest that survive because those are the onethat survives, of course (the catchphrase survive of the fittest was not

Darwins but by Herbert Spencer).

Teori evolusi menyatakan bahwa makhluk hidup di muka bumi tercipta sebagai

akibat dari peristiwa kebetulan dan muncul dengan sendirinya dari kondisi alamiah.

Berbagai cabang ilmu pengetahuan seperti paleontologi (cabang geologi yang mengkaji

kehidupan pra-sejarah melalui fosil), genetika, biokimia dan biologi molekuler telah

membuktikan bahwa tak mungkin makhluk hidup tercipta akibat kebetulan atau muncul

dengan sendirinya dari kondisi alamiah. Sel adalah struktur paling kompleks yang

pernah ditemukan manusia. Ilmu pengetahuan modern mengungkapkan bahwa satu sel

hidup saja memiliki struktur dan berbagai sistem rumit dan saling terkait, yang jauh

lebih kompleks daripada sebuah kota besar. Struktur kompleks seperti ini hanya dapat

berfungsi apabila masing-masing bagian penyusunnya muncul secara bersamaan dan

dalam keadaan sudah berfungsi sepenuhnya. Jika tidak, struktur tersebut tidak akan

berguna, dan semakin lama akan rusak dan musnah. Tak mungkin semua bagian

penyusun sel itu berkembang secara kebetulan dalam jutaan tahun, seperti pernyataan

teori evolusi.

Final Task of Zoogeografi Subject

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