Biodiversity

Thursday, May 11, 2006

DIGESTION IN HERBIVORES

Plants form the diet of herbivores and and therefore their digestion holds up the key for the availability of nutrients for these animals1. Plants cells have cellulose which is the primary structural component plant cells is a stable organic compound that is not easily digested. Digestive enzymes which the mammals produce cannot be able to breakdown cellulose to obtain glucose. As herbivores had to feed on the plants they had to overcome the problem of cellulose digestion. Cellulose can be broken down mechanically by chewing for a long time or fermentation by bacteria which dissolves cellulose. All herbivores stomachs have bacteria which dissolve cellulose but the process takes time. Various mechanical methods are employed by different herbivores to breakdown cellulose2.

Among the adaptations for digestion to evolve are exhibited by rabbits and rodents who re-eat their faeces which is soft, and normally deposited in the burrow2. This process is called coprophagy and ensures that the plant material consumed is processed twice and nutrients are extracted. After this second eating process is the faeces discarded outside the burrow as dry pellets2.

Elephants eat leaves, fibrous and woody material which poses a problem in their digestion, first to make it small and secondly to breakdown cellulose2. To handle this problem elephants have molars as their only teeth in their mouths. These molars are massive grinders which pound and crush the food with much power. The molars are continuously replaced as they wear out, by new ones growing on rear of the jaw and moving to replace those that are worn out2. Elephants feed on a lot of food and it takes along time before it is fully digested (up to two and a half weeks). To be able to store this food for those two weeks the elephants have to have big stomachs which also aid in the breakdown of the mostly woody material in the process of fermentation by bacteria in the elephants stomach. The big stomach serves as holders for the bacteria broth there for digestion. 2

Ruminants also evolved a different way to overcome this problem. Ruminants are animals that digest their food in two steps; first they chew the food for the first time roughly to break it to make them easy to swallow and then regurgitate and chew it a second time2, 3. The second chewing is called chewing the cud and animals practising ruminacy include cattle, deer, goats, sheep, camels, giraffes, buffalo, wildebeest, and antelope3. A ruminants stomach is divided in to four compartments namely; rumen, reticulum, omasum, and abomasums2. Grass and other foliage are clipped by use of lower incisors and pressing it against the tongue or gums of upper jaw with no front teeth. It’s briefly chewed by the molars before being swallowed the food into the rumen where there’s a broth of bacteria and is churned by this muscular stomach while bacteria break the cellulose3. The food moves to the reticulum where it is divided into solid and liquid before being brought back in to the mouth2. The food is then brought to the mouth in balls (bolus) and is chewed again and ground by the molars by forward, backwards and sideways movements combined with up and down movements3. The now well ground food and in semi liquid form goes to the omasum through the rumen where water is removed before going to the omasum3. All the final digestion and absorption takes place in this stomach2.

Chewing the cud normally takes place in safety and in a relaxed form thought to be a form of adaptation to escape predators and so the animal have to eat in a hurry. Also due to limited food and there’s competition makes the animals adopt this method first to fill their stomachs and then digest it later. Due to the many number of stomachs has made the animals grow bigger in size. They also take big amounts of food like the cows, wildebeests buffalos and the giraffe. This form of breaking down of cellulose is more advanced than that of the elephants2.

By being able to digest cellulose the animals are assured that their glucose requirements are provided for in their meals. This has come with various modifications to the body structure like teeth, stomach and an increase in their sizes2.

References:

1. Wikipedia contributors. Herbivore [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 30, 00:26 UTC [cited 2006 May 11]. Available from: http://en.wikipedia.org/w/index.php?title=Herbivore&oldid=50816562.

2. Knight, R. BCB Biodiversity chapter 2 The Invasion of the Land (Cited 2006 May 11) http://planet.uwc.ac.za/nisl/biodiversity/Chapter2/page_234.htm

3. Wikipedia contributors. Ruminant [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 22, 23:58 UTC [cited 2006 May 11]. Available from: http://en.wikipedia.org/w/index.php?title=Ruminant&oldid=49674058.

VINCENT MUCHAI WAIRIMU

Biodiversity and Conservation Biology

University of the Western Cape

Private Bag X17 Bellville

TEL: +27825103190

Email: 2648463@uwc.ac.za

Website:http://www.muchai.iblog.co.za

BIRDS ARE CLOSELY RELATED TO DINOSAURS

Dinosaurs are the vertebrates’ animals. The evidence of dinosaurs and birds are related. Birds are closely relatives of dinosaurs, but the bone tissue of Dinosaurs are similar to those of female’s birds. However the reproductions of dinosaurs are very closely related to birds. “Dinosaurs produced and shell their eggs like modern birds. The discovery of pigeon-size fossils called archaeopteryx had a bird like skull, perch feet, and was a powered flyer with wings of the basic pattern and proportions of the modern avian wing(1)”. One can say that dinosaurs are birds just because, Dinosaurs have identical feathers like a Morden birds.

There is different arguments concerning whether the birds are closely related to birds or not. Some scientist call a small creature named mononykus as a new link between birds and dinosaurs, they say so just because it shares some features with modern birds, such as keeled sternum and some fused wrist.

Evidence comes from dinosaurs footprints they indicate that dinosaurs walk upright, which is similar to modern birds. One can say that, the ancestors of birds are theropod dinosaurs. They are different evidence of dinosaurs. Archaeopteryx is one of the types of dinosaurs and it was found in Jurassic rocks of Germany. These types of dinosaurs have feathers and wishbone. Those feathers are like reptiles. Teeth, tail and forelimb structure are like reptiles. This characteristics is resembles a small theropod dinosaurs.


Another bird fossil of Archaeopteryx was discovered in Northern side of china and was named as a confuciusornis. “This new evidence of fossil was resembles Archaeopteryx with having wings claws, but unlike Archaeopteryx and like modern birds and it confuse, because it indicates, lacked teeth and making it birds like than Archaeopteryx. Both of these fossils were look like birds and dinosaurs. Probably it can fly but not modern birds due to their reptiles’ feathers” (1).

Scientist described the fossil protoavis as true birds which is closer to modern birds than Archaeopteryx. The evidence also shows that, the first birds lived at the same time as earliest dinosaurs. “This could force the modification of theory that, birds and dinosaurs are the same. Scientist from china has discovered the remains fossil of four winged dinosaurs, with modern feathers on both forelimbs and hind limbs. The new species micro raptor GUI, provide evidence that birds evolved from dinosaurs. Within the theropod group, birds are most closely related to cromaeossaurids”. Dinosaurs took care of their eggs much like birds do. They laid them in mass breeding ground and watched over them after they hatched. All these are the evidence that comes from different scientist. Legs of dinosaurs tend to develop towards the bird structure, and the development is not harmonious and toes are bird-like. The pelvic bones of bird always consolidated those of dinosaurs.

Just conclude dinosaurs and birds are looked like, not because they were closely related, but because they lived in similar environment and they survive in a similar way. The discovery of confuciusornis show us that, fossil of the same age as Archaeopteryx has given us more evidence on the evolution of birds and their link to dinosaurs. It is commonly thought by scientist, that birds evolved from dinosaurs, and more from theropod dinosaurs.


References
1. Ambeliz, R. 2002. Birds and Dinosaurs. [Online]. Available from:
http://geology.wcedu.pima.edu/~rambeliz/rafweb.htm [2006, May 11]

2. Willis, P. 1997. Working out relationship. [Online] [Cited 2006, May 11]. Available from: http://en.wikipedia.org/wiki/Birds

Linette Netshiheni
CSIR
Pretoria
0001
Cell: 0820446442
Tell: 012 841 2133
Fax: 012 842 3676
tnetshiheni@csir.co.za
Weblog: http://tnetshiheni-linette.blogspot.com/

THE REASON WHY HERBIVOROUS DIET IMPOSES CERTAIN PROBLEMS FOR DIGESTION AND HOW SOME ANIMALS HAVE OVERCOME SUCH PROBLEMS.

Herbivores are referred to animal that are adapted to feed on plant material, “herbivores are classified into sub groups depending on the type of feed they specialised on”.1 There are those that feed on fruits known as frugivores and folivores those that eat leave. However this does no mean that they do not eat other parts of the plant they mainly eat those selected parts fruits and leaves. Some is influenced by diet that the animal have which vary with season, so then they chose different diet when is available. [1]

Diet in which most of herbivores feed on is different depending on the environment they live in some become more abundant during some seasons. Other herbivores select their diet to feed on, because of the accessibility they have to that foliage. Small animal cannot choose the diet of big trees that found in the forest where there is predators so they have to choose area where they can access. While large animals such as giraffe chose foliage that are higher as their body can stretch to the height of the foliage.

Chosen diet has problems on most of herbivores, but these depend on the type of stomach that the herbivores species have. Some have true ruminants while other are non ruminants, this make those with true ruminants to have better digestion than non ruminants. Herbivores that have long digestive track minimize the problem that they have on digesting the cellulose from plant materials. Cellulose is the main cause of problem in the digestive system of herbivores.

The plant material that most herbivores feed on contain cellulose, it have high energy source and organic substances. And most of herbivores digest food through enzymes digestion; it is difficult for enzymes to break down cellulose because of its high organic substances and energy. so this pose problem in most of herbivores, those that have long digestive track reduce the problem by having extended chewing that the ruminants keep the foliage and fermented it before it comes back to the mouth for chewing. This cellulose is also broken down by micro-organisms that are present in the ruminants; this process is known as fermentation. [2]

This process of fermentation happens after the species have finish grazing, the foliage has been stored in the ruminats.the bacteria and protozoa digest it, during leisure the foliage return to the mouth for chewing and this simplify the breaking down of cellulose. Those problems that happen to herbivores during digestion tend to be reduced. But with the involvement of bacteria and protozoa in the process of fermentation it reduce the problem in herbivores with ruminants while in non- ruminant is still a problem. [2]

The process of fermentation reduce the problem, but in vegetarians takes time for digestion and this were suggested to be reduced by herbivores that have long digestive track. This is because they don’t have bacteria in the stomach. and for animal to have long digestive track their bodies need to grow big, so most of the animal that feed on plant material evolve giant so that they can have long digestive track. Having long digestive track help herbivores to extend their diet to tough plants, which there is less competition. [4]

Because of cellulose they eat, metabolism rate increase and it was suggested that animal with high metabolic process can grow rapidly. It mainly happens in animal that live on land. In terrestrial environment competition of food resource are great, so those that evolve long digestive track and become giant tend to feed on tough plant which other cannot feed on. While other feeds on the foliage that are high where other cannot access it. This reduce the problem that they where having as they cannot compete with other for food and they end up eating fresh material that do not require fermentation much. For example, elephant and giraffe, they reach 18 feet high and they can access high foliage, while elephant also reach 18 feet high with weight around 8 to 10 tonnes ,this enable them to use great bulk of tall trees.[3]

This enables many large herbivores to feed on high foliage, while small herbivores feed on grass or small foliage. Adopting large bodies for these herbivores helps then to maintain body temperature through high metabolic rate, and also to be less vulnerable to predators. This because having large body also increase the strength that can prevent small predators to attack them.

In nutshell, diet that herbivores choose to feed on has impact on digestion and this influence the change in body structure. They change their body structure to solve the digestion problem they encounter. And also to have better access to food resources as there is competition, large animal can access to high foliage. But all changes that herbivores have of becoming large is because of the problem they met, failing to digest cellulose pose an impact, that’s why we find large animals on land .

Reference:

1. Herbivores. The world’s greatest encyclodictionalmanacapedia [Internet] [cited 2006 May 10] Available from: http://www.answers.com/herbivores&r=67

2. Findlay A.L.R.: The Gastrointestinal System: an introduction Carnivores, Omnivores and Herbivores [Internet] 1998-February [cited 2006-May11]: http://www.chu.cam.ac.uk/~ALRF/giintro.htm

3. Chang.A. Is there any evolutionary advantage to gigantism? Did sauropods continue to grow throughout their lives, like some reptiles and fish do? [Internet] 2000-October-16[cited 2006-May-10]

4. Kaplan.M.1995. A very brief overview of digestion in green iguanas and other herbivorous lizard species. [Internet].2003-August-11[cited 2006-May-11].Available from: http://www.anapsid.org/tracydigestion.html

Mr Elelwani Muanalo
NISL- Ecological Informatics Student
CSIR Pretoria
Tel: +27 12 841 2133
Fax: +27 12 842 7024.
Email: emuanalo@csir.co.za
My bloger URL: http://www.emuanalo.blogspot.com

DESCRIBE HOW PLACENTAL MAMMALS HAVE COLONIZED LAND, WATER AND AIR

Placental mammals “are diverse group whose young are born at relatively advanced stage (more advanced than the young of other mammals)” (1). The placental mammals include such diverse forms as elephants, whales, shrews, and armadillos. They include pets such as dogs and cats, as well as many farm and work animals, such as sheep, cattle, and horses. A human falls under the placental mammals.

The placentals mammals are by far the largest of all three mammal groups. Before the Young placental mammals are born they spend relatively long time inside their mothers body. They are warmed and protected within the mothers womb; the unborn young are nourished by a soft organ called the placenta. This placenta plays a vital role in absorbing nutrients from the mothers blood and transfers them to the developing young in the bodies. By the time a young placental mammal is born it is usually fully formed, but their eyes are not opened and their teeth not fully formed.

Some placental mammals have adapted to life and colonise water, land and air. Placental Mammals have developed different body shapes and sizes. These body size and shape were the other driving forces behind colonising water, land and air. “On land, mammals live in many different habitats, and at a wide range of altitudes. Many mammals dig burrows as refuges or as places to raise their young, but some have developed a largely subterranean lifestyle, feeding on small animals or plant roots beneath the soil surface” (2). These placental mammals, “including moles and mole-rats, dig through the ground either with spadelike front paws or with their teeth, and they detect danger by being highly sensitive to vibrations transmitted through the soil” (2).

“Some mammals, such as otters and river dolphins, have adapted to life in freshwater habitats, but the great majority of the worlds aquatic mammals live in the ocean. Seals remain close to coasts or to floating ice, but whales and dolphins are truly pelagic, meaning that they wander far out into open water. Most of these marine mammals live in areas where food is abundant, but where water temperatures are low” (2). “They survive the cold in two different ways. Some, such as sea otters and fur seals have a double coat of fur, with extremely dense underfur hairs that are so closely packed that the skin never gets wet. By contrast, whales and dolphins have very sparse hair, and keep warm with a thick layer of fat called blubber” (2).

Other placental mammals such as the bats inhabited the skies. The limbs which they were characterised of evolved into wings. By developing these wings enable them to fly. They survive by catching their prey on air. They feed on insects, using different technique for catching their flying prey. “Using a system called echolocation; a bat sends out bursts of high-pitched sound toward objects and interprets the returning echoes as images that guide a bat toward its prey so that it can hunt even in total darkness” (2)

The placental mammals that live on land mostly have four legs, which they use for walking on search for food. For example, “the jaguar, a terrestrial carnivore with explosive running power, is adapted for speed on land and this carnivore colonise the land since it is a carnivore, most of its prey lived on land” (2).

Reference:

1. WGBH education foundation, convergence, marsupials and placental, 2001 [Internet] [cited 2006 May 24] Available:
http://www.pbs.org/wgbh/evolution/library/01/4/pdf/l_014_02.pdf

2. “Mammal,” Microsoft®, Encarta® Online, Encyclopedia 2006 [Internet] [Cited 2006 May 24] Available:
http://encarta.msn.com/encyclopedia_761561349/Mammal.html

Mr Lufuno Mukwevho
CSIR Pretoria
P.O. Box 395
Pretoria
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Tel: (012) 841 2133
Fax: 012 842 7024
Cell: 0723175626
E-mail: lmukwevho@csir.co.za
My blog URL: http://mukwevholufuno.blogspot.com

DISCUSION OF THE ADAPTIVE RADIATION IN THE ORDER INSECTIVORE

Adaptive radiation is the process which is thought to take place when one species change or evolve into two or more other species. On the other side insectivore are thought to be animals which feed on insects. The name insectivore is an indication of their adaptation on feeding on the insects. Insectivore are also thought to be have evolved from the placental mammals (Wikipedia contributors, 2006).

''Adaptive radiation takes place as a result of different population of the species when they become separated from each in terms of reproduction'' (Harbel, 1995: 2). This often occurs when the separated species are able to adapt into the new environments. The way the species diverse and their rapid spread influence the evolvement of organisms to the new ecological environment. Scientists also disagree with each other when coming to whether the morphology of the insectivore is closely related to the placental mammals. It is also said that in the late Eocene and early Oligocene, insectivore underwent an adaptive radiation. By undergoing the adaptive radiation, insectivore manage to produce different lines which seem to have the beginnings of the family of the placental mammals (Myers, 1999).

Insectivore which also look like the placental mammals have also been known by the scientists in the late Cretaceous period. The group Cimolestes, were thought to flourish in the late Cretaceous of the North America. This is evidence which seem to confirm those ''insectivore are the descendent of the placental mammals'' (Harbel, 1995: 1). It is also said that the molecular studies which are done in Madagascar also indicated that the golden moles and the tenrecs are not closely related to the insectivores which are found in the continent of Africa, especially in the Northern part of the continent.

It is further said that insectivore are classified in one order of the placental mammals. This family is thought to include other animals such as ''moles, shrews and hedgehogs'' (Wikipedia contributors, 2006). The name insectivore implies that the animals feed on other small organisms such as worms which are vertebrates animals even though they also feed on organic organisms. Some scientists also believe that the order insectivore generally evolve from the primitive placental mammals. Their argument is based in the study of the fossil remains which found in different continents.

Some scientists said that traditionally, insectivore serve as the basis of the adaptive radiation of the placental animals. Scientists further continue by saying that the insectivore which are living today indicate the closely relationship which comfirmed that they branched off from the evolutionary tree of the placental mammals. But most of the scientists who conducted their research earlier said those insectivore were occupying the central position in the group placelantia.

In conclusion, one can say that the adaptive radiation of the insectivore is still unclear. This is because that scientists themselves, they do not agree with each other whether placental mammals do evolve into the insectivore. Furthermore, scientists do not specify which species evolve after the insectivore. This is because there are still some scientists that believe that insectivore descended from the placental mammals.

References:

Harbel, W. 1995. Eurasian and Tree Shrews. [Online]. Available from:
http://members.vienna.at/shrew/itsesAP95-introduction.html [June 1995, 16:12]

Myers, P. 1999. Order Insectivore. [Online]. Available from:
http://animaldiversity.ummz.umich.edu/site/accounts/information/Insectivora.html [25 May 2005]

Wikipedia contributors. Insectivora [Internet]. Wikipedia, The Free Encyclopedia; 2006 April 11, 11:31 UTC [cited 2006 May 11, 14: 21]. Available from: http://en.wikipedia.org/wiki/Insectivora


Peter Muvhali
CSIR PTA
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Tell no 012 8142133
Fax 012 8423676
E-mail smuvhali@csir.co.za
URL: http://blogsoccer-peter.blogspot.com/

COMPARISON BETWEEN PLACENTAL AND MARSUPIAL MODES OF REPRODUCTION

Marsupials are animals that belong to the order Marsupiala and an infraclass Metatheria. Other members of the class include kangaroo, koala, Tasmanian devil and the Virginia opossum. Marsupials are also defined by biologists as a subdivision of mammals with several characteristics. They have more incisor teeth and in most of them the first toe of the hind foot is opposed to the other four and it also lack a claw. Their brain size is very small. They are generally accepted as non-placental mammal whose female carries her young in a pouch or marsupium, where young ones are provided with a proper environment, warmth, possess a placenta, although that placenta is non-invasive and functions in the transferring of nutrient and waste for a short period of time"(1)

"Placenta mammals are given this name because the placenta connects the growing embryo within the uterus to the circulatory system of the mother. It is the pathway provider for the nourishment of the fetus"(2). This enables the fetus to reach a higher level of maturity of the body and brain before birth, most of the placenta mammals invest most of their time in the stage of growth.

The major difference between the marsupial and placental mammals is the rate of gestation, or the time the offspring has taken in the uterus. Mating system vary in marsupials throughout the year. "Some species are solitary and they only come together to mate and this pattern of social behaviour reflect promiscuous mating systems. Male of some species defend their access to several females. In marsupials the developing embryo is separated from the body of its mother by amniotic membrane. After fertilisation the embryo will become a new organism and the immune system will attack it. The amniotic protects the embryo from this attack by isolating it from all biological interactions with the parent. The Marsupial embryo depends on the egg yolk for nutrients so it is limited to the quality of nutrients contained in the egg. The shortness of the gestation period is due to the type of yolk-type reproduction"(3). Birth in marsupials occur very fast compared in placental mammals including the helpless fetus journeys to the pouch where it becomes attached there for weeks or months depending on the species. The longest days a marsupial can spend in a reproductive tract are only twelve.

Placental mammals have a longer gestation period and this result in offspring that are born being fully developed. "The extended maturation of placental is caused by the placenta which, which allows nutrients to travel from the mother system to the embryo and waste to be carried away. The embryo and the mother do not share the same blood supply, but instead the placenta is composed of several layers which are richly supplied with blood vessels, and acts as a preferential immigration barrier letting nutrients and metabolites pass through, and preventing the transfer of immunity system components " (3).

When marsupials are pregnant it does not stop the oestrus cycle to take place but in placentals the oestrus cycle stop until the whole period of pregnancy is over and it will then re-start again. In marsupials the ovarian inhibition is mediated by lactation or suckling stimulus. This is important because the baby will no longer be carried internally so negative feedback stimulus from the presence of the babies must come from nursing activity.

Reference

1. Oppossaum Society Of The United States, 2003. Oppossaum Reproduction and Life Cycle [Internet] 2006 May 11; 08:45 UTC [Cited 2006 May 11] Available From:
http://www.opossumsocietyus.org/opossum_reproduction_and_life_cycle.htm

2. Andrienne, L. 2001. The Human Evolution Coloring Book [Internet] 2006 May 11, 09:25 UTC [Cited 2006 May 11] Available From:
http://www.pbs.org/wgbh/evolution/library/01/4/pdf/l_014_02.pdf

3. Culp, G. Richard. 1998. The Geographical Distribution of Animals and Plants [Internet] 2006 May 11; 10:30 UTC [Cited 2006 May 11] Available From:
http://www.nwcreation.net/marsupials.html

Dianah Nangammbi
Cilla CSIR
P.O Box 395
Pretoria
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Tel: +27 12 841 2133
Cell: +27 73 121 3589
Email: dnangammbi@csir.co.za
http://wwwdianah.blogspot.com/

ADAPTATION REQUIRED TO MAKE TRANSITION FROM AQUATIC TO TERRESTRIAL LIFE USING AMPHIBIANS.

Amphibians are cold blooded vertebrate that spend some time on land but must breed and develop into water. Frogs, salamanders and toods are examples of amphibians. Amphibians are animals who lay their eggs in water and spend at least part of life on land. Amphibians begin their lives under water and breathe through gills. Adults live on land and breathe through lungs. Amphibians do not have muscles to help them to inflate and deflate their lungs. They depend on oxygen through their thin, wet skin.


Amphibians keep their bodies moist inorder to prevent the loss of water through their skin. They avoid dry by ling near the river and they must return back to water to reproduce. Amphibians such as bullfrogs and some salamanders spend most of their life in water. Toads and salamanders are independence from water and they are forced to return to water to reproduce. Tadpoles have gills which is used to breathe in water. Amphibians lives on land has a lung to breathe. Most of terrestrial amphibians they feed on insects including mosquitoes and black flies, and on aquatic they feed on plants or fish. Amphibians on land they jump and on aquatic they used to swim. For examples frogs, on aquatic they walk on swim and in land they jump.

Some of the amphibians live their whole life in water, while others live on land and return to water only to mate and lay their eggs. Some amphibians have smooth skin and live in water. E.g frogs. Some amphibians have warty skins and live on land. E.g Toads, they adapted to dry condition it breed intemporary pools after. Most reptiles are not dependent upon body water for reproduction. They can live in desert. Some reptiles such as snakes and few lizards have gone back to living in water but breath air through their lungs and emerge from water to lay their eggs on lands.


Crocodiles, gavials and caimans are aquatic but come out of the water to relax and build nests for their eggs. Crocodile and alligators breathe with lungs but they spend much time in water. Turtles are live on streamlined for swimming. They have feet which makes them coming onto land to lay eggs. Snappers and softshells come out from water to walk easy. Painted turtles and red-eared sliders come out inorder to busk in the sun. land turtles such as box turtles and wood turtles spend most of life on land but it like to soak in water occasionally.


The limitations to a terrestrial life of amphibians exhibit are: habitat loss, road construction, livestock activity: these livestock has resulted in the following disturbances: grazing and trampling have ruduced vegetation cover and create drier soil condition, water diversion, "unnatural flow regimes, introduce non-native fishes and bullfrogs and activities which increase sediments such as road construction, logging and intensive cattle grazing within frog habitat
Clearcutting, disturbance related to roads trails and deseases are the most important limiting factors of terrestriallife"(1). Deseases mass mortality of amphibians are caused by different deseases found on land. Climate condition have a major influence, such as drought which cause the death of amphibians.

“Terrestrial egg masses are more diffusion limited, because gravity and surface tension collapse them, preventing convection between the eggs, and restricting the source for oxygen diffusion. Terrestrial embryos are often larger than their aquatic counterparts and have higher demands for oxygen. Terrestrial conditions have selected for adaptations that reduce respiratory competition between embryos, for example, separating of embryos by large volumes of jelly or reducing the number of eggs in a clutch. The size of foam nests is unlimited, because oxygen for each embryo is supplied directly from the foam”(2).
References


1. Living Things Amphibians. [Online].Available from: http://www.greenscreen.org/newsletter/articles/Amphibians.html%20[2006, May 11]

2. Jennings.1996.Amphibians of the Big Chico Creek.[Online]. Available from: http://www.csuchico.edu/bei/BCCER/Biota/amphibians.htm%20[2006,May 11:20]

3. Wikipedia Contributors, Amphibians [Internet]. Wikipedia, The free encyclopedia, 2006 may 09, UTC [Cited 2006 may 11]. Available From:http://en.wikipedia.org/wiki/Amphibian

Linette Netshiheni
CSIR
Pretoria
0001
Cell: 0820446442
Tell: 012 841 2133
Fax: 012 842 3676
tnetshiheni@csir.co.za
Weblog: http://tnetshiheni-linette.blogspot.com/

ADAPTATION REQUERED TO MAKE THE LAND LIFE TRANSITION FROM THE WATER TO LAND LIFE USING AMPHIMBIANS GROUP AS AN EXAMPLE

Amphibians are vertebrate animals that can inhabit on both land and in water, which lay their eggs in water. Some of these species have four feet and they do not have amniotic eggs. Amphibians was classify at the Amphibia. It was said that their transition from land to water was not completed because they live in water and this means that they require a transition from the aquatic to terrestrial environment and they first adapt air from the terrestrial environment. Species such as frog, tatropods and salamander etc are the example of amphibian’s animals.


The frog animals adapted to an arid and semi arid environment need water to lay their eggs meaning that water plays an important role during their reproduction. They lay their eggs inside the water, then the eggs will be hatched inside the water and the young eggs developed into adult. Small or adolescent fogs live in water and breathe with gills and adult live on land breathe through lungs. When adolescent reach sexual maturing stage, they goes back inside the water and spend a lot of time inside the water. Frogs feeds themselves on algae plants in water and when they are on land they eat insects such as flies etc. They depend on absorbing oxygen through their thin, wet skin.


Some of the amphibians manage their adaptation on land. Amphibian’s metamorphosis has four legs to support their body on the land. Their gills are replaced after being terrestrial dwellers and they also started to use lungs for breathing. Their skin change and develops glands to avoid loosing a lot of water from their body and this process is dehydration. They also develop eyelids on their eyes and they start to adapt vision when they are outside the water. They also develop an eardrum that locks off their middle ear. The species such as frog and toas lost their tails. Frogs uses their legs to swim in water and they jump when they are on land.


Early reptiles and other living organisms succeeded their adaptation on the land but frogs did not succeed because of the low biomass on the land and dry environment in dry areas. Amphibians are semi terrestrial inhabitant. Their skins are soft and moist meaning that they are at the higher risk of dehydration in the dry area. Their eggs were unprotected meaning that were not covered by the waterproof, these eggs must be laid near the plants that are found inside the water where they are fertilised. Some of these species place their eggs within their mouth and some place their eggs at their stomach after the external fertilization.


The declines in amphibian’s populations include population crashes and mass localization extinction and this is the threats to the global biodiversity. Amphibians started to decline after becoming a terrestrial dwellers and this caused by the limitation factors such as over exploitation, climate change, population growth, diseases, habitat distruction and modification. Most of an amphibians run away from the water to the land because of the above factors. The species manage to survive are frogs, tetrapod etc.
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Tetrapods species do not have amniotic eggs and they have adaptations to a terrestrial environment. Amphibians such as crocodiles lay their eggs in a mass of dead vegetation. Amphibians animals are adapted to the wetland or wet environment. They also have a skeleton bone and four legs which support them to stand on the land. The wetland is good for both arid and semi arid animals because water play an important role during their reproduction and on land they maintain their body temperature.


References:

Wikipedia contributors. Amphibians [Internet] wikipedia, the free encyclopaedia 2006 May 09, 12:25 UTC [cited May 11]. Available from:
http://en.wikipedia.org/wiki/Amphibians


Lizzy Maluleke
CSIR PTA
0001
Cell number 072 351 8488
Tell [012] 841 2133
Fax [012] 842 3676
E-mail mmaluleke@csir.co.za
Weblog: http://mmaluleke.blogspot.com

WHY REPTILES ARE BETTER ADAPTED TO A TERRESTRIAL ENVIRONMENT THAN AMPIBIANS

Reptiles are cold blooded animals (ectothermic). Reptiles are referred to as cold blooded they cannot generate their own heat so they have to get heat from outside i.e. the sun (1). Reptiles rely mostly on the environment to regulate their internal temperature, for example they move between sun and shade. They also move warmed blood into "their body core, while pushing cool blood to their periphery" (1). Since reptiles lack an internal heating mechanism and this becomes beneficial to them sometimes because it allows reptiles to survive on much less food (they do not have enough energy).

Lizards from the Scincomorpha family, which include "skinks, often have shiny, iridescent scales that appear moist" (2). However, like all other lizards, they are dry-skinned and generally prefer to avoid water but they can live in water mostly for their survival. All lizards are able to swim if needed for example if they fall inside the water by mistake they will swim in order to safe their lives. However, they do not feel comfortable in the aquatic environments but for some lizards they enjoy the aquatic life (2). For example marine iguana (a lizard which live in the water) when it is cold it is unable to move effectively, which makes it more vulnerable to predators. Since they cannot maintain their body temperature; they depend mostly on the sun. Marine iguanas are very aggressive against their predators in order to protect themselves before they have warmed up since they are unable to run away(they do not have any energy to fight back or escape) (3).

The physiology of frogs is generally like that of other "amphibians but differs from other terrestrial vertebrates" (5) because frog have a permeable skin and they sometimes use their skin to breath. The skin of a frog allows them to breathe largely since they can breath through their skin. Oxygen is dissolved in an aqueous film on the skin and passes straight to the blood. Their skin must remain moist at all times. The skin of a frog makes frogs to be susceptible to many toxins especially while they are on land because if the skin is permeable means that everything can pass through the skin into the body(4). Reptiles skin mostly consists of scale and it is not permeable like frog's skin. There is a lack of moisture on land so in order for amphibians to survive they require a lot of mosture unlike the reptiles which have adapted to live on land. Ampibians depend mostly on the amount of mosture available unlike the reptiles.

Many frogs are able to absorb water directly from the source through the skin, especially around the pelvic area which makes them more vulnerable to absorb a lot of poisonous gases from the atmosphere. The permeability of the skin of a frog can also result in water loss especially on land unlike the reptiles (3). Reptiles have a skin which mostly consists of scales which protect the reptiles from losing water than the reptiles (5).

The only thing that the amphibians and reptiles have in common is that they are both ectothermic- can not maintain their body temperature. They maintain their body temperature by basking on the sun. They absorb a lot of heat so that they can be active. The problem in amphibians is that they can not survive on land for longer periods unlike the reptiles which basically live on land. When the amphibians are on land their skin loses a lot of water. When amphibians are on land mostly they absorb a lot of heat within a short period of time so that by the time they dry out they should have collected enough heat and they also minimize the period of lethargy( they can inhale lot of dangerous gases) after emerging from the water. Reptiles can maintain and retain their water inside unlike amphibians.

Reference:

1. Wikipedia contributors. Reptiles [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 10, 02:57. UTC [cited 2006 May 10]. Available from: http://en.wikipedia.org/wiki/Reptiles
2. Wikipedia contributors. Lizards [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 10, 07:12. UTC [cited 2006 May 10]. Available from: http://en.wikipedia.org/wiki/Lizard
3. Wikipedia contributors. Anura [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 10, 02:38. UTC [cited 2006 May 10]. Available from: http://en.wikipedia.org/wiki/Anura
4. Wikipedia contributors. Marine Iguana [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 8, 23:48. UTC [cited 2006 May 10]. Available from: http://en.wikipedia.org/wiki/Marine_Iguana
5. Wikipedia contributors. Vertebrate [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 7, 13:12. UTC [cited 2006 May 10]. Available from: http://en.wikipedia.org/wiki/Vertebrate


Lethabo Mosomane
CSIR
Pretoria
0001
Tel: 27 12 841 2133
Fax: 27 12 842 3676
mail: lmosomane@csir.co.za
http://lmosomane.blogspot.com/

THE REASONS WHY SOME OF AMPHIBIANS BECAME LIMBLESS.

The amphibians are the simplest Tetrapods from the first class of the vertebrate to occupy the land. The Tetrapods includes approximately 18100 existing species of amniotes and approximately 300 existing species of amphibians. Tetrapoda refers to the species with four feet and it forms the largest group of the global vertebrates (Frank et al, 1995).

Some of the known amphibians animals, which lost their limbs or became limbless animals, include snakes and whales (2).

The loss of the limbs seems to be very common in all lineages of vertebrates. Both the fishes and the amphibians evolved several times and they both move by using the limbs. There is at least one group of mammal (whales) that never lost either of their limbs. They survived only because they developed a larger, broad tail which significantly strengthened their axial muscular. Some of the amphibians lost their limbs because the axial muscular mammals and the archosaurs were not able to support them. These animals lost their limbs because of the environmental conditions which were not stable (2).


Reasons were suggested on why the snake became limbless. It was suggested that the snake might have “burrowed underground searching for food in small crevices” (2). I tend to agree with this suggestion, because even to date snakes spent much of their times in small holes (hibernate). Most of the times, snake are seen during summer times, when they are searching for foods and sometimes when they are feeling hot in their habits. The snakes lost their limbs when they were struggling to enter the small holes” (2). There was not a way that the snake could have limbs after losing their limbs supporters (2).


According to the information gathered, it really shows that some of the amphibians became limbless, because their common ancestors are having four limbs. The two are found in front and another two at the back. When we talk about the limb we are referring to a leg, wing or an arm of an animal. The two major hypotheses called the fin – fold and the gill arch hypotheses explain better about the original of the limbs (3).


In conclusion, the amphibians lost their limbs because of the unstable environmental conditions and also because some of the amphibians were going underground to search for their food, by so doing they injured their pelvic that was then when they became limbless (2).

1. SeaWorld/Busch Gardens Animal Information Database. (2002) [http://www.buschgardens.org/infobooks/KillerWhale/adapaqkw.html, accessed on 09/05/2006, 10:00].


2. Scientific American. (2005). [http://www.scientificamerican.com/print_version.cfm?articleID=000DC8B8-EA15-137C-AA1583414B7F0000 , accessed on 10/05/2006, 12:30].


3. Frank H.T, Shaffer P.R, Perlman R. 1995. Fossils a Guide to Prehistoric Life. Page (139)


Ms Evelyn Maleka
CILLA CSIR
P.O. Box 395
Pretoria,
0001
Tel: (012) 841 2133
Fax: 012 842 7024.
Email:emaleka@csir.co.za
http://malekaevelyn.blogspot.com/

REVISION SHOWING THAT DINOSAURS WERE WARM-BLOODED ANIMALS

Dinosaurs are said to be the very large animals that have ever existed. According to the dinosaur fossils they were dated about 230 million years ago. Madagascar is situated on the South East side of Africa and this is were the oldest dinosaur fossil was discovered. The first dinosaurs that were found were slightly built and their height was about 3 to 3.5 metres long. They imposed very different diets, some were carnivores, herbivores, omnivores and others were insectivores.

There has been a great debate going on about whether dinosaurs were warm-blooded or cold-blood. Scientists have conflicting opinions on this matter. "Paleoanthropologists think that all dinosaurs were warm-blooded as modern mammals and birds because they have the same metabolic rate. Other scientists think that the biggest dinosaurs could have warm bodies because of their large body size. Generally if all the animals were examined at a proper time they will all appear to be warm blooded because their internal bodies are the same.
The mechanism by which the body temperature is maintained is more important. This can be explained simply by using two terms which are ectothermic and endothermic. Ectothermic animals rely on heat from the outside environment to maintain their body temperature while endothermic animals use the heat generated from inside their own bodies by the metabolic process, they are composed of bodies with a higher metabolic rate.Once it was believed that all dinosaurs were cold blooded but now much evidence proves that at least some were warm blooded. All creatures whether warm-or cold-blooded use the same biochemical processes, enzymes and substrate to produce energy. All chemical reactions involved have a particular optimal temperature"(1).
There is no definite answer about whether dinosaurs are warm- or cold- blooded but in the 1970s scientists began to look at some evidence showing that dinosaurs were maybe warm-blooded. Recent studies are showing that dinosaurs were neither warm-blooded like mammals nor cold-blooded like reptiles but in between.

The isotope of their bones shows that they are warm-blooded. Warm-blooded animals grow more quickly than cold blooded ones. "Dinosaurs grew very fast; this was proved by Jack Horner through the bones of a tiny baby dinosaur found in hadrosaur nests. The bones show that baby dinosaurs reach a considerable size while still in the nest. Additional evidence about the growth was found in the microscopic structure of the bones where it was observed that dinosaur bones are rich in the passage ways called Halversian canals which transport nutrient-laden blood to the cells that lay down new bones"(2). This conflict will never end because recent studies also show that the heart of a herbivore dinosaur was studied and it consisted of four chambers instead of three which is common in a warm-blooded animal.

If dinosaurs were warm-blooded then their lives would be more like mammals than reptiles, because reptiles like snakes and lizards spend most of their time moving from one place to another looking for a more warmer area just as they do during winter when they hibernate.
Reference

1. Feduccia, A. 1974. Dinosaurs and Archaeopteryx [Internet] 2006 May 10; 09:05 UTC [Cited 2006 May 10] Available From:
http://www.isgs.uiuc.edu/dinos/de_4/5c51d90.htm

2. Bakker, R. 1972. Anatomical and Ecological Evidence of Endothermy in Dinosaurs [Internet] 2006 May 10; 10:15 UTC [Cited 2006 May 10] Available From:
http://www.dinoruss.com/de_4/5c51d90.htm

Dianah Nangammbi
Cilla CSIR
P.O Box 395
Pretoria
0001
Tel: +27 12 841 2133
Cell: +27 73 121 3589
Email: dnangammbi@csir.co.za
http://wwwdianah.blogspot.com/


THE DINOSAURS WERE WARM-BLOODED ANIMALS

Dinosaurs were the warm-blooded vertebrate animals living on land for over 160 million years and it also said that they first appeared about 230 million years ago and their hearts was resembled of crocodiles. These organisms have back bone skeleton and also have four legs. Dinosaurs were discovered in "the 19th century and species such as pelycosaur Dimetrodon, the pterosaurs were found on the land. Another example of dinosaurs that were found in the water is ichthyosaurs, plesiosaurs, and mosasaurs. These species suffered a catastrophic extinction which made them dominated on land" (1).


During 1970s scientists started looking" the evidence indicating that the dinosaurs may be warm blooded animals and the evidence shows that the dinosaur started to stand straight and walk like animals because their legs were like the animals" (1). They also have big ribs cages like a mammal’s heart and lungs. The other thing is that they also had "bones containing channels for quick blood circulation which was also found in warm blooded animals" (1).


The palaeontologist believed that some of the dinosaurs were warm-blooded animals but at the beginning were believed to be the cold-blooded animals because of they were closely related to the cold-blooded animals known such as reptiles. The warm-blooded do" not rely on the environment, chemical reaction help them to create heat inside their body" (1) and this means that they can regulate their body temperature rather than relying their on the environment, they can also hunt anytime any where.


Beverly Eschberg says that dinosaurs were believed to be related to the reptiles, but some of these species behave like the warm blooded animals. It said that the dinosaurs were active and moving at a high speed. Other scientist says that they fossils about "the warm blooded animals that suffered from the heat in warmer climate were recognised" (1). Beverly says that the evidence such as bones, growth rate, histology, predators to prey, high speed, and rate of evolution etc shows that the dinosaurs are warm blooded animals and all these evidence convinced her that the dinosaurs were the warm blooded animals.


The palaeontologist discovered the fossils of the dinosaur’s heart and they decided to name it Willo. Russell believed that this heart shows that this species was a warm blooded animal. Warm blooded animals can maintain "their body temperature at any environment and they can also control it by increasing their metabolic rate when the temperature decreases" (1). Ostrom and Baaker are the ones of the Palentologists determined that dinosaurs are the warm blooded animals because they believed that these species grow quickly and cold blooded animals grow slowly.


In 1992 the scientists by names of Shower and Barrick believed that "dinosaurs were warm blooded animals because of the temperature that they were maintaining at their body core" (1). They provide the evidence of bones, so the isotopes from the dinosaur’s bones indicated that the dinosaurs were warm blooded animals. This is also because "the bones are composed of minerals and calcium phosphate (CaPO4) so the oxygen in this process exist in the form of two isotopes,160 and 180 and this ratio can be measured and this means that the species is warm blooded animals" (1). The bones of dinosaurs are rich in halversia canals that transport nutrients from the blood to the cells that down new bones.


Pateontologists have different thoughts about the evidence of the dinosaurs. There are some scientists who believed that dinosaurs were warm blooded animals and others believed that these animals were cold blooded animals and both have the evidence to prove their believe. I concluded saying that the dinosaurs were warm blooded animals because they can maintain their body temperature at favourable and unfavourable environmental conditions.


Reference:

1. Barrick, R and Shower, W. 1994. Bones isotopes [Internet] 2006 May 17,15:04 UTC [cited 2006 May 16:29] Available from:
http://www.dinoruss.org/de_4/5c52015.htm
2. Chang, G. 1999. Dinosaurs were hybrid of cold-blooded, warm-blooded animals [internet] 2006 May 09, 11:30 UTC [cited 2006 May 10] Available from: http://www.exn.ca/Html/Templates/topicpage.cfm?ID=19990122-51&Topic=Dinosaur

3. George, J. 1997. The isotopes in their bones suggest that dinosaurs were warm blooded [internet] 2006 May 09, 14:30 UTC [cited 2006 May 10] Available from: http://www.txtwriter.com/onscience/Articles/dinoblood.html

4. Discovery Channel. 1997. Bird-like dinosaur found in Argentina[online]2006 May 09, 15:03 UTC [Cited 2006 May 10] Available from:
http://www.exn.ca/Html/Templates/topicpage.cfm?ID=19970521-02&Topic=Dinosaur

5. Krystek, L. 1996. Hot and cold running dinosaurs [Online]2006 May 17,15:04 UTC [cited 2006 May 17] Available from:
http://unmuseum.mus.pa.us/colddino.htm

6. Morell, V. 1987. Were Dinosaurs warm-blooded? Evidence supporting the claim that dinosaurs were warm blooded from strongest to weakest [internet] 2006 May 07, 11:30 UTC [cited 2006 May 10] Available from:
http://www.cheathouse.com/essay/essay_view.php?p_essay_id=12829

7. Wikipedia contributors. Dinosaurs [Internet] wikipedia, the free encyclopaedia, 2006 May 09, 18:48 UCT [Cited 15:00 May 10]. Available from:
http://en.wikipedia.org.wiki/Dinosaurs


Lizzy Maluleke
CSIR PTA
0001
Cell number 072 351 8488
Tell [012] 841 2133
Fax [012] 842 3676
E-mail mmaluleke@csir.co.za
Weblog: http://mmaluleke.blogspot.com/