29 Haziran 2007 Cuma

Koala





Latin name:
Phascolarctos cinereus
(Greek: phaskolos means pouch; arktos means bear. Latin: cinereus means ash-colored.)
Koalas are marsupials, females having a pouch in which their young first develop. Their pouch faces the rear and has a drawstringlike muscle that the mother can tighten. They are the sole member of the family Phascolarctidae.

Taxonomy:
Kingdom: Animal
Phylum: Vertibrata
Class: Mammalia
Sub-Class: Marsupialia
Order: Diprotodontia
Sub-Order: Vombatiformes
Infra order: Phascolarctomorphia
Family: Phascolarctidae
Genus: Phascolarctos Cinereus

Subspecies:
There are three subspeies:
P.c. victor (Victoria)
P.c. cinereus (New South Wales)
P.c. adustus (Queensland).

Size:
Size is larger in the southern regions. Head-body length in the south average 30.7 in./78 cm for males and 28 in./72 cm for females.

Weight:
Average 26 lbs/11.8 kg for southern males and 17.4 lbs/7.9 kg for southern females. In the north, males average 14.3 lbs/6.5 kg; females 11.2 lbs/5.1 kg. At birth young weighs only 0.5 gm. (This is no typo; it is amazing how small they are at birth, about the size of a bee.)

Fur:
The fur of the koala in southern region is thick and woolly and is thicker and longer on the back than on the belly. Koalas in northern region have a short coat; this gives them a naked appearnace. The color and pattern of the coat varies considerably between individuals and with age.

Coat:
Thickest of the marsupials. Gray to tawny: white on the chin, chest, and forelimbs. Rump consists of tougher connective tissue dappled with white patches. Fluffy ears with longer white hairs. Coat is shorter and lighter in color toward northern regions.

Gestation period:
34-36 days.

Life span:
Their life span today varies considerably due to stress factors, probably averaging 13-18 years.

Principal predator:
Humans

First described in 1908 by E. Home.



A Brief History
koalas
There were once several different kinds of koala - all but one of which had died out. The earliest known member of the koala family was a browser, which lived 15 millions years ago. Evidence of a 'giant' koala, twice the size of its modern descendant, exists in fossils dating back more than 40,000 years. The sequence of koalas in the fossil record:

* 15 million years ago: Perikoala palankarinnica

* 10 million years ago: Litokoala kutjamarpensis

* 5 million years ago: Koobor notabilis & Koobor jimbarratti

* 0 million years ago: Phascolarctos cinereus & Phascolarctos stirtoni

* 1798, January 26: The 1st record of a koala being seen by an European, named John Price.

* 1803, August 21: The first detailed account of a koala was published in Sydney Gazette.

* 1816: the French naturalist de Blainwill gave the koala its scientific name, Phascolarctos, from the Greek words for 'leather pouch' and 'bear'. Later, the German naturalist Goldfuss gave it the specific name cinereus, meaning 'ash-coloured', after the color of the original specimen.

From: Koala Handbook by Simon Hunter

History of the name: "koala"
In their history of the koala, Tom Iredale and Gilbert Whitley (1934) suggest that the common name "koala" was derived from an Aboriginal dialect of eastern New South Wales. Ronald Strahan (1978) lists cullewine, koolewong, colo, colah, koolah, kaola and koala as published dialectal variations of the name in that region, "complicated by problems of transliteration and printers" errors.

The early settlers referred to koalas as sloths, monkeys, bears, and even monkey bears, adopting the unfortunate practice of transposing the names of animals which were already familiar to Europeans to Australian lookalikes. The virtual absence of a tail, together with their stocky build and their relatively long legs, gives the koalas a bear-like appearance, and undoubtedly led to their being referred to as, "koala bears", or, "native bears".

From: The Koala: A Natural History by Anthony Lee & Roger Martin


Birth and Pouch Life
koala

* Usually, koalas produce only a single young, rarely twins are born.

* At birth, the young is about 19 mm in length and weighs about 0.5 g.

* At 7 weeks, the young has a head length of about 26 mm. The head is large in proportion to the rest of the body.

* By 13 weeks, the young has attained a body weight of about 50 g and a head length of 50 mm.

* At about 22 weeks of age, the eyes open and the young begins to poke its head out of the pouch for the first time.

* By 24 weeks of age, the cub is fully furred and the first teeth erupt.


* At 30 weeks, the cub weighs about 0.5 kg and has a head length of 70 mm. It now spends most of the time out of the pouch clinging to the mother's belly.

* Some 6 weeks later, the cub weighs 1 kg and no longer enters the pouch. It spends much of the time sitting on the mother's back, but returns to the mother's belly in cold, wet weather and to sleep.

* At 37 weeks, the cub moves from contact with the mother; the excursions were brief and quickly terminated if the mother moved.

* At 44 weeks, the cub still ventures less than a meter from the mother.

* By 48 weeks, the cub is more adventurous and no longer squeaked when the mother was removed. At this age, mother and cub are often seen sleeping back to back.

* The cub remains with the mother until about 12 months of age when it weighs a little over 2 kg.

From: The Koala: A Natural History by Anthony Lee & Roger Martin


Koala Physiology
koala

* Unlike bears or seals, koalas do not rely on a layer of fat below the skin as a form of insulation.

* Blood flow to extremities in cold weather, as in humans, can be reduced, resulting in the conservation of heat.

* Shivering has also been observed in cold climes as a means of creating heat through rapid contractions of certain muscles. This seems to occur when outdoor temperatures drop below 10 degrees Centigrade.

* When temperatures exceed 25-30 degrees Centigrade, koalas use evaporative cooling in their airways to regulate body temperature by increasing respiration rates. They can simultaneously reduce water loss by decreasing the amount of water in their urine.

From: Koalas - Australia's Ancient Ones by Ken Phillips


More Koala Facts
picture of an albino koala

* Koalas don't live in families, but are solitary animals.

* Koalas sleep as long as 18 hours a day and have a low-energy diet of eucalyptus leaves.

* Koalas are not "drunk" or otherwise intoxicated by their leaves.

* Although koalas obtain most of their water from leaves -- the name koala is thought to mean "no drink" in several native Aboriginal tongues -- they do occasionally drink water at the edges of streams.

25 Haziran 2007 Pazartesi

Animals

Animals are a major group of organisms, classified as the kingdom Animalia or Metazoa. In general they are multi­cellular, responsive to their environment, and feed by consuming other organisms or parts of them. Their body plan becomes fixed as they develop, usually early on in their development as embryos, although some undergo a process of metamorphosis later on.

The word "animal" comes from the Latin word animal, of which animalia is the plural, and is derived from anima, meaning vital breath or soul. In everyday colloquial usage, the word usually refers to non-human animals. The biological definition of the word refers to all members of the Kingdom Animalia. Therefore, when the word "animal" is used in a biological context, humans are included.
Characteristics

Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and usually multicellular (although see Myxozoa), which separates them from bacteria and most protists. They are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking cell walls. All animals are motile, if only at certain life stages. Embryos pass through a blastula stage, which is a characteristic exclusive to animals.

Structure

With a few exceptions, most notably the sponges (Phylum Porifera), animals have bodies differentiated into separate tissues. These include muscles, which are able to contract and control locomotion, and nerve tissue, which sends and processes signals. There is also typically an internal digestive chamber, with one or two openings. Animals with this sort of organization are called metazoans, or eumetazoans when the former is used for animals in general.

All animals have eukaryotic cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells, bones, and spicules. During development it forms a relatively flexible framework upon which cells can move about and be reorganized, making complex structures possible. In contrast, other multicellular organisms like plants and fungi have cells held in place by cell walls, and so develop by progressive growth. Also, unique to animal cells are the following intercellular junctions: tight junctions, gap junctions, and desmosomes.

Reproduction and development

Nearly all animals undergo some form of sexual reproduction. Adults are diploid or polyploid. They have a few specialized reproductive cells, which undergo meiosis to produce smaller motile spermatozoa or larger non-motile ova. These fuse to form zygotes, which develop into new individuals.

Many animals are also capable of asexual reproduction. This may take place through parthenogenesis, where fertile eggs are produced without mating, or in some cases through fragmentation.
A newt lung cell stained with fluorescent dyes undergoing mitosis, specifically early anaphase.
A newt lung cell stained with fluorescent dyes undergoing mitosis, specifically early anaphase.

A zygote initially develops into a hollow sphere, called a blastula, which undergoes rearrangement and differentiation. In sponges, blastula larvae swim to a new location and develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement. It first invaginates to form a gastrula with a digestive chamber, and two separate germ layers - an external ectoderm and an internal endoderm. In most cases, a mesoderm also develops between them. These germ layers then differentiate to form tissues and organs.

Most animals grow by indirectly using the energy of sunlight. Plants use this energy to convert sunlight into simple sugars using a process known as photosynthesis. Starting with the molecules carbon dioxide (CO2) and water (H2O), photosynthesis converts the energy of sunlight into chemical energy stored in the bonds of glucose (C6H12O6) and releases oxygen (O2). These sugars are then used as the building blocks which allow the plant to grow. When animals eat these plants (or eat other animals which have eaten plants), the sugars produced by the plant are used by the animal. They are either used directly to help the animal grow, or broken down, releasing stored solar energy, and giving the animal the energy required for motion. This process is known as glycolysis.

Animals who live close to hydrothermal vents and cold seeps on the ocean floor are not dependent on the energy of sunlight. Instead, chemosynthetic archaea and eubacteria form the base of the food chain.

Origin and fossil record

Animals are generally considered to have evolved from a flagellated eukaryote. Their closest known living relatives are the choanoflagellates, collared flagellates that have a morphology similar to the choanocytes of certain sponges. Molecular studies place animals in a supergroup called the opisthokonts, which also include the choanoflagellates, fungi and a few small parasitic protists. The name comes from the posterior location of the flagellum in motile cells, such as most animal spermatozoa, whereas other eukaryotes tend to have anterior flagella.

The first fossils that might represent animals appear towards the end of the Precambrian, around 575 million years ago, and are known as the Ediacaran or Vendian biota. These are difficult to relate to later fossils, however. Some may represent precursors of modern phyla, but they may be separate groups, and it is possible they are not really animals at all. Aside from them, most known animal phyla make a more or less simultaneous appearance during the Cambrian period, about 542 million years ago. It is still disputed whether this event, called the Cambrian explosion, represents a rapid divergence between different groups or a change in conditions that made fossilization possible.

Groups of animals

The sponges (Porifera) diverged from other animals early. As mentioned above, they lack the complex organization found in most other phyla. Their cells are differentiated, but in most cases not organized into distinct tissues. Sponges are sessile and typically feed by drawing in water through pores. Archaeocyatha, which have fused skeletons, may represent sponges or a separate phylum.

Among the eumetazoan phyla, two are radially symmetric and have digestive chambers with a single opening, which serves as both the mouth and the anus. These are the Cnidaria, which include sea anemones, corals, and jellyfish, and the Ctenophora or comb jellies. Both have distinct tissues, but they are not organized into organs. There are only two main germ layers, the ectoderm and endoderm, with only scattered cells between them. As such, these animals are sometimes called diploblastic. The tiny Placozoans are similar, but they do not have a permanent digestive chamber.

The remaining animals form a monophyletic group called the Bilateria. For the most part, they are bilaterally symmetric, and often have a specialized head with feeding and sensory organs. The body is triploblastic, i.e. all three germ layers are well-developed, and tissues form distinct organs. The digestive chamber has two openings, a mouth and an anus, and there is also an internal body cavity called a coelom or pseudocoelom. There are exceptions to each of these characteristics, however - for instance adult echinoderms are radially symmetric, and certain parasitic worms have extremely simplified body structures.

Genetic studies have considerably changed our understanding of the relationships within the Bilateria. Most appear to belong to four major lineages:

1. Deuterostomes
2. Ecdysozoa
3. Platyzoa
4. Lophotrochozoa

In addition to these, there are a few small groups of bilaterians with relatively similar structure that appear to have diverged before these major groups. These include the Acoelomorpha, Rhombozoa, and Orthonectida. The Myxozoa, single-celled parasites that were originally considered Protozoa, are now believed to have developed from the Bilateria as well.

Deuterostomes
White's Tree Frog, Litoria caerulea.
White's Tree Frog, Litoria caerulea.

Deuterostomes differ from the other Bilateria, called protostomes, in several ways. In both cases there is a complete digestive tract. However, in protostomes the initial opening (the archenteron) develops into the mouth, and an anus forms separately. In deuterostomes this is reversed. In most protostomes cells simply fill in the interior of the gastrula to form the mesoderm, called schizocoelous development, but in deuterostomes it forms through invagination of the endoderm, called enterocoelic pouching. Deuterostomes also have a dorsal, rather than a ventral, nerve chord and their embryos undergo different cleavage.

All this suggests the deuterostomes and protostomes are separate, monophyletic lineages. The main phyla of deuterostomes are the Echinodermata and Chordata. The former are radially symmetric and exclusively marine, such as starfish, sea urchins, and sea cucumbers. The latter are dominated by the vertebrates, animals with backbones. These include fish, amphibians, reptiles, birds, and mammals.

In addition to these, the deuterostomes also include the Hemichordata or acorn worms. Although they are not especially prominent today, the important fossil graptolites may belong to this group.

The Chaetognatha or arrow worms may also be deuterostomes, but more recent studies suggest protostome affinities.

Ecdysozoa
Yellow-winged Darter, Sympetrum flaveolum
Yellow-winged Darter, Sympetrum flaveolum

The Ecdysozoa are protostomes, named after the common trait of growth by moulting or ecdysis. The largest animal phylum belongs here, the Arthropoda, including insects, spiders, crabs, and their kin. All these organisms have a body divided into repeating segments, typically with paired appendages. Two smaller phyla, the Onychophora and Tardigrada, are close relatives of the arthropods and share these traits.

The ecdysozoans also include the Nematoda or roundworms, the second largest animal phylum. Roundworms are typically microscopic, and occur in nearly every environment where there is water. A number are important parasites. Smaller phyla related to them are the Nematomorpha or horsehair worms, which are invisible to the unaided eye, and the Kinorhyncha, Priapulida, and Loricifera. These groups have a reduced coelom, called a pseudocoelom.

The remaining two groups of protostomes are sometimes grouped together as the Spiralia, since in both embryos develop with spiral cleavage.

Platyzoa
Bedford's flatworm, Pseudobiceros bedfordi
Bedford's flatworm, Pseudobiceros bedfordi

The Platyzoa include the phylum Platyhelminthes, the flatworms. These were originally considered some of the most primitive Bilateria, but it now appears they developed from more complex ancestors.

A number of parasites are included in this group, such as the flukes and tapeworms. Flatworms lack a coelom, as do their closest relatives, the microscopic Gastrotricha.

The other platyzoan phyla are microscopic and pseudocoelomate. The most prominent are the Rotifera or rotifers, which are common in aqueous environments. They also include the Acanthocephala or spiny-headed worms, the Gnathostomulida, Micrognathozoa, and possibly the Cycliophora. These groups share the presence of complex jaws, from which they are called the Gnathifera.

Lophotrochozoa
Big blue octopus, Octopus cyanea
Big blue octopus, Octopus cyanea

The Lophotrochozoa include two of the most successful animal phyla, the Mollusca and Annelida. The former includes animals such as snails, clams, and squids, and the latter comprises the segmented worms, such as earthworms and leeches. These two groups have long been considered close relatives because of the common presence of trochophore larvae, but the annelids were considered closer to the arthropods, because they are both segmented. Now this is generally considered convergent evolution, owing to many morphological and genetic differences between the two phyla.

The Lophotrochozoa also include the Nemertea or ribbon worms, the Sipuncula, and several phyla that have a fan of cilia around the mouth, called a lophophore. These were traditionally grouped together as the lophophorates, but it now appears they are paraphyletic, some closer to the Nemertea and some to the Mollusca and Annelida. They include the Brachiopoda or lamp shells, which are prominent in the fossil record, the Entoprocta, the Phoronida, and possibly the Bryozoa or moss animals.

LAS ARDILLAS

La ardilla es un mamífero roedor Mide entre 35 y 45 cm de longitud, de las que casi la mitad pertenecen a la cola. En las extremidades delanteras, el pulgar es reducido, pero los otros 4 dedos están bien desarrollados y dotados de largas, curvadas y afiladas uñas. Su cabeza es graciosa; en ella sobresalen los ojos brillantes y la boca en la que los dientes están muy desarrollados y salientes. Si se les captura jóvenes a las ardillas, es posible domesticarlas y una ardilla resulta un animal doméstico muy sensible y cariñoso.

Hay un gran número de especies de ardillas, muy distintas en color y tamaño, propagadas por todo el mundo excepto en Australia. Se alimentan de semillas, cortezas, frutos secos, brotes tiernos y bellotas, que entierran durante el verano en el suelo a unos centímetros de profundidad, para luego alimentarse de ellos durante el invierno. Este almacenamiento no lo hacen las ardillas en un solo punto, sino que lo reparten en una extensa zona del lugar en el que viven.

Las ardillas establecen su nido en los huecos de los arboles o en un hueco del ramaje, y en ocasiones, en los nidos desocupados de algún grajo (pájaro parecido al cuervo), urraca o ave de rapiña. Es curioso ver como cubren su nido por arriba con una cúpula de ramas muy entrelazadas, que tapizan del musgo para evitar que entre la lluvia en su casa.

El nido de las ardillas tiene dos entradas y dentro de esta casa las ardillas hembras dan luz entre 3 y 4 crías. Las crías de ardilla son muy pequeñas; no tienen pelo cuando nacen y tienen los ojos cerrados. La madre los amamanta durante 10 semanas y, poco a poco, les enseña moverse entre las ramas del árbol en el que viven. Su adiestramiento depende del buen desarrollo de su cola, ya que en la ardilla esta constituya el elemento esencial para mantener el equilibrio en los asombrosos saltos que efectúa de un árbol a otro. A los 5 o 6 meses ya se les puede considerar adultas, pues su cuerpo y cola ya habrán adquirido su total desarrollo.

Las ardillas de países muy fríos hibernan. Esto quiere decir que duermen durante todo el invierno envueltos en su cola. Sin embargo, su sueño nunca es muy profundo, y cualquier peligro, o sencillamente su apetito, les hace espabilar rápidamente para escapar o hurgar en el suelo a la búsqueda de su dispensa subterránea de frutos que enterró durante el verano.

LOS LEONES-Spanish

De toda la familia de gatos, el león siempre ha sido considerado por el hombre como el Rey de los animales. Admirado por su nobleza, lealtad, habilidades, fuerza y valentía a lo largo de la historia, se han encontrado dibujos de el tigre por hombres hace más de 15.000 años.

No obstante, el león es solo el segundo más grande de los felinos (el más grande es el tigre) y tampoco es el más rápido. Los leones machos en su hábitat natural pueden llegar a medir hasta 3 metros, incluyendo su cola, y las leonas un poco menos. Pesan entre 150 y 225 kilos y viven entre 15 y 20 de años.

A pesar de su fama de animal feroz, los leones se muestran muy sociables dentro de su manada. Siempre hay más leonas que leones en una manada que puede tener desde 3 hasta 40 animales.

Son las leonas que hacen la mayor parte de la caza y que cuidan a los cachorros y les enseñan a cazar. cachorro leonAdemás suelen parir sus cachorros al mismo tiempo (normalmente de 3 a 4 cachorros por leona) y se ayudan entre ellas con la crianza de los pequeños. Siempre hay mucho más hembras que machos en una manada. Cuando un macho se convierte en líder de su grupo, es frecuente que lo primero que haga es matar a todos los cachorros, para eliminar la herencia de su predecesor y asegurarse de que todos los futuros cachorros tengan sus genes.

El papel más importante de los machos en una manada de leones es defender el territorio.

LeonesEl rugido de un león se puede escuchar a una distancia de hasta 8 kilómetros, y está diseñado para advertir a posibles intrusos y para llamar a miembros de su manada para que vuelvan al grupo.

También se utiliza para comunicarse con otras manadas de leones que viven en el vecindario.

A pesar de su buena fama como cazador, el león es relativamente torpe y solo logra cazar su objetivo en un 20-30% de sus intentos. Cazan en equipo y, si no logran alcanzar nada, no tienen inconveniente en apoderarse de los restos de un animal cazado por otro especie. Por eso se les llaman "oportunistas". Después de la caza, los leones suelen comer primero, luego las leonas (muchas veces con peleas entre ellas) y por último, los cachorros.

Los leones que viven en África se consideran animales en peligro y los pocos que sobreviven en Asia se considera especie en peligro de extinción.

En este vídeo se pueden ver 3 leones jovenes persiguiendo a un búfalo.