174 résultats pour "hábitat"

• Rana - ciencias de la naturaleza.

  Rana excavadoraLas patas cortas y fuertes de esta rana son adecuadas para cavar. Se entierra en la arena del desierto del sur de Australia para eludirel calor y queda sumida en un estado similar a la hibernación. Otras lo hacen para esconderse o tender emboscadas. Muchas tienen elhocico afilado o dedos espatulados, que les ayudan a cavar.Kathie Atkinson/Oxford Scientific Films La mayoría de las ranas, en especial los machos, emiten sonidos. Al expulsar el aire de los pulmones, éste hace vibrar l...

• Duck - biology.

  from water. When ducks feed they push their tongue against the top of their mouth to squeeze water through the lamellae, leaving the food behind. Mergansers arefish-eating ducks with slender bills that are notched on the edges like the blade of a saw. These saw-toothed beaks help the ducks catch and hold their slippery prey. VI COURTSHIP AND REPRODUCTION Ducks form pairs long enough to mate, but most species find new mates each year. In a few species, including buffleheads and whistling ducks,...

• Owl - biology.

  Among the largest species of typical owls are the eagle owls. They have tufts of feathers on their heads that are called “ears.” The great horned owl is the only eagleowl found in the Americas. It is about 60 cm (25 in) in length with a wingspan of 1.4 m (60 in). Numerous species of eagle owls inhabit Europe, Africa, and Asia. Mostwidely distributed is the northern eagle owl, found from Scandinavia and Spain to Japan. It is about 71 cm (28 in) long with a wingspan of about 2m (72 in). Nearly asl...

• Algas - ciencias de la naturaleza.

  Con excepción de las cianobacterias, que también han recibido el nombre de algas verdeazuladas, las algas están formadas por células eucariotas —es decir el interior de lacélula está organizado en orgánulos separados por una membrana, entre los que se encuentran el núcleo y las mitocondrias. Las cianobacterias son organismos procariotas,es decir organismos unicelulares bastante simples que carecen de núcleo. Sin embargo, como su actual nombre indica, las cianobacterias tienen características sim...

• Clasificación - ciencias de la naturaleza.

  Clasificación de los organismosLa clasificación de los seres vivos es motivo de controversia desde hace mucho tiempo. Arriba: El sistema aristotélico solo reconocíaplantas y animales, que se diferenciaban por el movimiento, el mecanismo de alimentación y la forma de crecimiento. Este sistemaagrupa procariotas, algas y hongos con las plantas, y protozoos móviles capaces de alimentarse con los animales. Centro: Elperfeccionamiento de las técnicas y los materiales de laboratorio puso de manifiesto...

• Égypte ancienne, art de l' - peinture.

  Sous la III e dynastie, l’architecte Imhotep édifie la nécropole du souverain Djoser (régnant vers 2630-2611 av. J.-C.), le plus grand ensemble architectural de l’époque, sur le site de Saqqarah, non loin de Memphis. Ce complexe funéraire comporte une grande pyramide à degrés — bâtie sur d’anciennes galeries funéraires souterraines et surélevée à plusieurs reprises — et un groupe de chapelles et d'édifices associés. Haute de 60 m, la grande pyramide, dans laquelle est conservée la dépouille d...

• Égypte ancienne, art de l' - sculpture.

  Sous la III e dynastie, l’architecte Imhotep édifie la nécropole du souverain Djoser (régnant vers 2630-2611 av. J.-C.), le plus grand ensemble architectural de l’époque, sur le site de Saqqarah, non loin de Memphis. Ce complexe funéraire comporte une grande pyramide à degrés — bâtie sur d’anciennes galeries funéraires souterraines et surélevée à plusieurs reprises — et un groupe de chapelles et d'édifices associés. Haute de 60 m, la grande pyramide, dans laquelle est conservée la dépouille d...

• Evolución humana - ciencias de la naturaleza.

  Los cambios genéticos pueden mejorar la capacidad de los organismos para sobrevivir, reproducirse y, en animales, criar a su descendencia. Este proceso se denominaadaptación. Los progenitores transmiten mutaciones genéticas adaptativas a su descendencia y finalmente estos cambios se generalizan en una población —un grupo de organismos de la misma especie que comparten un hábitat local particular. Existen numerosos factores que pueden favorecer nuevas adaptaciones, pero los cambios delentorno d...

• Ocean and Oceanography.

  of sediment. When studied in sedimentary core samples, which can represent many millions of years of deposits, they provide a detailed and continuous history of theearth’s environmental changes. The record is particularly informative for the most recent 2 million to 5 million years, during which major fluctuations in global climatehave occurred. Successive ice ages can be traced by the relative scarcity or abundance of the shells of warm-water and cold-water diatoms in various layers of asedimen...

• Ocean and Oceanography - Geography.

  of sediment. When studied in sedimentary core samples, which can represent many millions of years of deposits, they provide a detailed and continuous history of theearth’s environmental changes. The record is particularly informative for the most recent 2 million to 5 million years, during which major fluctuations in global climatehave occurred. Successive ice ages can be traced by the relative scarcity or abundance of the shells of warm-water and cold-water diatoms in various layers of asedimen...

• Horse - biology.

  Horses reach sexual maturity at about one and a half years. The estrous cycle in the mare—a mature female horse—typically lasts 21 days. During the first five days ofthe cycle, the mare is usually receptive to mating. The estrous cycle stops during winter and resumes in the spring, which is the start of the breeding season. Astallion—a mature male horse—approaching a mare in estrus engages in various courtship rituals. These include uttering nickering sounds and sniffing and licking themare’s ge...

• Seattle - geography.

  Mountains. The area includes the suburban cities of Bellevue, Kirkland, Redmond, Renton, and Issaquah. The Eastside has become home to dozens of high-technologyindustries including Microsoft Corporation, ATL Ultrasound, Nintendo of America, divisions of The Boeing Company, and many other firms. In the 1960s commutersheaded to Seattle jobs from homes on the Eastside. Today, the “reverse commute” from Seattle homes to jobs on the Eastside is just as heavy, and both streams oftraffic cross the same...

• Ghana - country.

  times of depressed cacao prices, Ghana has significantly increased exports of timber to generate needed revenue. In 1988 Ghana initiated a conservation plan called the Forest Resource Management Project. In 1989 Ghana restricted the export of 18 tree species, and in 1994 thecountry banned the export of raw logs. About 4.8 percent (1997) of the country’s land is officially protected, but illegal logging threatens Ghana’s remaining forests. Deforestation, overgrazing, and periodic drought have led...

• Uzbekistan - country.

  E Environmental Issues The evaporation of the Aral Sea is one of the worst ecological disasters in the world. The Aral has shrunk so much that it now holds only about one-fifth the volume ofwater it held in 1960. The shrinkage is due to irrigation withdrawals from the Amu Darya and Syr Darya, a practice that began on a massive scale in the early 1960s aspart of the Soviet Union’s ill-conceived drive to increase cotton yields in Central Asia. Growing cotton in the naturally arid and saline soil...

• Northwest Territories - Geography.

  million years ago by the severe bending (folding) and faulting (breaking) of sedimentary rock that was once part of the Interior Plains. During the Wisconsin Ice Age,alpine glaciers covered the Cordillera, and the movement of the glaciers created razor-sharp peaks and ridges in these mountains. The moving glaciers also createdbroad U-shaped valleys. To the east of the Interior Plains, the ancient rocks of the Canadian Shield are exposed at the Earth’s surface, resulting in a rough, rolling terra...

• Northwest Territories - Canadian History.

  million years ago by the severe bending (folding) and faulting (breaking) of sedimentary rock that was once part of the Interior Plains. During the Wisconsin Ice Age,alpine glaciers covered the Cordillera, and the movement of the glaciers created razor-sharp peaks and ridges in these mountains. The moving glaciers also createdbroad U-shaped valleys. To the east of the Interior Plains, the ancient rocks of the Canadian Shield are exposed at the Earth’s surface, resulting in a rough, rolling terra...

• Virginia (state) - geography.

  C Coastline Virginia’s coastline, for both the mainland and the Eastern Shore counties, is 180 km (112 mi) long. The state’s tidal shoreline measures 5,335 km (3,315 mi), includingall bays, inlets, tidal estuaries, and other indentations. Major indentations include Chesapeake Bay; Hampton Roads, the excellent natural harbor on which are locatedNewport News, Norfolk, and Portsmouth; and the wide tidal estuaries of the lower Potomac, James, Rappahannock, and York rivers. Cape Henry, in the southe...

• Virginia (state) - USA History.

  C Coastline Virginia’s coastline, for both the mainland and the Eastern Shore counties, is 180 km (112 mi) long. The state’s tidal shoreline measures 5,335 km (3,315 mi), includingall bays, inlets, tidal estuaries, and other indentations. Major indentations include Chesapeake Bay; Hampton Roads, the excellent natural harbor on which are locatedNewport News, Norfolk, and Portsmouth; and the wide tidal estuaries of the lower Potomac, James, Rappahannock, and York rivers. Cape Henry, in the southe...

• Australia - country.

  itself forms most of the border between New South Wales and Victoria. Considerable lengths of the Murray, Darling, and Murrumbidgee rivers are navigable during thewet seasons. The central plains region, also known as the Channel Country, is interlaced by a network of rivers. During the rainy season these rivers flood the low-lying countryside,but in dry months they become merely a series of water holes. The Victoria, Daly, and Roper rivers drain a section of the Northern Territory. In Queensland...

• Australia - Geography.

  itself forms most of the border between New South Wales and Victoria. Considerable lengths of the Murray, Darling, and Murrumbidgee rivers are navigable during thewet seasons. The central plains region, also known as the Channel Country, is interlaced by a network of rivers. During the rainy season these rivers flood the low-lying countryside,but in dry months they become merely a series of water holes. The Victoria, Daly, and Roper rivers drain a section of the Northern Territory. In Queensland...

• Native Americans of North America.

  addition to smallpox and measles, explorers and colonists brought a host of other diseases: bubonic plague, cholera, typhoid fever, scarlet fever, pleurisy, mumps,diphtheria, pneumonia, whooping cough, malaria, yellow fever, and various sexually transmitted infections. Despite the undisputed devastation wreaked on Indian populations after European contact, native populations showed enormous regional variability in their response todisease exposure. Some peoples survived and, in some cases, even...

• Native Americans of North America - Canadian History.

  addition to smallpox and measles, explorers and colonists brought a host of other diseases: bubonic plague, cholera, typhoid fever, scarlet fever, pleurisy, mumps,diphtheria, pneumonia, whooping cough, malaria, yellow fever, and various sexually transmitted infections. Despite the undisputed devastation wreaked on Indian populations after European contact, native populations showed enormous regional variability in their response todisease exposure. Some peoples survived and, in some cases, even...

• Africa.

  The highest elevations in Africa are found in the various ranges of East Africa. After Kilimanjaro, the next highest peaks are Mount Kenya (5,199 m/17,057 ft), north ofKilimanjaro in central Kenya; Margherita Peak (5,109 m/ 16,762 ft) in the Ruwenzori Range on the border between Uganda and the Democratic Republic of the Congo(DRC); Ras Dashen (4,620 m/ 15,157 ft) in the Ethiopian Highlands of northern Ethiopia; Mount Meru (4,565 m/ 14,977 ft), close to Kilimanjaro in Tanzania; and MountElgon (4,...

• Africa - Geography.

  The highest elevations in Africa are found in the various ranges of East Africa. After Kilimanjaro, the next highest peaks are Mount Kenya (5,199 m/17,057 ft), north ofKilimanjaro in central Kenya; Margherita Peak (5,109 m/ 16,762 ft) in the Ruwenzori Range on the border between Uganda and the Democratic Republic of the Congo(DRC); Ras Dashen (4,620 m/ 15,157 ft) in the Ethiopian Highlands of northern Ethiopia; Mount Meru (4,565 m/ 14,977 ft), close to Kilimanjaro in Tanzania; and MountElgon (4,...