The main feature of the NCA is the Ngorongoro Crater, a large volcanic caldera. The crater, which formed when a giant volcano exploded and collapsed on itself some two to three million years ago, is deep and its floor covers .
Estimates of the height of the original volcano range from fifteen to nineteen thousand feet (4500 to 5800 metres) high.
Although thought of as "a natural enclosure" for a very wide variety of wildlife, up to 20% or more of the wildebeest ("Connochaetes taurinus") and half the zebra ("Equus burchelli") populations leave the Crater in the wet season. The Ngorongoro lions are significantly inbred, with many genetic problems passed from generation to generation. This is due to the very few new bloodlines that enter the local gene pool, because few migrating male lions enter the crater from the outside. Those who do enter the crater often cannot contribute to the gene pool. The crater's male lions, because of their large size (the result of an abundant food source), easily expel outside competitors.
Animal populations in the crater include most of the species in East Africa, but there are no impalas ("Aepyceros melampus"), giraffes ("Giraffa camelopardalis"), or crocodiles ("Crocodylus niloticus").
The crater highlands on the side facing the easterly trade winds receives 800–1200 mm of rain a year and is covered largely in montane forest, while the less-steep west wall receives only 400–600 mm; this side is grassland and bushland dotted with Euphorbia bussei trees. The crater floor is mostly open grassland with two small wooded areas dominated by "Acacia xanthophloea".
The Munge Stream drains Olmoti Crater to the north, and is the main water source draining into the seasonal salt lake in the center of the crater. This lake is known by two names: "Makat" as the Maasai called it, meaning salt; and "Magadi". The Lerai Stream drains the humid forests to the south of the Crater, and it feeds the Lerai Forest on the crater floor - when there is enough rain, the Lerai drains into Lake Magadi as well. Extraction of water by lodges and NCA headquarters reduces the amount of water entering Lerai by around 25%.
The other major water source in the crater is the Ngoitokitok Spring, near the eastern crater wall. There is a picnic site here open to tourists and a huge swamp fed by the spring, and the area is inhabited by hippopotamus, elephants, lions, and many others. Many other small springs are around the crater's floor, and these are important water supplies for the animals and local Masaai, especially during times of drought.
Aside from herds of zebra, gazelle, and wildebeest, the crater is home to the "Big Five Game" of rhinoceros, lion, leopard, elephant, and buffalo. The crater plays host to almost every individual species of wildlife in East Africa, with an estimated 25 000 animals within the crater.
Following the recommendations of a committee of scientists after the 2000 drought, an ecological burning program was implemented in the crater, which entails annual or biannual controlled burns of up to 20% of the grasslands. Maasai are now permitted to graze their cattle within the crater, but must enter and exit daily.
The conservation area also protects Olduvai Gorge, in the plains area. It is considered the seat of humanity after the discovery of the earliest known specimens of the human genus, "Homo habilis " as well as early hominidae, such as "Paranthropus boisei".
The Olduvai Gorge or Oldupai Gorge is a steep-sided ravine in the Great Rift Valley, which stretches along eastern Africa. Olduvai is in the eastern Serengeti Plains in northern Tanzania and is about thirty miles long. It is in the rain shadow of the Ngorongoro highlands and is the driest part of the region.
It is one of the most important prehistoric sites in the world. Research there has greatly developed our understanding of early human evolution. Excavation work there was pioneered by Mary and Louis Leakey in the 1950s. It is still continued today by their family. During the Pleistocene, the site was that of a large lake, the shores of which were covered with successive deposits of volcanic ash. Around 500,000 years ago seismic activity diverted a nearby stream which began to cut down into the sediments, revealing seven main layers in the walls of the gorge.
Spider
Spiders (class Arachnida, order Araneae) are air-breathing arthropods. They have eight legs, and mouthparts (chelicerae) with fangs that inject venom. Most make silk. The arachnids are seventh in number of species of all animal orders. About 48,000 spider species, and 120 families have been recorded by taxonomists. Over twenty different classifications have been proposed since 1900. Spiders live on every continent except for Antarctica, and in nearly every habitat with the exceptions of air and sea.
Almost all spiders are predators, and most eat insects. They catch their prey in several ways. Some build a spider web, and some use a thread of silk that they throw at the insect. Some kinds of spiders hide in holes in the ground, then run out and grab an insect that walks by. Others will make web 'nets' to throw at passing insects. Or they go out and simply attack their prey. Some can jump quite well and hunt by sneaking close to an insect and then jumping on it.
Spiders have a two-part body, the front part (cephalothorax) and the abdomen. Unlike insects, spiders do not have antennae. The more advanced spiders have a centralized nervous system, with their ganglia fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs, and extend them by hydraulic pressure.
The smallest of full-grown spiders can be less than 4 mm. (0.1 inch). The largest of spiders can have a body length of 10 cm. (4 inches) or more. The largest can weigh 150 grams (5.3 oz). The largest of spiders are the tarantulas and the huntsman spiders. Some huntsman spiders in South East Asia can have a leg span of around 250–300 mm (9.8–11.8 in).
Most spiders have four pairs of eyes on the top-front area of the body, arranged in patterns that vary from one family to another. The main eyes at the front are capable of forming images. Jumping spiders have visual acuity which is ten times better than that of dragonflies, which have by far the best vision among insects. The spiders do this by a telephoto-like series of lenses, a four-layered retina. They can swivel their eyes and put together images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow.
Spiders and other arthropods have modified their cuticles into elaborate arrays of sensors. Various sensors, mostly bristles, respond to touch, from strong contact to very weak air currents. Chemical sensors provide equivalents of taste and smell. Spiders also have in the joints of their limbs sensors that detect forces and vibrations. In web-building spiders all these mechanical and chemical sensors are more important than the eyes. The eyes are more important to spiders that hunt actively. Like most arthropods, spiders lack balance sensors, and rely on their eyes to tell them which way is up.
The fangs are hollow, like the needles used to give injections. Spiders use their fangs to inject toxins that kill the insects they will eat. Some kinds of spider venom attack the nervous systems of their prey, and other kinds of venom attack body tissues.
Spiders are predators, and eat insects and other arthropods (including other spiders). Most use venom from their fangs to kill their prey. It is rare for spiders to capture prey that are much larger than they are. It is also difficult for most spiders to capture prey that are very much smaller than they are. There are some spiders that form colonies. Spiders eat not only spiders of other species, but spiders of their own species.