Dave Taylor's African Safari: Abiotic Factors of the Serengeti-Mara Ecosystem - Abiotic Cycles

Abiotic Factors of the Serengeti-Mara Ecosystem
Abiotic Cycles
Page 13

Summary

Certain chemicals, while not in themselves alive, are crucial to life itself. All life forms on Earth are carbon-based. Another chemical which is important to living things is nitrogen. Nitrogen helps in the breaking down of food for processing. Water (hydrogen dioxide - H₂O) is essential to living things. This section looks at these three very important cycles.

Oxygen / Carbon Cycle

Whether plant or animal, living things are made up primarily of carbon and water. Through the process of photosynthesis (see Photosynthesis: Conserving the Sun’s Energy), plants are able to take carbon dioxide gas from the air and "fix" it as plant material. A waste product of this is oxygen. The oxygen is produced when oxygen molecules are released from the water compound (H₂0). The hydrogen molecule is combined with the carbon molecules to make sugars and starches.

The oxygen by-product of photosynthesis is used in the process of respiration. In respiration, living things take in oxygen from the air. In the case of higher animals, oxygen is used in the lungs. Oxygen molecules combine with carbon molecules in the "body" of the organism and "burn" them. This releases energy in the form of heat. The waste product of this process is carbon dioxide.

Plants also take in oxygen. During the day, more carbon dioxide is used by plants than is released through respiration. At night, without sunlight, photosynthesis stops and more oxygen is taken in and more carbon dioxide given out.

Nitrogen Cycle

Nitrogen makes up 80% of the Earth’s atmosphere. Carbon dioxide makes up only 0.035% of the atmosphere. Carbon dioxide can be taken from the air and "fixed" by plants through the process of photosynthesis. Nitrogen, however, cannot be taken directly from the air.

Nitrogen is a critical component of life on Earth. It is needed by living things so that they can build proteins. Plants obtain the nitrogen they need through a symbiotic relationship with microbes, fungi or algae. The plant roots provide nourishment to these other organisms which in turn convert nitrogen into ammonia. In this form, it can be used by plants to produce proteins.

Nitrogen is passed to the soil when a plant, or a consumer, (either herbivore, carnivore, scavenger or decomposer) dies and decays. Urinating and defecating also return nitrogen to the soil where the gas is reabsorbed by plant roots. Some plants (see: legumes) are able to "fix" more nitrogen than others. The common pea is an example.

Water Cycle

Water is the other key ingredient to healthy life on Earth (see also Abiotic Factors: Water). The water cycle describes the pathways that water molecules (H2O) follow through the environment. Water evaporates from the ocean and is carried inland by winds. As the molecules are cooled by rising air masses, they condense (condensation) and form water droplets and eventually clouds. When the weight of water is such that the air mass can no longer hold it, the droplets fall as precipitation.

In the Serengeti-Mara, this takes the form of rain. Some rainwater will be absorbed into the ground where it may follow one of several paths. Roots of trees or grass may absorb some molecules for the plant to use or store. Some of this moisture will be given off from the leaves of the plant and return to the atmosphere.

Some water may percolate down through the soil until it reaches a layer of rock that it cannot penetrate. As groundwater, it will seep through the soil until it returns to the surface as a spring or feeds into a river. The river will eventually empty into the ocean.

Other water may run off directly into rivers or it may pool up as surface ponds and lakes. Here animals drink it. Some is retained in the body but much of it is lost to sweat, urine and other waste products. Eventually it will evaporate and return to the atmosphere.

Droughts

Droughts are a regular and important feature of the Serengeti-Mara climate. Droughts occur when the rains fail, as they do twice each year. Gradually the land dries up and the herds are forced to find water in other locations. This is part of the normal pattern.

Once every 7 to 10 years, a severe drought occurs. This happens when climatic shifts create conditions where regular wind patterns no longer occur. The rains do not fall and, instead of a drought of several months, it may be over a year before the normal weather patterns restore the land.

Severe droughts are related to changes in the ocean temperatures off the west coast of South America. This effect is known as El Nino and it changes the world’s climate. Dry places may get severe rainstorms and wet places may dry up. La Nina follows El Nino and generally reverses the pattern.

It is only in recent years that these two effects have been fully studied and recognized. There is still much we do not understand about their causes and the effects they have on the world’s ecosystems.

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