Normally there are only up to four trophic levels because energy is limiting at the 4th trophic level of food chain. This is the reason why there are only few carnivores (Eagles, hawks, white sharks) that survive in the 4th tropic level because they are having difficulty sustaining the energy requirement from the limiting energy (food limits). With each rise in the level of food chain, there is a significant difference in the number of members of that trophic level.
For example from the first level to the second level, there are vast numbers of plants compared to the 2nd trophic level such as the insects that eats them. This progressive reduction in the number for every rise in the trophic level is related to the amount of energy available in each level. The reason for this is actually govern by the 2nd law of thermodynamics which basically states that in converting from one energy form to another, there are always some losses. So one can never get the same amount of energy as much as what was put.
Animals could not obtain as much as 100% of the energy it eats. According to the Answers. com (2007), it is more like just 10% of the food that an animal can absorb. So because of this inefficiency in converting from the energy of one trophic level to another, there is a progressive decrease of energy level as we move from lower trophic level to higher levels. So eventually at the fourth level, it reaches a maximum limit to sustain their energy needs. 99. What are coral reefs? How are they formed? Of what value are they?
Why are they vulnerable to damage? What are the harmful impacts of human activities on coral reefs According to the Wikipedia (2007), coral reefs, which are also known as sea gardens, are structures consisting of coral skeletons built upon coral skeletons. They grow in tropical seas in the photic zone, where there is mild wave action, not so strong it tears the reef apart yet strong enough to stir the water and deliver sufficient food and oxygen. They are formed from reef building corals and other organism that deposits calcium carbonate.
Through symbiosis with unicellular algae called zooxanthellae, reef building corals houses polyps that become the source of formation of reef communities. These algal cells within the tissues of the coral polyps carry out photosynthesis and produce excess organic nutrients that are then used by the coral polyps. Therefore they can only form on shallow waters where the depth is enough for sunlight to penetrate. Coral reefs are important to marine life, because they are home to a number of coral fishes and other small sea animals. They also help protect soil erosion within the coral beds.
Biologically active compounds produced by reef dwelling organisms possess antimicrobial and antiviral activity. These compounds may be an important source of drugs and medicine. In addition, coral reefs attracts tourist due its natural beauty. Tourist attraction can become a significant source of revenue. Humans are the greatest threats to coral reefs living in the oceans. Pollution and over-fishing are the primary causes of coral reef destruction. Pollution kills the algae and bacteria that contributes to the formation of coral reefs.
Physical destruction due to fishing boats is also contributory factory. Finally, above normal water temperatures, due to climate phenomena such as El Nino and global warming, can cause coral bleaching (Wikipedia, 2007). According to The Nature Conservancy, if destruction increases at the current rate, 70% of the world’s coral reefs will have disappeared within 50 years. This will have major economic impacts to humanity. 100. Without copying word-for-word from your text figures, describe the ways that human activities are degrading our a. forests
Illegal logging and massive deforestation has degraded our forest. Due to the growing population, the needs for timber and usable area for planting, residential or industrial use has also grown. This condition has depleted our forest area in return. More and more forests are converted to residential, agricultural or industrial lands destroying our delicate forest areas. b. deserts Less and less arable lands remain in the deserts because of population growth and urbanization. Poor land management on desert areas have also resulted in less usable areas in the deserts and resulted into poor soil.
c. grasslands Grasslands have also been degraded mostly because of conversions to industrial zones. Pollution and environmental stress have also partly degraded the growth of our grasslands which are essential sources of food for herbivores.
References Unknown. (2006). Food Web. Retrieved on January 14, 2007 from the answers. com web site : http://www. answers. com/topic/food-web Unknown. (2006). Coral Reef. Retrieved on January 14, 2007 from the Wikipedia web site : http://en. wikipedia. org/wiki/Coral_reef