Ecology Of A Rainforest Biology Essay


Ecology is defined as the study of the interactions that living things have with each other and with their environment, and tropical rainforest has its own ecosystem as well.

Tropical rainforests across the world are almost as diverse as the species they contain, but share several defining characteristics including climate, precipitation, canopy structure, complex symbiotic relationships, and diversity of species. Every rainforest does not necessarily conform to these characteristics. Most tropical rainforests do not have clear boundaries, but may blend with mangrove forest, moist forest and mountain forest.

Tropical rainforests are located in a band around the equator (Zero degrees latitude), mostly in the area between the Tropic of Cancer (23.5° N latitude) and the Tropic of Capricorn (23.5° S latitude). This 3,000 mile (4800 km) wide band is called the "tropics." First of all, all tropical rainforests lie in the tropics, which is between the Tropic of Capricorn and Tropic of Cancer. In this region, solar energy is most intense because sunlight strikes the earth directly and not at an angle as in regions farther from the equator. The sun shines consistently all year long: 12 hours a day, 365 days per year. This consistent sunlight provides the essential energy necessary and gives power to the forest through photosynthesis. There are rainforests in South and Central America, Africa, Oceania (the islands around Australia), and Asia. Tropical rainforests cover only about 7% of the Earth's surface. The following map shows the distributions of tropical rainforest in the world:

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With an abundant amount of solar energy, tropical rainforests are usually warm year round with temperatures from about 72-93F (22-34C), although forests at higher elevations, especially cloud forests, may be somewhat cooler. The temperature may fluctuate during the year, but on the equator the average may only vary as little as 0.5F (0.3C) throughout the year. The high amount of cloud cover and high humidity moderates temperatures in the rainforest, though to the temperate tourist they may seem unbearably hot as a result of the humidity. Tropical rainforests often have from 160 to 400 inches of rain a year. But they aren't the wettest or even the hottest places on Earth. (The wettest is Mount Waialeale, in Hawaii, USA, and the hottest is Libya in North Africa.) But just as important as the amount of rain in shaping the unique character of rainforests is the constant humidity and high average temperature. In the Amazon basin you can expect at least 130 days of rain a year and, in many places, up to 250 days. The relative humidity never falls below 80%, and temperatures vary little between daytime averages of 31 degrees Centigrade (88 Fahrenheit) and night-time lows of 22 degrees C (72 F).

Rainforests lie in the intertropical convergence zone where intense solar energy produces a convection zone of rising air that loses its moisture as frequent rainstorms. Rainforests are subject to heavy rainfall each year. In equatorial regions, rainfall can be year round without apparent "wet" or "dry" seasons. Sometimes this constancy of temperature and humidity leads people to argue that rainforests have no seasons, but in the tropics this is only partially correct. There may not be a cold winter and a hot summer, but there are DRY seasons and WET seasons, although many forests do have seasonal rains. Even in seasonal forests, the period between rains is usually not long enough for the leaf litter to dry out. During the parts of the year when less rain falls, the constant cloud cover is enough to keep the air moist and prevent plants from drying out. This also allows most rainforest trees to be evergreen, keeping their leaves all year, never dropping all leaves in any one season.

The moisture of the rainforest from rainfall, constant cloud cover, and transpiration (water loss through leaves), creates intense local humidity. Each canopy tree transpires some 200 gallons (760 liters) of water annually, translating to roughly 20,000 gallons (76,000 L) of water transpired into the atmosphere for every acre of canopy trees. Large rainforests (and their humidity) contribute to the formation of rain clouds, and generate as much as 75 percent of their own rain. The Amazon rainforest is responsible for creating as much as 50 percent of its own precipitation.  An estimated 70-90 percent of life in the rainforest exists in the trees, above the shaded forest floor. Primary tropical rainforest is vertically divided into at least five layers: the overstory, the canopy, the understory, the shrub layer, and the forest floor. Each layer has its own unique plant and animal species interacting with the ecosystem around them. The overstory refers to the crowns of emergent trees which soar 20-100 feet above the rest of the canopy. The canopy is the dense ceiling of closely spaced trees and their branches, while the understory is the term for more widely spaced, smaller tree species and juvenile individuals that form a broken layer below the canopy. The shrub layer is characterized by shrubby species and juvenile trees that grow only 5-20 feet off the forest floor. The forest floor is the ground layer of the forest made up of the trunks of trees, fungus, and low-growing vegetation. These layers are not always distinct and can vary from forest to forest, but serve as a good model of the vegetative and mechanical structures of the fores. Rainforests are characterized by a unique vegetative structure of several vertical layers including the overstorey, canopy, understorey, shrub layer, and ground level. The canopy refers to the dense ceiling of leaves and tree branches formed by closely spaced forest trees. The upper canopy is 100-130 feet above the forest floor, penetrated by scattered emergent trees, 130 feet or higher, that make up the level known as the overstorey. Below the canopy ceiling are multiple leaf and branch levels known collectively as the understorey. The lowest part of the understorey, 5-20 feet above the floor, is known as the shrub layer, made up of shrubby plants and tree saplings. The following is a descriptive picture of a typical tropical rainforest from a website.

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The heavy vegetation of the canopy effectively screens light from the forest floor, and in a primary equatorial rainforest, there is no thick jungle-like ground growth to impede movement. Ground vegetation in primary forest is minimal and usually consists mainly of lianas (vines) and tree seedlings.

An important characteristic of the canopy system is the presence of plants known as epiphytes, that grow on canopy trees. Epiphytes are not parasitic because they draw no nutrients away from the host, but use the host tree only for support. High in the canopy, epiphytes are better able to access the strong tropical sunlight, which they require for growth. Epiphytes have adapted well to their environment, developing various means to collect nutrients from their surroundings, the mechanisms for which are discussed in the rainforest canopy section.

An additional plant type characteristic of the canopy system is the liana-a sort of woody vine that begins life as a shrub on the forest floor and makes its way up to the canopy by latching on to canopy trees. A related plant type, the hemiepiphyte, begins life in the canopy and grows long roots that eventually reach the forest floor. Once rooted, hemiepiphytes do not have to rely on capturing nutrients from their canopy surroundings, but can access nutrients from the forest floor. 

Unknown numbers of plants and animals reside in the canopy, the vast majority of which are specifically adapted to life in this leafy world. In tropical rainforests, it is estimated that 90% of the species that exist in the ecosystem reside in the canopy. Since the tropical rainforests are estimated to hold 50% of the planet's species, the canopy of rainforests worldwide may hold 45% of life on Earth.

Life in the rainforests is competitive and countless species have developed complex symbiotic relationships with other species in order to survive. These relationships have been developing for millions of years and now form a cornerstone or "keystone" of the ecosystem which links many other species together, much like the keystone of an arch. When one species is removed from this system, the entire system is affected, usually for the worse. In the case that the lost species is a cornerstone species, the whole system could fail.

A symbiotic relationship is a relationship where both participant species benefit mutually. Symbiotic relationships appear to be the rule and not the exception in the rainforest. For example, ants have symbiotic relationships with countless rainforest species including plants, fungi, and other insects. One symbiotic relationship exists between ants and caterpillars. Certain caterpillar species produce sweet chemicals from "dew patches" on their backs, upon which a certain ants species will feed. In return, the ants vigorously protect the caterpillar and have even been observed carrying the caterpillar to the nest at night for safety. This relationship appears to be species specific in that only one caterpillar species will cater to a particular ant species.

Despite the fact that the tropical rainforest is so valuable to us, we are losing Earth's greatest biological treasures. Rainforests once covered 14% of the earth's land surface; now they cover a mere 6% and experts estimate that the last remaining rainforests could be consumed in less than 40 years. Rainforests are being destroyed because the value of rainforest land is percieved as only the value of its timber by short-sighted governments, multi-national logging companies, and land owners. Nearly half of the world's species of plants, animals and microoganisms will be destroyed or severely threatened over the next quarter century due to Rainforest deforestation. Deforestation refers to the clearing of tropical forests across the Earth has been occurring on a large-scale basis. Deforestation occurs in many ways. Most of the clearing is done for agricultural purposes-grazing cattle, planting crops. Poor farmers chop down a small area (typically a few acres) and burn the tree trunks-a process called Slash and Burn agriculture. Intensive, or modern, agriculture occurs on a much larger scale, sometimes deforesting several square miles at a time. Large cattle pastures often replace rain forest to grow beef for the world market. Common logging is another cause for it. Deforestation increases the amount of carbon dioxide (CO2) and other trace gases in the atmosphere. Experts estimate that we are losing 137 plant, animal and insect species every single day due to rainforest deforestation. That equates to 50,000 species a year. As the rainforest species disappear, so do many possible cures for life-threatening diseases. Currently, 121 prescription drugs sold worldwide come from plant-derived sources. While 25% of Western pharmaceuticals are derived from rainforest ingredients, less that 1% of these tropical trees and plants have been tested by scientists.

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Tropical deforestation also affects the local climate of an area by reducing the evaporative cooling that takes place from both soil and plant life. As trees and plants are cleared away, the moist canopy of the tropical rain forest quickly diminishes. Recent research suggests that about half of the precipitation that falls in a tropical rain forest is a result of its moist, green canopy. Evaporation and evapotranspiration processes from the trees and plants return large quantities of water to the local atmosphere, promoting the formation of clouds and precipitation. Less evaporation means that more of the Sun's energy is able to warm the surface and, consequently, the air above, leading to a rise in temperatures.

People go to the rainforest and use the plants and trees as raw materials, and serious deforestation takes place. However, a rainforest cannot be replaced. Once it has been destroyed it will be gone forever. Once the web of interdependence has been broken, plants and animals have no way to rebuild their complex communities. Hence, we should start to preserve raw materials like paper and wood, and stop destroying our tropical rainforest.