من انا

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الرياض, Saudi Arabia
مسلم، وأناأحوج ما أكون إلى معرفة نفسي

الثلاثاء، 31 يناير، 2012

What is an Ecosystem


Ecosystem





   What is an Ecosystem?


An ecosystem is a community of organisms that interact with each other and non living components for sustainable development and adaptation to changing conditions. There are different type of ecosystems around us which involves living organisms and non living organisms. If we combine all the ecosystems present on earth, it is called Biosphere.



Components of an Ecosystem:

There are two components of an ecosystem;

·        Biotic (living)  components .

·        Abiotic (non living) components.







Abiotic Components




The abiotic components of a grassland ecosystem are the non-living features of the ecosystem that the living organisms depend on. Each abiotic component influences the number and variety of plants that grow in an ecosystem, which in turn has an influence on the variety of animals that live there. The four major abiotic components are: climate, parent material and soil, topography, and natural disturbances.

Climate

includes the rainfall, temperature and wind patterns that occur in an area, and is the most important abiotic component of a grassland ecosystem. Temperature, in tandem with precipitation, determines whether grasslands, forests, or some combination of these two, form. The amount and distribution of the rainfall an area receives in a year influences the types and productivity of grassland plants.

The climate in our grassland ecosystems is usually hot and dry in the spring and summer growing season, and cool or cold in winter dormant season. Precipitation in the winter falls mostly as snow rather than rain. During the hottest months of the year (the height of summer) more water evaporates from parts of the grasslands than falls as rain, creating a moisture deficit.




Parent Material and Soil

Parent material

is the geological material that lies on top of the bedrock and is the foundation on which soil has developed. Much of the parent material underlying BC's grasslands was deposited as the last ice sheets melted away. The actual composition of the material at any specific location depends on how and where it was deposited in relation to the ice. In the Rocky Mountain Trench, for example, some material was deposited under a moving glacier, while on the Chilcotin plateau some was deposited under a stationary ice sheet; in many places throughout the grasslands material was carried and deposited by water on, in, or under the ice.

The material dropped in place under the ice varies in thickness from a thin veneer to several metres, and contains all sizes of rocks and particles from boulders to silts. Rivers and streams that flowed on, under and beyond the ice left hummocky ridges of water-rounded materials of all sizes. Material deposited in ice-damned lakes formed layers of fine silts. Winds picked up fine particles and blew them across the newly ice-free land surface, depositing thick layers of the particles in some places. These wind-blown materials are called aeolian deposits.

Soil develops in the upper portion of the parent material and is a mixture of abiotic and biotic components: minerals, organic matter, water and air. The type of parent material in a particular area influences the texture of the soil, how well water flows through it, and hence the chemistry and nutrients of the soil. This combination of texture, water flow and chemistry determines the vegetation that grows in the area.

The fine silt soils found on the terraces of the Okanagan, Kootenay and Thompson valleys hold water near to the surface where it either evaporates or is soaked up by the dense fine roots of grasses; trees are not common in these areas. By contrast, in areas with gravelly soils water moves quickly down to depths below the grass roots to levels where tree roots grow. As such, more trees are likely to be found in these areas.

Grasslands have a rich layer of organic matter that forms the top surface of the soil. This layer has developed largely as a result of the breakdown of plant roots. Roots form as much as half the volume of a grass plant and up to 50% are replaced every year.






Biotic Components



The biotic components of a grassland ecosystem are the living organisms that exist in the system. These organisms can be classified as producers, consumers or decomposers.





Producers

are able to capture the sun’s energy through photosynthesis and absorb nutrients from the soil, storing them for future use by themselves and by other organisms. Grasses, shrubs, trees, mosses, lichens, and cyanobacteria are some of the many producers found in a grassland ecosystem. When these plants die they provide energy for a host of insects, fungi and bacteria that live in and on the soil and feed on plant debris. Grasses are an important source of food for large grazing animals such as California Bighorn Sheep, Mule Deer and Elk, and for much smaller animals such as marmots, Pocket Gophers and mice.

Consumers

are organisms that do not have the ability to capture the energy produced by the sun, but consume plant and/or animal material to gain their energy for growth and activity. Consumers are further divided into three types based on their ability to digest plant and animal material:

  • Herbivores eat only plants, such as the elk that graze the grasslands of the Columbia valley, or an insect nibbling on the leaf of a sticky geranium.
  • Omnivores eat both plants and animals, such as the black bear.
  • Carnivores eat only animals, such as the red-tailed hawk or western rattlesnake.

Decomposers

include the insects, fungi, algae and bacteria both on the ground and in the soil that help to break down the organic layer to provide nutrients for growing plants. There are many millions of these organisms in each square metre of grassland.

Soil

has many biotic functions in a grasslands ecosystem. It provides the material in which plants grow, holds moisture for plants to absorb, is the "recycling bin" for plant and animal matter, and provides an important habitat for soil organisms. Soil is a vital link between the biotic and abiotic parts of a grassland ecosystem.











Ecosystem Processes






Energy Flow

Refer to the yellow arrows in the diagram to help you understand the way that energy moves through an ecosystem.

Energy enters an ecosystem in the form of heat from the sun. This energy is absorbed by organisms such as plants, and is then converted to other forms of energy and stored. Once stored, energy is used for necessary life functions, such as growth, movement and reproduction. Plants, animals and microorgnaisms release energy in the form of heat, for example through breathing and sweating. Energy is also released from an ecosystem during a fire.

Plants only capture about one percent of the energy that reaches the earth from the sun. In grasslands, that small amount of energy is used by the grasses and other plants, or producers. Some animals eat only these plants. Other animals eat both grasses and other plants, and animals, while yet other animals only eat animals. Animals are called consumers.

Food Chain

This movement of energy from producers to consumers is called a Food Chain.

Food Chains are found in two parts of an ecosystem. The "grazing" food chain includes the producers and consumers that cycle energy from living plants. The "detritus" food chain cycles energy from non-living remains of both plants and animals (also called detritus).

The "grazing" food chain has a number of steps that start with the producers, or the plants, and flows through a series of levels of consumers. At each step only about 10% of the energy is passed up through the chain. The rest is passed back into the atmosphere as heat through breathing and decomposition.

In the first step plants convert the sun’s energy to chemical energy through a process called photosynthesis. The chemical energy is stored both as food and as structural elements in the plant.



The next step involves the primary consumers, animals that eat only plants. In a grassland ecosystem this includes animals such as California Bighorn Sheep, Mule Deer, Elk, marmots, Pocket Gopher and mice. At step three are the secondary consumers, also called predators; these animals eat primary consumers. In a grassland ecosystem this includes a Coyote eating a mouse, a woodpecker eating an ant, or a frog eating an insect. At step four are the tertiary consumers that eat secondary consumers, and sometimes primary consumers as well. In a grassland ecosystem this includes a snake eating a frog.

The "detritus" food chain is a system where the energy produced by the breakdown of dead plant and animal matter is cycled into the "grazing" food chain. Detritus is organic matter formed by decaying animal or plant tissue, or fecal matter. Detritus eaters (or detritivores) such as insects, worms and other small organisms feed on dead plants, waste products from animals and dead animals. Decomposers are fungal or bacterial organisms that work within the dead material to help break it down, activating decay and decomposition. This important part of the ecosystem takes the last of the energy that was originally absorbed by the plants and returns it to the soil.

Carbon can be traced through the ecosystem in a cycle that is similar to the water cycle. Plants take in carbon in the form of carbon dioxide from the atmosphere through respiration. Through a process called photosynthesis, the carbon dioxide combines with oxygen to form carbohydrates that range from simple sugars to the complex carbohydrate cellulose, which forms cell walls. When plants are eaten the carbon is transferred to the consumers. As plant material is broken down in the digestive system of an animal, carbon is absorbed as a nutrient for use by that animal. It is released back into the atmosphere as carbon dioxide through respiration and through the decomposition of dead animals and fecal matter. Grassland fires also release carbon dioxide into the atmosphere.

Water Cycling

All organisms require both water and nutrients (food) to survive.

Where do the water and nutrients come from and how do they move around a grassland ecosystem?

The water cycle is illustrated by the blue parts of the diagram.

Water exists in three forms: solid (ice and snow), liquid and gas (water vapour). Water is the vital link between the ecosystem and the weather or climate.

Water falls from clouds onto the grasslands as rain or snow.

Rain runs off plants and rocks onto the ground, where some water is absorbed into the soil. The rest runs over the surface of the ground and collects in low areas to form into wetlands, lakes and rivers. Finally, some water that reachs the ground is evaporated back into the atmosphere.

Snow, which is crystallized water droplets, may form a blanket over the grasslands during the winter. Snow undergoes similiar processes to rain when it reaches the ground. Some of it evaporates back into the atmosphere, and as snow melts, the water produced is absorbed into the soil, or runs over the ground into wetlands, lakes and rivers.

Plants take up some of the water contained in the soil through their roots. Other water that permeates (soaks through) the soil flows into wetlands, lakes, and rivers. The rest becomes part of the water table. The water table is water that remains in the soil, filling the pores between rocks and soil particles. Water is returned to the atmosphere as water vapour through evaporation and transpiration. Transpiration is a process performed by plants whereby water molecules leave the plant's surface through evaporation.

The water that reaches wetlands, lakes and rivers flows eventually to the ocean, with some of it evaporating along the way. Evaporation provides the moisture in clouds that condenses to form droplets of rain or snow. These droplets of water return to the earth as precipitation, and the cycle starts again.

The portions of grassland ecosystems that occur in low elevations and especially on south-facing slopes suffer from a water deficit during the hottest and driest months of the year. The amount of water that is released into the atmosphere through transpiration and evaporation is larger than the amount that falls as rain at this time of year. Grassland plants have adopted a variety of ways to survive under these difficult growing conditions.

Bright yellow sagebrush buttercups are some of the earliest flowers to be seen in the grasslands early spring. They start to grow before all the snow has left the grasslands, their shallow roots take advantage of all the water stored in the thawed upper layers of the soil. By the end of May the available moisture is well below the reach of the roots of the plants, and little remainsof the sagebrush buttercup but some dried out leaves.

Plants such as low pussytoes and silky lupine start growing a little later in the spring and bloom before the summer drought begins. They may grow again as soil moisture increases after fall showers. Some of the bunchgrasses have a similar early growth habit but become semi-dormant during the summer drought. They put on a significant amount of growth when fall rains arrive. Deeply-rooted shrubs such as big sagebrush and rabbitbrush start growing later in the year and are covered with yellow flowers in the fall.



Nutrient Cycling

The nutrient cycle follows the green parts of the diagram below.

All organisms need many nutrients, for food and for proper functioning, in order to thrive. Nutrients are found in the soil as the products of decomposition of dead matter, both plant and animal, and of waste materials such as animal feces and urine; dust; water runoff and erosion; and through weathering of rocks. They are also released from plants by fire and through nitrogen fixation by cyanobacteria.

Nutrients combine with water in the soil and are transported through the roots of the plant to those parts that need them. They are then passed through the food chain as the consumers eat the plants and each other. The final decomposition of both producers and consumers returns the nutrients back to the soil.

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