Energy Flow in Ecosystem.
Energy Flow in Ecosystem
An ecosystem is defined as a community of various organisms interacting with each other and their environment in a particular area. It accounts for all interactions and relationships between both biotic (living) and abiotic (non-living) factors.
Energy has been defined as the capacity to do work. Energy exists in two forms potential and kinetic.
Potential energy is the energy at rest {i.e., stored energy) capable of performing work. Kinetic energy is the energy of motion (free energy).
It results in work performance at the expense of potential energy. Conversion of potential energy into kinetic energy involves the imparting of motion.
Energy is what drives the ecosystem to thrive. And while all matter is conserved in an ecosystem, energy flows through an ecosystem, meaning it is not conserved. Energy enters all ecosystems as sunlight and is gradually lost as heat back into the environment.
However, before energy flows out of the ecosystem as heat, it flows between organisms in a process called energy flow. It's this energy flow that comes from the sun and then goes from organism to organism that is the basis of all interactions and relationships within an ecosystem.
The definition of energy flow is the transfer of energy from the sun and up each subsequent level of the food chain in an environment.
Each level of energy flow on the food chain in an ecosystem is designated by a trophic level, which refers to the position a certain organism or group of organisms occupies on the food chain. The start of the chain, which would be at the bottom of the energy pyramid, is the first trophic level. The first trophic level includes producers and autotrophs that convert solar energy into usable chemical energy via photosynthesis.
The next level up in the food chain/energy pyramid would be considered the second trophic level, which is usually occupied by a type of primary consumer like an herbivore that eats plants or algae. Each subsequent step in the food chain is equivalent to a new trophic level.
Besides trophic levels, there are a few more terms you need to know to understand energy flow.
Biomass: Biomass is organic material or organic matter. Biomass is the physical organic material that energy is stored in, like the mass that makes up plants and animals.
Productivity:
Productivity is the rate at which energy is incorporated into the bodies of organisms as biomass. You can define productivity for any and all trophic levels. For example, primary productivity is the productivity of primary producers in an ecosystem.
Gross primary productivity (GPP): GPP is the rate at which the energy from the sun is captured in glucose molecules. It essentially measures how much total chemical energy is generated by primary producers in an ecosystem.
Net primary productivity (NPP): NPP also measures how much chemical energy is generated by primary producers, but it also takes into account the energy lost due to metabolic needs by the producers themselves. So, NPP is the rate at which the energy from the sun is captured and stored as biomass matter, and it's equal to the amount available energy to the other organisms in the ecosystem. NPP is always a lower amount than GPP.
NPP varies depending on the ecosystem. It depends on variables such as:
- Available sunlight.
- Nutrients in the ecosystem.
- Soil quality.
- Temperature.
- Moisture.
- CO2 levels.
This energy flow is based on two important Laws of Thermodynamics which are as follows:
The first law of Thermodynamics:
It states that the amount of energy in the universe is constant. It may change from one form to another, but it can neither be created nor destroyed. Light energy can be neither created nor destroyed as it passes through the atmosphere. It may, however, be transformed into another type of energy, such as chemical energy or heat energy. These forms of energy cannot be transformed into electromagnetic radiation.
The second law of Thermodynamics:
It states that non-random energy (mechanical, chemical, radiant energy) cannot be changed without some degradation into heat energy. The change of energy from one form to another takes place in such a way that a part of energy assumes waste form (heat energy). In this way, after transformation, the capacity of energy to perform work is decreased. Thus, energy flows from higher to lower level.
Main source of energy is sun. Approximately 57% of sun energy is absorbed in the atmosphere and scattered in the space. Some 35% is spent to heat water and land areas and to evaporate water. Of the approximately 8% of light energy striking plant surface, 10% to 15% is reflected, 5% is transmitted and 80 to 85% is absorbed; and an average of only 2% (0.5 to 3.5%) of the total light energy striking on a leaf is used in photosynthesis and rest is transformed into heat energy.
Energy Flow in Ecosystem:
Living organisms can use energy in two forms radiant and fixed energy. Radiant energy is in the form of electromagnetic waves, such as light. Fixed energy is potential chemical energy bound in various organic substances which can be broken down in order to release their energy content.
Organisms that can fix radiant energy utilizing inorganic substances to produce organic molecules are called autotrophs. Organisms that cannot obtain energy from abiotic source but depend on energy-rich organic molecules synthesized by autotrophs are called heterotrophs. Those which obtain energy from living organisms are called consumers and those which obtain energy from dead organisms are called decomposers.
When the light energy falls on the green surfaces of plants, a part of it is transformed into chemical energy which is stored in various organic products in the plants. When the herbivores consume plants as food and convert chemical energy accumulated in plant products into kinetic energy, degradation of energy will occur through its conversion into heat. When herbivores are consumed by carnivores of the first order (secondary consumers) further degradation will occur. Similarly, when primary carnivores are consumed by top carnivores, again energy will be degraded.
Trophic level:
The producers and consumers in ecosystem can be arranged into several feeding groups, each known as trophic level (feeding level). In any ecosystem, producers represent the first trophic level, herbivores present the second trophic level, primary carnivores represent the third trophic level and top carnivores represent the last level.
Food Chain:
In the ecosystem, green plants alone are able to trap in solar energy and convert it into chemical energy. The chemical energy is locked up in the various organic compounds, such as carbohydrates, fats and proteins, present in the green plants. Since virtually all other living organisms depend upon green plants for their energy, the efficiency of plants in any given area in capturing solar energy sets the upper limit to long-term energy flow and biological activity in the community.
The food manufactured by the green plants is utilized by themselves and also by herbivores. Animals feed repeatedly. Herbivores fall prey to some carnivorous animals. In this way one form of life supports the other form. Thus, food from one trophic level reaches to the other trophic level and in this way a chain is established. This is known as food chain.
A food chain may be defined as the transfer of energy and nutrients through a succession of organisms through repeated process of eating and being eaten. In food chain initial link is a green plant or producer which produces chemical energy available to consumers. For example, marsh grass is consumed by grasshopper, the grasshopper is consumed by a bird and that bird is consumed by hawk.
Thus, a food chain is formed which can be written as follows:
Marsh grass → grasshopper → bird → hawk
Food chain in any ecosystem runs directly in which green plants are eaten by herbivores, herbivores are eaten by carnivores and carnivores are eaten by top carnivores. Man forms the terrestrial links of many food chains.
Food chains are of three types:
- Grazing food chain
- Parasitic food chain
- Saprophytic or detritus food chain
Grazing food chain:
The grazing food chain starts from green plants and from autotrophs it goes to herbivores (primary consumers) to primary carnivores (secondary consumers) and then to secondary carnivores (tertiary consumers) and so on. The gross production of a green plant in an ecosystem may meet three fates—it may be oxidized in respiration; it may be eaten by herbivorous animals and after the death and decay of producers it may be utilized by decomposers and converters and finally released into the environment. In herbivores the assimilated food can be stored as carbohydrates, proteins and fats, and transformed into much more complex organic molecules.
The energy for these transformations is supplied through respiration. As in autotrophs, the energy in herbivores also meets three routes respiration, decay of organic matter by microbes and consumption by the carnivores. Likewise, when the secondary carnivores or tertiary consumers eat primary carnivores, the total energy assimilated by primary carnivores or gross tertiary production follows the same course and its disposition into respiration, decay and further consumption by other carnivores is entirely similar to that of herbivores.
Thus, it is obvious that much of the energy flow in the grazing food chain can be described in terms of trophic levels as outlined below:
Parasitic food chain:
It goes from large organisms to smaller ones without outright killing as in the case of predator.
Detritus food chain:
The dead organic remains including metabolic wastes and exudates derived from grazing food chain are generally termed detritus. The energy contained in detritus is not lost in ecosystem as a whole, rather it serves as a source of energy for a group of organisms called detritivores that are separate from the grazing food chain. The food chain so formed is called detritus food chain.
In some ecosystems more energy flows through the detritus food chain than through grazing food chain. In detritus food chain the energy flow remains as a continuous passage rather than as a stepwise flow between discrete entities. The organisms in the detritus food chain are many and include algae, fungi, bacteria, slime moulds, actinomycetes, protozoa, etc. Detritus organisms ingest pieces of partially decomposed organic matter, digest them partially and after extracting some of the chemical energy in the food to run their metabolism, excrete the remainder in the form of simpler organic molecules.
The waste from one organism can be immediately utilized by a second one which repeats the process. Gradually, the complex organic molecules present in the organic wastes or dead tissues are broken down to much simpler compounds, sometimes to carbon dioxide and water and all that are left are humus. In a normal environment the humus is quite stable and forms an essential part of the soil.
Food web:
Many food chains exist in an ecosystem, but as a matter of fact these food chains are not independent. In ecosystem, one organism does not depend wholly on another. The resources are shared specially at the beginning of the chain. The marsh plants are eaten by variety of insects, birds, mammals and fishes and some of the animals are eaten by several predators.
Similarly, in the food chain grass → mouse → snakes → owls, sometimes mice are not eaten by snakes but directly by owls. This type of interrelationship interlinks the individuals of the whole community. In this way, food chains become interlinked. A complex of interrelated food chains makes up a food web. Food web maintains the stability of the ecosystem. The greater the number of alternative pathways the more stable is the community of living things.
Ecological pyramid:
The trophic structure of an ecosystem can be indicated by means of ecological pyramid. At each step in the food chain a considerable fraction of the potential energy is lost as heat. As a result, organisms in each trophic level pass on lesser energy to the next trophic level than they actually receive. This limits the number of steps in any food chain to 4 or 5. Longer the food chain the lesser energy is available for final members. Because of this tapering off of available energy in the food chain a pyramid is formed that is known as ecological pyramid. The higher the steps in the ecological pyramid the lower will be the number of individuals and the larger their size.
The idea of ecological pyramids was advanced by C.E. Elton (1927). There are different types of ecological pyramids. In each ecological pyramid, producer level forms the base and successive levels make up the apex. Three types of pyramidal relations may be found among the organisms at different levels in the ecosystem.
Productivity:
The relationship between the amount of energy accumulated and the amount of energy utilized within one trophic level of food chain has an important bearing on how much energy from one trophic level passes on to the next trophic level in the food chain. The ratio of output of energy to input of energy is referred to as ecological efficiency.
Different kinds of efficiencies can be measured by the following parameters:
- Ingestion which indicates the quantity of food or energy taken by trophic level. This is also called exploitation efficiency.
- Assimilation indicates the amount of food absorbed and fixed into energy rich organic substances which are stored or combined with other molecules to build complex molecules such as proteins, fats etc.
- Respiration which indicates the energy lost in metabolism.
Environmental factors affecting the production processes in an ecosystem are as follows:
- Solar radiation and Temperature
- Moisture. Leaf water potential, soil moisture and precipitation fluctuation and transpiration.
- Mineral nutrition. Uptake of minerals from the soil, rhizosphere effects, fire effects, salinity, heavy metals, nitrogen metabolism.
- Biotic activities. Grazing, above ground herbivores, below ground herbivores, predators and parasites, diseases of primary producers.
- Impact of human population. Pollutions of different sorts, ionizing radiations like atomic explosions, etc.
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