4 Energy Flow in Ecosystem

Dr. Poonam Sharma

Structure

1.Introduction

2.  Energy

2.1 Forms of Energy

2.2 Energy Tranformation

3.  Energy and Ecological system of the Earth 3.1 Solar Energy Available

3.2 Distribution of Solar Energy

4 Energy dynamics in the Earths’ Environment

4.1 Geophysical Path and Ecosystem

4.2 Organic Path and Ecosystems

4.2.1 Producers

4.2.2 Consumers

4.2.3 Decomposers

5 Energy flow and Efficiency

Objectives:

i. To understand the concept of energy flow in ecosstem

ii. To recognize forms of energy and energy transformation

iii. To explain ecological systems

iv. To have clear understanding of energy dynamics in earth’s environment

v. To explain energy flow and efficiency

    1. Introduction

The organisms, the plants and the microbes all exists in interdependence of other life forms are called biotic community. The peculiar type of biotic community that develops or witnessed in an area is fundamentally determined by abiotic or non-living factors. These abiotic factors include all physical and chemical aspects of a region which act as support as well as limitation both to the biota. The non-biological or aboitic factors include climatic component such as sunlight, temperature, air, moisture , salinity ,soil, soil nutrients which are significantly contributing factors of ecosystem functioning.

The basic organisational unit of the complex web of life forms and their biotic conditions that it live in is called ecosystem. In other words ecosystem is functional categorisation of plants, animal, microbes that dwell in an explicit unit of space, interrelated and interact with each other, and also with their environment to reproduce and continue to sustain. Ecosystems are nearly self contained so that the exchange of nutrients within the system is much greater than exchange with other system. There are no distinct boundaries in the ecosystem, from one type of ecosystem to another there is a transition of from steady decrease of life forms and habitat to gradual increase of the next type of life niche. In fact many species occupy or move in more than one habitat for example migratory birds. These transitional regions called ecotones (from the word eco (logy) +tone which in Greek mean tension, the places where ecosystems are in tension) have a unique natural setting which gives them distinctive characteristics. Thus ,a pond, a wetland , a marsh, a forest, an island , a desert , a grassland and so on is a specific ecosystem with its peculiar life form and physical environment complementing each other. All ecosystems have their own set of determining factors. Terrestrial ecosystems work with different environment while aquatic ecosystem works with its own settings. It is interesting to witness that within this broad category there are subset systems for example within aquatic there are oceans, coastal oceans, estuaries, inland wetlands and rivers. Ecosystems can be seen in different scale such as micro level for example a pond , under a rock or a tree trunk ; the medium level includes a large forest or sea and biome are the massive ecosystems or group of similar ecosystems. Whether it is the major category of ecosystem or a subset ecosystem all are unified and interdependent. All biotas share the same atmosphere, the same land and the same hydrological circulation leading to one whole unified ecosystem called biosphere. The ecosystems are the foundations for the biosphere.

      The basic concept of ecosystem is actually an energy system which constitutes different groups or levels of organisms. It appears to be as a complete supply chains system or production line system of nature working in its own unique automotive mechanism. Each level of organism depends on the previous level for energy (food) supply viz. herbivores on plants and carnivores on herbivores. The ecosystem connections among the producers, various levels of consumers (primary, secondary and tertiary) with consumers at the bottom and higher order tertiary consumers at the top set the basic energy flow. The higher order consumers’ energy requirements to sustain and reproduce put huge demand on producers. The three major categories of ecosystems based on the kind of environment are terrestrial, salt water and fresh water and under this broad classification numerous sub – ecosystems that are interdependent, interconnected and overlapping exists. For functioning properly these ecosystems depend on the supplies of basic ingredient such a solar energy, heat, water and nutrients; and many other external environmental factors as well. This implies that various small or big systems are able to generate huge amount of resources from their environment (mainly light energy) and transform it into organic matter.

 2. Energy

    Let us understand the concept of energy. The universe is made up of matter and energy. In terms of defining the words; matter is anything that occupy space and has mass (this means thing can be weighed in the presence of gravity). Therefore, it includes all liquids, gases and solids, biotic and abiotic components of the ecosystem. A solid have a definite shape and mass, a liquid have mass but takes the shape of the container and gases have mass but no shape.

Energy in its various forms is the ability to work and it moves the matter. Energy is categorised in two major types generally i.e. Kinetic and potential energy. Kinetic energy is energy in motion for example light heat, electric current or any physical motion. Potential energy is stored energy; thus, a material or a system or a structure with stored energy and has the potential or capability to release one or more forms of energy of kinetic energy, for example various petroleum fuel release kinetic energy to put the vehicle or a machine to move, stored energy in batteries, or stretched elastic to throw a stone etc.

2.1 Forms of Energy

The broad categorisation of forms of energy divides it into four types chemical, electrical, mechanical and radiant energy. Chemical energy is stored in the bonds of chemical substances and later released from potential to kinetic e.g. fuel molecules. Electric energy results from movement of charged particles e.g. electric current flow in our homes. Mechanical energy is involved in the physical movement of any matter e.g. pushing a table or paddling a bicycle. Radiant energy is energy of electromagnetic spectrum, it travels in waves e.g. X rays, infrared, radio wave etc. The radiant energy is in the form of electromagnetic waves which are released from the sun during the transformation of hydrogen to helium constitutes the fundamental source of energy. The basic supply of energy requisite by all life forms is the chemical energy of their food. The chemical energy is acquired by the conversion of the radiant energy of sun which is stored in the food of living organisms is converted into potential energy by the constituent atoms of food in a particular manner.

Energy is neither created nor destroyed it may be changed from one form to another form in numerous paths nor the total energy in the universe remains the same. It may transform from radiant energy to chemical energy, from chemical to mechanical energy, from kinetic to potential, and from potential to kinetic and variety of other pathways. For example:

     2.2 Energy Tranformation

The energy tranformation or change of form from one to another are infact based on energy laws known as Laws of thermodynamics. In the following lines these two laws are explained:

The First law of Thremodynamics which is also called the law of conservation of energy which states that energy is neither created nor destroyed rather it is only transformed from one form to another form. Thus, if the energy form compared at reception point , how much it is consumed to the point total produced energy in its various forms would be equal.

The second law of Thermodynamics which is also referred as entropy says that in the process of energy conversion part of the usable energy inevitably is lost. Entropy here implies the degree of imperfection or fault or degradation in the system that leads to this loss of usable energy. In each conversion stage some energy is lost as heat. Thus, the energy flows from higher to lower levels; this implies that the capacity of energy to work is reduced in the process of transformation.

     3. Energy and Ecological system of the Earth

All the essential processes and systems on the earths’ surface are determined by solar energy. Both the biotic as well as abiotic components are completely dependent on Sun for all energy requirements. The main functions of the surface environment comprises fundamental life processes which includes plant growth, food chains, reproduction and sustaining the ecosystems; these life processes are based on life support mechanism of water cycle, soil formation and other nutrient flows. All these processes are influenced by this solar energy.

3.1 Solar Energy Available

The incoming solar radiation entering the earths’ atmosphere, is not fully received by the Earth, of this about 35% is pushed back to the space by the reflection due to clouds, other gas molecules and particles present in the air. From the surface of the earth water, ice snow etc also reflects about 4 % of the radiation. Finally earths’ environment is power-driven by 65 % of the total solar energy to be contributed to the earth and it is this massive energy that flows through the earth continuously.

3.2 Distribution of Solar Energy

Due to the curved shape of the earth and other factors such as position of Sun, the solar energy is not evenly distributed over the globe. The polar areas of the planet receive much less than the equatorial zone. It is this pattern of in-solation that determines the biotic as well as well as abiotic components as plants, animals, climate, soils and other elements of our physical environment. Measured in millions of kilocalories of solar energy per year, the high latitudes receive 60 million kilocalories of solar energy; the mid-latitudes receive around 80-120 million kilocalories per year; the highest values of 180-220 million kilocalories per year are found in subtropics between 20-30 degrees latitude. Along the equator it is 120-160 million kilocalories a year. This difference in the values of equator and subtropics is because of heavy cloud covers near equator which reflects. There is a process to sustain a long-term energy balance on the surface of earth by an auto-generated redistribution of energy. The energy is redistributed by circulation of the atmosphere and oceans. From the higher latitudes cooler air and cold ocean currents move towards equator to cool the lower latitudes. From the tropics heat is transported towards pole by the global circulation of air and warm ocean currents to warm higher latitude regions.

4 Energy dynamics in the Earths’ Environment

The solar energy available to the Earth is stored in its environment and it is always in the process of transformation from one form to another particularly heat and chemical (organic) compound.This energy passes through the ecosystem and follows two different courses of heat and organic.

    4.1 Geophysical Path and Ecosystem

This path begins when the solar energy is recieved , reflected back to the space, absorbed and tranformed to heat by the atmosphere and by the surface layers of the ocean and continents. The environment becomes a transitory resorvoir for this converted heat and it is accumulated here for a short time. It is witnessed that more 99 percent of the solar energy goes through the heat path. This heat is responsible for all physical and chemical processes and systems functioning on the surface of the Earth . It is these systems which transforms heat energy into other types of enregy such as kinetic energy in the form of variuos movements and ciculations system of wind and water or potential energy as seen in the mass of snow or precipitation.These processes comprise :

A. The surface and atmospheric circulation system which implies the formation of pressure cells, planetary wind system, upper air motion.

B. The exchange of phosphorous and nitrogen through air soil and water through the nutrient system or cycle.

    C. From the initial point of evaporation through its various forms as clouds and different precipitations, cycling of water happens between surface and the atmosphere is called hydrological cycle.

4.2 Organic Path and Ecosystems

The relationship between formation and breaking down of organic matter and storing and releasing energy are the important routes. The organic path begins with the vital process of photosynthesis where producers (green plants) does a massive conversion of energy from solar radiation to prepare high potential energy organic molecules for their bodies from the raw material in the available in the environment i.e. carbon dioxide, water and other elements. The green pigment chlorophyll in the green plants absorbs the light energy from Sun and makes this huge task of energy transformation possible. This organic path makes use of only one percent of the solar energy available but the whole biological system or existence of life on the Earth is possible owing to the energy conversion.

The energy flow in the ecosystem is the movement of energy through a system from external source through a series of organisms and in the end biosphere gives up all the chemical energy in the ecosystems to the atmosphere as heat. Chemical energy is stored in the form of organic deposits in soil and rock formations that represents topsoil and fossil fuels. This organic matter is used as a source of energy in homes, industry and automobiles, in the processes it is transformed into heat and along with other chemicals compounds that are released into the atmosphere.

In the sequence of this flow only a small fraction of energy is used for the production of new growth and reproduction at each trophic level of the food chain, most of it is used for body respiration and maintenance. The producers and consumers in ecosystem can be classified into various feeding groups, each known as trophic level. A particular position occupied by a group of organism in a food chain is known as trophic level for example primary producer, primary consumer, secondary consumer or tertiary consumer. Heterotrophics acquire their energy by consuming herbivores, carnivores and other higher order consumers’ feed on herbivores and detritivore feed on generated waste. The food chains are structured in three to five levels of energy conversions referred as trophic levels and each of the trophic level illustrates a particular function in the ecosystem. Integrated food chains are called food webs.

4.2.1 Producers

The absorption of light energy and its conversion into stored chemical energy by autographs (plants) provide ecosystem with its primary energy source at the base of food chain. Plants are the gateway to the Sun’s energy to the entire ecosystem. The organic compound manufactured by plants is passed on to the other organisms through the food chain in which series of consumers are dependent on each other. Food chain is the sequence of organisms depends upon each other as source of food. Organisms that consumes plant material synthesize portion of this in their own bodies becomes flesh of plant eating animal which further provides nutrition to other animal, along this chain energy keeps flowing in the ecosystem from one organism to another.

     Since plants set table for the all other biotic components of the ecosystem which comprises the herbivores, carnivores, other higher, order consumers and decomposers; as they create the new organic matter for the ecosystem the plants are called primary producers. The total amount of energy converted into organic matter is called gross primary production (GPP). From this GPP some energy plants use for their own maintenance and rest is known as Net primary production (NPP). Therefore, NPP implies to the pace at which new organic matter is available to the consumers in the ecosystem. The total NPP of an ecosystem provides the energy base utilised by the non-photosynthetic (heterotrophic) organisms.

4.2.2 Consumers

Consumers need energy to synthesize all the molecules required for growth, maintenance and repair of the body. The release of potential energy contained in organic molecules is needed by the organism to carry out the activities is vital point of cell respiration. Organic molecules (glucose) are broken down in the cell respiration process. In the process oxygen is absorbed and carbon dioxide is released as a by product.

       At this trophic level the primary consumers or herbivores make up the second level in the feeding chain. These include cattles and all other plant eating organisms followed by carnivores or secondary consumers includes meat eaters such as snake, cats and lions, etc. The tertiary consumers are the fourth level for example hawks and eagles are among this group that eat other carnivores. Omnivores such as humans, ape, monkey racoons, and black bears function as both carnivores and herbivores.

The energy conversions involved in the body’s use of potential energy from glucose are not completely efficient as per the law of thermodynamics. Substantial heat is produced as waste which becomes the source of body heat. Cold blooded and warm blooded animals’ body heat is measureable. The organic substance eaten by the consumer, about 60 percent of the food is oxidised for energy and waste released to the environment, nearly 10 percent is converted for body tissue growth ,maintenance and repair and undigested goes as faecal waste. This process is known to as secondary production. It is important to understand here that the small portion of food which becomes body tissue of the consumer is the only energy which is available as food for the next organism in the food chain.

4.2.3 Decomposers

They are heterotrophic organism that feed on dead organic matter and faecal waste. Detritivores are organisms that live on the refuse of the ecosystem, they include scavengers like vulture, worms and crabs that feed on dead remains and decomposers as fungi, bacteria and protozoa that feed dead organic matter and eventually the waste products of the final line of decomposition are mineral nutrients which are reabsorbed by the soil, that important for primary producers and thus recycled by plants back to the ecosystem.

5 Energy flow and Efficiency

The common ecological measure of efficiency is at trophic level, it is ration of production at one trophic level to that of the next level. The ecosystems integrate both biotic (living) that comprises producers, consumers and decomposers; abiotic (non-living) elements such as solar radiation, soil, water air and heat. Ecosystems are energy systems that include numerous food chain and food webs connecting the enormous number of organisms with their environment. The energy passes through the categorised various feeding (trophic) levels and in this transformation of energy most of it is goes as heat in the respiration. It is estimated that there is a loss of about 90 percent energy as it moves from one level to another, therefore the efficiency of energy transfer is only 10 percent. Thus, energy budget of an ecosystem declines with each energy conversion and the available energy at higher trophic level becomes too small. The law of thermodynamics says that there is actually no energy be lost, but entropy increases and most of the energy degrades and not available for any further conversions because of innumerable energy conversions among the various trophic activities. Energy flow between trophic levels represents the sum of feeding performances of many species and communities. This entire process of energy transformation explains that energy flow is uni-directional (one-way flow) through the ecosystem and it is not recycled rather it is replenished by the solar radiation.

The flow of energy through the food chain depends on the efficiency with which organisms consume their food resources and convert them into biomass. This is called trophic level efficiency of ecological efficiency which is depends on two types of factors; the limitations on the availability of basic resources for photosynthesis and disturbance due to the external relationship to the environment. The fundamental biological rule of the principles of limiting factors clear indicates that for a maximum photosynthesis the ingredient such as light ,heat water carbon dioxide and nutrient shall be available at a certain level ,and if any factor is short supply for the photosynthesis then it is considered limited by the one factor value or an excessive quantity of any factor might also prove to be a limiting factor for example any kind of pollution in the atmosphere or water shall become limiting factor for the particular ecosystem. Thus, there are optimum conditions for an organism, low and high limiting factor creates a condition of tolerance threshold and if not the conditions may become acute or chronic where the survival is at stake. The disturbance from the external environment include the sudden events of flood, storms, draughts etc these situation disrupts the flow of the basic components of the photosynthesis for example extreme soil erosion will reduce availability of nutrient, or physical damage of plant foliage due storm. Ecosystems are in state of incessant adjustments with these sudden and progressive changes.

The ecological efficiency can also be seen with respect to climatic limitations. For example the environments with no limitation which includes the tropical areas with an annual average output of 2200 grams of organic output per square meter. This is followed by environments of seasonal limitation like Mid-latitude zones with the annual average organic output of 600 to 1200 grams per square meter. The others are environments with permanent limitation which include arid/arctic and Polar Regions with 5 to 90 grams per square meter annual average. Similarly aquatic ecosystems also show variation in energy efficiency depending upon the depth of oceans.

But besides these natural limiting factors it has been witnessed that human intervention is adding complexity to the ecosystems of the earth. The energy flow efficiency of the ecosystem faces indirect losses due to the various anthropogenic actions of deforestation, overgrazing, and pollution etc. The overall trend in historical progression has been towards enhanced magnitude and frequency of disturbances by humans as the numbers, resource exploitation and expanding occupancy of land and marine areas of the planet has increased many folds.

     The measurement of energy flow through the entire community is very complex. The total input of solar energy and the efficiency of its transformations at each level determine the basic trophic structure; the number of trophic levels, the intricacies of the food webs and the annual rate of production of organic matter is of vital significance to the sustenance of the ecosystem.

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