- Energy flow, also called the calorific flow, refers to the flow of energy through a food chain.
- Energy flow is based on two important Laws of Thermodynamics.
- The first law of Thermodynamics: 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: The 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.
- Except for the deep sea hydrothermal ecosystem, the sun is the only source of energy for all ecosystems on Earth.
Energy flow in Ecosystems:
- 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.
- Autotrophs – Organisms that can fix radiant energy utilizing inorganic substances to produce organic molecules.
- Heterotrophs – Organisms that cannot obtain energy from abiotic source but depend on energy-rich organic molecules synthesized by autotrophs.
- Consumers – Those who obtain energy from living organisms are called consumers.
- Decomposers – Those who obtain energy from dead organisms are called decomposers.
Flow of Energy at different Levels of Ecosystem
- Photosynthetically Active Radiation (PAR) is the amount of light available for photosynthesis, which is light in the 400 to 700-nanometer wavelength range. Of the incident solar radiation, less than 50 per cent of it is Photosynthetically active radiation (PAR).
- Plants and photosynthetic bacteria (autotrophs), fix suns’ radiant energy to make food from simple inorganic materials. Plants capture only 2-10 per cent of the PAR and this the small amount of energy sustains the entire living world.
- 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 an ecosystem can be arranged into several feeding groups, each known as trophic level (feeding level).
- Food chain – It may be defined as the transfer of energy and nutrients through a succession of organisms through the repeated process of eating and being eaten.
- A food chain starts with producers and ends with top carnivores.
- For example, marsh grass is consumed by grasshopper, the grasshopper is consumed by a bird and that bird is consumed by the hawk.
- Thus, a food chain is formed which can be written as follows:
- Marsh grass —-→ grasshopper —-→ bird → hawk
- 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.
- Plants themselves and herbivores use food manufactured by green plants.
- 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 a food chain.
Types of the food chain
Food chains are of three types –
- Grazing food chain
- Parasitic food chain
- Saprophytic or detritus food chain
1. Grazing food chain (GFC)
- The grazing food chain starts with green plants which are the producers. The green plants or producers are grazed by herbivorous animals which are further eaten by carnivores.
- Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as catabolism.
- Humification and mineralization occur during decomposition in the soil.
- Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.
- Being colloidal in nature, hummus serves as a reservoir of nutrients. The hummus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralization.
- Warm and moist environment favour decomposition whereas low temperature and anaerobiosis inhibit decomposition resulting in a buildup of organic materials.
- Example – Primary producers (Autotrophs)-> Primary consumers (Herbivores)-> Secondary Consumers (Carnivores)
- The chain begins with green plants (producers) at the first trophic level.
- Energy for this food chain comes from the sun.
- Food chain adds energy to the ecosystem.
- The food chain fixes inorganic nutrients.
- It consists of all macroscopic organisms.
- For example, in a terrestrial ecosystem, the grass is eaten by a caterpillar, which is eaten by lizard and lizard is eaten by the snake.
- In Aquatic ecosystem phytoplankton (primary producers) are eaten by zooplanktons which are eaten by fishes and fishes are eaten by pelicans.
2. Parasitic food chain
- If in the food chain, the primary and other levels of consumers are parasitic, then the food chain is described as the parasitic food chain.
- For example – Birds → Bird lice → Protozoan
3. Detritus food chain (DFC)
- This type of food chain starts from dead organic matter of decaying animals and plant bodies.
- Dead organic matter or detritus feeding organisms are called detrivores or decomposer. The detrivores are eaten by predators.
- It is made up of decomposers which are heterotrophic organisms, mainly fungi and bacteria.
- Energy for this food chain comes from remains of detritus.
- Decomposers are also known as saprotrophs (sapro: to decompose).
- Decomposers secrete digestive enzymes that breakdown dead and waste materials into simple, inorganic materials, which are subsequently absorbed by them.
- In a terrestrial ecosystem, a larger fraction of energy flows through the detritus food chain than through the GFC. While it is the opposite in the aquatic ecosystem.
- This food chain takes up energy from the detritus, ensuring maximum utilization and minimum wastage.
- The food chain helps in fixing inorganic nutrients.
- It consists of sub soil organisms.
- GFC and DFC are linked.
- A food web (or food cycle) is the natural interconnection of food chains and generally a graphical representation (usually an image) of what-eats-what in an ecological community.
- Another name for the food web is a consumer-resource system.
- An ecosystem may consist of several interrelated food chains.
- The same food resource is part of more than one chain, especially when that resource is at the lower trophic levels.
- If a keystone species is removed, then not only the succeeding links of the chain will be affected but also the whole ecosystem is affected.
- The food web provides more than one alternative for food to most of the organisms in an ecosystem and therefore increases their chance of survival.
- For example, grasses may serve food for rabbit or grasshopper or goat or cow. Similarly, a herbivore may be a food source for many different carnivorous species.
- Food availability and preferences of food of the organisms may shift seasonally e.g. we eat watermelon in summer and peaches in the winter.
- Thus there are interconnected networks of feeding relations that take the form of food webs
- A pyramid-shaped diagram representing quantitatively the numbers of organisms, energy relationships, and biomass of an ecosystem.
- Numbers are high for the lowest trophic levels (plants) and low for the highest trophic level (carnivores).
- The pyramid consists of a number of horizontal bars depicting specific trophic levels which are arranged sequentially from primary producer level through herbivore, carnivore onwards.
- The length of each bar represents the total number of individuals at each trophic level in an ecosystem.
- There are three types of Ecological pyramid –
Pyramid of Numbers
- This deals with the relationship between the numbers of primary producers and consumers of different levels.
- It is a graphic representation of the total number of individuals of different species, belonging to each trophic level in an ecosystem.
- Depending upon the size and biomass, the pyramid of numbers may not always be upright, and may even be completely inverted.
a) Pyramid of Numbers – Upright
- In this pyramid, the number of individuals is decreased from lower level to higher trophic level.
- Example of this pyramid – Pond Ecosystem
- Lowest trophic level occupied by snails because of their abundance.
- Next higher trophic level – primary consumer – herbivore (example – Small fishes)
- Number of small fishes is less than that of snails.
- The next energy level is primary carnivore (example bigger fishes).
- The number of bigger fishes are less than small fishes because they feed on smaller fishes.
- The next higher trophic level is a secondary carnivore (example- Crane). They feed on bigger fishes.
- With each higher trophic level, the number of individual decreases.
b) Pyramid of Numbers – Inverted
- In this pyramid, the number of individuals is increased from lower level to higher trophic level.
- Example of this pyramid – A tree in the forest ecosystem.
- In the above diagram, you can see that a big tree (primary producer) supports many birds (herbivores).
- These birds eat lots of tapeworms, fleas, and barnacles (parasites) which live on this tree. The number of parasites is more than the number of birds.
- These parasites eat hyperparasites. The number of hyperparasites is greater than number of parasites.
- With each higher trophic level, the number of individual increases and so the resulting pyramid is of inverted shape.
- A pyramid of numbers does not take into account the fact that the size of organisms being counted in each trophic level can vary.
- It is difficult to count number of trees, birds and grasses etc. so the pyramid of no. doesn’t completely define the trophic structure of ecosystem.
Pyramid of Biomass
- This pyramid overcomes the shortcomings of the pyramid of numbers (size difference problem)
- It weighs the organism of each trophic level instead of counting.
- It gives us the total dry weight of all organism at each trophic level.
- Biomass is measured in g/m2.
a) Upward pyramid
- It also has large base of primary producers with smaller trophic level at top.
- Producer’s biomass is maximum.
- Next trophic level biomass – i.e. primary producer’s biomass is less than the primary
consumers and same is true for subsequent higher levels.
- The top trophic level has very less amount of biomass.
b) Inverted pyramid
- This kind of pyramid is found in many aquatic ecosystems.
- Reason – producers are tiny phytoplanktons that grow and reproduce rapidly.
- The base of the pyramid is small while the top is larger showing biomass is increasing from bottom to top and so pyramid assumes inverted shape.
Pyramid of Energy
- Most suitable pyramid.
- Reflects the law of thermodynamics as it reflects the conversion of solar energy into chemical energy and heat energy (lost) at each trophic level.
- This is the reason that it is always upward (large energy base at bottom) and no inversion.
- For example – if sunlight has 1 lakh joule energy and grasses or trees of forest utilized part of this energy and made their food.
- The grasses or forest has 10000-joule energy.
- Deer receives only 1000 joule energy after eating the grasses because remaining energy is used by its body for respiration and other activities.
- Lion, who had eaten the deer receives only 100-joule energy because of the same reasons mentioned above.
- In all the pyramids energy moves only in one direction i.e. unidirectional flow of energy. It never travels from producer to sun.
- 10% law – According to this law, during the transfer of energy from organic food from one trophic level to the next, only about ten percent of the energy from organic matter is stored as flesh. The remaining is lost during transfer, broken down in respiration, or lost to incomplete digestion by higher trophic level.
- Energy pyramid concept helps to explain the phenomenon of biological magnification the tendency for toxic substances to increase in concentration progressively at higher levels of the food chain.
Pollutants and trophic level
- Pollutants are substances that pollute the environment, especially gases from vehicles and poisonous chemicals produced as waste by industrial processes.
- Non-degradable pollutants move from one trophic level to another in an ecosystem.
- Non-degradable pollutants mean those which cannot be decomposed by living organisms.
- Example – Chlorinated Hydrocarbons, Diclofenac.
- Chlorinated Hydrocarbons or Organochloride or CHC are hydrocarbons whose some or most hydrogen atoms have been replaced by chlorine atoms. E.g. DDT, endosulfan, etc.).
- A variety of simple chlorinated hydrocarbons including dichloromethane, chloroform, and carbon tetrachloride.
Applications of CHC
- Production of vinyl chloride almost all of which was converted into polyvinyl chloride (PVC) [PVC pipes].
- Chloroform, dichloromethane, dichloroethane, and trichloroethane are useful solvents. These solvents are immiscible with water and effective in cleaning applications such as degreasing and dry cleaning.
- Pesticides and insecticides such as DDT, heptachlor, and endosulfan are CHCs.
Effects of CHC
- Dioxins (a highly toxic organic compound produced as a by-product in some manufacturing processes), produced when organic matter is burned in the presence of chlorine, and some insecticides, such as DDT, are persistent organic pollutants.
- DDT, which was widely used to control insects in the mid-20th century, accumulates in food chains and causes reproductive problems (e.g., eggshell thinning) in certain bird species.
- DDT residues continue to be found in humans and mammals across the planet many years after production and use have been limited.
- In Arctic areas, particularly high levels are found in marine mammals. These chemicals concentrate in mammals and are even found in human breast milk.
- In some species of marine mammals, particularly those that produce milk with high-fat content, males typically have far higher levels, as females reduce their concentration by transfer to their offspring through lactation.
- Endosulfan, an agrichemical has acute toxicity, the potential for bioaccumulation, and is an endocrine disruptor (enhances the effect of estrogens causing reproductive and developmental damage in both animals and humans).
- Because of its threats to human health and the environment, a global ban on the manufacture and use of endosulfan was negotiated under the Stockholm Convention in April 2011.
Movement of these pollutants involves two main processes:
- It is defined as an increase in the concentration of a substance in an organism or a part of the organism.
- Example – DDT, mercury, lead
- It also accumulates pollutant but not in the organism but in the food chain.
- It is also called as bioamplification.
- Example – POPs (persistent organic pollutant) – chemical substances that persist in the environment, bioaccumulates and have adverse impacts on all living organisms. E.g. of POPs Pesticide(DDT), industrial chemicals and industrial processes (dioxin and furans)
- In order for biomagnification to occur, the pollutant must be: long-lived, mobile, soluble in fats, biologically active. E.g. DDT.
- If a pollutant is short-lived, it will be broken down before it can become dangerous.
- If it is not mobile, it will stay in one place and is unlikely to be taken up by organisms.
- If the pollutant is soluble in water, it will be excreted by the organism. Pollutants that dissolve in fats, however, may be retained for a long time.
- It is traditional to measure the number of pollutants in fatty tissues of organisms such as fish.
- In mammals, we often test the milk produced by females, since the milk has a lot of fat in it and is often more susceptible to damage from toxins (poisons).