Concepts of trophic structure, food chain and food web. energy flow in ecosystems

Prepared by Senjuti Saha, Associate Professor, Women's Christian College, Kolkata

1. Topic 8 Concepts of Trophic Structure , Food Chain and Food Web . Energy Flow in Ecosystems Senjuti Saha Associate Professor Women’s Christian College Kolkata 2.19 GEO-A-CC-4-10-TH – Soil and Biogeography Unit II: Biogeography

2. What is Trophic Structure A characteristic feature of any ecosystem, measured and described either in terms of the standing crop per unit area, or energy fixed per unit area per unit time, at successive trophic levels It can be shown graphically by the various ecological pyramids It is the pattern of movement of energy & matter through an ecosystem It is the result of compressing a community food web into a series of trophic levels

3. Example:

4. What is Trophic Level Every ecosystem has a trophic structure: a hierarchy of feeding relationships which determines the pathways for energy flow and nutrient cycling The first trophic level comprises the green plants or the PRODUCERS The second is the herbivores or the PRIMARY CONSUMERS The third is the Carnivores which eat the herbivores or the SECONDARY CONSUMERS The fourth is the DECOMPOSERS who lives on the herbivores and carnivores Species are assigned to trophic levels on the basis of their nutrition

5. Trophic Level Vs. Trophic Structure Trophic Level Trophic Structure All organisms in an ecosystem can be placed in Trophic Levels depending on what energy source they rely upon and how they provides energy for other organism in the food web It refers to the way in which organisms use food resources to get their energy for growth and reproduction and is often referred as ‘Food Web’ or ‘Food Chain’ Any healthy ecosystem consists of trophic levels that have complex linkages to form a Food Web

6. Special Cases Hydrothermal Vent Communities are an exception: the producers are Chemosynthetic bacteria that derive energy by oxidising hydrogen sulphide A special class of consumers, the detrivores, derive their energy from the detritus representing all trophic levels

7. Energy Flow in an Ecosystem The existence of living world depends upon the flow of energy and circulation of materials through the ecosystem. The energy is required for the performance of all the life activities. The living organisms utilize solar energy. In photosynthesis, this radiant energy is transformed into chemical energy and in cellular metabolism the chemical energy is transformed into mechanical or heat energy Energy flow is the movement of energy through an ecosystem: from the external environment through a series of organisms and back to the external environment, It is one of the fundamental processes common to all ecosystems

8. Energy Flow & Trophic Level Forms of Energy 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

9. 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 The first law of thermodynamics says energy is neither created nor destroyed; it may be changed from one form to another form in numerous paths . The second law of thermodynamics says each time energy is converted from one form to another, a part of it is lost in the form of heat (entropy). No energy conversion is 100% efficient.

10. Progressive decrease in energy utilization at each trophic level It is estimated that there is a loss of about 90 percent energy as heat during metabolism 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 Energy Pyramid

11. Energy flow and Efficiency 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 chains 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 goes as heat in the respiration

12. 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 Energy flow models are basically of two types Single Channel Energy Flow Model characterised by unidirectional flow of energy through different Trophic Levels, involving a single food-chain and indicating dissipation of energy at each transfer Single Channel Energy Flow Model

13. 2. Y – Shaped Energy Flow Model , also known as Two Channel Energy Flow Model that includes both the Grazing and Detritus food chain of an ecosystem, This model is more realistic because They conform to the basic stratified structure of ecosystems They separately indicate the direct consumption of living plants and utilization of dead organic matter both in space and time The detrivores differ greatly in size- metabolizm relations and in study techniques The proportion of the net primary production energy that flows down the two pathways varies with different ecosystems, as well as with seasonal or annual cycles in the same ecosystem. However in all ecosystems the Grazing and Detritus food-chain are interconnected, so shifts in energy flows can occur quickly in response to forcing function inputs from outside the system

14. Y – Shaped Energy Flow in an Ecosystem

15. 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 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

16. Universal Energy Flow Model It is applicable to any living component of any ecosystem For any given trophic level, such figure consist of a ‘box’ representing the ‘biomass’ at any given time and pathways through it representing the flow of energy The size of the box is proportional to the total biomass at the trophic level Energy enters the trophic level as the food is ingested by the organism. Some of the ingested energy is not used and egested out, while the rest is assimilated Some of the assimilated energy is used in respiration or is stored in the form of fat. The rest is used for growth or egested The rest amount of energy or biomass or production becomes available for the trophic level Such model may well represent the dynamics of an entire trophic level or of a single individual within the trophic level Thus, universal model the energy inputs and outputs of a particular individual or of all the individuals at a trophic level

17. 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

18. Food Chain and Food Web

19. Food Chain Describe the energy flow between species within an ecosystem Producers use energy from the sun to make food and therefore start the chain The arrows represent the direction of energy flow, pointing from the organism being consumed to the organism receiving the energy

20. Food Chain Types Several types of Food Chains are there. Two of them are discussed here: Grazing & Detritus

21. Significance of Food Chain The knowledge of food chain helps in understanding the feeding relationship as well as the interaction between organism & ecosystem It also helps in understanding the mechanism of energy flow & circulation of matter in ecosystem It also helps to understand the movement of toxic substance and the problem associated with biological magnification in the ecosystem

22. Food Web Group of interconnected food chains Organisms within a food web can belong to more than one trophic level, or feeding level

23. Food Web Types Soil food web Aquatic food web Forest food web Grassland food web Food web of Terrestrial & Aquatic ecosystem

24. Significance of Food Web Food webs distinguish levels of producers and consumers by identifying and defining the importance of animal relationship and food sources, beginning with primary producers such as plants, insects and herbivores Food webs are important tools in understanding that plants are the foundation of all ecosystems and food chains, sustaining life by providing nourishment and oxygen needed for survival and reproduction The food web provide stability to the ecosystem

25. Ecological Pyramid Ecological pyramid is a graphical representation in the form of a pyramid showing the feeding relationship of groups of organisms. It is often represented in a way that the  producers are at the bottom level and then proceeds through the various  trophic levels in which the highest is on top Ecological pyramid also shows the flow of energy or biomass at each trophic level in a particular ecosystem. Biomass pertains to the amount of living or organic matter in an organism. Biomass pyramids are shaped that way to show that  biomass  is largest at the base, and decreasing in amount as it goes through the  apex

26. Pyramid of Numbers It depicts the number of individual organisms at different trophic levels of food chain. This pyramid was advanced by Charles Elton (1927), who pointed out the great difference in the number of the organisms involved in each step of the food chain Successive links of the trophic structure decrease rapidly in number until there are very few carnivores at the top

27. Two types of biomass pyramids are there the  upright  and the inverted The upright pyramid is found in most ecosystems. It results when the combined weight of producers is larger than the combined weight of consumers An inverted type results when the combined weight of producers is smaller than the combined weight of consumers Pyramid of Biomass

28. Pyramid of Productivity / Energy When production is considered in terms of energy, the pyramid indicates not only the amount of energy flow at each level, but more important, the actual role the various organisms play in the transfer of energy. An energy pyramid illustrates how much energy is needed as it flows upwards to support the next trophic level The pyramid is constructed according to the rate at which food material(in the form of energy) passes through the food chain. Some organisms may have a small biomass, but the total energy they assimilate and pass on, may be considerably greater than that of organisms with a much larger biomass Energy pyramids are always slopping because less energy is transferred from each level than was paid into it. In cases such as in open water communities the producers have less bulk than consumers but the energy they store and pass on must be greater than that of the next level

29. Disturbances in Ecosystem Bioaccumulation: When plants/animals take up a chemical from the environment do not excrete it, the chemical builds up in the organisms over time to a potentially lethal level Biomagnifications: Refers to the sequence of processes that results in higher concentrations of the chemical in organisms at higher levels in the food chain. The concentration of chemical may not affect lower levels of the food chain but the top levels take in so much it can cause disease or death Extinctions of Species : Due to decrease in population of various species the balance of various trophic levels have more accumulation of species while others have very less population

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