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SAM GIRLS COLLEGE, BHOPAL DEPARTMENT OF LIFE SCIENCES FOOD CHAIN Presented by Ms. Razda Asst. Proff. Life Science Department Energy Flow and Energy Loss in Ecosystems: Food Chains • Scientists use different methods to represent energy moving through ecosystems. – Food chains – Food webs – Food pyramids FOOD CHAIN • The foods are synthesized by producers are utilized by primary consumers. • The primary consumers are eaten by secondary consumers & in turn they are consumed by tertiary consumers which are utilized by decomposers. • In this way a chain is formed by consuming food of different trophic levels, sequentially which is called FOOD CHAIN. The transfer of energy from sun to producer to primary consumer to secondary consumer to tertiary consumer can be shown in a FOOD CHAIN. TYPES OF FOOD CHAIN • GRAZING FOOD CHAIN – Begins from green plants & proceeds towards herbivores & then towards carnivores. DETRITUS FOOD CHAIN- starts from rotten organic substances & proceeds towards carnivores through detrivores. FOOD CHAINS CONSUMER (CARNIVORE) Food chain that includes the following organisms: grasshopper mouse grass owl CONSUMER (CARNIVORE) CONSUMER (HERBIVORE) PRODUCER FOOD CHAINS Examples of terrestrial and aquatic food chains FOOD CHAINS • A food chain shows the path of energy from one organism to the next – energy flows from producers to consumers – arrows point to who is eating (plant is eaten by herbivore) – Usually decomposers are left out FOOD WEBS In an ecosystem, numerous food chain are interrelated to each other & form a food web. A food web shows all feeding relationships in an ecosystem (made of many food chains) Food Webs: • Are interconnected food chains • They show the feeding relationships in an ecosystem Red-tailed hawk Producer to primary consumer Gambel's quail Primary to secondary consumer Yucca Jack rabbit Agave Collared lizard Prickly pear cactus Secondary to higher-level consumer All producers and consumers to decomposers Roadrunner Diamondback rattlesnake Darkling beetle Bacteria Fungi Kangaroo rat Food Webs • Food chains don’t exist in real ecosystems • Almost all organisms are eaten by more than one predator • Food webs reflect these multiple and shifting interactions TROPHIC LEVELS • The various steps of food chain where food or energy are transferred are called TROPHIC LEVEL. • Energy is lost with each trophic – ~90% is released to the environment as heat – ~10% of the energy is used Only about 10% of the energy from one level is passed on to the next level TROPHIC LEVELS • In an ecosystem following trophic level are present– Producers = 1st trophic level – Primary consumers that eat producers(herbivores) = 2nd trophic level – Secondary consumers that eat primary consumers (carnivores)= 3rd trophic level – Tertiary consumers that eat secondary consumers(top carnivores /omnivores) = 4th trophic level – Saprophytes that obtain their food from all the trophic level th by decomposition = 5 trophic level. ENERGY PATHS 3 ways to illustrate energy flow 2. Food Web: many paths 1. Food Chain: Single path 3. Food Pyramid FOOD CHAINS • A food chain shows the path of energy from one organism to the next – energy flows from producers to consumers – arrows point to who is eating (plant is eaten by herbivore) – Usually decomposers are left out Another way of showing the transfer of energy in an ecosystem is the ENERGY PYRAMID. Energy Pyramids • The graphical representation of number, biomass & stored energy of various trophic levels of food chain in an ecosystem is called ecological pyramids. Energy pyramids show • That the amount of available energy decreases down the food chain • It takes a large number of producers to support a small number of primary consumers • It takes a large number of primary consumers to support a small number of secondary consumers Ecological Pyramids Pyramid of numbers Pyramid of biomass Pyramid of energy flow Fig. 4-20 p. 79 Pyramid of numbers • A pyramid of numbers indicates the number of individuals in each trophic level. # of carnivores # of herbivores # of producers Pyramid of biomass • A pyramid of biomass indicates how much biomass is present in each trophic level at any one time. biomass of carnivores biomass of herbivores biomass of producers Pyramid of energy • A pyramid of energy depicts the energy flow, or productivity, of each trophic level. carnivores herbivores producers Ecological pyramids • The standing crop, productivity, number of organisms, etc. of an ecosystem can be conveniently depicted using “pyramids”, where the size of each compartment represents the amount of the item in each trophic level of a food chain. • carnivores herbivores producers Note that the complexities of the interactions in a food web are not shown in a pyramid; but, pyramids are often useful conceptual devices-they give one a sense of the overall form of the trophic structure of an ecosystem. Pyramid of energy • A pyramid of energy depicts the energy flow, or productivity, of each trophic level. • Due to the Laws of Thermodynamics, each higher level must be smaller than lower levels, due to loss of some Energy flow in : energy as heat (via respiration) within each level. carnivores herbivores producers FOOD CHAINS/WEBS & ENERGY PYRAMIDS • Food chains/webs can be written as a pyramid: – Producers form the base of the pyramid Consumers form the upper layers ENERGY PYRAMIDS The energy pyramid shows energy flow in an ecosystem: Top • A level of the energy pyramid is called a TROPHIC LEVEL • Each trophic level represents the energy for those organisms Consumer Energy stored by Secondary Consumers Energy stored by Primary Consumers ENERGY STORED BY PRODUCERS QUICK REVIEW • Practice! If 100% of the energy is available at the first trophic level, what percentages of the energy are available at the second and third trophic levels? 1% 10% 100% QUICK REVIEW! All organisms in an ecosystem need _______ from energy food to live. An energy ________ shows how much pyramid food energy is passed from one ________ to another organismthrough food chains. __________ have the largest spot at the base of the pyramid. Altogether, Producers only about _____ of the food energy at each level 10% gets passed up to the next level. Energy Flow and Energy Loss in Ecosystems: Food Chains Consumers in a food chain can be classified as: 1. Detrivores – consumers that obtain energy and nutrients from dead organisms and waste matter Examples include earthworms, bacteria and fungi. Detrivores feed at every trophic level. Detrivores have their own, separate food chains and are very numerous. 2. Herbivores – primary consumers Herbivores eat plants (producers) only. 3. Carnivores – secondary or tertiary consumers Secondary consumers eat non-producers, such as herbivores. Tertiary consumers eat secondary consumers. Also called top consumers or top carnivores. 4. Omnivores – consumers that eat both plants and animals Examples include humans and bears. Energy Flow and Energy Loss in Ecosystems:Food Webs • Most organisms are part of many food chains. – Food webs represent interconnected food chains. – Food webs are models of the feeding relationships in an ecosystem. – Arrows in a food web represent the flow of energy and nutrients. – Following the arrows leads to the top carnivore(s). This food web represents a terrestrial ecosystem that could be found in British Columbia. Energy Flow and Energy Loss in Ecosystems: Food Pyramids • Food pyramids show the changes in available energy from one trophic level to another in a food chain. – Energy enters at the first trophic level (producers), where there is a large amount of biomass and therefore much energy. – It takes large quantities of organisms in one trophic level to meet the energy needs of the next trophic level. • Each level loses large amounts of the energy it gathers through basic processes of living. • 80 – 90 percent of energy taken in by consumers is used in chemical reactions in the body and is lost as thermal energy. • There is very little energy left over for growth or increase in biomass. Ninety percent of this mouse’s food energy is used to maintain its life functions. • Lower trophic levels have much larger populations than upper levels. • This shows the importance of maintaining large, biodiverse populations at the lowest levels of the food pyramid. Food pyramids are also known as ecological pyramids – Ecological pyramids may show biomass, population, or energy numbers. – The amount of life an ecosystem can contain is based on the bottom level of the ecological pyramid, where producers capture energy from the Sun. – Each level in the energy pyramid = a loss of 90 percent of total energy available. Energy Flow & Nutrient Cycle Food Chains • Artificial devices to illustrate energy flow from one trophic level to another • Trophic Levels: groups of organisms that obtain their energy in a similar manner Food Chains • Total number of levels in a food chain depends upon locality and number of species • Highest trophic levels occupied by adult animals with no predators of their own • Secondary Production: total amount of biomass produced in all higher trophic levels Nutrients • Inorganic nutrients incorporated into cells during photosynthesis - e.g. N, P, C, S • Cyclic flow in food chains • Decomposers release inorganic forms that become available to autotrophs again Energy • Non-cyclic, unidirectional flow • Losses at each transfer from one trophic level to another - Losses as heat from respiration - Inefficiencies in processing • Total energy declines from one transfer to another - Limits number of trophic levels Energy Flow Energy Flow through an Ecosystem sun Food Chain Primary Producer phytoplankton Primary Consumer Secondary Consumer zooplankton Tertiary Consumer larval fish fish heat heat heat water Nutrients Fungi & bacteria Decomposer Transfer Efficiencies • Efficiency of energy transfer called transfer efficiency • Units are energy or biomass Et = Pt Pt-1 Pt = annual production at level t Pt-1 = annual production at t-1 Transfer Efficiency Example • Net primary production = 150 g C/m2/yr • Herbivorous copepod production = 25 g C/m2/yr Et = Pt Pt-1 = Pcopepods Pphytoplankton = 25 = 0.17 150 • Typical transfer efficiency ranges *Level 1-2 ~20% *Levels 2-3, …: ~10% Energy and Biomass Pyramids Kaneohe Bay Tertiary consumers 10 J Secondary consumers 100 J Primary consumers Primary producers 1000 J 10,000 J Limu 1,000,000 J of sunlight Algae eaten by Uhu Cellular Respiration Feces Growth Food Webs • Food chains don’t exist in real ecosystems • Almost all organisms are eaten by more than one predator • Food webs reflect these multiple and shifting interactions Antarctic Food Web Some Feeding Types Many species don’t fit into convenient categories • • • • • • • • • • • • • • Algal Grazers and Browsers Suspension Feeding Filter Feeding Deposit Feeding Benthic Animal Predators Plankton Pickers Corallivores Piscivores Omnivores Detritivores Scavengers Parasites Cannibals Ontogenetic dietary shifts Food Webs… Competitive relationships in food webs can reduce productivity at top levels Phytoplankton (100 units) Herbivorous Zooplankton (20 units) Carnivorous Zooplankton A (2 units) Fish (0.2 units) Phytoplankton (100 units) Herbivorous Zooplankton (20 units) Carnivorous Zooplankton A (1 units) Fish (0.1 units) Carnivorous Zooplankton B (1 units) Recycling: The Microbial Loop • All organisms leak and excrete dissolved organic carbon (DOC) • Bacteria can utilize DOC • Bacteria abundant in the euphotic zone (~5 million/ml) • Numbers controlled by grazing due to nanoplankton • Increases food web efficiency Microbial Loop Solar Energy Phytoplankton Herbivores CO2 nutrients Planktivores DOC Piscivores Bacteria Nanoplankton (protozoans) An Ecological Mystery Keystone Species Kelp Forests An Ecological Mystery • Long-term study of sea otter populations along the Aleutians and Western Alaska • 1970s: sea otter populations healthy and expanding • 1990s: some populations of sea otters were declining • Possibly due to migration rather than mortality • 1993: 800km area in Aleutians surveyed - Sea otter population reduced by 50% Vanishing Sea Otters • 1997: surveys repeated • Sea otter populations had declines by 90% - 1970: ~53,000 sea otters in survey area - 1997: ~6,000 sea otters • Why? - Reproductive failure? - Starvation, pollution disease? Cause of the Decline • 1991: one researcher observed an orca eating a sea otter • Sea lions and seals are normal prey for orcas • Clam Lagoon inaccessible to orcas- no decline • Decline in usual prey led to a switch to sea otters • As few as 4 orcas feeding on otters could account on the impact - Single orca could consume 1,825 otters/year Energy Flow Through an Ecosystem Food Chains, Food Webs, Energy Pyramids •Begins with the SUN •Photosynthesis 6CO2 + 6H2O + sunlight & chlorophyll C6H12O6 + 6O2 • The chemical reaction by which green plants use water and carbon dioxide and light from the sun to make glucose. • ENERGY is stored in glucose; glucose is stored as starch. Organisms that can make glucose during photosynthesis are called PRODUCERS. Producers use most of the energy they make for themselves. Producers use cellular respiration to supply the energy they need to live. 6O2 + C6H12O6 --> 6H2O + 6CO2 + energy CELLULAR RESPIRATION is the chemical reaction that releases the energy in glucose. The energy that is not used by producers can be passed on to organisms that cannot make their own energy. Organisms that cannot make their own energy are called CONSUMERS. Consumers that eat producers to get energy: • Are first order or primary consumers • Are herbivores (plant-eaters) Most of the energy the primary consumer gets from the producer is used by the consumer. Some of the energy moves into the atmosphere as heat. Some energy in the primary consumer is not lost to the atmosphere or used by the consumer itself. This energy is available for another consumer. A consumer that eats another consumer for energy: • Is called a secondary or second order consumer • May be a carnivore or a herbivore • May be a predator • May be a scavenger Most of the energy the secondary consumer gets from the primary consumer is used by the secondary consumer. Some of the energy is lost as heat, but some energy is stored and can passed on to another consumer. A consumer that eats a consumer that already ate a consumer: • Is called a third order or tertiary consumer • May be a carnivore or a herbivore • May be a predator • May be a scavenger Consumers that eat producers & other consumers • Are called omnivores • Omnivores eat plants and animals Consumers that hunt & kill other consumers are called predators. They animals that are hunted & killed are called prey. Consumers that eat other consumers that have already died are called scavengers. Another way of showing the transfer of energy in an ecosystem is the ENERGY PYRAMID. Energy pyramids show • That the amount of available energy decreases down the food chain • It takes a large number of producers to support a small number of primary consumers • It takes a large number of primary consumers to support a small number of secondary consumers