Food chain, web, pyramids and interconnected view of ecological interactions

In ecology, food chains and food webs describe the flow of energy and nutrients through ecosystems.

food chains provide a linear representation of energy transfer

food webs offer a more realistic and interconnected view of ecological interactions.

1. Food chain, food webs and pyramids Dr. Vividha Raunekar

2. Introduction In ecology, food chains and food webs describe the flow of energy and nutrients through ecosystems . food chains provide a linear representation of energy transfer food webs offer a more realistic and interconnected view of ecological interactions. Food Chains: Definition A food chain is a linear sequence showing how energy and nutrients pass from one organism to another. It consists of several trophic levels: Producers (Autotrophs) – Convert solar energy into chemical energy via photosynthesis (e.g., plants, algae). Primary Consumers (Herbivores) – Eat producers (e.g., deer, grasshoppers). Secondary Consumers (Carnivores/Omnivores) – Consume herbivores (e.g., frogs, small birds). Tertiary Consumers – Eat secondary consumers (e.g., snakes, hawks). Quaternary Consumers (Apex Predators) – Occupy the top trophic level, with few natural predators (e.g., sharks, eagles). Decomposers (Detritivores & Saprotrophs) – Break down organic matter, recycling nutrients (e.g., fungi, bacteria).

3. Types of Food Chains Grazing Food Chain : Starts with producers (e.g., grass → grasshopper → frog → snake → hawk). Detrital Food Chain : Begins with decomposing organic matter (e.g., dead leaves → earthworms → beetles → birds). Energy Flow and Efficiency 10% Rule : Only ~10% of the energy from one trophic level is transferred to the next, with the rest lost as heat (Lindeman’s Rule). Lindeman’s Rule (10% Rule of Energy Transfer) Lindeman’s Rule, also known as the "10% Rule" , was proposed by Raymond Lindeman in 1942. It describes the transfer of energy between trophic levels in an ecosystem. The rule states that only about 10% of the energy from one trophic level is transferred to the next , while the remaining 90% is lost as heat, respiration, and metabolic processes.

4. Energy Flow in an Ecosystem Producers (Autotrophs) : Plants, algae, and some bacteria capture solar energy through photosynthesis and convert it into chemical energy (glucose). Primary Consumers (Herbivores) : Feed on producers and obtain energy. Secondary Consumers (Carnivores/Omnivores) : Feed on herbivores. Tertiary Consumers (Top Predators) : Feed on secondary consumers. At each step, only 10% of the energy is passed to the next level, while 90% is lost . Why is Energy Lost? The 90% energy loss occurs due to: Respiration & Metabolism – Energy used for growth, reproduction, movement, and maintaining body temperature. Heat Loss – Cellular processes release energy as heat. Incomplete Digestion – Some parts of food (like bones and cellulose) are indigestible and lost as waste. Decomposition – Some energy is lost when organisms die and decompose.

5. Example of Energy Transfer Consider a simple food chain: 🌞 Sunlight → 🌱 Grass (Producers, 1000 kcal) → 🐛 Grasshopper (Primary Consumer, 100 kcal) → 🐦 Bird (Secondary Consumer, 10 kcal) → 🦅 Hawk (Tertiary Consumer, 1 kcal) If plants capture 1000 kcal of energy , only 100 kcal is transferred to herbivores. The herbivores pass 10 kcal to carnivores. The top predator receives only 1 kcal of the original energy.

6. Ecological Pyramid Representation Lindeman’s Rule explains why energy pyramids are always upright . Since energy decreases at each level, higher trophic levels support fewer individuals . 🟩 Producers (Largest Energy) ⬇ 10% Transfer 🟦 Primary Consumers ⬇ 10% Transfer 🟥 Secondary Consumers ⬇ 10% Transfer 🟪 Tertiary Consumers (Least Energy Available) This explains why higher-level carnivores are fewer in number than herbivores or producers.

7. Implications of Lindeman’s Rule Limited Number of Trophic Levels : Most ecosystems have only 4-5 trophic levels because energy becomes too limited to support more. Food Chain Efficiency : Herbivory is more energy-efficient than carnivory. More humans can be fed if they consume plants instead of meat. Biomagnification : Since predators eat more biomass to meet energy needs, toxins (like DDT and mercury) accumulate in higher concentrations at top trophic levels. Exceptions and Modifications Some ecosystems have more efficient transfer (e.g., aquatic ecosystems may transfer 20% energy). Ectothermic organisms (cold-blooded animals) lose less energy as heat, making their energy transfer slightly more efficient than in endotherms.

8. Food Webs Definition and Complexity A food web is a network of interconnected food chains that represent the diverse feeding relationships in an ecosystem. It accounts for omnivory , predation, and scavenging, offering a more accurate depiction of ecological interactions Types of Food Webs Connectedness Web : Focuses on who eats whom. Energy Flow Web : Highlights the transfer of energy between species. Functional Web : Examines the impact of species on ecosystem stability. Trophic Cascades and Keystone Species Top-Down Control : Predators regulate lower trophic levels (e.g., wolves controlling deer populations in Yellowstone). Bottom-Up Control : Primary producers regulate higher trophic levels. Keystone Species

9. Stability and Disturbances in Food Webs Stability Factors Species Diversity : More species create redundancy, making ecosystems resilient. Omnivory and Alternative Food Sources : Reduce the impact of species loss. Ecosystem Size and Productivity : Larger and more productive ecosystems tend to be more stable. Disturbances and Human Impact Climate Change : Alters species interactions and energy flow. Invasive Species : Disrupt established food webs. Overfishing & Habitat Destruction : Leads to trophic imbalances. Pollution (e.g., Bioaccumulation and Biomagnification) : Toxic substances accumulate in higher trophic levels (e.g., DDT in bird populations).

10. Ecological Pyramids Ecological pyramids graphically represent trophic structure and energy distribution in ecosystems Pyramid of Numbers Represents the number of organisms at each trophic level. Can be upright (e.g., grassland: many producers, few top predators) or inverted (e.g., forest: few large trees support many herbivores). Limitations : Does not consider organism size or energy content.

11. Pyramid of Biomass Represents the total dry mass of organisms at each trophic level. Typically upright (e.g., terrestrial ecosystems: high plant biomass supports lower consumer biomass). Can be inverted in aquatic ecosystems (e.g., phytoplankton biomass is lower than zooplankton due to rapid turnover rates).

12. Pyramid of Energy Represents energy flow per unit area per time (e.g., kcal/m²/year). Always upright , as energy decreases at each trophic level. Most accurate representation of ecosystem energy dynamics

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