Ecosystems

• Lindeman's 10% Law: During the transfer of energy from one trophic level to the next higher level, only about $10\%$ of the energy is conserved and converted into new animal biomass; the remaining $90\%$ is dissipated as metabolic heat and waste.
• Calculation across Trophic Levels:
1. Trophic Level 1 (Plants / Producers): $20,000\text{ Joules}$
2. Trophic Level 2 (Grasshopper / Primary Consumer): $20,000 \times 10\% = \mathbf{2,000\text{ Joules}}$
3. Trophic Level 3 (Frog / Secondary Consumer): $2,000 \times 10\% = \mathbf{200\text{ Joules}}$
4. Trophic Level 4 (Snake / Tertiary Consumer): $200 \times 10\% = \mathbf{20\text{ Joules}}$
5. Trophic Level 5 (Hawk / Quaternary Consumer): $20 \times 10\% = \mathbf{2\text{ Joules}}$!.
• Only $2\text{ Joules}$ of energy reaches the hawk.

• Why Pyramid of Energy is Always Upright:
According to the First and Second Laws of Thermodynamics and Lindeman's 10% Law, the flow of energy in an ecosystem is strictly unidirectional.
At every successive trophic level, approximately $90\%$ of energy is lost as respiratory heat and bodily maintenance work.
Therefore, energy available at a higher trophic level is ALWAYS less than the energy at the preceding lower level. It can NEVER be inverted.
• Why Numbers/Biomass Can Invert:
• Inverted Number Pyramid: A single large oak tree (producer, $N=1$) can support thousands of herbivorous insects and parasite birds.
• Inverted Biomass Pyramid: In marine ecosystems, microscopic phytoplankton have a tiny standing biomass at any instant because they are consumed rapidly by zooplankton, yet their rapid reproduction rate sustains a larger standing biomass of fish.

• Food Chain: A single, linear, unbranched feeding pathway showing the transfer of energy from one organism to another.
• Food Web: A complex, interwoven network of multiple interconnected food chains within an ecological community.
• Why Greater Stability?
In a simple food chain, if one species is eliminated (e.g., rabbits die of disease), the dependent predator (hawk) faces starvation.
In a complex food web, there are alternative feeding pathways: the predator switches to feeding on mice, lizards, or squirrels.
The population balances naturally, preventing the collapse of the entire ecosystem.

• Ecological Role: Decomposers (bacteria, saprophytic fungi) secrete extracellular hydrolytic enzymes to break down dead plant and animal carcasses and organic wastes, converting complex macromolecules back into simple inorganic minerals (nitrogen, phosphorus, potassium, carbon) that return to the soil and atmosphere.
• If Decomposers Disappeared:
1. The surface of the Earth would be covered under mountains of undecayed corpses, dead trees, and animal waste.
2. The biogeochemical nutrient cycling would grind to a complete halt: soil would become exhausted of mineral elements.
3. Green plants would starve from lack of soil nutrients, photosynthesis would collapse, and all life on Earth would perish.

• Autotrophs (Producers):
1. Organisms capable of synthesizing their own organic food from simple inorganic raw materials ($\text{CO}_2, \text{H}_2\text{O}$) using sunlight (photosynthesis) or chemical energy.
Examples: Green plants (neem, wheat), cyanobacteria, phytoplankton.
• Heterotrophs (Consumers):
1. Organisms that cannot synthesize their own food and must depend directly or indirectly on producers for nutrition.
Examples: Animals (deer, tiger, human), fungi.

• Abiotic Component: The non-living physical and chemical factors of the environment that influence the survival, behavior, and reproduction of living organisms.
• Three Categories:
1. Climatic Factors: Sunlight, temperature, rainfall, wind, atmospheric humidity.
2. Edaphic Factors: Soil structure, soil texture, soil moisture, and pH.
3. Inorganic and Organic Substances: Water, dissolved oxygen, carbon dioxide, nitrogen, minerals, and organic humus.

• According to Lindeman's 10% Law, approximately $90\%$ of energy is lost as heat at each trophic transfer step.
• After $4$ or $5$ transfers, the remaining fraction of energy is so minuscule ($0.01\%$ to $0.001\%$ of initial producer energy) that it is insufficient to sustain the metabolic requirements and hunting lifestyle of a viable population of higher apex predators.
• Therefore, energy exhaustion physically limits food chain length.

• Biomagnification: The phenomenon of progressive increase in the concentration of toxic, non-biodegradable chemical pollutants (such as pesticides or heavy metals) at each successive trophic level of a food chain.
• DDT Example:
1. Traces of DDT run off into a lake ($0.000003\text{ ppm}$).
2. Phytoplankton absorb DDT, concentrating it to $0.04\text{ ppm}$.
3. Small fish consume tons of plankton, accumulating $0.5\text{ ppm}$.
4. Large predatory fish accumulate $2.0\text{ ppm}$.
5. Fish-eating birds (eagles, pelicans) accumulate toxic levels of $25\text{ ppm}$ (a million-fold magnification!), causing eggshell thinning and catastrophic population crashes.