Description

Chapter 11: Ecosystem

This chapter details the functional aspect of ecology, analyzing how living organisms (biotic factors) interact with their non-living physical environment (abiotic factors) as a self-sustaining unit. It moves away from individual organisms to focus on the collective dynamics of entire systems, tracking how energy enters, flows through, and exits nature.

### **Key Areas Covered**

* **Structure and Function of an Ecosystem:** Breaks an ecosystem down into its core components. It details the four essential functional traits that keep an ecosystem running: **Productivity**, **Decomposition**, **Energy Flow**, and **Nutrient Cycling**.

* **Productivity:** Differentiates between how biomass is generated.

* *Primary Productivity:* The rate at which solar energy is captured by producers via photosynthesis. It is divided into **Gross Primary Productivity (GPP)** (total organic matter produced) and **Net Primary Productivity (NPP)** (GPP minus respiration losses, which is the actual biomass available to consumers).

* *Secondary Productivity:* The rate of formation of new organic matter by consumers.

* **Decomposition:** The breakdown of complex organic matter (detritus) into inorganic raw materials. The five key sequential steps are: *Fragmentation, Leaching, Catabolism, Humification, and Mineralization*.

* **Energy Flow:** Tracks the unidirectional path of energy. Less than 50% of incident solar radiation is **Photosynthetically Active Radiation (PAR)**, and plants capture only 2-10% of that. Energy movement is analyzed via the **Grazing Food Chain (GFC)** and the **Detritus Food Chain (DFC)**.

* **Ecological Pyramids:** Graphical representations of trophic structures. Covers pyramids of **Number**, **Biomass**, and **Energy**. It highlights key exceptions, such as the *inverted pyramid of biomass* in aquatic ecosystems (where small phytoplankton support a larger mass of fish). The **Pyramid of Energy** is always upright due to the 10% law of energy transfer.

* **Ecological Succession:** The gradual and predictable change in species composition over time in a given area, moving from a pioneer community to a stable **climax community**. It contrasts *Primary succession* (starting on bare rock/water) with *Secondary succession* (starting in areas where previous vegetation was destroyed).

* **Nutrient Cycling (Biogeochemical Cycles):** The storage and movement of vital elements. It explores **Gaseous cycles** (like Carbon, where the reservoir is the atmosphere/ocean) and **Sedimentary cycles** (like Phosphorus, where the main reservoir is Earth’s rocky crust).

**Exam Note:** Highly tested areas include calculating NPP (NPP = GPP – R), memorizing the exact sequence of decomposition steps, and explaining why an aquatic pyramid of biomass is uniquely inverted. Direct questions regarding primary vs. secondary ecological succession paths are also very common.

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