Detailed notes CHAPTER 12- ECOSYSTEM

CHAPTER 12 ECOSYSTEM

Introduction

1. Definition of an Ecosystem:

   • An ecosystem is a functional unit of nature.
   • It involves interactions between living organisms and their physical environment.

2. Variability in Size:

   • Ecosystems can range widely in size, from small ponds to vast forests or oceans.
   • Some scientists consider the entire biosphere as a global ecosystem, comprising all local ecosystems on Earth.

3. Basic Categories of Ecosystems:

   • Terrestrial ecosystems: forests, grasslands, deserts.
   • Aquatic ecosystems: ponds, lakes, wetlands, rivers, estuaries.
   • Man-made ecosystems: crop fields, aquariums, where human activities influence interactions.

4. Structure of Ecosystems:

   • Includes input (productivity), energy transfer (food chains/webs, nutrient cycling), and output (degradation, energy loss).

5. Terrestrial Ecosystem Examples:

   • Forests: complex habitats with trees, plants, animals, and decomposers.
   • Grasslands: areas dominated by grasses, supporting grazers and predators.
   • Deserts: arid regions with specialized flora and fauna adapted to low water availability.

6. Aquatic Ecosystem Examples:

   • Ponds: small bodies of freshwater supporting diverse life forms.
   • Lakes: larger water bodies with varied depths and ecosystems.
   • Wetlands: areas with waterlogged soil, vital for biodiversity and water purification.
   • Rivers: flowing water systems supporting aquatic organisms and surrounding habitats.
   • Estuaries: transition zones between rivers and seas, rich in nutrients and biodiversity.

7. Man-Made Ecosystem Examples:

   • Crop fields: agricultural areas with cultivated plants, pests, and beneficial organisms.
   • Aquariums: controlled environments housing aquatic life, managed by humans.

8. Energy Flow in Ecosystems:

   • Describes how energy moves through ecosystems via food chains, webs, and nutrient cycles.
   • Energy enters ecosystems through producers (plants, algae) and flows to consumers (herbivores, carnivores) and decomposers (bacteria, fungi).

9. Relationships Within Ecosystems:

   • Cycles: Nutrient cycles like the carbon cycle, water cycle, and nitrogen cycle sustain life within ecosystems.
   • Chains: Linear pathways of energy transfer from producers to consumers and decomposers.
   • Webs: Complex networks of interconnected food chains, showing multiple feeding relationships.

10. Interactions and Inter-relationships:

    • Energy flows and nutrient cycling create interdependent relationships between organisms.
    • These interactions form the basis of ecosystem stability, resilience, and biodiversity.

12.1 ECOSYSTEM – STRUCTURE AND FUNCTION

1. Integrated Components of an Ecosystem:

   • Ecosystems comprise both abiotic (non-living) and biotic (living) components.
   • These components interact, resulting in a physical structure unique to each ecosystem type.

2. Species Composition and Stratification:

   • The identification and enumeration of plant and animal species determine the species composition of an ecosystem.
   • Vertical distribution of species, known as stratification, occurs in ecosystems like forests where trees occupy the top layer, shrubs the second, and herbs/grasses the bottom layers.

3. Functions of an Ecosystem:

   • Ecosystem components function as a unit through: (i) Productivity – the rate of production of biomass by producers. (ii) Decomposition – breakdown of organic matter by decomposers. (iii) Energy flow – movement of energy through trophic levels. (iv) Nutrient cycling – recycling of nutrients within the ecosystem.

4. Example of an Aquatic Ecosystem (Pond):

   • A pond serves as a self-sustainable unit and a simple example of complex interactions in an aquatic ecosystem.
   • Components include abiotic factors like water, dissolved substances, and soil deposits, as well as biotic factors like phytoplankton, algae, plants, zooplankton, and decomposers (fungi, bacteria, flagellates).
   • Functions include:
     • Conversion of inorganic to organic material by autotrophs (using solar energy).
     • Consumption of autotrophs by heterotrophs (consumers).
     • Decomposition and mineralization of dead matter by decomposers.
     • Unidirectional energy flow towards higher trophic levels, with energy dissipation as heat to the environment.

12.2 PRODUCTIVITY

1. Solar Energy and Primary Production:

   • Solar energy is the fundamental input required for ecosystems to function and sustain.
   • Primary production refers to the amount of biomass or organic matter produced per unit area over time by plants during photosynthesis.

2. Units of Measurement:

   • Primary productivity is expressed in terms of weight (gm^-2) or energy (kcal m^-2).
   • Productivity rates are usually measured in terms of gm^-2 yr^-1 or kcal m^-2 yr^-1 to compare different ecosystems.

3. Types of Productivity:

   • Gross Primary Productivity (GPP): Rate of organic matter production during photosynthesis.
   • Net Primary Productivity (NPP): GPP minus the energy used by plants in respiration (R). NPP represents the available biomass for consumption by heterotrophs.

4. Factors Influencing Productivity:

   • Plant species composition influences productivity in an area.
   • Environmental factors such as nutrient availability and photosynthetic capacity of plants also play a crucial role.
   • Different ecosystems exhibit varying levels of productivity due to these factors.

5. Productivity in the Biosphere:

   • The annual net primary productivity of the entire biosphere is approximately 170 billion tons (dry weight) of organic matter.
   • Oceans, despite covering about 70% of the Earth’s surface, have a lower productivity (55 billion tons) compared to land ecosystems.

6. Reasons for Low Ocean Productivity:

   • The main reason for the lower productivity of oceans compared to land is the limited availability of nutrients, especially in surface waters.
   • Nutrient levels, particularly nitrogen and phosphorus, are lower in oceanic regions due to factors such as oceanic currents, limited mixing, and nutrient deposition in deeper layers.
   • Additionally, light availability for photosynthesis decreases with depth in the ocean, further limiting primary productivity in deeper waters.