Structure and Function of Ecosystems
Introduction
Ecological Balance: Refers to the natural equilibrium in ecosystems, often called the "balance of nature," where living (biotic) and non-living (abiotic) components interact to maintain stability.
Ecosystem: A functional unit of nature comprising biotic (living organisms) and abiotic (physical environment) components that interact through energy flow and nutrient cycling.
1. Definition and Types of Ecosystems
Definition: An ecosystem includes all living organisms (plants, animals, microbes) and their physical environment (air, water, soil, sunlight) interacting in a specific area.
Types:
Terrestrial Ecosystems: E.g., forests, grasslands, deserts.
Aquatic Ecosystems:
Lentic: Still water (e.g., ponds, lakes).
Lotic: Flowing water (e.g., rivers, streams).
Artificial Ecosystems: Human-made, e.g., aquariums, croplands.
2. Components of Ecosystems
Abiotic Components: Non-living factors like sunlight, temperature, water, soil, air, and nutrients.
Biotic Components:
Producers (Autotrophs): Organisms like plants and algae that produce energy via photosynthesis. Example: Grass.
Consumers (Heterotrophs):
Primary Consumers: Herbivores that eat producers. E.g., deer, rabbit, grasshopper.
Secondary Consumers: Carnivores or omnivores that eat primary consumers. E.g., frog, spider.
Tertiary Consumers: Carnivores or omnivores that eat secondary consumers. E.g., snake, hawk.
Top Consumers: Apex predators not preyed upon. E.g., lion, tiger, eagle.
Decomposers (Saprotrophs): Break down dead organic matter (detritus) into simpler substances, recycling nutrients. E.g., bacteria, fungi.
3. Energy Flow
Primary Source: The sun.
Flow: Energy moves unidirectionally from producers to consumers and decomposers.
10% Rule: Only about 10% of energy is transferred from one trophic level to the next, with the rest lost as heat or used in metabolism.
Food Chain: A linear sequence showing energy transfer (e.g., grass → grasshopper → frog → snake).
Food Web: A network of interconnected food chains, more stable due to multiple food sources.
4. Biomass and Productivity
Biomass: Total dry weight of living organisms in a given area, measured in g/m² or kg/ha. Also called "standing crop."
Productivity: Rate of biomass production.
Primary Productivity:
Gross Primary Productivity (GPP): Total energy captured by producers via photosynthesis.
Net Primary Productivity (NPP): Energy available to consumers after subtracting respiration losses (NPP = GPP - Respiration).
Secondary Productivity: Rate of biomass production by consumers.
Ecological Pyramids:
Pyramid of Numbers: Shows the number of organisms at each trophic level; can be inverted (e.g., in a tree ecosystem with many insects).
Pyramid of Biomass: Shows biomass at each level; inverted in aquatic ecosystems (e.g., phytoplankton < zooplankton).
Pyramid of Energy: Always upright due to energy loss at each trophic level.
5. Key Ecological Concepts
Nutrient Cycling: Recycling of nutrients like carbon, nitrogen, and phosphorus through biotic and abiotic components.
Ecological Succession: Gradual process of ecosystem development or recovery after a disturbance.
Keystone Species: Species with a disproportionately large impact on the ecosystem relative to their biomass.
Biomes: Large geographic areas defined by climate and vegetation (e.g., tropical rainforests, deserts).
6. Practice Questions (MCQs)
The document includes 50 multiple-choice questions testing knowledge of ecosystems, covering:
Definitions and types of ecosystems.
Biotic and abiotic components.
Roles of producers, consumers, and decomposers.
Energy flow, food chains, and food webs.
Biomass, productivity, and ecological pyramids.
Factors affecting productivity (e.g., sunlight, water, nutrients).
Specific examples like phytoplankton’s role as producers and the impact of removing producers from a food chain.