Biomes, Ecosystems & Floristic Regions

1. Principles of Ecology & Ecosystems

• Ecology: The scientific study of interactions among organisms and their environment, including biotic (living) and abiotic (non-living) components.
• Ecosystem (Tansley, 1935): A biological community of interacting organisms and their physical environment. It functions as a single, self-sustaining functional unit of nature.
  • Components: Producers (autotrophs like plants), Consumers (heterotrophs like herbivores, carnivores), and Decomposers (saprotrophs like fungi, bacteria).
  • Energy Flow: Unidirectional. Solar energy -> Producers -> Consumers. Governed by the 10% law (Lindeman).
• Biogeochemical Cycles: The movement of elements (Carbon, Nitrogen, Phosphorus, Water) through the biotic and abiotic spheres. Essential for maintaining balance.

2. Factors Influencing Plant and Animal Distribution

The global distribution of flora and fauna is not random. It is determined by:

1. Climatic Factors: Temperature (defines latitudinal belts) and Moisture/Precipitation (determines forest vs. grassland vs. desert). Light is critical for photosynthesis and circadian rhythms.
2. Edaphic (Soil) Factors: Soil texture, pH, organic content, and mineral composition dictate plant types (e.g., mangroves need saline mud).
3. Topographical Factors: Altitude mimics latitude. South-facing slopes (in NH) are warmer and sunnier than north-facing ones.
4. Biotic Factors: Competition, predation, symbiosis, and disease.
5. Historical/Geological Factors: Continental drift separated landmasses, leading to endemic species (e.g., Marsupials in Australia).

3. Major Biomes of the World

A biome is a large naturally occurring community of flora and fauna occupying a major habitat on a global scale, defined largely by climate.

Tropical Biomes

• Tropical Evergreen Rainforest: Located near the equator (Amazon, Congo). Characterized by high temperatures and heavy rainfall year-round. It has the highest terrestrial biodiversity, layered canopy structure, and lianas/epiphytes. Nutrient-poor, heavily leached laterite soils.
• Tropical Savanna/Grassland: Found in regions with a distinct dry season (Llanos, Campos, Sahel). Tall, coarse grasses (elephant grass) and scattered drought-resistant trees (Acacia, Baobab). Rich in large herbivores and carnivores.
• Tropical Desert: Located in sub-tropical high-pressure zones (Sahara, Kalahari, Atacama). Extreme diurnal temperature ranges and <25cm rain. Xerophytic vegetation (cacti, thorny bushes) structured to minimize transpiration.

Temperate Biomes

• Temperate Grassland: Continental interiors far from oceans (Prairies, Steppes, Pampas, Veld). Extreme seasonal temperatures. Dominated by highly nutritious short grasses. Features deep, extremely fertile black soils (Chernozems).
• Mediterranean: Regions with hot, dry summers and mild, rainy winters (California, Southern Europe, SW Australia). Sclerophyllous vegetation (thick, waxy leaves to retain moisture) like Olive and Cork Oak.
• Deciduous Forest: Regions with cold winters and warm summers. Trees shed leaves in autumn to conserve moisture (Oak, Maple, Elm).

Cold Biomes

• Taiga (Boreal Forest): Exists only in the NH (Canada, Russia). The largest terrestrial biome. Dominated by Coniferous softwood trees (Pine, Fir, Spruce) used extensively for timber and paper pulp. Soils are acidic Podzols.
• Tundra: Arctic regions above the tree line. Ground is permanently frozen (Permafrost) below the surface. Freezing, harsh winters. Vegetation is limited to mosses, lichens, and dwarf shrubs. Fauna includes polar bears, reindeer, and arctic foxes.