2.4B Biomes Notes

1. Biomes are global-scale communities characterized by distinctive climate patterns, vegetation structure, and adapted organisms.
2. Each biome represents a unique combination of temperature, precipitation, and insolation, which shapes its biodiversity and productivity.
3. Ecosystems within the same biome type often evolve parallel structures and adaptations because of similar environmental pressures.

Factors Influencing Biome Distribution

1. Insolation (Solar Energy Input)
   1. The amount of sunlight an area receives influences temperature and photosynthesis.
   2. Equatorial regions (e.g., the Amazon Rainforest) receive high insolation, supporting lush vegetation.
   3. Polar regions receive low insolation, limiting plant growth and resulting in tundra ecosystems.
2. Temperature
   1. Cold biomes: Tundras and boreal forests dominate regions with low temperatures (e.g., Siberia, Canada).
   2. Warm biomes: Deserts and tropical rainforests thrive in hot climates (e.g., the Sahara, the Congo Basin).
   3. Seasonal temperature variations affect growing seasons and biodiversity.
3. Precipitation
   1. High rainfall → Dense vegetation: Rainforests (Amazon, Congo) receive 2000+ mm of rain annually, supporting high biodiversity.
   2. Low rainfall → Sparse vegetation: Deserts (Sahara, Atacama) receive <250 mm of rain, limiting plant and animal life.
   3. Seasonal rainfall: Grasslands and savannas (Serengeti, North American prairies) experience wet and dry seasons, influencing plant adaptations.

Parallel Features Across Similar Biomes

1. Different parts of the world can host analogous ecosystems shaped by similar climates.
2. Ecosystems that evolve under comparable climatic regimes often display convergent evolution.

Abiotic Factors and Terrestrial Biome Distribution

1. The distribution of terrestrial biomes is primarily determined by abiotic factors, especially temperature and precipitation.
2. Given specific patterns of temperature and rainfall, certain natural ecosystems are likely to develop in a region.

1. Temperature

1. Higher temperatures → Support tropical biomes like rainforests and deserts.
2. Moderate temperatures → Support temperate biomes like temperate forests and grasslands.
3. Lower temperatures → Lead to cold biomes like boreal forests (taiga) and tundras.

2. Precipitation

1. High rainfall (>2000 mm/year) → Supports rainforests with dense vegetation and high biodiversity.
2. Moderate rainfall (500–1500 mm/year) → Supports grasslands and temperate forests.
3. Low rainfall (<250 mm/year) → Leads to deserts, where sparse vegetation thrives.

Climate Graphs and Biome Distribution

1. For any given temperature and rainfall pattern, one natural ecosystem type (biome) tends to develop.
2. This relationship is commonly visualized using a climograph or Whittaker’s diagram.
3. A climograph (or climate diagram) visually shows how temperature and precipitation determine which biomes develop in different regions.
   1. Horizontal axis: Mean annual temperature
   2. Vertical axis: Mean annual precipitation
   3. Each biome occupies a distinct zone based on these variables.

Biomes and Their Characteristic Limiting Factors, Productivity, and Biodiversity

1. Biomes are classified into broad groups based on common abiotic conditions and climatic factors.
2. Within each biome, there are variations in limiting factors, productivity, and biodiversity.

1. Tropical Rainforests

1. Limiting Factors:
   1. Nutrient cycling: While rainfall is abundant, the soil is often nutrient-poor due to rapid decomposition and leaching.
   2. Temperature: Consistently high temperatures (25-30°C) limit variation in growing seasons.
2. Productivity:
   1. Extremely high primary productivity due to constant warmth and moisture, allowing for year-round growth.
   2. Dense vegetation and rapid cycling of nutrients support a variety of plant life.
3. Biodiversity:
   1. High biodiversity, with thousands of plant and animal species.
   2. Complex ecosystems include epiphytes (plants growing on other plants), large herbivores, and predators such as jaguars.

2. Hot Deserts

1. Limiting Factors:
   1. Water availability: Extreme scarcity of water, with annual rainfall of less than 250 mm.
   2. Temperature: High temperatures during the day (30-50°C) and cold nights (0-10°C), limiting plant and animal activity.
2. Productivity:
   1. Low primary productivity due to water stress makes it difficult for plants to grow.
   2. Vegetation is sparse, and many plants have adaptations like deep roots and water storage mechanisms (e.g., cacti).
3. Biodiversity:
   1. Low biodiversity compared to tropical rainforests, but still supports specialized species adapted to harsh conditions.
   2. Mainly xerophytes (cacti, succulents) and reptiles

3. Tundra

1. Limiting Factors:
   1. Temperature: Extremely cold temperatures (below freezing for most of the year), limiting the growing season.
   2. Short growing season: Limited by frost, permafrost (permanently frozen ground), and a lack of sunlight for part of the year.
2. Productivity:
   1. Very low productivity due to the short growing season and poor soils (low nutrients, permafrost).
   2. Limited vegetation like mosses, lichens, and small shrubs.
3. Biodiversity:
   1. Low biodiversity, but some specialized animals like arctic foxes, polar bears, and caribou are adapted to survive.
   2. Few plant species can thrive, mainly those that are cold-resistant and adapted to survive in low-nutrient soils.

4. Temperate Forests

1. Limiting Factors:
   1. Temperature: Moderate temperature variations between seasons, with cold winters and warm summers.
   2. Precipitation: Moderate, with rainfall ranging from 750-1500 mm annually, which supports tree growth.
2. Productivity:
   1. Moderate to high productivity, especially in spring and summer when temperatures rise and water availability is consistent.
   2. Trees like oak, maple, and pine dominate, along with undergrowth plants like ferns.
3. Biodiversity:
   1. Moderate biodiversity
   2. Diverse species of trees, shrubs, and animals such as deer, foxes, and birds.

5. Savannas

1. Limiting Factors:
   1. Precipitation: Seasonal rainfall, with a long dry season and a wet season. This creates water stress during the dry season.
   2. Temperature: High temperatures (25-30°C), combined with periodic droughts, limit plant growth during dry months.
2. Productivity:
   1. Moderate productivity during the rainy season, which supports grasses and scattered trees.
   2. Grasslands are dominant, with a few trees like acacia and baobab.
3. Biodiversity:
   1. Moderate biodiversity
   2. Supports herbivores like elephants, zebras, and giraffes, and carnivores like lions and cheetahs.

6. Boreal Forest (Taiga)

1. Limiting factors:
   1. Temperature: –30°C winter to 20°C summer.
   2. Rainfall: 300–900 mm, mainly snow.
   3. Soil: Acidic, nutrient-poor, slow decomposition.
2. Productivity: Moderate productivity
3. Biodiversity:
   1. Low biodiversity
   2. Evergreen conifers (pine, spruce, fir).
   3. Adaptations such as Needle leaves conserve water and withstand snow load.