B4.1.6 Abiotic factors as the determinants of terrestrial biome distribution Notes

Abiotic Factors Are Determinants of Terrestrial Biome Distribution

1. Despite being geographically distant, biomes of the same type (e.g., deserts) share comparable abiotic conditions.
2. Two primary abiotic factors, temperature and rainfall, govern the development of these distinct ecosystems.

1. Temperature: The Energy Factor

1. Influence on Metabolism and Growth
   1. Warm regions (e.g., tropics) foster rapid plant growth and high biodiversity due to abundant energy.
   2. Cold regions (e.g., tundra) limit plant growth and species diversity because metabolic activities slow in low-temperature environments.
2. Impact on Ecosystem Productivity
   1. Higher temperatures generally boost photosynthesis and nutrient cycling, resulting in lush vegetation.
   2. Lower temperatures restrict these processes, often yielding more sparse and specialized communities.

2. Rainfall: The Water Factor

1. Essential Resource
   1. Water is vital for all living organisms; varying levels of rainfall create gradients of vegetation density.
   2. High rainfall supports tropical rainforests, while low rainfall leads to desert conditions.
2. Seasonality
   1. The timing of rainfall influences growing seasons and the life cycles of organisms.
   2. Regions with unpredictable or seasonal rainfall patterns (e.g., savannas) exhibit adapted species that survive fluctuating water availability.

Visualizing Biome Distribution: Temperature-Rainfall Graph

1. Mean Annual Temperature (x-axis) vs. Mean Annual Precipitation (y-axis)
   1. Each biome occupies a distinct zone on this graph.
   2. Examples:
      1. Tropical Rainforests: High temperature, high rainfall.
      2. Deserts: High temperature, very low rainfall.
      3. Grasslands: Moderate temperature, moderate rainfall.
      4. Tundra: Low temperature, low to moderate rainfall.
2. Convergent Evolution
   1. Similar abiotic pressures (e.g., low moisture) cause unrelated species to develop analogous traits.
   2. Explains why grasslands on different continents share ecosystem structures despite distinct species.