Biomes and Climate
Biomes are large-scale ecological zones characterized by distinct plant and animal communities adapted to specific climate conditions. The distribution of biomes across the Earth is primarily determined by climate factors, particularly temperature and precipitation patterns.
Climate as the Primary Determinant
The type of biome in a given area is largely dictated by its climate. However, it's important to note that individual ecosystems within a biome may vary due to local abiotic and biotic factors. For instance, while the Amazon rainforest is broadly classified as a tropical rainforest biome, specific areas within it may have unique characteristics due to factors like soil composition, elevation, or the presence of rivers.
ExampleThe Sahara Desert biome is characterized by its hot, arid climate. However, within this biome, you might find oasis ecosystems that differ significantly from the surrounding desert due to the presence of water sources.
Key Climatic Factors
The main factors governing the distribution of biomes are:
- Insolation: The amount of solar radiation received by an area
- Precipitation: The quantity and pattern of rainfall or snowfall
- Temperature: Average temperatures and temperature ranges
These factors interact in complex ways to create the conditions that support different biome types.
Tricellular Model of Atmospheric Circulation
The tricellular model of atmospheric circulation is crucial for understanding the global distribution of biomes. This model explains how air circulates in three distinct cells in each hemisphere, influencing precipitation and temperature patterns worldwide.
How It Works
- Hadley Cell: Near the equator, warm air rises, creating a low-pressure zone. This air moves towards the poles at high altitudes and descends around 30° latitude, creating high-pressure zones.
- Ferrel Cell: Between 30° and 60° latitude, air circulates in the opposite direction to the Hadley cell.
- Polar Cell: Cold air descends at the poles and moves towards the equator at the surface, rising again around 60° latitude.
This circulation pattern leads to distinct precipitation and temperature zones:
- Tropical rainforests near the equator (high precipitation, warm temperatures)
- Deserts around 30° latitude (low precipitation, high temperatures)
- Temperate forests and grasslands in mid-latitudes
- Tundra and ice caps near the poles (low precipitation, cold temperatures)
Understanding this model is key to explaining why certain biomes occur where they do on a global scale.
Climate Change and Biome Shifts
Climate change is causing significant alterations in the distribution of biomes worldwide. As global temperatures rise and precipitation patterns change, many biomes are experiencing shifts in their boundaries and characteristics.
Examples of Biome Shifts
- Arctic Tundra: Warming temperatures are causing the tree line to move northward, encroaching on tundra ecosystems.
- Tropical Rainforests: Changes in rainfall patterns are affecting the extent and composition of rainforests in some areas.
- Deserts: Some arid regions are expanding due to increased temperatures and reduced rainfall.
It's a misconception that biome shifts occur uniformly or predictably. In reality, these changes are complex and can vary significantly from one region to another.
Zonation in Ecosystems
Zonation refers to the change in community composition along an environmental gradient. This concept is crucial for understanding how species distribute themselves within a larger ecosystem.
Key Factors Influencing Zonation
- Altitude: Changes in elevation lead to variations in temperature, precipitation, and air pressure.
- Latitude: Similar to altitude, but on a global scale.
- Tidal level: In coastal ecosystems, the degree of exposure to seawater creates distinct zones.
- Distance from shore: In aquatic ecosystems, depth and light penetration change as you move away from the shore.
A classic example of zonation is seen in intertidal ecosystems. Moving from the low tide mark to the high tide mark, you'll encounter distinct zones with different species adapted to varying levels of exposure to air and seawater:
- Subtidal zone (always submerged)
- Lower intertidal zone (exposed only at lowest tides)
- Middle intertidal zone
- Upper intertidal zone (exposed most of the time)
- Splash zone (rarely submerged)
Succession in Ecosystems
Succession is the process of change in the species structure of an ecological community over time. It involves a series of predictable changes that occur in an ecosystem following a disturbance.
Types of Succession
- Primary Succession: Occurs in areas where no soil or previous ecosystem existed, such as newly formed volcanic islands or areas exposed by retreating glaciers.
- Secondary Succession: Takes place in areas where an ecosystem previously existed but was disrupted, such as after a forest fire or agricultural abandonment.
Stages of Succession
- Pioneer Communities: The first organisms to colonize an area, typically hardy species adapted to harsh conditions.
- Intermediate Communities: As conditions improve, more complex species begin to establish themselves.
- Climax Communities: The final stage of succession, characterized by a stable, self-perpetuating community of organisms.
