Biomes, Climate, and Species Distribution: An Overview

Biomes and Species Distributions

Introduction to Biomes and Climate

Biomes are major ecological communities defined primarily by their dominant vegetation and climate. The distribution of biomes and the species within them is determined by a combination of abiotic factors (such as temperature, precipitation, sunlight, and wind) and biotic interactions. Understanding the structure and function of biomes is essential for studying ecology and the biosphere.

Earth’s Climate: Patterns and Determinants

Macroclimate and Microclimate

• Macroclimate: Refers to large-scale climate patterns, such as those affecting entire regions or continents.

• Microclimate: Refers to fine-scale variations in climate, often influenced by local features like vegetation, water bodies, or topography.

Global Climate Patterns

Global climate is largely determined by solar energy and the movement of Earth in space. The sun’s warming effect causes temperature variations, which drive evaporation and the circulation of air and water, shaping climate zones and biomes.

• Sunlight intensity varies with latitude, being most direct at the equator and more diffuse toward the poles.

• This variation leads to distinct climate zones (tropical, temperate, polar).

• Rising air masses release water and cause high precipitation in the tropics.

• Descending dry air creates arid climates near 30° north and south.

• Prevailing winds (trade winds and westerlies) are driven by these circulation patterns.

Regional and Local Effects on Climate

• Seasonality: Caused by the tilt of Earth’s axis and its orbit around the sun, leading to seasonal changes in temperature and precipitation.

• Bodies of Water: Oceans and lakes moderate climate by absorbing and releasing heat, influencing temperature and precipitation patterns.

• Mountains: Affect climate by creating rain shadows and influencing sunlight exposure and temperature with elevation.

Terrestrial Biomes

Definition and Classification

Terrestrial biomes are classified by their predominant vegetation and climate. They often transition gradually into one another through ecotones, rather than having sharp boundaries.

• Named for physical or climatic factors and dominant plant types.

• Vertical layering (e.g., canopy, understory, ground layer) is common in forest biomes.

• Convergent evolution can result in similar adaptations in distant biomes (e.g., cacti and euphorbs).

Examples of Major Terrestrial Biomes

• Tropical Forest: High biodiversity, constant high temperatures, and significant rainfall. Competition for light is intense due to layered vegetation.

• Desert: Low and variable precipitation, can be hot or cold, with plants and animals adapted to aridity.

• Savanna: Grasslands with scattered trees, seasonal rainfall, and frequent fires.

• Temperate Grassland: Cold, dry winters and hot, wet summers; dominated by grasses and forbs, adapted to fire and drought.

• Temperate Broadleaf Forest: Deciduous trees, significant precipitation year-round, and distinct vertical layers.

Aquatic Biomes

Overview and Zonation

Aquatic biomes cover most of Earth’s surface and are classified by physical and chemical characteristics. Marine biomes have higher salt concentrations than freshwater biomes. Zonation in aquatic systems is based on depth, light penetration, and distance from shore.

• Photic Zone: Sunlit upper layer where photosynthesis occurs.

• Aphotic Zone: Deeper layer with little or no light.

• Benthic Zone: Bottom substrate of aquatic environments.

• Pelagic Zone: Open water away from the shore.

Lake Types

• Oligotrophic Lakes: Nutrient-poor, oxygen-rich, often deep and clear.

• Eutrophic Lakes: Nutrient-rich, often oxygen-poor, usually shallow and turbid.

Streams and Rivers

• Headwaters: Cold, clear, turbulent, and oxygen-rich.

• Downstream: Warmer, more turbid, less oxygenated, wider, and meandering.

Estuaries

Estuaries are transition zones between rivers and seas, characterized by variable salinity and high productivity. They support diverse communities of plants and animals.

Marine Benthic Zone

• Located on the seafloor below the surface waters.

• Organisms are adapted to cold, high pressure, and low light.

• Hydrothermal vents support unique communities based on chemoautotrophic bacteria.

Species Distribution and Limiting Factors

Ecological and Evolutionary Time

• Ecological Time: Short-term interactions between organisms and their environment.

• Evolutionary Time: Long-term adaptations through natural selection.

Factors Limiting Species Distribution

• Dispersal: Movement of individuals away from their origin or high-density areas.

• Behavior and Habitat Selection: Some species do not occupy all suitable habitats due to behavioral preferences.

• Biotic Factors: Interactions with other species (e.g., predation, competition, disease).

• Abiotic Factors: Nonliving factors such as temperature, water, sunlight, wind, rocks, and soil.

Global Climate Change and Species Ranges

• Past and predicted climate changes can shift species distributions, reduce ranges, or cause extinctions if dispersal is limited.

Summary Table: Major Abiotic and Biotic Factors Affecting Species Distribution

Factor Type	Examples	Effect on Distribution
Abiotic	Temperature, Water, Sunlight, Wind, Soil	Limits physiological tolerance and habitat suitability
Biotic	Predation, Competition, Disease, Mutualism	Influences survival, reproduction, and community structure