Climate and Biomes Notes- CH 47

Climate and Biomes

Lecture Objectives

  • Explain the factors that contribute to the distribution of major climatic zones on Earth.
  • Describe the factors that give rise to specific types of biomes.
  • Describe how climate, nutrient availability, and evolutionary history influence global patterns of primary production and biological diversity.

Climate and Biomes

  • Biomes are broad geographic areas with similar sets of communities.
  • Climate exerts a major influence on the nature and distribution of biomes across the globe.
  • Climate is long-term average weather.

Climate: Solar Radiation

  • Climate varies markedly from one region to another.
  • The principal control on Earth’s surface temperatures is the angle at which solar radiation strikes the surface.
  • Earth is hot near the equator and cold at the poles. This temperature distribution reflects incoming solar radiation.

Influences on Climate: Topography

  • Topography, or the physical features of Earth, also contributes to global temperature patterns.
  • Temperature drops about 44°F for every 10001000 feet in elevation ( 6.56.5°C per kilometer).
  • Mountains exhibit a pattern in which climate and biomes change as elevation increases, mirroring the spatial pattern from lower to higher latitudes.

Seasonality: The Tilt of Earth on Its Axis

  • Earth’s axis of rotation is not oriented perpendicular to incoming sunlight but rather tilts at an angle of 23.523.5 degrees.
  • Because of the tilt of Earth’s axis, solar radiation strikes the Northern and Southern Hemispheres unevenly at different parts of Earth’s orbit, causing seasonality.
  • The tilt results in solar radiation striking North America and Europe more directly in July than it does in January, so warmer temperatures occur in July.
  • The opposite is true for the Southern Hemisphere, where the solar radiation strikes more directly in January.
  • These patterns of temperature variation go a long way toward explaining the geographic distribution of biomes across the globe.

Cycles of Warm and Cool Air

  • The gas molecules that make up air are constantly in motion.
    • When they are heated, they move faster, and (unless confined) the volume of the air expands.
    • Warm air is less dense than colder air and rises through the atmosphere.

Coriolis Effect

  • Earth rotates in a counterclockwise direction, moving from west to east. In the course of one daily rotation, a spot at the equator will move through a distance equivalent to our planet’s circumference – nearly 25,00025,000 miles, or 40,00040,000 km.
  • Points at higher or lower latitude travel a shorter distance in a single rotation.
  • Therefore, in a period of 2424 hours, a point at the equator will have traveled farther than a point at a higher or lower latitude.
  • The point at the equator moves more quickly than the point closer to the poles.
  • As the wind moves air north and south from the equator, the land beneath it rotates to the east but at a slower speed than the land at the equator.
  • The wind then appears to have deflected to the right in the Northern Hemisphere, and winds in the Southern Hemisphere deflect to the left – a phenomenon called the Coriolis effect.
  • In conjunction with the cells of rising and descending air masses, the Coriolis effect explains the pattern of prevailing winds.

Ocean Currents

  • Winds push on water in the oceans, directing surface currents.
  • Water can carry much more heat than air, so ocean currents transport a great deal of heat to higher latitudes.
  • The heat it carries helps keep northwestern Europe much warmer than land at equivalent latitudes in North America.
  • Just as colder air sinks below warmer and less dense air, cold waters sink beneath less dense water masses.
  • At high latitudes, the sinking cold waters begin to move slowly along the seafloor toward the equator.
  • The result is a complex three-dimensional circulation of water through Earth’s oceans that plays an important role in the determination of regional climates.
  • The Coriolis effect governs the direction of ocean currents.

Regional Climates and Biomes

  • Distributions of terrestrial biomes around the world reflect regional climates.
  • Terrestrial biomes include tundra, alpine, taiga, temperate coniferous forest, deciduous forest, temperate grassland, desert, chaparral, savanna, and tropical rainforest.

Terrestrial Biomes

  • The principle terrestrial biomes include tundra, alpine, taiga, temperate coniferous forest, deciduous forest, temperate grassland, desert, chaparral, savanna, and tropical rainforest.
Tundra
  • Tundra occurs close to the North Pole, above 6565° N and is the coldest biome with permanent layer of ice beneath the soil, with short days in winter that limit the growing season.
Alpine
  • The alpine biome is similar to tundra, but alpine lacks permanent ice below the soil, and temperatures in alpine vary more widely.
  • Alpine occurs throughout the world, often at about 10,00010,000 feet at lower latitudes, but always just below the snow line.
Temperate Coniferous Forest
  • Temperate coniferous forest occurs below 5050° N. There are two broad areas of temperate coniferous forest in North America:
    • Along the Pacific coast where the climate consists of warm summers, mild winters, and abundant precipitation.
    • In the interior where there is less precipitation and colder winters.
Deciduous Forest
  • The deciduous forest biome is characterized by trees that lose their leaves at the end of each growing season.
  • The climate of deciduous forest features moderate temperatures and precipitation all year long.
Savanna
  • Tall, perennial grasses dominate the savanna biome, which occurs in eastern Africa, southern South America, and Australia.
  • In savanna, rain is seasonal and ranges from 7575 to 150150 cm per year.
Tropical Rainforest
  • Tropical rainforest is the most diverse of all terrestrial biomes.
  • The tropical rainforest biome extends north and south of the equator from 1010° N to 1010° S.
  • In tropical rainforest, temperatures are warm, and annual precipitation commonly exceeds 250250 cm.

Aquatic Biomes

  • Aquatic biomes include freshwater, estuary, and saltwater biomes.
  • Aquatic biomes reflect climatic differences around the globe.
  • The challenges for aquatic organisms are different from those of terrestrial organisms.
  • One of the most important phenomena when considering the aquatic biome is the depth to which sunlight penetrates through water. It affects the primary producers in aquatic biomes, and it influences food webs in aquatic biomes.
Freshwater Biomes
  • Freshwater biomes can vary with climate and topography, both of which affect nutrient input and oxygen availability.
  • Only about 2.52.5% of Earth’s water is fresh, and most of this water occurs in glaciers, permafrost, and groundwater within soils.
  • Examples include Lakes and Rivers
Rivers
  • Rivers and streams are freshwater biomes characterized by moving water. Rivers and streams, like lakes, vary tremendously in size and chemistry.
Estuary Biomes
  • An estuary is an ecotone (transitional zone) between freshwater and saltwater environments.
  • Between freshwater and saltwater environments, there is a gradient of nutrients and chemistry that results in species that commonly change along a gradient.
  • Estuaries are also highly productive, providing hatchery areas for many commercial fishes and shellfish.
Saltwater Biomes
  • The oceans constitute Earth’s largest biomes, covering 7171% of Earth’s surface and reaching a depth of nearly 11,00011,000 m (almost 77 miles).
  • Oceans are so large and so diverse in their biology that ecologists commonly subdivide them into distinct zones based on depth and proximity to the shoreline.
    • Photic zone is the top layer, nearest to the surface of the ocean. It lies between the surface and about 200200 m deep. Because sunlight rarely penetrates much deeper than about 200200 m, most of the ocean’s volume is off limits for photosynthetic organisms.
    • Neritic zone encompasses environments that are near the shore, with a shallow seafloor, relatively high availability of nutrients, and persistent sunlight. Distinct biomes within the neritic zone include intertidal and coral reef biomes.
    • Oceanic zone is an area of deeper waters beyond the continental shelf. Within the oceanic zone, biologists commonly distinguish between the pelagic biome in open ocean water and the deep-sea biome on the deep seafloor.
  • Nutrients are commonly most abundant in shallow waters along continental margins.

Global Patterns of Primary Production

  • Global patterns of primary production reflect planetary-scale variations in climate and nutrient availability.
  • In most terrestrial ecosystems, sunlight, water, and nutrients limit rates of primary production.
  • The intensity of solar radiation and seasonality both influence the ability of primary producers to sustain growth throughout the year at higher latitudes.
  • In the ocean, nutrients commonly limit primary production.
  • The idea that primary production is limited by the nutrient that is least available relative to the needs of primary producers is called Liebig’s Law of the Minimum.
  • Climate and nutrient availability determine global patterns of primary production in terrestrial and ocean ecosystems.

Latitudinal Diversity Gradient

  • Species diversity generally peaks near the equator and declines towards the poles, a pattern known as the latitudinal diversity gradient.
  • Hypotheses on why this pattern exists include:
    • Tropical habitats have existed much longer than temperate habitats.
    • It is more difficult to adapt to the cold, dry winters and extreme temperature ranges at higher latitudes than to the warm, wet, and less extreme temperature ranges at lower latitudes.

Lecture Terminology

  • Biome
  • Topography
  • Coriolis effect
  • Evapotranspiration
  • Water cycle
  • Ecotone
  • Ecocline
  • Estuary
  • Photic zone
  • Neritic zone
  • Oceanic zone
  • Liebig’s Law of the Minimum
  • Latitudinal diversity gradient