Climate, which is the combination of water, winds, temperature, and light, helps determine which organisms will live in any particular place on Earth. The rocky environment and soils also have a large effect. An environment that is dry will be home to species that can conserve water. These organisms are also often adapted to warmer temperatures and poor soil conditions. Organisms living in wet areas may have adaptations for surviving where root systems are constantly under water. The organisms that are best adapted to live in a particular environment will eventually form a stable community where the biodiversity does not change much over time. These stable communities are called climax communities.

Scientists group ecosystems that have similar climax communities into broad categories of organization called biomes. A biome is, simply put, a large grouping of ecosystems that share the same kinds of climax communities. Since approximately 75% of Earth's surface is covered by water, it is possible to describe biomes that exist in salty water or in fresh water. Some parts of the ocean are very deep so we can describe biomes that exist in the cold, dark depths of the ocean.

Humans are land dwelling creatures so we are generally much more familiar with biomes found on land. These terrestrial, or land, biomes are described based largely on their climates and the major organisms found in them. Here are the major terrestrial biomes:

• Desert - The driest biome with less than 25 cm of precipitation annually and very little plant or animal life.
• Grassland - A biome composed of large communities of grasses and other small plants. It gets between 25-75 cm of precipitation annually.
• Taiga - This biome has forests of evergreens; pine, fir, hemlock and spruce. Soils are acidic and poor in minerals. It gets between 50 and 100 cm of precipitation annually.
• Temperate Forest - This biome is composed of forests of broad-leaved hardwood trees that loose their leaves every year. It receives between 70-150 cm of precipitation annually.
• Tropical Forest - The tropical biome found nearest to the equator with warm temperatures and the most plant growth of any biome. It receives over 200 cm of rain annually.
• Tundra - The coldest land biome is found near Earth's north and south poles. It has no trees but has low, slow growing vegetation with permafrost below the topsoil. The tundra usually receives less than 25 cm of precipitation annually.

The following photographs will help you compare the diversity of life in various biomes. As you study each photograph respond to the following questions in your laboratory journal:

1. Which biome do you think this photograph represents?
2. List the things you saw in the photograph that make you think of a particular biome and tell why you think they belong in that biome.

Biome #1

Biome #2

Biome #3

Biome #4

Biome #5

Photo 5 Credit: U. S. Fish and Wildlife Service

Biome #6

Photo 6 Credit: U. S. Fish and Wildlife Service

Analysis:

1. Rank each of the biomes in the photographs from the one that appears to have the greatest variety of species to the one with the least variety.
2. Rank each of the biomes in the photographs from the one you think has the greatest biomass per acre to the one with the least. Biomass is the total amount of living material in a given area.