Abiotic Factors: Marine & Terrestrial (DP IB Biology)

Coral Reef Formation

• Corals are the result of a symbiotic relationship between an animal known as a coral polyp, and a zooxanthellae algae

  • The polyp provides shelter and protection

  • The algae carry out photosynthesis and produce carbon compounds such as carbohydrates

• Some species of coral polyps secrete calcium carbonate which builds up in layers to form a hard outer structure; over time these deposits from thousands of individuals can form a coral reef

CC BY 2.0, via Wikimedia Commons

Some coral species secrete layers of calcium carbonate that forms the hard structure of coral reefs

Distribution of coral reefs

• The distribution of reef-building corals is limited to the topics and subtropics

  • Non reef-building species can be found in other regions

• The formation of coral reefs is limited by abiotic factors, including: 

  • Water depth

  • pH

  • Salinity (salt concentration)

  • Water clarity

  • Temperature

• Coral has a narrow range of tolerance for all of these abiotic factors, resulting in its limited distribution

Coral reef distribution map

The distribution of reef building corals is limited by abiotic factors

Abiotic factors affecting coral reef formation table

Terrestrial Biome Distribution

• The term biome can be defined as follows:

A large community of plants and animals that has occurred as a result of environmental factors

• Biomes occur over large geographical areas, and are usually named after their dominant vegetation type, e.g. a geographical area dominated by tropical rainforest will be a tropical rainforest biome

• Examples of biomes include:

  • Temperate rainforest

  • Tropical rainforest

  • Temperate deciduous forest

  • Boreal, or coniferous forest, sometimes known as taiga

  • Grassland, e.g. temperate or savanna

  • Tundra

  • Desert, e.g. hot desert or cold desert

• Biome distribution is affected by abiotic factors in the environment

Biome distribution map

The distribution of biomes is affected by abiotic factors

• Average temperatures and rainfall patterns are significant factors in determining the development of a biome

  • For any given combination of these two factors, a specific biome will result

• Biome development can be plotted on a graph known as a climograph, with mean annual rainfall and temperature on its axes

Biome development graph

For any given temperature and rainfall pattern, a particular biome will develop

• The likely biome at any given rainfall and temperature can be determined from the climograph, e.g.

  • At a mean average rainfall of 200 cm and mean average temperature of 25 °C, tropical seasonal forest will develop

  • At a mean average rainfall of 300 cm and mean average temperatures of 15 °C, temperate rainforest will develop

  • At a mean average rainfall of 100 cm and mean average temperatures of 0 °C, taiga, or boreal forest, will develop

• Bear the following points about climographs in mind when drawing conclusions:

  • Climographs shows a distinct boundary between biome types, but the reality is that there will be a gradual shift from one biome type to another

  • Rainfall and temperature are not the only factors that influence biome development; the dotted lines in the graph above show situations where other variables, such as soil type and animal grazing, may play an important role

  • Because neither rainfall or temperature can be described as being an independent variable or a dependent variable, the allocation of temperature and rainfall to the graph axes may vary

    • The graph above has rainfall on the x axis and temperature on the y axis, but this could just as correctly be plotted the other way around

    • The graph above has temperature plotted from high to low on the y axis, but this could be plotted from low to high