Introduction to Ecology; Major patterns in Earth’s climate

Learning Objectives

  1. Define ecology and describe the major sub-disciplines: behavior, population ecology, community ecology
  2. Recognize the temperature and precipitation profile for 6 terrestrial biomes and the ocean biome
  3. Explain the physical features of Earth that cause patterns in atmospheric and ocean circulation and lead to discrete regions of climate (temperature and precipitation patterns) with associated plant and animal communities (e.g. biomes)
  4. Predict how changes in climate can alter species ranges and biome locations (climate change effects)

Ecology and its sub-disciplines

Ecology is the study of how organisms interact with their environment. These interactions range from how an individual responds to a stimulus (behavior), how individuals of the same species interact with each other (population ecology), different species interact (community ecology), and how organisms interact with non-living components of the environment (ecosystem ecology). The entire set of interactions on a planet is called the biosphere.

Climate Patterns affect where communities live in the biosphere

Where organisms live on the planet is governed by global scale processes caused by the orientation of the earth’s axis toward the sun, heat retention versus loss in the atmosphere, and by the rotation of the earth. The atmosphere-ocean system is a very, very large heat engine (refer to the Hadley Cell Cross-Section figure below). Sunlight input at the equator heats the water and air along the equator. Water becomes water vapour and rises with the heated air to up into the atmosphere (1). The rising air cools, causing precipitation in equatorial regions. The warm by dry air is pushed out of the way by the expanding hotter air below (2). Once it cools, the air falls back to earth, this time without accompanying moisture (3). The high pressure created by the falling air redistributes to locations of lower pressure (4), such as the equator, establishing an air conveyor.

Hadley cell cross-section.The Hadley cell is one of three atmospheric circulation cells which transport heat poleward and drive Earth's weather. Created with Photoshop. 2004 D. Windrim

Hadley cell cross-section, showing both Hadley cells, one north of and one south of the equator (EQ). H represents regions of high pressure, L low pressure. (Source: D. Windrim, 2004, Wikimedia)

Study Tip: Determine where the planet’s cross section fits into the atmospheric cross section above (then read on to the next figure).

Scaled up to the entire, spherical planet, the Hadley cell and it’s companion cells at the latitude and pole establish significant north-south air and precipitation gradients. Because the earth is rotating on it’s axis, the north-south patterns become disrupted by the Coriolis effect to establish the prevailing wind patterns seen as trade winds and westerlies in the figure below.

Atmospheric circulation patterns arising from Hadley cells and the Coriolis effect. “The source of this material is the COMET® Website at of the University Corporation for Atmospheric Research (UCAR), sponsored in part through cooperative agreement(s) with the National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce (DOC). ©1997-2016 University Corporation for Atmospheric Research. All Rights Reserved.”

Based on where these patterns of heat, wind, and precipitation, where do you predict the world’s deserts should be?

Deserts are one of many common communities, which are classified according to temperature and precipitation profiles into biomes. Biomes can be terrestrial (shown below), aquatic, or marine.

terrestrial biomes Wikimedia commons

Terrestrial Biomes by geographic location (Source:

This view of biomes arranged by their location on the planet allows us to see global community patterns, such as how deserts or forest communities are organized with respect to latitude. Interruptions to the this pattern occur when major geologic features run counter to latitude. For example, the Andes in South America set up north-to-south biomes along the west coast, disrupting the east-to-west patterns evident in Africa.

Alternatively, if we categorize biomes along axes of temperature and precipitation then we can use the graphical organization to predict how environmental changes can alter the biome found in a specific location.

PrecipitationTempBiomes Wikimedia


If a wet tundra biome experiences an increase in average annual temperature, what biomes would you predict the community in that location to shift to over time?

In biomes governed by water, precipitation matters less while temperature and winds take on a more dominant role. One example of this is ocean upwelling, depicted in the figure below.

Ocean upwelling is an important process that recycles nutrients and energy in the ocean. As wind (green arrows) pushes offshore, it causes water from the ocean bottom (red arrows) to move to the surface, bringing up nutrients from the ocean depths. (Source: OpenStax Biology)

In smaller freshwater aquatic systems, seasonal temperature change causes the greatest fluctuations in water temperature and water movement, called turnover. In winter, the lake or pond has stratified temperature layers, and nutrients slowly settle to the bottom in the still waters. Water remains liquid to 0 degrees C, but it’s most dense at 4 degrees C, so once the air temperatures rise in spring, the surface waters warm slightly and become more dense than the colder layer below. The dense surface waters sink, pushing the deeper, nutrient rich waters to the surface, and turning over the nutrients from bottom to top. Waters still and stratify again in the summer, and experience turnover again in the fall as surface temperatures drop down, making surface water more dense.

The spring and fall turnovers are important processes in freshwater lakes that act to move the nutrients and oxygen at the bottom of deep lakes to the top. Turnover occurs because water has a maximum density at 4 °C. Surface water temperature changes as the seasons progress, and denser water sinks. How might turnover in tropical lakes differ from turnover in lakes that exist in temperate regions? (Source: Open Stax Biology

The spring and fall turnovers are important processes in freshwater lakes that act to move the nutrients and oxygen at the bottom of deep lakes to the top. Turnover occurs because water has a maximum density at 4 °C. Surface water temperature changes as the seasons progress, and denser water sinks. (Source: Open Stax Biology)

How would you relabel the temperatures in the diagram above so that they accurately reflect the turnover process?

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