- Define ecology and describe the major sub-disciplines: behavior, population ecology, community ecology
- Explain the physical forces that lead to atmospheric and ocean circulation patterns and predict the local, regional, and global effects if forces change
- Predict how changes in temperature and precipitation patterns (climate) can alter species ranges and biome locations
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), how species interact with other species (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 but 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.
With respect to a Hadley cell, where should it rain? Where should deserts be?
Scaled up to the entire, spherical planet, the Hadley cell and its companion cells at mid-latitudes and the poles establish significant north-south air and precipitation gradients. Because the earth is rotating on its 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.
Here’s a fun pair of videos that use a kiddie pool experiment to explain the Coriolis effect, where the earth’s spherical shape and rotation generate a curved path for water and air as they travel at the planet’s surface:
Consider how the Coriolis effect contributes to the westerlies and trade wind patterns at the earth’s surface in the diagram below.
This video demonstrates the Coriolis effect and its influence on the direction wind moves in major storms:
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 recurring ecosystems on the planet. When an ecosystem pattern recurs, we identify it as a biome and classify it according to temperature and precipitation profiles. Biomes can be terrestrial (shown below), aquatic, or marine.
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 mountains in South America set up north-to-south biomes along the west coast, disrupting the east-to-west patterns evident in Africa.
This video reviews the relationship between the Hadley Cells and terrestrial biomes:
If we categorize biomes graphically along the 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.
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. Here, the wind pushes surface waters away from shore and create a zone of lower water pressure. Deeper waters well upward into that low pressure zone, and bring with them any nutrients settled to the ocean floor from decomposed dead organic matter.
In smaller freshwater aquatic systems, seasonal temperature change causes the greatest fluctuations in water temperature and water movement, called turnover. In winter, a lake or pond covered by surface ice 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 stratify again in the summer, and experience turnover again in the fall as surface temperatures drop down, making surface water more dense.
How would you relabel the temperatures in the diagram above so that they more accurately reflect the turnover process?
This video describes a rare, but catastrophic event that can occur in lakes that do not undergo seasonal turnover: