Food Webs

http://www.mscs.dal.ca/~myers/bio2060/foodwebs.html

This lecture will discuss food webs. Read chapter 14 in Molles or chapter 22 in Begon et al. These lectures will contain material not included in Molles. I will discuss the idea of bottom-up control, and look at questions

Theoretical Properties of Food Webs

Models are used to interpret (read "think about") real ecosystems. Notions such as stability cannot be even defined without rather complex mathematics.

Stability

What models tell us

Why do Food Webs only Have 3 or 4 Levels?

Most food webs comprise only 3 or 4 levels. Why?

Trophic Cascades

Trophic cascades are examples of top-down control. Removal of large predators can have impacts all out of proportion to their abundance. Trophic Cascades are characterized by 3 features.

Example: Sea Otters in the North Pacific Coastal Ecosystem

Meta-analysis of Freshwater Trophic Cascades

>Example: Bottom Up Control in the Serengeti

The Serengeti ecosystem of east Africa is probably the best studied example of an ecosystem with its large animal component present.

>Example: How many Green Sea Turtles Lived in the Caribbean?

  • A short explanation of meta-analysis
    I will expect you to know the basic ideas of meta-analysis but you do not have to remember the formulas.