Biology 301 - Wethey

Food Webs and Trophic Structure

• Alfred Russell Wallace 1858, (Proceedings of the Linnean Society of London Vol 3: 53-62) noted that large animals cannot be as abundant as small ones, and that carnivores must be less abundant than herbivores
• Charles Elton - 1927 book "Animal Ecology" described the idea of "food chains" and the "pyramid of numbers"
• Raymond Lindeman 1942 (Ecology Vol 23: 399-418) provided a mechanistic explanation of food web patterns based on energy flow. He defined "trophic levels", and a pyramid of energy (rather than numbers or biomass). The energy pyramid is related to the efficiency of energy transfer among trophic levels.
• Lindeman defined energy content of trophic levels from field data:

• Increasing efficiency of energy transfer at higher trophic levels.
• Efficiency = (Productivity at Higher Trophic Level)/(Productivity at Lower Trophic Level)
• Energy flow presumably limits the number of trophic levels.
• Elton notes that 5 trophic levels are usually the limit in most systems.

Global Productivity Patterns