1. Ecology (BIO C322)

2. Ecological Pyramids

3. Pyramid of Numbers – upright or inverted??

4. Pyramid of biomass - upright or inverted??

5. Food Chain Transfer of food energy from source to consumers. Two types: grazing food chain & detritus food chain. Food web: Interconnected food chains.

9. Practice Concept The proportion of net production energy that flows down the two pathways (i.e. grazing & detritus food chains) varies in different kinds of ecosystems. In heavily grazed pastures or grasslands, 50% or more of net production may pass down the grazing pathway. In contrast, marshes, oceans & forests operate as detrital systems, in that 90% or more of the autotrophic production is not consumed by heterotrophs until the leaves, stems & other plant parts die, & are decomposed.

10. Detritus Food Chains Detritus  Detritivores  Predators In some ecosystems, detritivory >> herbivorous grazing. Such food chains may involve 90% or more of energy flow.

11. Hubbard Brook Experimental Forest (Units in kCal/m 2 /year) P G 10,400 Respiration 5720 (55%) P N 4680 (45%) Detritus F.C. 3446 (74%) Grazing F.C. 35 (1%) Storage 1199 (25%)

12. Review Article: “The Long and Short of Food Chain Length” By David M. Post, Trends in Ecology & Evolution, Vol. 17, No. 6, June 2002.

13. What is Food Chain Length (FCL)? FCL = Number of transfers of energy or nutrients from the base to the top of food web. FCL influences community structure. Maximum trophic position = FCL + 1 In nature, linear food chains are rare.

14. FCL = ? FCL = 4

15. 12 1011 789 56 1 23 4 Energy Web: Max FCL = ? Min FCL = ? Max FCL = 4 Min FCL = 2

16. What determines FCL in natural ecological systems? History of Community Organization Resource Availability Ecosystem Size Predator-prey Interactions Disturbance

17. History of Community Organization Colonization history influences food-web structure and FCL most strongly in ecologically isolated or evolutionarily young systems.

18. History limits which type of species can join the local community & food web. Constraints on local community membership might modify predator-prey interactions. If a top or key intermediate predator is unable to invade a system or evolve in situ, FCL might remain short.

19. Resource Availability Energy/resource availability might limit FCL when colonization does not.

20. There is a diminishing amount of energy available to support each subsequent trophic level. FCL should increase as the energetic efficiency of organisms within a food web increases. FCL should increase as the amount of resources available at the base of the food web increases. FCL should increase as primary production or detrital input increases. Energetic or Productivity Hypothesis

21. Productive Space Hypothesis: A variant of Energetic Hypothesis Energetic hypothesis considered only per-unit- size resource availability. Productive Space hypothesis includes a spatial component also – ecosystem size. FCL should increase as a function of total ecosystem productivity = product of ecosystem size (area or volume) and some measure of per-unit-size productivity or resource availability (e.g. gram carbon per m 2 per year).

22. Larger ecosystems support food webs with longer FCL. The observed relationship b/w FCL and ecosystem size could derive from the positive relationship b/w ecosystem size & species richness.

23. Resource Availability – The Other Side Longest food chains are often found at inter- mediate, rather than at high resource availability. At high resource availability, top predators can reach higher densities and can exterminate intermediate predators, thereby shortening FCL.

24. An efficient higher predator, with limited food supply, might eliminate his prey and be forced either to drop to a lower trophic level or to become extinct. Studies suggest a threshold (10 g C/m 2 /year) below which resource availability constrains FCL, but above which FCL is determined by other factors. Conclusion: Resources limit FCL only in small systems with very low total resource availability.

25. Predator-Prey Interactions Where resource availability and colonization are not limiting, the size structure of predator-prey interactions influence FCL. When predators are similar in size to their prey, FCL is around 3 trophic levels.

26. There is little evolutionary advantage to feeding on other carnivores when herbivores are generally more abundant, offer similar energetic and nutritional value & are less well-defended. But most food webs are dominated by size- structured predator-prey interactions where body size increases with trophic position. In these food webs, some other factor, such as disturbance, might determine FCL.

27. Dynamical Constraints & Disturbance (Dynamical Stability Hypothesis) Developed by Pimm and Lawton (1978).

28. They found that longer food chains had longer return times therefore less stable than shorter food chains. Food chains with short FCL should dominate natural systems, particularly those subject to frequent disturbance.

29. Models to understand Food Web Structure Rank of Omnivory – Number of predator-prey interactions in excess of those in the model with no omnivory. Food webs with large number of omnivores (high ranking omnivory) are rare in the real world. It is less probable to find species that feed simultaneously both high & low in a food web.

30. Any Species left !? Human Omnivore

31. 4 3 2 1 Trophic Level 4 Trophic Levels; Rank = 0; No Omnivory 4 Trophic Levels; Rank = 1; Rare species 3 Trophic Levels; Rank = 2 2 Trophic Levels; Rank = 0; No Omnivory

32. Human Influences on FCL Humans overexploit top predators; Change ecosystem size through habitat fragmentation; Change resource availability by translocating large quantities of nutrients, water and CO 2. Move species around the landscape.

33. In passing… Ecological Footprint (E.F.): Area of productive ecosystems (crop/forest-lands, water bodies) outside a city required to support life in the city. e.g. U.S.A.  E.F. is 5.1 hectares/person; India  0.4 ha/person.

34. E. P. Odum: If highly developed countries would reduce their resource and energy consumption, then international conflicts & terrorist threats would be reduced.