BIO 105 Lecture Notes - Lecture 26: Food Web, Polychlorinated Biphenyl
Document Summary
Remaining 33 j move on to the next trophic level. Food chain: linear sequence of feeding relationships that describe energy transfer. Food web: network of food chains more realistic than food chain. Remainder of energy available to make the transition to the next trophic level e. g. caterpillar. Trophic efficiency = 33 j/ 200 j = 16. 5% efficiency. Generally (across systems) approximately 10-20% of energy present makes it to the next trophic level. Energy pyramids 90% reduction in energy at each trophic level. Explain how chemicals (specifically c, n, p) cycle in ecosystems. *organisms at higher trophic levels depend on lots of organisms at lower levels. Higher level organisms consume a large biomass of lower-level organisms. High level of toxins accumulate at high trophic levels e. g. 1- bald eagles and ddt on catalina island. Ddt causes egg shell thinning impacts reproductive success (because shells break, leading to less viable eaglets)
