1. ECOSYSTEMS & HUMAN INTERFERENCES I

2.  Ecosystem: the biological communities & their abiotic environment  Ecosystems are Characterized by: Energy flow Mineral cycling Ecosystems are not self-contained (leaky!) Natural ecosystems are affected by human activities

3. The Biotic Community  Living organisms in an ecosystem are divided into two trophic levels:  Autotrophs: primary producers  Heterotrophs: consumers (secondary P., Include: Herbivores Carnivores Omnivores Detritivores Decomposers

5. Energy flow Mineral cycling Reflection & Absorption Decomposers Oxidation (Respiration etc.) Heat Light 2° Carnivores Detritus Primary Producers Photosynthesis 1° Consumers (Herbivores)

6. Mader, 2001 Gross Primary Productivity (GPP): the total energy captured from the sun by autotrophs Net Primary Productivity (NPP): GPP – Respiration = Energy passed on to herbivores

7. Secondary Production  The amount of chemical energy in consumers’ food converted to new biomass per unit time.

8. The efficiency of energy transfer between trophic levels is usually less than 20% 33/200x100=16.5%

9. Which is more efficient for human population: eating corn or beef? ? ?

10. Trophic Efficiency and Ecological Pyramids  Trophic efficiency is the % of production transferred from one trophic level to the next.  Pyramids of production represent the multiplicative loss of energy from a food chain

11. Ecological Pyramids  Energy & biomass pyramids are upright.  As a rule, only 10% of energy or biomass are passed on to the next level. Energy Pyramid

12. Biomass Pyramids  Represent the ecological consequence of low trophic efficiencies.  Most biomass pyramids narrow sharply from primary producers to top-level carnivores because energy transfers are inefficient.

13. Numbers Pyramids  Show how the levels in the pyramids of biomass are proportional to the number of individuals present in each trophic level.

14. Inverted Pyramids  In lakes & open sea algae & cyanobacteria are the main primary producers.  Algae multiple fast but also consumed at a higher rate therefore the pyramid appears inverted