Roadmap for remaining lectures:

1. Roadmap for remaining lectures: • Combine the abiotic world (Earth + Climate) with the biotic world (life). • A. First talk about “Ecosystems”, and generally about how life, elements, and energy move and interact on Earth (this lecture). • B. Second talk about global cycles of important elements – Carbon, Water, Nitrogen. * Need to introduce “microbes” because of their importance in controlling these cycles(next lecture, then two lectures, starting after Thanksgiving) • C. Third talk specifically about how “energy” moves and cycles on Earth, and how that relates to food supplies and human impacts (lecture on productivity and trophic levels). • Present “Case Studies” of important ecosystems (tropical rainforests lecture). • Give examples of applying scientific principles to real-life environmental problems –(climate change in the Great Lakes lecture), and(exploding lakes lecture)

2. The Concept of the Ecosystem What we wish to learn: • What is an ecosystem, and how can we study one? • Is the earth an open or closed system with respect to energy and elements? • What is a biogeochemical cycle? • What controls the function of ecosystems? • What factors determine the distribution of ecosystems and biomes?

3. Levels of Ecological Study • The ecology of individual organisms includes their physiological adaptations, their niche use, and their behavior. • The ecology of populations includes individual ecology, but also examines population growth, limiting factors, and interactions with other species. • The ecology of communities examines how species affect one another in two-way and multi-way interactions. • The ecology of ecosystems examines the dynamics of the entire system, with a particular emphasis on energy pathways and limiting nutrients.

4. What is an ecosystem? • An ecosystem consists of the biological community that occurs in some place, and the physical and chemical factors that make up its non-living or abiotic environment. • The main processes governing ecosystem function are: Energy Transformationsand Biogeochemical Cycling. • The study of ecosystems emphasizes certain processes that link the living, or biotic, components to the non-living, or abiotic components and that determine how they all function together.

5. ABIOTIC COMPONENTS sunlight temperature precipitation water or moisture soil chemistry etc. BIOTIC COMPONENTS primary producers herbivores carnivores omnivores detritivores etc. Components of an Ecosystem All of these vary over Space and Time

6. Energy Transformations • Primary producers capture energy from the sun through photosynthesis (and they are a “functional group”). • Carbohydrates (CHO) are formed, with C derived from CO2 fixation (photosynthesis). • Ultimately, all energy or carbon “fixed” by primary producers is “respired” by the entire community. CO2Organic matterCO2 • Organisms that obtain their energy in the same way occupy the same trophic (feeding) level: primary producers, herbivores, carnivores, decomposers.

7. Energyand Element Flow • The earth is an “open” system with respect to energy. • The earth is a “ ??? ” system with respect to elements.

8. A Simple Food Chain

9. A Real Food Web

10. A Web of Interactions

11. Take Home Message “Everything is connected to everything else” - the trick is determining the strength of the interactions - But HOW?

12. Biogeochemical Cycles • Chemical elements such as P and N “cycle” between the abiotic (geological and chemical) and biotic components of ecosystems. • Elements cycle because their supply is fixed. The earth is a closed system with respect to elements essential to life. • All major environmental problems today can be understood through “biogeochemistry” • Element cycles interact !!

13. Biogeochemical Principles and Tools 1. ELEMENT RATIOS* Important elements are “conservative” and found in relatively constant proportions in organisms Algal Composition: Called the “REDFIELD RATIO” In Normal Algae, N:P = 16:1 = 16 If N:P = 32 ??

14. Input Input Internal Change Output 2. MASS BALANCE * Describes whether a system is changing and how fast NET CHANGE =INPUT + OUTPUT+ INTERNAL CHANGE

15. INPUTS: RAIN to the Catchment = 100 moles H+/yr • STREAM to the Lake = 50 moles H+/yr (b) OUTPUT IN STREAM = - 20 moles H+/yr (c) INTERNAL CHANGE = - 10 moles H+/yr NET CHANGE =INPUT+ OUTPUT+ INTERNAL CHANGE = 50– 20– 10 = 20 moles H+/yr Lake is acidifying!

16. Algae Algae Fish Fish NH4 NH4 NH4 NH4 3. NUTRIENT OR ELEMENT CYCLING A. CLOSED SYSTEM 1. Rate = # of cycles / time • As rate increases, productivity increases 2. Pathways are important B. OPEN SYSTEM 1. Rate 2. Pathways 3. Residence time = RT = time spent cycling before being lost from the system • RT = [total amount of NH4 in box (system) / Input or output rate of NH4] • Units = kg / (kg/yr) = year

17. Input Rate = 100 kg / year Stock = 100 kg Output Residence Time Example RT = Stock / Input Rate = 100 kg / 100 (kg/yr)= 1 yr * System must be at “STEADY STATE” or “EQUILIBRIUM” • - Homework -

18. Controls on Ecosystems 2 Theories: • Nutrient supply drives 1o Prod, and 1o production drives 2o production … = “Bottom-Up” Control 2. Predation and grazing control all trophic levels … = “Top-Down” Control

19. Which theory is correct? • Bottom-up applies “direct” control upward on trophic levels • Top-down applies “alternating” control downward on trophic levels * Evidence to date shows that both theories operate and exert control, but not complete control, on ecosystems. Nutrients 1o 2o 3o Top Producers Prods Prods Predators “Bottom-Up”Effect Strong(Bottom-Up Weak) (Top-Down Weak) “Top-Down” Effect Strong

20. The Geography of Ecosystems • Many different ecosystems are found on earth, from tundra to rain forest. • When an ecosystem type extends over a large area, we often refer to this as a “biome” • Climate is the primary determinant of the distribution of biomes

21. The Distribution of Biomes

22. Climate Patterns Affect Biome Distributions

25. Summary • An ecosystem consists of the biological community and the physical and chemical factors making up the abiotic environment. • Energy enters an ecosystem in the form of light energy, and is transformed into organic energy by photosynthesis. All energy fixed in photosynthesis is also consumed in respiration. • Organic energy is transferred by consumers in both grazing and detritus-based food chains. • Biogeochemistry is the study of how elements cycle and interact in the environment. • Ecosystems are controlled by both top-down and bottom-up processes. • The global distribution of ecosystem types and biomes is determined by climate.