Understanding Ecosystem Dynamics and Energy Flow

1. Ecosystem Ecology Chapters 55

2. Concept 5: Ecosystems – Analyzing productivity, energy flow, and chemical cycling. • Ecosystems (Ch 55) • How energy flows though the ecosystem by understanding the terms that relate to food chains and food webs • The difference between gross primary productivity and net primary productivity • The carbon and nitrogen biogeochemical cycles

3. Ecosystems • consist of all the organisms living in a community, as well as the abiotic factors with which they interact • Ecosystems range from a microcosm (aquarium) to a large area such as a (forest, lake) • Ecosystem Dynamics involve two main processes: energy flow and chemical cycling

4. Flow of Energy • The first law of thermodynamics states that energy cannot be created or destroyed, only transformed • Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as heat • The second law of thermodynamics states that every exchange of energy increases the entropy of the universe • In an ecosystem, energy conversions are not completely efficient, and some energy is always lost as heat

5. Cycling of Chemicals • The law of conservation of massstates that matter cannot be created or destroyed • Chemical elements are continually recycled within ecosystems • Ex) In a forest ecosystem, most nutrients enter as dust or solutes in rain and are carried away in water Overall: Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products

6. Trophic Levels • Autotrophs - build molecules themselves using photosynthesis or chemosynthesis as an energy source • Ex) plants and algae • Ex) chemosynthetic bacteria on hydrothermal vents • Heterotrophs - depend on the biosynthetic output of other organisms

7. Trophic Levels Energy and nutrients pass from: • Primary producers (autotrophs) to • Primary consumers (herbivores) to • Secondary consumers (carnivores) to • Tertiary consumers (carnivores that feed on other carnivores) • Detritivores,or decomposers, are consumers that derive their energy from detritus, nonliving organic matter • Prokaryotes and fungi are important detritivores • Decomposition connects all trophic levels

9. Try This! • Which of the following is absolutely essential to the functioning of an ecosystem? • A) producers • B) producers and herbivores • C) producers, herbivores, and carnivores • D) detritivores • E) producers and detritivores

10. Primary Productivity (Lab 12!) • The amount of light energy converted to chemical energy (organic compounds) by an ecosystem’s autotrophs during a given period of time • Background: • Photosynthesis (required light energy) • carbon dioxide + water → glucose + oxygen • Cellular Respiration (generates ATP – energy currency) • glucose + oxygen → carbon dioxide + water

11. Primary Productivity • Gross primary production (GPP) – Total primary production of the ecosystem • Net primary production (NPP)– GPP minus energy used by primary producers for respiration • Only NPP is available to consumers • Ecosystems vary greatly in NPP and contribution to the total NPP on Earth

12. Ecological Efficiency • Describes the proportion of energy represented at one trophic level that is transferred to the next trophic level • On average, efficiency is only ~10% • 10 percent of the productivity of one trophic level is transferred to the next level. The remaining 90% is consumed by individual metabolic activity or to detritovores • Applications: • Farming: Energy required to raise and sustain carnivores is far greater than that of herbivores… we eat cows, we ride horses • Bioaccumulation as you go up the trophic levels • Ex)High mercury in tuna and swordfish • Ex) High toxicity levels in orcas

13. Ecological Pyramids • Used to show relationship between trophic levels • Horizontal bars or tiers: represent relative size in terms of either: • Energy (productivity) • Biomass • Numbers of organisms • Tiers are stacked in the order in which energy is transferred.

16. Try This • Which of the following is not true of a pyramid of production? • A) Only about 10% of the energy in one trophic level is passed into the next level. • B) Because of the loss of energy at each trophic level, most food chains are limited to three to five links. • C) The pyramid of production of some aquatic ecosystems is inverted because of the large zooplankton primary consumer level. • D) Eating grain-fed beef is an inefficient means of obtaining the energy trapped by photosynthesis • E) A pyramid of numbers is usually the same shape as a pyramid of production

17. Biogeochemical Cycles • Describes the flow of essential elements from the environment to living things and back to the environment. • p. 1209-1214 in Campbell • For each of the following essential elements, you much know: • The reservoirs (major storage location) • The process of assimilation (incorporation into plants and animals) • The process of release (how it returns to the environment)

18. Biogeochemical Cycles • Hydrolytic Cycle (water cycle) • Carbon Cycle (required for the building of all organic compounds) • Nitrogen Cycle (required for the manufacture the building blocks of proteins and nucleic acids) • Phosphorus Cycle (required for the manufacture of ATP and all nucleic acids. Cycle is similar to other mineral cycles like calcium)

23. Try This • The finding of harmful levels of DDT in grebes (fish-eating birds) following years of trying to eliminate bothersome gnat populations in a lakeshore town is an example of...

24. Try This • The finding of harmful levels of DDT in grebes (fish-eating birds) following years of trying to eliminate bothersome gnat populations in a lakeshore town is an example of... • BIOLOGICAL MAGNIFICATION

25. Concept 5: Ecosystems – Analyzing productivity, energy flow, and chemical cycling. • Ecosystems (Ch 55) • How energy flows though the ecosystem by understanding the terms that relate to food chains and food webs • The difference between gross primary productivity and net primary productivity • The carbon and nitrogen biogeochemical cycles