1. Energy Flows in Ecological Systems
Producers and Consumers
Green pigments in plants, chlorophylls, absorb light energy from the sun
Plants combine carbon dioxide and water, using energy from the sun, into high-energy carbohydrates such as starches, cellulose, and sugars, during photosynthesis
Photosynthesis produces oxygen

2. Energy Flows in Ecological Systems
Producers and Consumers
Organisms with the ability to capture energy and manufacture matter are known as autotrophs, or producers
All other organisms are known as heterotrophs, or consumers
There are two kinds of autotrophs: phototrophs and chemoautotrophs
Phototrophs get their energy from light, while chemoautotrophs obtain their energy from chemicals in the environment

3. Energy Flows in Ecological Systems
Producers and Consumers
Both phototrophs (plants algae, and bacteria) and chemoautotrophs (mainly bacteria, play a critical role in Earth’s biogeochemical cycles – nitrogen cycle, carbon cycle, phosphorous cycle, sulfur cycle, hydrologic cycle, rock cycle)
The process of photosynthesis produces billions of tons of biomass (living matter) throughout the world, despite energy degradation and loss

4. Energy Flow in Ecological Systems
Energy and Material Transformations
Energy continually flows through systems.
Almost all ecosystems are driven by energy from the sun.
Energy is converted from a higher form to a lower form as it is utilized
Matter (organic and inorganic materials) are cycled and recycled within ecosystems.
Matter can be stored for long or short terms.

5. Energy Flows in Ecological Systems
Remember
Energy Flows
Matter Cycles

6. Energy Flows in Ecological Systems
Producers and Consumers
Besides photosynthesis, cellular respiration is another essential energy pathway in organisms
carbohydrates are broken down into inorganic molecules, carbon dioxide, and water
energy is released and can be used for many purposes by the organism
Aerobic organisms must have access to oxygen for cellular respiration to take place, or they will die

7. Energy Flows in Ecological Systems
Food Chains
Some of the energy captured by autotrophs is passed on to other organisms, the consumers, through a food chain
Each level of the food chain is called a trophic level
Herbivores eat producers and are the energy source for higher-level consumers, or carnivores
Omnivores, such as humans, raccoons, sea anemones, and cockroaches, can get their energy from multiple trophic levels

8. Energy Flows in Ecological Systems
Food Chains
Primary Consumers: eating plants
Secondary Consumers: eating herbivores
Tertiary Consumers: eating animals that are secondary consumers or higher

9. A Food Chain

10. Energy Flows in Ecological Systems
Food Chains
Decomposer food chains are just as important as grazing food chains
These chains are based on dead organic material called detritus, which is high in potential energy but difficult for typical consumer organisms to digest
Decomposer food chains play a key role in breaking down plant and animal material into products such as carbon dioxide, water, and inorganic forms of phosphorus and nitrogen and other elements

11. A Decomposing Food Chain

12. Energy Flows in Ecological Systems
Food Chains
Detrital food chains tend to dominate in forest ecosystems, and freshwater ecosystems
Grazing food chains dominate in marine ecosystems
Producers are photosynthetic phytoplankton
Zooplankton graze on the phytoplankton
The more species in an ecosystem, the more resilient it is to stress because there are more alternative energy pathways
Ecological redundancy, or functional compensation

13. Energy Flows in Ecological Systems
Food Chains
Food chains tend to exist as part of complex food webs in which many alternative routes exist for energy to flow through the ecosystem
The most complex food webs tend to exist under most favourable conditions for life
Ecologists debate whether ecosystems are mostly controlled by predators (top-down control) or by prey populations (bottom-up control)

14. Food Web

15. Energy Flows in Ecological Systems
Biotic Pyramids
The second law of thermodynamics explains how energy flows from trophic level to trophic level, with a loss of usable energy at each transformation
Energy efficiency: portion of energy entering system that is transformed into useful form of energy or work
In natural food chains may be as low as 1%; 90% lost at each trophic level
Some ecosystems have an inverted biomass pyramid (natural grasslands, oceans)

16. Pyramid of Energy Flow

17. Energy Flows in Ecological Systems
Biotic Pyramids
Natural food chains are inefficient because
Only 10–20% of biomass is converted to food for next level
Assimilated food energy is often low (not all food is digested)
Energy is released as heat during cellular respiration
The longer the food chain, the less efficient
The energy pyramid has important implications for humans
In terms of energy efficiency, it would be better to operate as low on the food chain as possible—as primary consumers or vegetarians

18. Energy Flows in Ecological Systems
Productivity
The rate at which energy is changed into biomass; usually expressed in kilocalories per square metre /year
Gross primary productivity (GPP) is the overall rate of biomass production
Cellular respiration (R), must be subtracted from the GPP to reveal the net primary productivity (NPP); the amount of energy available to heterotrophs
The most productive ecosystems are wetlands and tropical rainforests; the least are deserts, the Arctic and open Ocean
Humans use 40% of all terrestrial NPP for their own use and human population is expected to increase by 40% in the next 50 years

19. Photosynthetic Efficiency =
3.7 x 104
x 100
172 x 104
= 2.15%
Gross Primary Production is the total energy fixed by producers (autotrophs) during photosynthesis
Net Primary Production is the energy stored as biomass (gross production – energy lost as heat in respiration)

20. NPP =
800 kJ m-2year-1
Photosynthetic
efficiency = 1.3%
GPP =
24 x106 kJ m-2year-1
NPP =
69.7 x 103 kJ m-2year-1
NPP =
200 kJ m-2year-1
114 x 103 kJ m-2year-1

21. NPP in Ecologcial Systems

22. Energy Flows in Ecological Systems
Productivity
Measurements can also be made of net community productivity (NCP), including heterotrophic and autotrophic respiration
Over time, natural systems mature towards maximization of NCP
Auxiliary energy flows allow some ecosystems and sites to be very productive
For example, tidal energy in an estuary brings in nutrients and helps dissipate wastes

23. Net Community Productivity

24. Discussion Questions To Be Answered on your Blog Page
Throughout the last hundred years, humans have exerted increasing influence over the environment. How do humans influence the flow of energy through ecosystems, and what are some of the impacts of this?
Given what you have learned about the transformation of energy, how might a vegetarian diet reduce the pressures on ecosystems?
Why are some of the most productive ecosystems at greatest risk from human disturbances? What are the kinds of human activities that lead to these disturbances?