• Ecology.

• Ecosystem dynamics involve two processes: energy flow and chemical cycling.

• We will Quickly follow the flow of energy by grouping species into trophic levels of feeding relationships.

CHAPTER 41 ECOSYSTEMS

Food Webs & Food Chains

• Food chains follow who eats whom: sun -> grass -> cow -> mansun -> oats -> mice -> cat.

• Food webs show interactions in a community, i.e. cows eat grass & oats, cats eat mice & cows, man eats oats, cows, etc.

• Simple food chain shown here.

• The autotrophs, primary producers, are photosynthetic (green plants, algae, microbes).

• Use light energy to synthesize sugars & other molecules, obtaining chemical nutrients fr/ soil/water.

• A few chemosynthetic autotrophs use chemicals instead of light to make sugar (bacteria, sea vents).

• Heterotrophs, consumers, depend on producers to obtain their energy/food & chemicals (animals, decomposers, microbes).

An ecosystem’s energy flow & chemical cycling derive from trophic relationships.

• Energy/food flow thru an ecosystem, (red arrows).

• Chemical nutrient cyling (blue arrows).

• Here, all energy starts from the sun & most is lost as heat.

Figure is a copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Primary consumers are herbivores that eat primary producers.

• Secondary consumers are carnivores that eat herbivores.

• Tertiary consumers eat secondary consumers; higher order consumers possible but rare (carnivores).

• Another important group of heterotrophs are the detritivores and decomposers.

• They get energy from detritus (dead matter) and are important in chemical recycling in the ecosystem.

• They return chemical nutrients in dead matter back to the soil for use by primary producers.

• Primary production -the amount of light energy converted to chemical energy (sugar) by primary producers.

• Only ~1% of sunlight reaching the Earth is converted to chemical energy. The rest is reflected back or converted to heat.

• Although only a small amount of the total, primary production makes about 170 billion tons of organic material/year.

Primary Production In Ecosystems

Energy Conversions in Ecosystems (Quick)

• Plants convert light energy into chemical energy (sugar) and sugar into new biomass.

• Consumers convert the chemical energy in food to make their new biomass.

• In these conversions, most energy is lost as heat. The efficiency of energy transfer between trophic levels is usually about 10%.

Ecological Pyramids -represent the percentage of production transferred from one trophic level to the next. Energy is shown here and is lost at each trophic level.

Ecological pyramids may use biomass, numbers or energy to display the trophic levels.

•Pyramids narrow sharply from bottom to top because energy transfers are inefficient (~10%).

Figure is a copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• The dynamics of energy through ecosystems have important implications for the human population.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Food Chain Review

• Food Chains & Food Webs

• Food Chains (Nasa says it’s a food web)

Student Presentations

• The next 7-9 slides, student individuals or groups will present:

• First, understand the topic of the slide by doing your reading

• Present the slide(s) to the class. Do not make more slides.

• Nutrients recirculate in ecosystems; three cycles of importance:

1. The carbon cycle.2. The nitrogen cycle.3. The water cycle.

• The rates of nutrient recycling in ecosystems depends on the rates of decomposition.

• May be 50+ years in the tundra or desert.• May be 2 years in a tropical rainforest.

The Cycling of Chemical Nutrients

The Carbon Cycle

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The Nitrogen Cycle

The Water Cycle

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Disrupting nutrient cycles by removing nutrients from one part of the biosphere, adding them to another. Especially from agriculture.

• Doubled the worldwide supply of fixed nitrogen from the use of fertilizers, growing legumes, and burning. May increase nitrogen oxides in the atmosphere, contribute to atmospheric warming, depletion of ozone, and acid rain.

• Deforestation link: Deforest.

Human disruption of chemical cycles

• Burning fossil fuels releases sulfur & nitrogen oxides that react with water to produce acids.

• These acids fall back to earth as acid rain, changing the pH of the soil and water, killing plants and aquatic organisms.

Acid Precipitation

Figure is a copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Global Warming from Greenhouse Gases

Since the Industrial Revolution burned fossil fuels, the atmospheric concentration of CO2 has increased 30% as of 2007. Temps have risen.

Atmospheric Carbon Dioxide Over Time

• The range of the American Beech can be predicted under 2 climate-change scenarios.

Biological magnification

• Applies to fat soluble toxins, accumulates in fat

• Becomes increasingly concentrated in higher levels of the food chain

• Shows the importance of food chains

One Consequence of Global Warming

• Flooding

• Less ice, more …

• Water expands ...

• Animation

• Ch2 -Chemistry