Ecosystem Processes

Thinking Question: While browsing through the drinks offered at a convenience store, you notice a new soft drink advertised as a “low-calorie energy drink.” Write out your definition of “energy,” and then decide if this drink label is accurate or a case of false advertising.

Energy Energy is defined as the ability to do work. Energy is NOT a material. Energy is a phenomenon. Energy can be transformed (i.e. mechanical to heat) and transferred, but is not recycled.

Energy flows Energy for most ecosystems on earth comes from the sun. Light energy is converted to chemical energy by producers to power their own metabolism. Energy is lost from the earth as heat.

Nutrients “Nutrient” in an ecological sense refers to the inorganic materials taken in by producers and converted into organic molecules. Nutrients include carbon (as carbon dioxide), nitrogen, phosphorous, oxygen, and other building blocks of biological molecules.

Nutrients Cycle Because nutrients ARE materials, they cycle in the earth’s ecosystems. Carbon from carbon dioxide may become carbon in a sugar made by a plant. Decomposers break down organic molecules and release inorganic nutrients to the ecosystem.

Photosynthesis Energy is converted and nutrients are fixed by the process of photosynthesis. Producers use the sun’s energy to convert inorganic carbon dioxide into organic molecules, such as sugars.

Net Productivity Net primary productivity is the energy that producers can make available to a community at any one time. Net productivity determines how much life an ecosystem supports. Productivity can be measured in calories (units of energy) or biomass (amount of organic material).

Biomass (g/m 2 )

Thinking question discussion So what about that “low-calorie energy drink?”

Energy Flows

Thinking Question: One reason that some people become vegetarians is to reduce their impact on the environment. List as many positive ecological effects of vegetarianism as you can think of. Then list as many negative effects.

Food Chain Concept Chemical energy is passed through the ecosystem as organisms consume other organisms. Organisms occupy one or more trophic levels (“feeding” levels) depending on what they are eating.

Trophic Levels Producers: Use light energy to manufacture organic molecules. Primary consumers: eat producers Secondary consumers: eat primary consumers Tertiary consumers: eat secondary consumers.

Food Webs A food web is a model of energy flow in a community. Arrows indicate the direction in which energy flows from one organism to the next. (Note that this is NOT a cycle.) A single organism will be involved in many food chains, and some will occupy several trophic levels.

“Death Eaters” Decomposers: Bacteria and fungi, which use external digestion to break organic matter down into inorganic substances. Detritivores: Animals that feed on dead plant material. Scavengers: Animals that feed on dead animal flesh.

Energy Loss At each step in a food chain or food web, energy is lost as heat. Each organism takes in energy to meet its own needs, so most of the energy taken in is converted to motion and heat. 10% or less of the energy consumed will be available to the next consumer.

Energy Pyramid Because 90% or more of consumed energy is used by the organism, and only a small amount can be passed on, the entire system is inefficient. The higher an organism is on the food chain, the greater amount of biomass is required to support that organism.

Humans are omnivores, capable of eating a wide variety of foods. We can create a human food chain by looking at our meat sources. Human Food Chain

Grass-fed Food Chain A cow can convert grass, which we cannot eat, into meat, which we can. We obtain 8-10% of the energy that a pasture-fed cow consumes.

Industrial Food Chain Corn, which could be fed to humans, is fed to feedlot cattle. Because of overproduction, corn is cheap. A cow’s digestive system is not adapted to eating corn. The cattle are often sick, and much of the energy is wasted. Cheap burgers come at a high ecological cost. The industrial food chain is about 1/3 as efficient as the grass food chain.

Thinking question discussion What are possible positive and negative effects of “going veggie?” How can your everyday food choices have an impact on the environment?

Nutrients Cycle

Thinking Question: Global climate change has everyone’s attention these days. One action that some people take in response is to plant trees. What does planting trees have to do with alleviating global climate change?

Material Cycles Material cycling follows the law of conservation of matter. Elements used by living organisms are taken up and used by producers, used passed down the food chain by consumers, and are released back to the environment by decomposers.

Nitrogen Cycle The earth’s atmosphere is 78% nitrogen, but in this form it cannot be used by producers. Nitrogen-fixing bacteria convert nitrogen gas into nitrogen compounds that plants can absorb and use in making amino acids to build proteins.

Nitrogen Cycle

Phosphorous Cycle Unlike other nutrients, phosphorous does not exist as an atmospheric gas. Rock phosphates dissolve in rain as rock weathers, carrying phosphates into streams and soil. Phosphates settle out on the bottoms of ponds, and may consolidate back into phosphate-rich rock.

Phosphorous Cycle

Water Cycle Weather patterns form part of the water cycle. Water remains chemically unchanged during the water cycle. It is evaporated as water vapor, condensed into rain clouds, and finally falls as precipitation. Water may collect in rocks as groundwater.

Water Cycle

Carbon Cycle Carbon forms the backbone of all organic molecules. Carbon from the atmosphere is “fixed” by producers, which manufacture organic molecules using the sun’s energy. Breakdown of these molecules releases carbon dioxide back to the atmosphere.

Carbon Cycle

Global “Warming” “Global Warming” — better termed “Global Climate Change” — has been strongly linked to levels of carbon dioxide in the atmosphere. While natural events add carbon dioxide to the atmosphere, humans activity also contributes to carbon levels.

Fossil Fuels Fossil fuels are the remains of ancient swamps. Plants fixed carbon as carbon- rich organic compounds. Carbon compounds accumulated in swamps over hundreds of millions of years. In less than 200 years, humans have burned nearly half of the world’s fossil fuels.

Greenhouse Effect

Carbon and Temperature

Future Trends? The outcome depends on what happens to the west Antarctic ice shelf.

Current Effects

Thinking question discussion What do trees have to do with global climate change? In what other ways can people reduce their carbon footprint?

Big, scary question: Is the “typical American lifestyle” ecologically sustainable?