Chapter 55 Ecosystems Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

The second law of thermodynamics states that entropy must always increase with every energy transaction. This directly implies that ecosystems cannot accumulate high-value sources of energy. energy cannot be converted into matter. complex ecosystems cannot evolve from simple ecosystems. in any energy transaction, some of the energy is lost, typically as heat. entropy controls succession. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Unlike energy, matter cycles. This means that an ecosystem cannot lose chemicals from it. we can always find new sources for chemicals. when we build models of a chemical in an ecosystem, we should be able to account for all of the chemical. matter is being continually converted into heat and back into matter. chemicals contain energy but energy doesn’t contain chemicals. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Gross primary productivity is higher than net primary productivity Gross primary productivity is higher than net primary productivity. The difference between the two is the amount of energy producers burn when they metabolize. typically the ratio between the biomass of producers and the biomass of consumers. an important measure of ecosystem productivity. energy that is lost into outer space due to physiological inefficiencies. untapped energy that is stored in plant roots. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Why are big, fierce animals rare Why are big, fierce animals rare? Most big, fierce animals are tertiary consumers, which implies that typically, they are highly territorial. it’s hard for an ecosystem to support many of them because so much energy is lost at each level of energy exchange. humans have caused most big, fierce animals to become extinct. it takes a long time for big animals to evolve, and the K-T evidence for an ancient meteor strike eliminated dinosaurs and most other big, fierce animals. it’s hard for a big animal to move through dense vegetation. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

respiration, decomposition, and excretion Look at the diagram (Figure 55.13 in the textbook), a general model of nutrient cycling. There are major differences between kingdoms of organisms; for example, plants tend to do most assimilation and photosynthesis. However, all living things contribute to one of the arrows on this diagram. Which one is done by every living thing? weathering respiration, decomposition, and excretion photosynthesis fossilization combustion Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

denitrifying bacteria. nitrogen-fixing bacteria. legumes. Look at the nitrogen cycle on page 1233 of the textbook. 80% of our atmosphere is nitrogen gas, yet every year farmers spray ammonia manufactured from natural gas on their fields as a fertilizer. This is because the only way to convert nitrogen from a gas into an available form is done by decomposers. nitrifying bacteria. denitrifying bacteria. nitrogen-fixing bacteria. legumes. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

This figure (Figure 55.18 in the textbook) shows the dead zone in the Gulf of Mexico. The dead zone is larger in the summer than in the winter. This is probably because temperatures are cooler in the winter. less water flows down the Mississippi in the winter. there is more nitrogen and other nutrients being delivered to the Gulf of Mexico in the summer. decomposition of leaf litter is lower in the winter. hurricanes are more likely in the summer. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

We can conclude several things from this figure (Figure 55 We can conclude several things from this figure (Figure 55.21 in the textbook), including scientists believed the top of Mauna Loa was a good place to measure carbon dioxide. over the 50 years of data, carbon dioxide concentrations have increased. over the 50 years of data, average global temperatures have increased. there was more variation in temperature than in carbon dioxide concentrations. all of the above Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

We are concerned about carbon dioxide increases in our global atmosphere. Imagine that we planted trees over a large area to grow into a forest perhaps the size of Australia. Would this be a good way to stop or slow the accumulation of carbon dioxide in the atmosphere? No, because plants release carbon dioxide when they do photosynthesis. Yes, because the trees would convert carbon dioxide into wood. Perhaps, but when the trees died and decayed, the carbon dioxide would be returned to the atmosphere. It is unlikely that plants could make much difference in global air concentrations. Yes, because it would show the world we were serious about stopping global warming. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Because decomposition is slow when it is cold, boreal forests, tundras, and peatlands have stored enormous quantities of carbon. Scientists are concerned that warmer temperatures will increase decomposition rates, putting even more carbon dioxide into the atmosphere. warmer temperatures will shift these biomes further south, resulting in even more accumulation of carbon-containing compounds. warmer temperatures will increase the growth of plants in these biomes, resulting in even more accumulation of carbon- containing compounds. warmer temperatures will remove keystone predators and destabilize these biomes, resulting in unpredictable changes to carbon emissions. all of the above Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.