Chapter 56

Ecosystems and

Global Ecology

Compartments of the Global Ecosystem

• Earth is a closed system with respect to matter, but open with respect to energy.

• Many of these processes are cyclic.

Earth’s unusual features:

• Life, oceans, moderate surface temperature, continental drift, a large moon.

• The moon stabilizes the tilt of Earth on its axis. The degree of tilt strongly influences climate. It also produces tides, and slows Earth’s rotation.

Compartments of the Global Ecosystem

• The physical environment can be divided into four compartments: - Oceans- Freshwaters- Atmosphere- Land

• The compartments and the types of organisms living in them are very different.

Compartments of the Global Ecosystem

Oceans• Over very long time scales, most materials that cycle

through the four compartments end up in the oceans.

• Oceans exchange materials with the atmosphere only at their surface, respond slowly to inputs, receive material from land in river runoff, and mix slowly.

Compartments of the Global Ecosystem

• Materials from other compartments sink to the ocean floor and remain for millions of years, until being uplifted by mountain-building events.

• Upwelling zones - Most fisheries are in upwelling zones.

Compartments of the Global Ecosystem

Fresh waters• Rivers, lakes, groundwater

(water in soils and rocks).• Water moves rapidly

through this compartment. Mineral nutrients enter through weathering of rock.

• In lakes, nutrients taken up by aquatic organisms end up as part of the sediments.

Compartments of the Global Ecosystem

Atmosphere• A thin layer of gases surround Earth; 78 percent

N2, 21 percent O2, 1 percent argon, and 0.03 percent CO2.

• The CO2 is the source of carbon used by terrestrial plants, and dissolved carbonate used by marine producers.

• Lowest layer―troposphere―has 80 percent of the air molecules.

Compartments of the Global Ecosystem

• Most global air circulation and all water vapor is in the troposphere.

• The stratosphere extends out to about 50 km.

• A layer of ozone in the stratosphere absorbs most of the biologically-damaging UV radiation from the sun.

Compartments of the Global Ecosystem

• The atmosphere plays a role in regulating Earth’s temperature.

• Atmosphere is transparent to visible light, but traps some of the heat radiated back to space. H2O, CO2, and other greenhouse gases trap the heat energy.

• Human-caused increases in these gases is contributing to global warming.

Compartments of the Global Ecosystem

Land• Elements move slowly on land.

• The terrestrial compartment is connected to the atmospheric compartment by organisms that remove and release elements.

• Soil types depend on type of parent rock, climate, topography, and organisms. Nutrients leach out over time, reducing soil fertility.

Compartments of the Global Ecosystem

Energy Flow• Solar energy is the main

energy source for all but a few types of ecosystems (caves, deep-sea hydrothermal vents).

• Fossil fuels are reserves of solar energy stored in the remains of organisms that lived millions of years ago.

• Solar energy enters ecosystems via plants and other photosynthesizers.

• Gross primary productivity: rate at which energy is incorporated into photosynthesizers.

• The accumulated energy is gross primary production.

• Producers use some of this production for their own metabolism; the rest is stored. The amount available for primary consumers is net primary production.

Energy Flow

• Different types of ecosystems have different rates of production.

Energy Flow

Figure 56.6 Primary Production in Different Ecosystem Types (Part 1)

Figure 56.6 Primary Production in Different Ecosystem Types (Part 2)

Figure 56.6 Primary Production in Different Ecosystem Types (Part 3)

• Primary production tends to be highest near the equator, where temperatures are warm and moisture is plentiful all year long.

• In places where plant growth is limited by moisture or temperatures, production is less.

• Production in aquatic systems is limited by light, which decreases with depth.

Energy Flow

Figure 56.7 Net Primary Production of Terrestrial Ecosystems

• Human activities modify energy flow.

• Converting forests to grassland and urban areas decreases net primary productivity.

• Use of fossil fuels supplements solar energy.

• Humans appropriate 20 percent of the average annual net productivity of Earth.

Energy Flow

Global Ecosystem Cycle• The movements of elements through organisms

to the physical environment and back again are called biogeochemical cycles.

• The hydrologic cycle is the cycling of water.

Global Ecosystem Cycle

• Carbon cycle All organisms are made of carbon compounds.

Global Ecosystem Cycle

• Fossil fuels resulted from the burial of animals in anaerobic environments—organic molecules were not broken down by detritivores, but accumulated.

• Fossil fuel burning has increased dramatically. CO2 is being released into the atmosphere faster than it can be dissolved in oceans and taken up by organisms.

Global Ecosystem Cycle

Figure 56.11 Atmospheric Carbon Dioxide Concentrations Are Increasing

• The buildup of atmospheric CO2 is warming Earth.

• The oceans have been absorbing a lot of heat energy.• The upper 100–200 meters have warmed dramatically, and

warming has penetrated as far as 700 meters deep in some areas.

Global Ecosystem Cycle

• Computer models are used to predict consequences of a doubling in atmospheric CO2 concentration.

• Increase in mean annual temperatures; increased drought in some areas, increased precipitation in others; melting ice caps and glaciers; sea level rise; increased number and intensity of tropical storms.

• Diseases may proliferate. Winter cold typically kills many pathogens.

• Warming may allow some diseases to become more common in temperate regions.

Global Ecosystem Cycle

• Nitrogen cycle N2 gas makes up 78 percent of the atmosphere

Global Ecosystem Cycle

• Effects of increased N fixation:

- Nitrate contamination of groundwater, the greenhouse gasses N2O and tropospheric ozone, smog.

- Eutrophication can result from excess nitrogen in runoff.

Global Ecosystem Cycle

• Phosphorus cycle Phosphorus is an essential nutrient for DNA, RNA, ATP, and phospholipids.

Global Ecosystem Cycle

• Phosphorus is mined and used to make fertilizers and animal feed.

• Phosphorus is now accumulating in soils, and can result in increased runoff which can cause eutrophication.

• Excess nutrients in water stimulates the growth of algae and other photosynthesizers.

Global Ecosystem Cycle

Ecosystems Services

• Humans have modified ecosystems to increase production of some services, especially food, timber, fuel, etc.

• These benefits have not been equally distributed; some people, and many other species, have been harmed by these modifications.

Figure 56.22 Some Ecosystem Types Have Suffered Extensive Losses

Ecosystems SustainablySome barriers to sustainable management include:

• Education of people on the importance of ecosystems and their services.

• Recognition that long-term goals of sustainability are more valuable than profits in the short term.

• Government action may be needed to provide incentives for sustainable ecosystem management.

• Implementing the many options that exist for sustainable management will not be easy.

Ecosystems Sustainably