Chapter 29. How Do Ecosystems Work? Lectures by Gregory Ahearn. Ammended by John Crocker. University of North Florida

Transcription

1 Chapter 29 How Do Ecosystems Work? Lectures by Gregory Ahearn University of North Florida Ammended by John Crocker Copyright 2009 Pearson Education, Inc..

2 29.1 How Do Ecosystems Obtain Energy And Nutrients? The activities of life are powered by the energy of sunlight. Solar energy is captured in ecosystems by photosynthetic organisms transformed and ultimately converted to heat energy that radiates back into space. Energy moves through ecosystems in a continuous, one-way flow, and is constantly replenished from outside by the sun. Because of this constant flow of energy from an outside source ecosystems can both thrive and obey the laws of thermodynamics

3 29.1 How Do Ecosystems Obtain Energy And Nutrients? In contrast to energy, nutrients are not replenished. Nutrients are elements and small molecules that form the chemical building blocks of life. Nutrients are transported, redistributed, and converted to different molecular forms, but do not leave Earth; they are recycled within and among ecosystems.

4 29.1 How Do Ecosystems Obtain Energy And Nutrients? An ecosystem consists of all of the communities within a defined area, along with the aabiotic environment. Ecological study of ecosystems focuses on flows of energy and nutrients. Ecosystem ecologists follow the pathways of energy and nutrients to understand the factors that shape the complex interactions within communities, and between communities and the abiotic environment.

5 producers HEAT Energy from sunlight HEAT NUTRIENTS primary consumers detritus feeders and decomposers HEAT solar energy higher-level consumers heat energy energy stored in chemical bonds nutrients HEAT Fig. 29-1

6 29.2 How Does Energy Flow Through Ecosystems? Hydrogen molecules in the sun fuse to form helium molecules, releasing tremendous amounts of energy. A tiny fraction of this energy reaches Earth, arriving in the form of electromagnetic waves including heat, light, and ultraviolet energy. Much of the energy reaching Earth is absorbed or reflected back into space by Earth s atmosphere, clouds, and surface. Only about 1% of the solar energy that reaches Earth makes it to the surface as light that is available to power life.

7 29.2 How Does Energy Flow Through Ecosystems? Energy enters ecosystems mainly through photosynthesis. During photosynthesis, solar energy powers reactions that store energy in the chemical bonds of sugar and other high-energy molecules. Photosynthetic organisms produce food for themselves, using nonliving nutrients and sunlight. Organisms that can produce their own food are called autotrophs, or producers.

8 29.2 How Does Energy Flow Through Ecosystems? Photosynthesis Energy is captured from sunlight Oxygen is released Carbon dioxide is absorbed from the air photosynthesis Sugar is synthesized and used in plant tissues plant tissues, growth Water is absorbed from soil, used in photosynthesis, and stored in cells Inorganic mineral nutrients (nitrate, phosphate) are absorbed from soil and used in plant tissues Fig. 29-2

9 29.2 How Does Energy Flow Through Ecosystems? By manufacturing food for themselves producers directly or indirectly produce food for nearly all other organisms as well. Organisms that cannot produce their own food are called heterotrophs, or consumers. Heterotrophs must acquire energy and many of their nutrients from other organisms.

10 29.2 How Does Energy Flow Through Ecosystems? Energy captured by producers is available to the ecosystem. The amount of life that a particular ecosystem can support is determined by the amount of energy captured by the producers in that ecosystem. The energy that producers store and make available to other organisms is called net primary productivity. Net primary productivity is measured as the biomass added by producers per unit area over a given time.

11 29.2 How Does Energy Flow Through Ecosystems? Energy captured by producers is available to the ecosystem (continued). Net primary productivity of an ecosystem is influenced by many environmental variables amount of nutrients available amount of available sunlight availability of water temperature In deserts, productivity is low due to lack of water; in the open ocean productivity is limited because nutrients are lost to deeper water.

12 29.2 How Does Energy Flow Through Ecosystems? An ecosystem s overall contribution to the Earth s productivity depends upon both the ecosystem s net primary productivity per unit area and the area it covers. In ecosystems with abundant resources productivity is high. ex/ tropical rain forests and estuaries. Rain forests and the open ocean each account for about a quarter of the planet s total productivity Oceans are much less productive per unit area but cover 65% of the Earth Tropical rainforests cover only about 4% but are fantastically productive

13 29.2 How Does Energy Flow Through Ecosystems? Ecosystem productivities compared. open ocean (125) estuary (1,500) continental shelf (360) tundra (140) tropical rain forest (2,200) coniferous forest (800) temperate deciduous forest (1,200) grassland (600) desert (90) Fig. 29-3

14 29.2 How Does Energy Flow Through Ecosystems? Energy passes from one trophic level to another. Energy flows through communities from producers at the first trophic level, through several levels of consumers. Primary consumers (herbivores) feed directly on the producers and form the second trophic level. The third and fourth trophic levels are the secondary and tertiary consumers, and consist of meat-eating predators.

15 29.2 How Does Energy Flow Through Ecosystems? Feeding relationships within ecosystems form chains and webs. It is common to identify a representative of each trophic level such that each representative species eats another on the level below it. This linear feeding relationship is called a food chain. Different ecosystems have radically different food chains.

16 29.2 How Does Energy Flow Through Ecosystems? A simple terrestrial food chain TERTIARY CONSUMER (4th trophic level) PRIMARY CONSUMER (2nd trophic level) PRODUCER (1st trophic level) SECONDARY CONSUMER (3rd trophic level) (a) A simple terrestrial food chain Fig. 29-4a

17 29.2 How Does Energy Flow Through Ecosystems? A simple marine food chain SECONDARY CONSUMER (3rd trophic level) Phytoplankton PRODUCER (1st trophic level) Zooplankton PRIMARY CONSUMER (2nd trophic level) TERTIARY CONSUMER (4th trophic level) (b) A simple marine food chain Fig. 29-4b

18 29.2 How Does Energy Flow Through Ecosystems? In natural communities, the actual feeding relationships form a food web of many interconnected food chains. Some animals act as primary, secondary, and tertiary consumers (omnivores). Many carnivores eat both herbivores and other carnivores, and act as both secondary and tertiary consumers.

19 Fig. 29-5

20 29.2 How Does Energy Flow Through Ecosystems? Detritus feeders and decomposers release nutrients for reuse. The detritus feeders are an army of mostly small and often unnoticed animals and protists that live on the refuse of life molted exoskeletons, fallen leaves, wastes, and dead bodies. The network of detritus feeders is complex, and on land, it may consist of earthworms, mites, protists, centipedes, insects, pillbugs, nematodes, and a few large vertebrates (vultures etc).

21 29.2 How Does Energy Flow Through Ecosystems? Detritus feeders and decomposers release nutrients for reuse (continued). These organisms consume dead organic matter, extract some of the energy stored in it, and excrete it in a further decomposed state. Their excretory products serve as food for other detritus feeders and for decomposers.

22 29.2 How Does Energy Flow Through Ecosystems? The decomposers are primarily fungi and bacteria. Decomposers digest food outside their bodies by secreting digestive enzymes into the environment. They then absorb the nutrients they need, and the remaining nutrients are released into the environment.

23 29.2 How Does Energy Flow Through Ecosystems? Detritus feeders and decomposers are absolutely essential to life on Earth. Their activities reduce the bodies and wastes of other organisms to simple molecules, such as carbon dioxide, water, minerals, and organic molecules, which return to the atmosphere, soil, and water. They perform the vital role of nutrient recycling.

24 29.2 How Does Energy Flow Through Ecosystems? Energy transfer through trophic levels is inefficient. When a caterpillar (a primary consumer) eats the leaves of a tomato plant (a producer), only a portion of the solar energy originally trapped by the plant is available to the insect. Only a small fraction of the energy captured by the first trophic level is available to organisms in the second trophic level. Some of the original energy was used by the plant for growth and maintenance, and some was converted into the chemical bonds of molecules such as cellulose.

25 29.2 How Does Energy Flow Through Ecosystems? Energy transfer through trophic levels is inefficient (continued). Additional energy is lost in each transfer to a higher trophic level. Some of the energy consumed by the caterpillar is used to power crawling and chewing, and some is given off as heat. All of that energy is unavailable to a bird that eats that caterpillar. Energy flow through different trophic levels may be illustrated by a deciduous forest ecosystem.

26 29.2 How Does Energy Flow Through Ecosystems? Energy transfer and loss in a forest HEAT heat energy stored in chemical bonds producer primary consumer secondary consumer detritus feeders and decomposers HEAT Fig. 29-6

27 29.2 How Does Energy Flow Through Ecosystems? Energy pyramids illustrate energy transfer between trophic levels. About 90% of the energy stored at a trophic level is lost in the transfer to the next level. Therefore, the energy stored by an ecosystem s primary consumers is only about 10% of the energy stored in the bodies of producers. This inefficient energy transfer between tropic levels is called the 10% law.

28 29.2 How Does Energy Flow Through Ecosystems? Energy pyramids illustrate energy transfer between trophic levels (continued). An energy pyramid, which shows maximum energy at the base and steadily diminishing amounts at higher levels, illustrates the energy relationships between trophic levels. Energy pyramids also show why producers are the most abundant organisms in an ecosystem and carnivores the rarest.

29 29.3 How Do Nutrients Move Within And Among Ecosystems? Unlike the energy of sunlight, nutrients are not continuously supplied to Earth in a steady stream from above. The same pool of nutrients has been supporting life for more than 3 billion years. Macronutrients, required by organisms in large quantities, include carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, and calcium. Micronutrients, including zinc, molybdenum, iron, selenium, and iodine, are only required in trace quantities.

30 29.3 How Do Nutrients Move Within And Among Ecosystems? Nutrient cycles (biogeochemical cycles) describe the pathways that substances follow as they move through communities to the nonliving portions of the ecosystem and then back again to communities. Storage sites for nutrients are called reservoirs. For example, carbon s reservoirs are as carbon dioxide in the atmosphere, solutes in the ocean, stored fossil fuels, and other organic matter protected from decay.

31 29.3 How Do Nutrients Move Within And Among Ecosystems? Carbon cycles through the atmosphere, oceans, and communities. Carbon enters the living part of the ecosystem when producers capture CO 2 during photosynthesis and incorporate its carbon atoms in organic molecules. Primary consumers, such as rabbits, shrimp, and grasshoppers, eat the producers and acquire the carbon stored in their tissues. Producers and consumers die, and the carbon in their bodies is returned to the reservoirs by decomposers.

32 reservoirs processes trophic levels respiration CO 2 dissolved in the ocean CO 2 in the atmosphere burning of fossil fuels photosynthesis fire consumers producers decomposition of wastes and dead bodies soil bacteria and detritus feeders fossil fuels limestone Fig. 29-8

33 29.3 How Do Nutrients Move Within And Among Ecosystems? The major reservoir for nitrogen is the atmosphere. The atmosphere contains 79% nitrogen gas (N 2 ), and is thus the major reservoir for this nutrient. Nitrogen enters the food web mainly through certain bacteria in soil and water that engage in nitrogen fixation, a process in which nitrogen and hydrogen are combined to form ammonia (NH 3 ). The ammonia is converted into nitrate (NO 3 ).

34 29.3 How Do Nutrients Move Within And Among Ecosystems? The major reservoir for nitrogen is the atmosphere (continued). Plant roots can absorb ammonia and nitrate, and plants incorporate the nitrogen from these molecules into amino acids, proteins, nucleic acids, and some vitamins. As nitrogen passes through the food web, some is returned to soil or water when decomposer bacteria convert wastes and dead bodies back to nitrate and ammonia. Atmospheric nitrogen is replenished by denitrifying bacteria, which break down nitrate, releasing nitrogen gas back into the atmosphere.

35 nitrogen in the atmosphere burning fossil fuels produces nitrogen oxides electrical storms produce nitrate reservoirs processes trophic levels/ organisms producers consumers application of manufactured fertilizer decomposition of wastes and dead bodies denitrifying bacteria uptake by plants soil bacteria and detritus feeders nitrogen-fixing bacteria in legume roots and soil ammonia and nitrate in soil and water Fig. 29-9

36 29.3 How Do Nutrients Move Within And Among Ecosystems? The major reservoir for phosphorus is rock. The phosphorus cycle does not include the atmosphere. The reservoir for phosphorus in ecosystems is rock, where phosphorus is bound to oxygen to form phosphate. Dissolved phosphate is readily absorbed through the roots of plants and is passed on to other organisms through the food web. Phosphorus is important in ATP and NADP, nucleic acids, and the phospholipids of membranes.

37 reservoirs processes trophic levels phosphate in rock geological uplift consumers runoff from rivers producers runoff from fertilized fields detritus feeders phosphate in soil phosphate in water phosphate in sediment Fig

38 29.3 How Do Nutrients Move Within And Among Ecosystems? Phosphorus in the living part of ecosystems is eventually returned to the nonliving parts. Organisms excrete excess phosphate into their surroundings, and decomposers return phosphate from dead bodies back to the soil and water. Some of the phosphate that dissolves in fresh water is carried to the oceans, and may be absorbed by marine producers. From marine producers, the phosphate may travel along a marine food web.

39 29.3 How Do Nutrients Move Within And Among Ecosystems? Water remains unchanged during the water cycle. The hydrologic cycle differs from most other biogeochemical cycles in that most water is not incorporated into other molecules during the cycle. The major reservoir of water is the ocean. The hydrologic cycle is driven by solar energy evaporating water and by gravity drawing the water back to Earth as precipitation. A small amount of this water is incorporated into the living parts of the ecosystem.

40 reservoirs processes water vapor in the atmosphere precipitation over land evaporation from land and transpiration from plants evaporation from the ocean precipitation over ocean lakes and streams runoff from land surface water in the ocean groundwater Fig

41 29.4 What Happens When Humans Disrupt Nutrient Cycles? Many of the environmental problems that plague modern society are caused by human disruption of biogeochemical cycles. Some disruptions are direct, as when industrial processes transfer toxic substances such as lead, arsenic, mercury, uranium, and oil from their normal reservoirs into the environment. Other human-caused cycle disruptions, such as addition of herbicides and pesticides to lawns and shrubs, have more indirect effects.

42 29.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the phosphorus and nitrogen cycles damages aquatic ecosystems. In farm fields, gardens, and suburban lawns, ammonia, nitrate, and phosphate are supplied by chemical fertilizers. This phosphorus is removed from its reservoirs in rocks, converted to phosphate fertilizer, and applied to cultivated land. Similarly, nitrogen is applied to these areas in the form of ammonia and nitrate fertilizers.

43 29.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the phosphorus and nitrogen cycles damages aquatic ecosystems (continued). The soil that erodes from fertilized fields carries large quantities of phosphorus and nitrogen into lakes, streams, and the ocean. In the water, the nutrients stimulate growth of photosynthetic algae, and when they die, their bodies are consumed by decomposer bacteria that use up most of the oxygen in the water, killing other organisms.

44 29.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading with nitrogen and sulfur cycles causes acid deposition. The combustion of fossil fuels in our cars, power plants, industrial boilers, smelters, and refineries releases sulfur dioxide and nitrogen oxides into the atmosphere. The amounts present can far exceed what natural systems can absorb and recycle. Because of this, the acids fall as acid rain, or more accurately, as acid deposition.

45 29.4 What Happens When Humans Disrupt Nutrient Cycles? Reactions in the atmosphere form acid deposition. When combined with water vapor in the atmosphere, nitrogen oxides and sulfur dioxide are converted to nitric acid and sulfuric acid. The acids fall in rain or snow, eating away at statues and buildings and can render lakes lifeless. Acid rain interferes with the growth and yield of many farm crops by leaching out essential nutrients, such as calcium and potassium, killing decomposer microorganisms, and direct physical damage.

46 29.4 What Happens When Humans Disrupt Nutrient Cycles? Acid deposition can destroy forests. Fig

47 29.4 What Happens When Humans Disrupt Nutrient Cycles? Reactions in the atmosphere form acid deposition (continued). Acid deposition also increases the exposure of organisms to toxic metals, including aluminum, lead, mercury, and cadmium, which are more soluble in acidified water than in neutral ph water.

48 29.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the carbon cycle contributes to global climate change. Much of Earth s carbon is stored in reservoirs such as fossil fuels formed from the buried remains of plants and animals. Over millions of years, the carbon in the organic molecules of these organisms is transformed by high temperature and pressure into coal, oil, or natural gas. Burning fossil fuels transfers the carbon locked in these reservoirs into atmospheric CO 2.

49 29.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the carbon cycle contributes to global warming (continued). Since the Industrial Revolution, humans have increasingly relied on the energy stored in fossil fuels. When we burn them for power CO 2 is released into the atmosphere. The amount of CO 2 in the atmosphere has increased by more than 36% since 1850, from ~280 parts per million (ppm) to ~380 ppm.

50 29.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the carbon cycle contributes to global warming (continued). Deforestation adds CO 2 to the atmosphere by removing a CO 2 sink. When forests are cut and burned or allowed to decompose the carbon stored in the bodies of the trees returns to the atmosphere. Altogether, humans release almost 7 billion tons of CO 2 into the atmosphere each year.

51 heat radiated into space sun sunlight CO 2 methane nitrous oxide atmosphere deforestation heat trapped in the atmosphere power plants and factories forest fires vehicle emissions homes and buildings agricultural activities Fig

52 29.4 What Happens When Humans Disrupt Nutrient Cycles? Greenhouse gases trap heat in the atmosphere. Atmospheric CO 2 acts like glass in a greenhouse allowing solar energy to pass through it to reach Earth s surface then trapping it preventing or slowing its release back into space, resulting in increasing heat content of the atmosphere. Most climate scientists have concluded that this greenhouse effect has been intensified by human activities that produce greenhouse gases such as CO 2 and methane.

53 29.4 What Happens When Humans Disrupt Nutrient Cycles? The average global temperature has increased since 1860, parallel to the increase in CO 2. F C average world temperature CO 2 temperature CO 2 concentration (parts per million by volume) year Fig

54 29.4 What Happens When Humans Disrupt Nutrient Cycles? Global warming will have consequences some of which may be severe. Scientists have documented effects of warming on glaciers and polar ice caps, on weather patterns, and on ecosystems. The speed and magnitude of these changes are expected to increase as warming continues.

55 29.4 What Happens When Humans Disrupt Nutrient Cycles? A global meltdown is underway (continued). As glaciers and polar caps melt, global sea levels rise threatening coastal cities and island nations. Permafrost in northern lands are also melting releasing more organic matter to be decayed adding more carbon and methane. Thawing permafrost also impacts adjacent ecosystems as previously firm ground is now subject to shifting and sliding.

56 29.4 What Happens When Humans Disrupt Nutrient Cycles? Glaciers are melting. Fig

57 29.4 What Happens When Humans Disrupt Nutrient Cycles? Weather is growing more extreme. Scientists predict that global warming will increase the severity of extreme weather events. As the world warms further, droughts in certain areas will likely last longer and be more severe, disrupting agriculture.

58 29.4 What Happens When Humans Disrupt Nutrient Cycles? Ecosystems are affected. On land, plant distributions will change as rainfall and temperature change. Sugar maples may disappear from northeastern U.S. forests while southeastern forests could be partially replaced by grasslands. Coral reefs are likely to suffer damage from warmer waters and increased acidity from dissolved CO 2. Accumulated data from scientific studies around the world provide strong evidence that warming-related biological changes are well underway.