Communities and Ecosystems Trophic structure is a key

Communities and Ecosystems

Trophic structure is a key factor in community dynamics • Every community has a trophic structure –A pattern of feeding relationships consisting of several different levels –The sequence of food transfer from producer to consumer is called a food chain. • Producers are autotrophs (“self feed”) • Consumers are heterotrophs (“different feed”) Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Food chains interconnect, forming food webs • A food web –A network of interconnecting food chains –Arrows indicate direction of nutrient transfer –Several 1° Consumers depend on same producer –Some eat at multiple levels Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Figure 37. 10

Ecosystem ecology emphasizes the processes energy flow and chemical cycling Transfer substances through trophic levels. But one flows out the other cycles within. An ecosystem Includes a community and the abiotic factors with which it interacts. Chemical cycling Energy flow Chemical energy Light energy Heat energy Chemical elements Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Figure 37. 11

Each day Earth receives energy from the sun equivalent to 100 million atomic bombs… Most is absorbed, scattered, and reflected by our atmosphere or by the Earths surface. Only 1% of all the light energy the Earth receives is converted into chemical energy by primary producers through photosynthesis (the process of changing light into sugar and other foods/chemical energy). However, on a global scale this is enough to produce 170 billion tons of organic material per year. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

The amount of living organic material in an ecosystem is its Biomass. The amount of solar energy converted to chemical energy (organic material) by producers in a given area at a given time is called primary production. Primary production Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Primary production sets the energy budget for ecosystems • Is the rate at which producers convert sunlight to chemical energy in organic matter (biomass) Open ocean Estuary Algal beds and coral reefs Tundra Temperate grassland Contributes most to Earth’s total net production due to its size Desert and semidesert scrub Cultivated land Boreal forest (taiga) Savanna Temperate deciduous forest Tropical rain forest 0 Figure 37. 12 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 500 1, 000 1, 500 2, 000 Average net primary productivity (g/m 2/yr) 2, 500

Energy supply limits the length of food chains • A pyramid of production – Shows the flow of energy from producers to primary 1/1000 of the consumers and to higher trophic levels Tertiary consumers sun’s energy makes it this far 10 kcal 100 kcal Secondary consumers Can’t eat all Can’t digest all Primary consumers 1, 000 kcal 2/3 digested used by cells Rest to mass (growth) Producers 10, 000 kcal (1% of sun’s energy) Figure 37. 13 1, 000 kcal of sunlight Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Only this can be eaten by next level.

Only about 10% of the energy stored at each trophic level is available to the next level • Only a tiny amount of the energy converted by primary producers flows through he food chain to the top consumer • This is why top level consumers require so much territory… – It takes a lot of vegetation to support trophic levels so many steps removed from photosynthetic production. • Also why food chains are limited in size – Limited by availability of energy Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

CONNECTION A production pyramid explains why meat is a luxury for humans • A field of corn – Can support many more human vegetarians than meat-eaters (less energy is wasted) Trophic level Secondary consumers Primary consumers Human meat-eaters Human vegetarians Corn Producers Figure 37. 14 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Cattle Corn

Chemicals are recycled between organic matter (organisms) and abiotic reservoirs Biogeochemical cycle 3 Consumers 2 Producers 1 Detritivores 4 Nutrients available to producers Decomposers Figure 37. 15 Soil Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Abiotic reservoir

Water moves through the biosphere in a global cycle Solar energy Solar heat drives the global water cycle through precipitation, evaporation, and transpiration Net movement of water vapor by wind Precipitation over ocean Evaporation from ocean Evaporation and transpiration from land Runoff and groundwater Figure 37. 16 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Transport over land Precipitation over land Percolation through soil

Human activity affects the global water cycle 1) Important source of atmospheric water is transpiration, so destruction of the rain forests will change amount of water in the atmosphere and can alter local and global weather patterns. 2) 2) Pumping large amounts of ground water to the surface for irrigation can increase evaporation and deplete ground water supplies. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

The carbon cycle relies on photosynthesis, respiration, and decomposition Carbon compounds (organic) are consumed. Respiration returns CO 2 to the atmosphere. Photosynthesis = Respiration Burning fossil fuels is increasing CO 2 levels and is causing global warming. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

The nitrogen cycle relies heavily on bacteria Nitrogen is a constituent of DNA and proteins…is essential for life. Various bacteria in soil convert gaseous N 2 to compounds that plants use: ammonium (NH 4+) and nitrate (NO 3–) Detritivores decompose organic matter and recycle nitrogen to plants. Figure 37. 18 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Humans are altering the nitrogen cycle 1) Sewage treatment facilities often empty large amounts of nitrogen into rivers and streams 2) 2) Fertilizer is routinely applied • These nitrogen sources continue to fertilize when they enter lakes and streams causing algae blooms • Nitrates enter ground water used as drinking water and can be toxic Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

The phosphorus cycle depends on rock weathering Phosphorus is needed for nucleic acids (DNA), phospholipids (cell membranes), bones and ATP (energy) It and other soil minerals are recycled locally. Weathering is a slow process so phosphorus Copyright © 2005 Pearson Education, is Inc. Publishing as Benjamin Cummings Figure 37. 19

In aquatic systems that have not been altered by humans the limited amount of phosphorus keeps algae to a minimum. In areas affected by humans (sewage, fertilizers, pesticides) phosphate pollution leads to heavy algal growth. Major algae blooms can kill aquatic organisms and be toxic to humans. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings