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”)

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 Figure 37.10

Includes a community and the abiotic factors with which it interacts. 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 Light energy Chemical elements Heat Figure 37.11

Each day Earth receives energy from the sun 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 produce170 billion tons of organic material per year.

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

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 Cultivated land Boreal forest (taiga) Savanna Temperate deciduous forest Tropical rain forest 500 1,000 1,500 2,000 2,500 Average net primary productivity (g/m2/yr) Figure 37.12 Desert and semidesert scrub Contributes most to Earth’s total net production due to its size

Energy supply limits the length of food chains A pyramid of production Shows the flow of energy from producers to primary consumers and to higher trophic levels 1/1000 of the sun’s energy makes it this far Tertiary consumers Secondary consumers Primary Producers 10 kcal 100 kcal 1,000 kcal 10,000 kcal 1,000,000 kcal of sunlight Can’t eat all Can’t digest all 2/3 digested used by cells Rest to mass (growth) Only this can be eaten by next level. (1% of sun’s energy) Figure 37.13

Limited by availability of energy 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

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 Producers Human vegetarians Corn meat-eaters Cattle Figure 37.14

Chemicals are recycled between organic matter (organisms) and abiotic reservoirs Biogeochemical cycle Consumers Producers Nutrients available to producers Abiotic reservoir Detritivores 3 2 1 4 Decomposers Figure 37.15 Soil

Water moves through the biosphere in a global cycle Transport over land Solar energy Net movement of water vapor by wind Runoff and groundwater Percolation through soil Precipitation over land Evaporation and transpiration from land Precipitation over ocean Evaporation from ocean Solar heat drives the global water cycle through precipitation, evaporation, and transpiration Figure 37.16

Human activity affects the global water cycle 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) Pumping large amounts of ground water to the surface for irrigation can increase evaporation and deplete ground water supplies.

The carbon cycle relies on photosynthesis, respiration, and decomposition Carbon compounds (organic) are consumed. Respiration returns CO2 to the atmosphere. Photosynthesis = Respiration Burning fossil fuels is increasing CO2 levels and is causing global warming.

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 N2 to compounds that plants use: ammonium (NH4+) and nitrate (NO3–) Detritivores decompose organic matter and recycle nitrogen to plants. Figure 37.18

Humans are altering the nitrogen cycle Humans are altering the nitrogen cycle Sewage treatment facilities often empty large amounts of nitrogen into rivers and streams 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

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 is limited. 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.