Ecosystems THE REALM OF ECOLOGY Biosphere An island ecosystem A desert spring ecosystem Biosphere Ecosystem Ecology: Interactions between the species in a given habitat and their physical environment. Community Population Organism Ecosystems Communities Populations Organisms Figure 55.2 Factors that Limit Communities Abiotic (nonliving) Limiting Factors Temperature Water Soil type light Salinity Wind stress Altitude, depth The two main ecosystem processes: Energy flow and Chemical cycling Biotic (living) Limiting Factors Food source Competition Predators Social factors, mates Pathogens, parasites Vegetation SIMPLE TERRESTRIAL ECOSYSTEM Precipitation Falling leaves and twigs Water Producer Producers consumer (rabbit) Soluble mineral nutrients Oxygen (O 2 ) Carbon dioxide (rabbit) consumer (fox) Soil decomposers Energy flow is one-way 1 st Law of thermodynamics: energy is not created, nor destroyed. But transformed. Energy enters ecosystems through photosynthesis or chemosynthesis. Some energy is transformed as used by producers; some is passed through Microorganisms and other food chain detritivores All energy eventually dissipates as heat. Thus must always be replenished. Key Detritus Chemical cycling Energy flow producers Heat Figure 55.4 1
Chemical matter is recycled Law of conservation of mass: Actual atoms are constantly rearranged into new molecules Energy needed to form new bonds, but atoms are reused Microorganisms and other detritivores Carbon cycle Detritus Nitrogen cycle Solar Energy Different ecosystems have dissimilar solar illumination Latitude Topography Depth (aquatic) Reflectance producers Key Chemical cycling Energy flow Heat Figure 55.4 Reflectance vs. Available Solar Energy Percent reflectance 8 Snow Clouds 6 Vegetation 4 Soil 2 Liquid water 4 6 8 1, 1,2 Visible Near-infrared Wavelength (nm) Figure 55.5 Energy flows through the food web Energy from lower trophic levels is transferred to higher trophic levels 5% - 2% of energy consumed is available to next trophic level Energy returns to the physical environment as heat Remember thermodynamics! Energy is neither created nor destroyed! Hardwood forest Energy pyramid reflects loss of energy at each trophic level Only 1% of solar energy reaching Earth is used by living systems Only ~1% of energy consumed is available to next trophic level Energy Pyramid Plant material eaten by caterpillar 2 J Oak trees, caterpillars, birds Feces Not assimilated 33 J Growth (new biomass; secondary production) 67 J Cellular respiration Assimilated Figure 55.1 2
Pyramid of net production 1 J 1, J Energy pyramid reflects loss of energy at each trophic level Caterpillar Feeding efficiency = growth/consumed = 17% Production efficiency = growth/assimilated = 33% Feces Plant material eaten by caterpillar 2 J 33 J 67 J Cellular respiration producers 1, J 1,, J of sunlight Figure 55.11 Production Efficiency: Endothermic vertebrates: 1 3% Ectothermic vertebrates: ~1% Inverts: 2 4% Not assimilated Growth (new biomass; secondary production) Assimilated Figure 55.1 Eating high on the food chain is expensive! Most chains limited to 4 5 steps Pyramid of net production 1 J Figure 55.11 1, J producers 1, J Less than 1% passed on to next trophic level 1,, J of sunlight Energetic hypothesis Too little energy passed through steps to support another step. Dynamic stability hypothesis Even if average 1 primary production is sufficient, oscillations/deviations in 1 production cause fluctuations in higher steps below minimum viable population Biogeochemical cycles: "life-earth-chemical" Materials enter producers from atmosphere or soil. Return to abiotic world through respiration and decomposition. Biologically important materials: Water (H 2 O) Carbon (CO 2 ) Nitrogen (N 2, NO 3-, NO 2-, NH 4 ) Pools or Reservoirs of Materials Pools available: Abiotic: atmosphere, soil, water, geological Biotic: living or dead organic matter Materials cycle between pools Size of pools constant only if entry equals exit 3
Global Water Cycle Humidity: water in atmosphere Global Water Cycle Precipitation: rain, snow Surface transport: puddles, groundwater, rivers, oceans Groundwater transport aquifers Evaporation: transpiration: water loss from plants; helps maintain local humidity from organisms: sweat, urine, respiration Water cycle & NPP Actual evapotranspiration = annual amount of water evaporated from a landscape and transpired by plants Watershed Net primary production (g/m 2 /yr) 3, 2, 1, Desert shrubland Arctic tundra Temperate forest Mountain coniferous forest Temperate grassland Tropical forest 5 1, 1,5 Actual evapotranspiration (mm H 2 O/yr) Impacted watersheds Natural/Forested Ecosystem permeability percolation surface runoff interflow & retention evapotranspiration primary productivity groundwater aquifer pool gaining stream Developed/Impacted Ecosystem permeability percolation surface runoff erosion flooding sedimentation interflow& retention evapotranspiration primary productivity groundwater aquifer pool losing stream Human activity disrupts local water cycles Diversion of surface transport Irrigation Dams Disruption of soil water retention (watershed disturbance) Clear cutting of forests Overgrazing Permeability compaction & loss of organic content Also causes loss of minerals through runoff Further losses of vegetation Desertification 4
Desertification DESERTIFICATION Africa U.S. 193 s Dust Bowl Moderate Severe Very Severe 5