Transcript Ecosystems
Ecosystems Chapter 16 Overview Food Chains and Food Webs Productivity Ecological Pyramids Biomagnification Nutrient Cycles Global Warming Ecosystems -The Community along with: Nutrient Cycling Energy Flow Energy Flow – Trophic Levels The Food Chain Sunlight is captured by Autotrophs or Producers using photosynthesis. selffeeders. Stored energy in autotrophs is transferred to Heterotrophs – other feeders Includes Plants, Algae and Phytoplankton. Also some chemosynthetic bacteria Carnivores, omnivores Decomposers use energy remaining in dead organisms Simple Food Chains Trophic Levels Both Marine and Terrestrial Productivity –Amount of food in an ecosystem Primary productivity is growth of producers Gross productivity is the total amount of food produced or ingested Net productivity is amount available to next trophic level, after respiration Measured by weight or calories See Table 2.1, pg. 26 Productivity Amount of photosynthesis in an ecosystemEquals amount of food available for food chain Seasonal effects in north / south seas Productivity rates: Kelp beds have highest productivity Tropical rainforest highest per sq. meter on land, but only covers 3.3 % of globe Open ocean, one of the lowest, but because it covers 65.0 % it equals rainforest Marsh lands nearly equal tropical rainforest productivity Summary of satellite data on global primary productivity from 1997 to August 2000 Winter NORTH AMERICA SPAIN ATLANTIC OCEAN AFRICA Spring Food Webs Energy transfer follows trophic levels Many animals eat at several trophic levels Omnivores: like most of us At salad bar you’re a herbivore Eating a burger makes you a carnivore marsh hawk Higher Trophic Levels crow Sampling of connections in a Tall grass prairie food web upland sandpiper garter snake frog weasel spider Second Trophic Level sparrow earthworms, insects First Trophic Level badger coyote prairie vole grasses, composites pocket gopher ground squirrel Energy Transfer in Ecosystems Food / Energy Pyramid Primary Consumers eat producers, incorporating the energy into the next level. Only 10 % of energy consumed moves to next level Animals loose 90% of the energy at each level Why are Big Fierce Animals so Rare?? Consumers are Heterotrophs Limited by Thermodynamcis Energy Pyramid Pyramid of Numbers Nutrients Cycle Elements change form, but are not lost May be trapped in bio-inactive forms No more carbon now than when the dinosaurs lived !! Ice, fossil fuels Held together in chemical bonds Breaking bonds – releases energy Uses energy to form bonds Nutrient cycles to learn: Water Carbon Nitrogen Carbon Cycle Large reservoirs in rocks (99%), fossil fuels Marine component as well Energy flows through carbon cycle as the food chain Associated with greenhouse effect Build up of CO2 , CH4 etc. in atmosphere Raise sea levels – flooding islands, coasts More severe weather ?? Nitrogen Cycle Largest pool is in atmosphere (80%) a generally bio-inactive form Nitrogen fixing bacteria capture it from air Many native plants have nitrogen fixing root nodules After water nitrogen is the most growthlimiting nutrient for plants Nitrogen important for Autotrophs to make proteins (enzymes) Protein breakdown releases it back to environment in urine Nitrogen Cycle Always need to replenish agriculture fields with fertilizer. Denitrifying bacteria release it back to atmosphere Much of it is leached away, gets in drinking water supplies, pollutes lakes Now add antibacterial agents to fertilizers ! Tightly cycled in Ecosystems Forests and Nitrogen Cycle Most of nitrogen tied up in a tree’s Biomass Soils tend to be nutrient poor Burning trees releases nutrients Soil fertility only lasts a few seasons Nitrogen is leached out with rains Classic problem with Slash and Burn Hubbard Brook Loss of Nitrate from a forest after clear cutting 1620 1850 1850 (pocket only) 1990 Remaining virgin forest Extent of deforestation in the United States