Ecosystem Ecology for Wildlife Scientists Don White, Jr., Ph.D.
Key Concepts: An ecosystem is an association of organisms and their environment Every ecosystem is an open system, in that it has inputs and outputs of both energy and nutrients Energy flows in only one direction through an ecosystem
Key Concepts: Each chain in a food web extends in a straight-line sequence from producers through all the consumers Water, carbon, nitrogen, and phosphorus move through geochemical cycles that are global in scale Each substance moves through a hydrologic, atmospheric, or sedimentary cycle Humans are disrupting the natural cycles
The Nature of Ecosystems Primary producers Consumers Decomposers Detritivores
Trophic Levels Structure of Ecosystems 1st - Primary producers Autotrophs 2nd - Primary consumers Herbivores, Decomposers, Detritivores 3rd - Secondary consumers Primary carnivores 4th - Tertiary consumers Secondary carnivores and parasites
Food Webs Network of crossing, interlinked food chains involving primary producers, consumers, and decomposers
How Does Energy Flow Through an Ecosystem? Primary source Grazing food webs Photosynthetic organisms to herbivores Detrital Food Webs Photosynthetic organisms to detritivores and decomposers
Ecological Pyramids Decomposers Top carnivores Primary carnivores Herbivores Primary Producers
Energy Flow at Silver Springs, Florida Energy loss with each trophic level
Geochemical Cycles
Hydrologic Cycle Rain and snow returns water to land Ocean currents and winds Evaporation Watershed Deforested area had greater calcium loss than undisturbed area.
Sedimentary Cycle Phosphorus Cycle From land to sediments at bottom of the sea then back to land Earth s Crust Largest reservoir of phosphorus
Eutrophication Activities that increase the concentration of dissolved nutrients Nutrient enrichment of any aquatic ecosystem Most minerals enter sedimentary cycles Fertilizers use phosphates Dense algae blooms
Carbon Cycle Aerobic respiration ------> Carbon dioxide Fossil fuel burning Volcanic eruptions Atmosphere, soils, plant biomass Largest holding stations for carbon Carbon dioxide fixation Photosynthetic autotrophs
From Greenhouse Gases to a Warmer Greenhouse effect Planet? Increase in CO 2 Increase in CFC s
From Greenhouse Gases to a Warmer Greenhouse effect Planet? Increase in methane Increase in nitrous oxide
Nitrogen Cycle N 2 gases converted to usable forms Bacteria Nitrogen fixation Bacteria and fungi Decomposition Ammonification Nitrification Denitrification
Ecosystem Modeling Prediction of unforeseen effects of disturbance Computer programs Models Biological magnification Use of DDT
In Conclusion An ecosystem is an array of producers, consumers, detritivores, and decomposers and their environment Sunlight is the initial energy source for nearly all ecosystems Feeding relationships are structured as trophic levels in an ecosystem
In Conclusion Isolated food chains of who eats whom in an ecosystem are rare in nature The rate at which primary producers capture and store energy is the primary productivity Energy fixed by photosynthesizers passes through grazing food webs and detrital food webs
In Conclusion Primary productivity depends on water and nutrients Carbon dioxide is the main atmospheric gas in the carbon cycle Burning fossil fuels and converting natural ecosystems to farming and grazing add to imbalances and may be factors in long-term global warming
In Conclusion Nitrogen availability is a limiting factor for the total net primary productivity of land ecosystems Most mineral elements enter sedimentary cycles and become available Disturbances of an ecosystem can have unexpected effects Computer modeling helps identify ecosystem relationships and can incorporate them into models