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Ecosystems (Ch 20; p. 374-375 in ch. 18) Interactions of organisms with each other and their environment: ● ● Driving force behind much of natural selection & evolution. Pivotal concept in biology. The Ecosystem Concept ● ● ● Ecosystem: An interacting system consisting of all organisms plus the physical (abioltic) environment. Community: all the organisms present; the living component of an ecosystem. Ecology: “Scientific study of interactions between organisms and their environment” (p. 374). – Different from 'environmentalism' (p. 374) – But may help solve environmental problems. Interactions Between Organisms (p. 429-432) ● ● Competition: Struggle for resources (light, nutrients, water, space, habitat, etc). – Within & between species. – both partners inhibited (p. 429) Mutualism: both partners benefit (p. 430). – Mycorrhizae. – Many plant-pollinator interactions. – Corals. – Lichens. Interactions Between Organisms (p. 429-432) ● ● ● Herbivory: heterotroph consumes autotroph (p. 431). – Plant-herbivore interactions: – Defense mechanisms: thorns, tough leaves, distasteful or toxic substances. Predation –A heterotroph kills & eats another (p. 430). Parasitism: (p. 432). – Parasite: lives on, gets nourishment from host organism ● Often small or microscopic. – Pathogen: disease-causing parasite. – Autotrophs or heterotrophs may be parasitized. Structure of Ecosystems: Trophic Structure (p. 422) ● “Trophic” = energy /feeding relationships. ● Energy enters ecosystem via photosynthesis. ● ● ● Flows through ecosystem as organisms consume each other. Trophic level = “feeding level” . Food chain: Sequence of energy transfer (feeding) from organism to organism (P. 432; Fig. 20.15). Autotrophs or Producers (P.432): ● ● ● Photosynthetic autotrophs: – Plants. – Algae. – Photosynthetic bacteria. Chemo-autotrophs: – Certain bacteria. Energy Flow in Ecosystems: (p. 438) – Primary Production (productivity): ● Energy captured by photosynthesis in an ecosystem. ● Or organic material (Biomass) accumulated as result of photosynthesis. ● Globally, roughly 165 billion tons. Consumers or Heterotrophs (p.433): ● Consume food (originally manufactured by autotrophs) – Herbivores – Carnivores – Parasites – Omnivores – Detritivores ● – mainly animals: Scavenge non-living organic matter. Decomposers (especially fungi & bacteria) ● consume non-living organic matter. Food Web (p. 434): Pattern of energy flow (feeding). Series of possible food chains. Consumers Sunlight Producers Decomposers & Detritivores Energy Pyramids (p. 438): Energy losses limit the number of possible trophic levels Roughly 90% energy lost from one level of food chain to another. 3rd-level consumers Sunlight: Roughly 1% captured 2nd-level consumers 1st-level consumers Producers Disturbances and Ecological: Succession (p. 436). ● ● ● ● Change in community over time. Ecological response to disturbance: Human-caused. Natural. Denuded or disturbed area: Plants & animals colonize, & species change over time. Disturbance & Succession occur in all ecosystems: Enhance diversity: more kinds of habitat. Primary Succession (p. 436): Succession begins in virtually lifeless area with no soil. Secondary succession: (p. 437). Soil, other remnants of former community remain. Usually faster than primary succession. Example of Secondary Succession: Bare Ground after Logging in in East Texas Recently Disturbed: Bare Ground Pioneer Stage: weeds, annuals. Early succession Stages: Perennial herbs, Shrubs Succession Example: After logging, East Texas Early/ Mid-succession: Trees (pines/ sweetgum) invade. Mid-succession: Pinedominated forest. Late succession (Climax): broadleaf “hardwood” trees (oak, beech). Primary Succession: Tolbachik (Толбачик) Volcano, Kamchatka, Russia ● Summer 2010: Succession following 1975 eruption. Chemical Cycling in Ecosystems: Biogeochemical (nutrient) Cycles: (P. 442) ● ● Energy flows through a system; materials (essential elements) recycle. Biogeochemical cycles: ● ● ● ● ● ● ● Water (p. 391) Oxygen Nitrogen (p. 442) Carbon (p. 441) Potassium Phosphorus (p. 441) Others Hydrologic (water) cycle The Carbon Cycle (p. 395; p. 441) ● Global distribution of carbon: ● Organic carbon Living organisms (600 GT*). – dead organisms & soil organic matter (1,600 GT). Atmosphere (766 GT; mostly as CO2) – ● ● Dissolved carbon-forms in oceans & other waters (40,000 GT). ● Long term carbon storage: Fossil fuels (4,000 GT) – Ocean sediments, limestone rocks, etc (100,000,000 GT). ● Main source:1-celled protists with calciumcarbonate-rich cell walls * GT = “gigaton” =1 billion tons. – The Carbon Cycle (p. 395; p. 441) Atmospheric CO2 Combustion Photosynthesis Respiration Feeding Decomposition Rock weathering Dissolved C Fossil fuels Sedimentation; Limestone, etc. Greenhouse Gases & Global Warming (p 395) ● ● ● ● Human activity---disrupting respiration/ photosynthesis balance: – Fossil fuel burning – Deforestation CO2 buildup, increased heat trapping (Fig. 42.17. Result: climate change, climate instability, rising sea levels, & flooding. Solutions?? Human threats to the Biosphere ● ● Problem: loss of biodiversity (p. 426) – Extinctions – Loss of ecosystem services (water/ air purification, climate regulation, erosion control as ecosystems are degraded. Four main Causes of Declining Biodiversity: 1)Habitat destruction & fragmentation 2)Introduction of invasive species In E. TX: pigs, privet, water hyacinth, hydrilla, Chinese tallow tree, giant salvinia 3)Overexploitation ● 4)Pollution The Root Cause: Ever Expanding Size & Dominance of Human Population (p. 426) ● Exponential human population growth since 1700's ● Urbanization (red): San Francisco area 1900-1990 1900 1940 1954 1962 1974 1990 How the Science of Ecology Can Help ● ● ● ● Conservation Biology – Goal-oriented science seeking to understand & counter biodiversity loss. – Identify biodiversity “hot spots” to focus on. – Research to determine Minimum /optimum preserve sizes. Restoration ecology: ecological principals to develop methods of returning degraded areas to natural or functional state. – Kissimmee river project, Fl, (p. 447). Landscape Ecology: applying ecological principals to study of land use patterns (p. 445). – Goal: make ecosystem conservation part of land use planning. – Importance of corridors connecting otherwise fragmented habitat patches (p. 445) “Biophilia” & an Environmental ethic (p. 448) The End Version 13.04