34-1 An ecosystem contains: Biotic (living) components and Abiotic (nonliving) components. The biotic components of ecosystems are the populations of organisms. The abiotic components include inorganic nutrients, water, temperature, and wind. Ecology Review

34-2 Biotic Components of an Ecosystem Autotrophs are producers that produce food for themselves and for consumers. Most are photosynthetic organisms but some chemosynthetic bacteria are autotrophs. Heterotrophs are consumers that take in preformed food.

34-3 Biotic components

34-4 Consumers may be: Herbivores – animals that eat plants, Carnivores – animals that eat other animals, Omnivores, such as humans, that eat plants and animals, or Decomposers, bacteria and fungi, that break down dead organic waste. Detritus is partially decomposed organic matter in the soil and water; beetles, earthworms, and termites are detritus feeders.

34-5 Consumers

34-6 Primary consumer – an organism that gets its energy from plants (producers) Secondary consumer – a consumer that gets its energy from primary consumers Tertiary consumer – carnivores that eat other carnivores; a top-level consumer, which is usually the top predator in the food chain

34-7 Energy Flow and Chemical Cycling Every ecosystem is characterized by two phenomena: 1)Energy flows in one direction from the sun to producers through several levels of consumers, and 2)Chemicals cycle when inorganic nutrients pass from producers through consumers and returned to the atmosphere or soil.

34-8 Only a small portion of energy and nutrients made by autotrophs is passed on to heterotrophs, and only a small amount is passed to each succeeding consumer; much energy is used at each level for cellular respiration and much is lost as heat. Ecosystems are dependent on a continual supply of solar energy. The laws of thermodynamics support the concept that energy flows through an ecosystem.

34-9 Energy balances

34-10 Nature of an ecosystem

34-11 Food chains vs. food webs A food chain is diagram that link organisms together by who eats whom; starts with plant life and ends with an animal. Most food chains have no more than 4 or 5 links Ex: tree  giraffe  lion Most animals are part of more than 1 food chain & eat more than 1 kind of food in order to meet their food and energy requirements. These interconnected food chains form a food web.

34-12 Food chain

34-13 Forest food webs

34-14 Generally, the upper portion of a food web is a grazing food web, based on living plants, and the lower portion is a detrital food web, based on detritus and the organisms of decay.

34-15 Trophic Levels A trophic level is all the organisms that feed at a particular link in a food chain. A grazing food chain: Leaves → caterpillars → tree birds → hawks A detrital food chain: Dead organic matter → soil microbes → worms

34-16 Ecological Pyramids The shortness of food chains can be attributed to the loss of energy between trophic levels. Generally, only about 10% of the energy in one trophic level is available to the next trophic level. This relationship explains why so few carnivores can be supported in a food web.

34-17 The flow of energy with large losses between successive trophic levels can be depicted as an ecological pyramid that shows trophic levels stacked one on the other like building blocks. Usually a pyramid shows that biomass and energy content decrease from one trophic level to the next, but an inverted pyramid occurs where the algae grow rapidly and are consumed by long-lived aquatic animals.

34-18 Ecological pyramid

34-19 Water Cycle Carbon Cycle Nitrogen Cycle Phosphorous Cycle Biochemical cycles

34-20 The Water Cycle In the water, or hydrologic cycle, the sun’s rays cause fresh water to evaporate from the oceans, leaving the salts behind. Vaporized fresh water rises into the atmosphere, cools, and falls as rain over oceans and land. Precipitation, as rain and snow, over land results in bodies of fresh water plus groundwater, including aquifers.

34-21 Water is held in lakes, ponds, streams, and groundwater. Evaporation from terrestrial ecosystems includes transpiration from plants. Eventually all water returns to the oceans.

34-22 The water cycle

34-23 The Carbon Cycle In the carbon cycle, a gaseous cycle, organisms exchange carbon dioxide with the atmosphere. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil fuels are all reservoirs for carbon. Fossil fuels were formed during the Carboniferous period, 286 to 360 million years ago.

34-24 The carbon cycle

34-25 The Nitrogen Cycle Nitrogen makes up 78% of the atmosphere but plants are unable to make use of this nitrogen gas and need a supply of ammonium or nitrate. The nitrogen cycle, a gaseous cycle, is dependent upon a number of bacteria. During nitrogen fixation, nitrogen-fixing bacteria living in nodules on the roots of legumes convert atmospheric nitrogen to nitrogen-containing organic compounds available to a host plant.

34-26 Cyanobacteria in aquatic ecosystems and free-living bacteria in the soil also fix nitrogen gas. Bacteria in soil carry out nitrification when they convert ammonium to nitrate in a two-step process: first, nitrite-producing bacteria convert ammonium to nitrite and then nitrate-producing bacteria convert nitrite to nitrate. During denitrification, denitrifying bacteria in soil convert nitrate back to nitrogen gas but this does not quite balance nitrogen fixation.

34-27 The nitrogen cycle

34-28 The Phosphorus Cycle The phosphorus cycle is a sedimentary cycle. Only limited quantities are made available to plants by the weathering of sedimentary rocks; phosphorus is a limiting inorganic nutrient. The biotic community recycles phosphorus back to the producers, temporarily incorporating it into ATP, nucleotides, teeth, bone and shells, and then returning it to the ecosystem via decomposition.

34-29 The phosphorus cycle