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CHAPTER 5. Ecosystems: Energy, Patterns, and Disturbance. Introduction to ecosystems. In 1988, lightning started fires in Yellowstone National Park 165,000 acres were burned National Park Service policies have changed over time In the early years, all fires were extinguished
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CHAPTER 5 Ecosystems: Energy, Patterns, and Disturbance
Introduction to ecosystems • In 1988, lightning started fires in Yellowstone National Park • 165,000 acres were burned • National Park Service policies have changed over time • In the early years, all fires were extinguished • Before 1988, only fires that threatened human habitations were extinguished • This fire started a great controversy over this policy • Snow in September finally put the fires out
Yellowstone recovered from the 1988 fire • The fires burned 36% of the park • Burned and unburned areas were interspersed • Within 2 weeks, grasses and other vegetation sprouted • Within a year, vegetation covered the burned areas • Bison and elk fed on the new vegetation • Within 25 years, plant and animal diversity will have completely recovered in the burned areas • Fire is vital to many ecosystems • It may even impact evolution
Characteristics of ecosystems Ecosystems contain communities of interacting species and their abiotic factors They function on different scales It’s hard to delineate fixed boundaries
Scientists study ecosystems Biomes: ecosystems having similar vegetation and climactic conditions Greater Yellowstone Ecosystem belongs to the northern temperate forest biome Scientists study ecosystem properties Trophic levels Productivity Consumption
Trophic levels Food chain: describes where energy and nutrients go as they move from one organism to another Energy moves “up” the food chain Not all energy and nutrients are passed to other levels Food web: interconnection of food chains to form complex webs of feeding relationships
Trophic categories Autotrophs: produce organic material from inorganic constituents through the use of an external energy source Also referred to as producers Green plants, some single-celled organisms and bacteria
Heterotrophs: must consume organic material to obtain energy • Consumers: eat living prey • Decomposers: scavengers, detritus feeders, chemical decomposers eat dead organic material
Producers are essential to every ecosystem They capture energy from the Sun or chemical reactions Most producers are green plants Chlorophyll: a green pigment that captures light energy Range in size from microscopic bacteria to gigantic trees Chemosynthesis: some bacteria use energy in inorganic chemicals to form organic matter from CO2 and water Primary production: production of organic matter through photosynthesis and growth of producers
Consumers Organisms feed on organic matter for energy Divided into subgroups according to their food source Primary consumers (herbivores): feed on producers Secondary consumers: feed on primary consumers Third (tertiary), fourth (quaternary), or higher levels Carnivores: secondary or higher-order meat eaters Omnivores: feed on both plants and animals Animals can occupy various levels, depending on the food
Decomposers Detritus: dead plant material (leaves, etc.), fecal wastes, dead bodies Detritus is organic and high in potential energy for Decomposers Scavengers (vultures): break down large pieces of matter Detritus feeders (earthworms): eat partly decomposed matter Chemical decomposers (fungi and bacteria): break down matter on the molecular scale
Decomposers act like any other consumer Some decomposers (e.g., termites) digest woody material They have a mutualistic, symbiotic relationship with decomposer microorganisms in their guts Most decomposers use oxygen for cell respiration
Some decomposers (bacteria and yeasts) partially break down glucose in the absence of oxygen (fermentation) • Results in ethyl alcohol, methane gas, acetic acid • Anaerobic (oxygen-free) respiration: in sediments of lakes, marshes, swamps, and animal guts • Cattle and their fermenting bacteria release methane
Limits on trophic levels Terrestrial ecosystems usually have three or four trophic levels Marine systems sometimes have five
Biomass: the total combined (net dry) weight of organisms • Each higher trophic level has about 90% less biomass • One acre of grassland has 907 kg (2,000 lbs) • It has 90.7 kg (200 lbs) of herbivores • It has 9.7 kg (20 lbs) of primary carnivores • Biomass pyramid: the different levels of producer and consumer mass
The flow of energy in ecosystems In most ecosystems, sunlight is the initial source of energy Primary production (production of organic molecules) is only 2% of the incoming solar energy Although small, it’s enough to fuel all life
Standing-crop biomass: the actual biomass of primary producers in an ecosystem at any given time • Not always a good measure of productivity • Biomass and primary production vary greatly • Forests have large biomass • Grasslands have high primary production
The fate of food Between 60 and 90% of food consumed is oxidized for energy 10−40% is converted to body tissues for growth, repair, and maintenance
Undigested food passes through the digestive system and is excreted • Cellulose: material in plant cell walls • Excreted from herbivores • Forms fiber, bulk, or roughage: a necessary part of the diet • Carbon dioxide, nitrogen, phosphorus: excreted in urine
Energy flow and efficiency There is a huge inefficiency at each trophic level Only a small fraction of energy is passed on when energy flows from one trophic level to the next Much of the biomass is not consumed by herbivores Some food is used as energy to fuel the hetrotroph’s cells and tissues Some food is not digested and is excreted as waste Secondary production: incorporating matter and energy from a lower trophic level into a consumer’s body
Inefficiency at trophic levels Individuals at higher levels represent a greater amount of the Sun’s energy for the same amount of body tissue More energy is needed to produce a top-order consumer than a producer It takes more time, water, and resources to produce a top-order consumer
Some materials are hard to excrete (e.g., chemicals dissolved in fat) • They biomagnify as you go up the food chain • They bioaccumulate (build up in tissues)
Aquatic systems These systems go through the same process as terrestrial ecosystems, with two major differences Less energy is required in aquatic systems More cold-blooded animals, which require less energy Less energy is needed to support body weight in water With less energy needed at each level More energy is available to the next level Food chains can be longer
Aquatic systems may have a reversed biomass pyramid • Larger, older fish eat algae that turn over rapidly
From ecosystems to biomes Broad ecosystem patterns translate into a predictable set of organisms that live under particular conditions Different regions have distinct biotic communities Creating variety in ecosystems, landscapes, and biomes
A biome: a large geographical biotic community • Controlled by climate • Is named after the dominant vegetation • Has fuzzy boundaries • Aquatic areas are not called biomes • (aquatic life zones) • But they function similarly
The role of climate in a terrestrial ecosystem Climate: a description of the average temperature and precipitation (weather) of a region Climates vary widely Equatorial areas: warm, high rainfall, no seasons Above and below the equator: temperatures become seasonal (warm/hot summers, cool/cold winters) Toward the poles: longer and colder winters Colder temperatures are also found at higher elevations
Effects of precipitation on biomes Precipitation varies widely in different regions From almost 0 to over 250 cm (100 in.)/yr It can be evenly distributed throughout the year or concentrated in certain months (wet and dry seasons)
A given climate supports species that can tolerate the temperature and precipitation levels of the area • Highest densities occur where conditions are optimal • A species is excluded where any condition is beyond its limit of tolerance
Biome examples Individual ranges of tolerance to temperature and precipitation determine where a species can live Species’ distributions describe a biome’s placement Six major types of biomes exist
Rainfall effects are primary in determining biomes • Temperate deciduous forest: rainfall of 72–200 cm (30–80 in.)/yr • Grassland (prairie) biome: rainfall is less or seasonal • Desert biome: rainfall is less than 25 cm (10 in.)/yr
The effects of temperature on biomes Temperature effects are superimposed on rainfall effects It determines the kind of forests in an area with 75 cm (30 in.) or more of rainfall per year Tropical rain forests have broad-leaved evergreens that cannot tolerate freezing Deciduous trees tolerate freezing by dropping their leaves and becoming dormant Coniferous forests tolerate the harsh winters and short summers of northern regions
Leaf Adaptations Cold Climate is dominated by coniferous trees -evergreen, small surface area, waxy coating, clustered Warm Climate is dominated by broadleaf evergreen trees -evergreen, large surface area Moderate Climate is dominated by deciduous trees -leaves drop in winter, rapid leaf growth, broadleaf
Biomes with little precipitation Permafrost: permanently frozen subsoil Prohibits tree growth because their roots cannot penetrate the soil Tundra biome: has grasses, clover, and other small plants that grow above the permafrost Desert: any region with less than 25 cm (10 in.) of rain/yr Hot deserts have different species than cold deserts
Aquatic systems Aquatic systems have major categories But are not called biomes Aquatic and wetland ecosystems are determined by depth, salinity, and permanence of water Lakes, marshes, streams, rivers, estuaries, bays Ocean systems
Microclimates and other abiotic factors Microclimate: the conditions in a specific, localized area Temperature and moisture may be different from the overall climate of the region Conditions result in variations of ecosystems in a biome
Biome productivity Biomes have different levels of primary productivity Highly productive biomes support organisms from other biomes (e.g., seabirds migrating through marshes) They also remove and trap CO2 from the atmosphere
Different ecosystems have different productivity Tropical rain forests are highly productive Warm temperatures and rainfall are ideal for photosynthesis Open oceans cover a large part of Earth But they have low productivity per m2 Primary production is limited by scarcity of nutrients They are veritable deserts
