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Ecosystems

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detritus = dead animals and plant tissue, consumed by 1 decomposers (bacteria, ... Large amounts of S leave ecosystem as detritus (washes into streams) ... – PowerPoint PPT presentation

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Title: Ecosystems


1
Chapter 54
  • Ecosystems

2
Outline
  • Energy flow
  • Trophic structure
  • Biogeochemical Cycles
  • nutrient cycling
  • water cycle
  • N cycle
  • C cycle
  • Global warming and human impacts

3
Intro
  • Ecosystems all organisms living in area and
    abiotic components (nutrients, air, water,
    sunlight, soil, temp.)
  • composed of multiple communities along w/ abiotic
    environment
  • S and nutrient flows link biotic and abiotic
    environments
  • ecosystem ecology study of how S flows among
    components of an ecosystem how C, Nn, and other
    elements cycle through organisms, sediments,
    oceans, and atmosphere and how humans affect
    abiotic environment
  • Many global environmental problems (global
    warming, acid rain, ozone hole, anaerobic dead
    zones, algal blooms)
  • humans changed chemical/physical characteristics
    of environment

4
Energy Flow and Trophic Structure
  • All ecosystems consist of 4 components linked by
    flow of S
  • 1 producers autotrophs use solar or chemical
    S to manufacture their own food
  • form basis of ecosystems by transforming S in
    sunlight or reduced inorganic compounds into
    chemical S (sugar)
  • chemical S for maintenance, R, growth,
    reproduction
  • S invested in new tissue
    net
    primary productivity (NPP)
  • available for others to eat
  • consumers eat other organisms
  • herbivores eat plants
  • carnivores eat animals
  • decomposers detritivores
    feed on
    dead remains and waste

5
Global Patterns in Productivity
  • NPP varies among ecosystems by region and biome

6
Global Patterns in Productivity
  • Terrestrial NPP lowest in deserts and arctic
    regions
  • limited by combination of temp., water and
    sunlight
  • highest productivity wet tropics
  • 16 of surface but 43 of NPP
  • deserts and tundra lowest productivity

7
Global Patterns in Productivity
  • Except for major deserts, terrestrial
    productivity declines from equator toward poles
  • Marine productivity high along coast/upwells, low
    in open ocean
  • limited by nutrient availability
  • coastal areas receive input from terrestrial
    systems
  • upwelling returns nutrients to surface

8
0100 100200 200400 400600 600800 gt800
Terrestrial productivity
Productivity ranges (g/m2/yr)
lt35 3555 5590 gt90
Productivity ranges (g/m2/yr)
Marine productivity
9
Energy Flow and Trophic Structure
  • S flow through temperate forest ecosystem in
    Hubbard Brook
  • begins when plants capture S via Ps
  • 1,254,000 kCal of solar radiation per m2
    reached forest per year
  • gross Ps total Ps per area per year 10,400
    kCal/m2
  • gross photosynthetic efficiency efficiency that
    plants use total S available to them
  • ratio of gross Ps to solar radiation 0.8
    (tiny fraction of total radiation received)
  • 1 producers use S captured by Ps in 2 ways
  • 45 for synthesis of new tissue (NPP) (S
    available to herbivores)
  • 55 for maintenance or respiratory costs

10
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11
Energy Flow and Trophic Structure
  • Grazing food web network of herbivores (1
    consumers) organisms that eat herbivores (2
    consumers)
  • amnt of S entering grazing food web varies btwn
    1 to 40 NPP
  • 1 consumers harvested 31 kCal/m2 each year
  • 82 assimilated and 18 excreted
  • 1.6 used in production of new tissue
  • production of new tissue by 1 consumers 2
    production
  • 2 production higher in ectotherms than
    endotherms
  • tiny fraction of available solar radiation
    involved in 2 production

12
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13
Energy Flow through Ecosystems
  • Plant tissue not consumed by herbivores
    eventually dies and enters decomposer food web of
    sp. that eat dead remains
  • detritus dead animals and plant tissue,
    consumed by 1 decomposers (bacteria, fungi,
    worms, millipedes)
  • 1 decomposers consumed by carnivores (spiders,
    shrews)
  • 75 NPP enters
    decomposer food web
  • not all detritus consumed
  • OM in soil
  • leave community

14
Energy Flow and Trophic Structure
  • Large amounts of S leave ecosystem as detritus
    (washes into streams)
  • major source of S for aquatic organisms
  • represents flow of S out of ecosystem
  • Ps by aquatic plants 10 kCal/m2/yr of energy
  • in contrast, 6039 kCal/m2/yr washed from
    surrounding forest
  • most of S inputs to aquatic system come from
    terrestrial plants

15
Energy Flow and Trophic Structure
  • Key points about S flow through ecosystems
  • S enters ecosystems as sunlight via Ps by 1
    producers
  • plants use tiny fraction of total radiation
    available
  • tiny fraction of fixed S actually available to
    consumers
  • most NPP enters decomposer food web
  • only small fraction used for 2 production by
    herbivores/carnivores
  • most S fixed during Ps used for R, not syn. of
    new tissues

16
Trophic Levels
  • Organisms that use same type of S source occupy
    same trophic level (position in
    food chain)
  • organisms at top trophic level not eaten by other
    organisms
  • productivity highest at lowest trophic level
  • productivity declines from one level to next

17
Food Chains and Food Webs
  • Food chain connects trophic levels in
    particular ecosystem
  • describes how S moves btwn trophic levels
  • typically embedded in more complex food webs
  • maximum links in food chain 1 to 6
  • only 2 to 7 trophic levels

18
Energy Loss between Trophic Levels
  • Pyramid of productivity productivity greatest
    at first (bottom) trophic level and declines at
    higher levels
  • S lost in keeping organism alive

19
Energy Flow and Trophic Structure
  • 3 hypotheses to explain why ecosystems dont have
    8 trophic levels
  • S transfer hypothesis food-chain length is
    limited by productivity
  • as S transferred up food chain, large fraction of
    S is lost
  • by time S reaches top trophic level, not enough
    left to support additional group of consumers
  • should be more trophic levels in ecosystems w/
    higher productivity or higher S -transfer
    efficiency

20
Energy Flow and Trophic Structure
  • stability hypothesis long food chains are more
    fragile (Pimm)
  • easily disrupted by environmental disturbances
    thus eliminated
  • long food chains unlikely to persist in variable
    environment and likely to take longer to return
    to previous state following a disturbance
  • should be longer in more stable environments
  • environmental complexity hypothesis food-chain
    length function of ecosystems physical structure
  • 3-dimensional ecosystems should have longer food
    chains than 2-dimensional ones

21
Biogeochemical Cycles
  • Nutrients also transferred when one organism eats
    another
  • biogeochemical cycle path an element takes as
    it moves from abiotic systems through living
    organisms and back again
  • Humans disrupting biogeochemical cycles on global
    scale
  • Researchers study 3 basic aspects of
    biogeochemical cycling
  • nature and size of reservoirs of elements
  • rate of movement btwn reservoirs and factors
    influencing these rates
  • how biogeochemical cycles interact

22
Biogeochemical Cycles
  • Nutrients cycle from organism to organism via
    assimilation, consumption, and decomposition
  • nutrients exported from by migration of organisms
    out of area or water
  • Nutrients are recycled/reused

23
Biogeochemical Cycles
  • Summary of process
  • nutrients taken up from soil and incorporated
    into plant tissue
  • if plant is eaten, nutrients pass to animals of
    ecosystem
  • nutrients excreted in fecal matter or urine,
    taken up by parasite or predator, or enter dead
    biomass pool
  • if plant dies, nutrients and plant biomass become
    litter
  • decomposers break down nutrients in plant litter,
    animal excretions, and dead animal bodies
  • nutrients then part of OM of soil
  • nutrients in OM converted to inorganic form
  • nutrients available for uptake by plants

24
Biogeochemical Cycles
  • Factors controlling rate of nutrient cycling in
    ecosystems
  • decomposition of detritus
  • influenced by temperature and precipitation
  • quality of detritus as nutrient source for
    decomposers
  • presence of large compounds difficult to digest
  • growth of decomposers also inhibited if low N
  • rate of nutrient loss 10x as high in devegetated
    site vs. control site
  • devegetation has huge impact on nutrient export
  • devegetated areas much less productive than
    intact, vegetated sites

25
The Water Cycle
26
The Carbon Cycle
27
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28
The Nitrogen Cycle
29
Human Impacts on Ecosystems
  • 2 factors responsible for human impacts on
    ecosystems
  • rapid increase in human population
  • rapid increase in human resource use
  • people in industrialized countries have
    disproportionately large impact b/c consumption
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