The ecosystem concept

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Ecosystem Ecology

• Study of interactions among organisms and their
  physical environment as an integrated system

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What is an ecosystem?

• bounded ecological system consisting of all the
  organisms in an area and the physical environment
  with which they interact

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The ecosystem concept
Biogeochemistry
Ecological succession
Trophic dynamics
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1. Ecological succession

• The Midwestern botanists

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Henry Cowles (1869-1939), U. of Chicago

• Vegetation changes in time in response to stress
• Orderly development against backdrop of
  unpredictable physical disturbance
• Plant communities are dynamic ever-changing

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Frederic Clements (1874-1945), U of MN and
Carnegie Institute

• Succession is a predictable linear process to a
  climax community
• Community is analogous to an organism the
  superorganism

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Henry Gleason (1882-1975), U of MI and NY
Botanical Garden

• Individualistic concept of plant communities
• Communities are an assemblage of organisms, not
  an organismal entity
• Major critic of Clements
• Bryologist!

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1. Ecological succession

• The Midwestern botanists
• Plant communities are dynamic
• Communities are analogous to organisms -versus-
• Communities are assemblages of individuals

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2. Trophic dynamics

• The animal ecologists

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Charles Elton (1900-1981), Oxford U. and the
Bureau of Animal Populations

• Niche concept
• Niches are linked into food chains
• Pyramid of numbers
• Matter flows through food cycle

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2. Trophic dynamics

• The animal ecologists
• Groundwork for thinking about energy flow
• But largely a whos there approach

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3. Biogeochemistry

• Linsley pond, CT

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G. Evelyn Hutchinson (1903-), Yale U.

• Biogeochemical mode energy/material cycles are
  influenced by the biota
• Biodemographic mode mathematical studies of
  variations in population size

3. Two modes conceptually linked by concept of
self-regulation modes 4. Feedback cycles
regulate coupling of biotic and abiotic processes
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3. Biogeochemistry

• Linsley pond, CT
• Biota influences chemical and physical processes,
  which in turn affects biota

Plants
Nutrient cycling
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Emergence of the ecosystem concept
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Arthur Tansley (1871-1955), Journal of Ecology

• Melded Clementsian and Gleasonian perspective
• Objected to holism and organismal concept, but
  also objected to reductionism

3. Proposed the ECOSYSTEM as middle ground a
system made up of partially overlapping systems
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Ray Lindeman (1915-1942), Yale U.

• Energy flows, while materials cycle
• Changes in energy and material over succession,
  not just whos there
• Ecosystem as integrated physical and biological
  system
• Died before he published his dissertation

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The Odums Eugene (1913-2002), UGA and Howard
(1922-2002), UFL

• Introduced new ecosystem tools to ecologists
  (bomb tracers)
• Used electrical circuits, cybernetics,
  thermodynamics to describe ecosystems
• The macroscope spp. do not matter
• Embraced Clements's ecosystem as organism,
  alienated evolutionary and pop. ecologists with
  discussions of strategies and determinism

Howard
Eugene
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Hans Jenny, U.C.-Berkeley (1899-1992)
State Factors
Climate
Time
Ecosystem structure and function
Soil
Relief (Topography)
Organisms
Parent material
Ecosystem (Cl, O, R, P, T)
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State Factors 1. are independent of the system
being studied
2. control (in the ultimate sense) the
characteristics and properties of ecosystems
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• Lecture ended here

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The recent past
1960s and 70s International Biological
Program Hubbard Brook Food webs and
bioaccumulation 1980s Gaia Non-equilibrium
ecology Long Term Ecological Research Acid
rain 1990s Elevated CO2 Diversity and
Ecosystem function Hawaii as a model
system BorEAS and LBA 2000s The millenium
report The IPCC Macro-ecology scaling ind. to
ecosystems The nitrogen cycle
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Where are we today?

• New toolsrapid analysis, isotopes, models,
  global networks

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Where are we today?

• Putting individualistic perspective within
  context of overlapping systems
• Increasing awareness that organisms cannot be
  black-boxed
• and identity of species can affect ecosystem
  processes

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Where are we today?

• Understanding human-caused change in the earth
  system
• Understanding feedbacks between terrestrial
  ecosystems and global climate
• Putting people into the picture