CHARACTERISTICS OF ECOSYSTEMS, continued

 5. In ecosystems, everything is connected to everything else, directly or indirectly.
 Can’t affect one thing without affecting another.
  Ripple effects.
 So, what kinds of ripples or waves do humans make?
  Just us being in this room has effects. How?

6. The complex interactions in ecosystems provide checks and balances, and alternatives.
 Checks and balances.
  E.g. predator (wolf) and deer.
 Alternatives.
  When one species is removed from an ecosystem, other species can take its place.
   E.g. chestnut and Appalachian forest.
    When chestnut disappeared due to fungal disease, other species took its place structurally (i.e. its space) and  functionally (i.e. its niche, or what it does).
   Diversity and complexity in forest allowed other species to take the place of chestnut

7. Interactions result in more efficient cycling of nutrients.
 A ‘tighter’ ecosystem with fewer ‘leaks’.
 As minerals are released, e.g. due to decomposition, they are quickly taken up again by other organisms.
  Therefore, less is lost by leaching.
 One species may have a preference for one form of an element, e.g. NH4+, while another species may prefer a different form, e.g. NO3-. Another fixes N2. Fig. 25.7

8. The more complex an ecosystem is, the more resistant it is to change.
 More complex means...
  more species diversity
  more interactions and recycling
  more productivity
  more checks and balances and alternatives
  resistant to change
                           Where does David Tilman of the University of Minnesota fit into all this?

 This means ecosystems exhibit dynamic equilibrium, not stasis.
  There are fluctuations in time and space
   fires, storms, disease,  etc.
  But overall, the system is stable on the scale of 100s and 1000s of years.   E.g. Great Yellowstone fire of 1988.
      Mount St. Helens.
      Chestnut blight of Appalachians.

9. Over the very long term, i.e. thousands and millions of years,
 Ecosystems EVOLVE.
 Evolution involves competition in ecosystems for resources.
 The most stable collections of organisms and interactions are selected in a particular environment.
  Involves the most efficient use of resources among organisms.
Ecology is the theater for the evolutionary play -- G.E. Hutchinson
 Can’t really understand ecology without appreciating that ecosystems are a product of evolution.
 Mycorrhizae are a good example.  What are mycorrhizae?
 Evolution tends to multiply and diversify niches, due to competition.
  That increases complexity and flexibility.

10. Human activity tends to simplify ecosystems.
 Fewer species, fewer interactions.
 We replace natural populations with food producers. Remove competitors, herbivores, carnivores, etc.
 We make environments more homogeneous.
  Monotypic communities. Can you think of an example?
 Human derived ecosystems are less complex, less stable, less resistant to change.
 Human derived ecosystems are less complex genetically.

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CELL STRUCTURE

Cells are the structural and functional units of life.
 Cells make up organisms, physically.
  Some organisms contain just one cell. They’re UNICELLULAR.
  Others are MULTICELLULAR.  (Most?)
 Cells are the smallest, or elementary unit that can do everything associated with life.
  Caveat: in multicellular organisms, cells SPECIALIZE functionally.
    Some lose the ability to divide at maturity.
        E.g. red blood cells in humans, sieve elements in plants.

Our modern conceptualization of cells is called The Cell THEORY.
 Note, I used the word ‘theory’. What is a theory in science?

We still call it a theory even though it’s been established for about 150 years.
 Why?

  What other scientific theories can you think of?
 

The cell theory says,
 1. All organisms are composed of cells.
  Up to trillions in humans and more in large plants.
 2. All cells come from pre-existing cells.
  No spontaneous generation.

BRIEF DIVERSION: What are viruses?

There are 2 basic kinds of cells.
 Prokaryotic and eukaryotic.
  Delineates life’s three basic kinds of organisms.
   Archaeans and Eubacteria -- prokaryotes.
   Plants, animals, fungi, protists -- Eukaryotes.

Prokaryotic cells:
 Generally small, 1-10 micrometers, or um, in diameter (but some much larger).
    What's a micrometer?
 DNA not bounded by a special membrane.
 DNA circular, not associated with specialized histone proteins.
 Cell organization relatively simple.
  A few specialized membranes, but no true organelles.
 The most ancient cells known, about 3.5 billion years.

Eukaryotic cells:  (Fig. 3.4, Stern et al.)
 Cells much larger: 5-100 um, or larger (ostrich egg...)
 DNA housed in discrete nucleus, bounded by a nuclear envelope.
 DNA associated with histone proteins to comprise CHROMATIN
  (what we recognize as chromosomes).
 Cell organization highly compartmentalized into organelles that house discrete processes.
  Regulate exchange between cell processes.
  Makes metabolism very efficient.