Download Why is the competition paradigm so prevalent? based on

Why is the competition paradigm so prevalent?
• based on mathematical theory
• so, straight forward to test in field & lab
• subsequent models developed as spin-offs of
competition theory:
i. Coexistence
ii. Theory of the niche
iii. Resource division
Prior to 1980s:
Several researchers felt that competition was more NB
than other ecological processes
After 1980s:
Researchers questioned why competition was necessarily
the most NB interaction. Predation seems more NB in
marine habitats.
Do communities have to be in equilibrium?
Does competition ever depart from equilibrium?
Findings suggest that species diversity is
affected by:
competition
disturbances
predation
Community Structure - Chapter 21
Communities: an assemblage of plants & animals
that occur together in the same place & dominated
by > dominant species
Communities as assemblages of species…
Do communities exist as well defined units?
There are 2 historical viewpoints
Open Community
H.A. Gleason
Closed Community
F.E. Clements
Coincidence
associations
Superorganism
Diffuse
Sharp boundaries
Ricklefs 2001
Fig. 21.4
F.E. Clements
H.A. Gleason
Ecotone: a zone of transition between habitat types
Ricklefs 2001, Fig. 21.5
Molles 2002, Fig. 1.9
Ricklefs 2001, Fig. 21.6
Some species
grow only
in nonserptine
soils
Some spp. have
no preference
Others grow
in ecotone.
Others grow
in serpentine
soils.
Ricklefs 2001, Fig. 21.6
Concentration of soil minerals
determine the plants that make
up each community
Ricklefs 2001,
Fig. 21.6
But, evidence supports Gleason
(open communities)
This is true even though some communities
have very distinct boundaries. e.g., boundary
between aquatic & terrestrial communities