L-V models formed core of ecological theory. How do they relate to the real world?
Experiments by Gause (1930’s)
Good description of competition by protozoa in artificial culture vessels; saw both
stable coexistence and competitive exclusion: can be unstable
Predator-prey strongly tended to be unstable (predators eat up all the prey, then
starve) unless habitat complexity added)
(View lecture slides for graphs of Gause’s data.)
How are competitive effects manifested in nature, rather than in containers?
Competitive exclusion is less likely to go to completion…
…but abundances can be drastically affected…
… and distributions in space altered.
Biological effects interact with physical effects
Natural selection tends to favour higher competitive ability.
E.g., lynx – hare cycle. Not as simple; the plant quality available to the hares falls
when there are many hares. Social stresses (endocrine collapse) in overcrowded hare
Models of Mutualisms?
Not as much work on population dynamics
L-V type models blow up, N’s grow toward infinity; something outside the
mutualism must limit numbers
So, more attention has focused on evolutionary aspects…
Although losses of mutualists can cause population declines.
Connecting L-V competition to niche theory, 1960’s to 1970’s:
Assume competitive exclusion is the important force, so coexistence requires
How to measure differentiation? Ecological niche concept, can incorporate abiotic
and biotic factors
Leap of faith: competition alphas could be represented by niche overlap measures
Emerging theory: community composition determined by features that allow
coexistence: limiting similarity; resource partitioning, assembly rules, character
Niche partitioning, the inspirational case:
Insectivorous warblers – many similar species breed in coniferous forest. Alphas
should be high (sharing of resources should be high). How do they coexist?
Niche overlap measures ecological similarity