Necessity of biodiversity for maintaining community stability
C. Elton (1958) :
Simple communities are more easily
upset than richer ones - i.e., they are more subject to destructive oscillations
in populations, and more vulnerable to invasions.
Field observations indicate that greatly simplified communities are characterized by more violent fluctuations in population density than diversified communities:
Invasions most frequently occur on cultivated land - which have far less diversity than natural wilderness.
Insect outbreaks are rare in diverse tropical forests - but common in less diverse sub-tropical forests.
R. H. MacArthur attempted
a theoretical justification for this observation:
Multiplicity in the number of prey and predator species associated with a population, frees it from dramatic changes in abundance when one of the prey or predator species declines in density.
However these ideas were challenged by the theoretical
analysis of random ecological networks by Robert
May (1972) - and prior numerical experiments on the stability of
random networks by M. R. Gardner and W.
R. Ashby (1970).