6 Approaching Planktonic Food Webs:
Competition, Coexistence, and Chaos
... both theoretical and experimental analyses
have produced a number of mechanisms that
permit coexistence despite competition.
Therefore, the time has come to turn
Hutchinson's paradox upside down and to ask
the reverse question, "Why are there so few
species of phytoplankton in a given lake?" ...
the large discrepancy between the actual
number of phytoplankton species in a lake and
the maximal possible one shows that it is at
least a plausible hypothesis, that quite a lot of
competitive exclusion has occurred already.
Ulrich Sommer (1989b).
Resource competition is defined as an indirect form of competition where
the participating species are exploiting a shared resource. An increase in
one species will, under this condition, decrease the amount of resource
available to the other species, and thereby reduce their chances to
proliferate. If the resource availability is reduced to such a low level that a
species is unable to maintain non-negative net growth rate, this species will
eventually be competitively excluded from the community. For an arbitrary
number of species competing for a single resource in a constant environment, it can be shown that all but one species will be competitively
excluded. This result can be stated more generally as the principle of
competitive exclusion; that two species can coexist only if they exploit their
environment differently (Hardin 1960), or that an arbitrary number of species can coexist at constant levels, if they are limited by the same number of
resources (Levin 1970).
The competitive exclusion principle lead Hutchinson (1961) to formulate
the paradox of the plankton: how can so many species of phytoplankton
apparently coexist in a homogeneous epilimnion on so few resources (i.e.,
light, temperature, and a few mineral nutrients)? Since then, explaining the
plankton paradox has become one of the favorite activities among theoretically inclined ecologists. Most explanations that have been offered point
out that the simple n species-n resources relationship has been proven only
for species coexisting at constant densities in a constant environment, and
that either environmental variability or internally generated density fluctuations could promote the coexistence of more species.
Competition, Coexistence, and Chaos
... both theoretical and experimental analyses
have produced a number of mechanisms that
permit coexistence despite competition.
Therefore, the time has come to turn
Hutchinson's paradox upside down and to ask
the reverse question, "Why are there so few
species of phytoplankton in a given lake?" ...
the large discrepancy between the actual
number of phytoplankton species in a lake and
the maximal possible one shows that it is at
least a plausible hypothesis, that quite a lot of
competitive exclusion has occurred already.
Ulrich Sommer (1989b).
Resource competition is defined as an indirect form of competition where
the participating species are exploiting a shared resource. An increase in
one species will, under this condition, decrease the amount of resource
available to the other species, and thereby reduce their chances to
proliferate. If the resource availability is reduced to such a low level that a
species is unable to maintain non-negative net growth rate, this species will
eventually be competitively excluded from the community. For an arbitrary
number of species competing for a single resource in a constant environment, it can be shown that all but one species will be competitively
excluded. This result can be stated more generally as the principle of
competitive exclusion; that two species can coexist only if they exploit their
environment differently (Hardin 1960), or that an arbitrary number of species can coexist at constant levels, if they are limited by the same number of
resources (Levin 1970).
The competitive exclusion principle lead Hutchinson (1961) to formulate
the paradox of the plankton: how can so many species of phytoplankton
apparently coexist in a homogeneous epilimnion on so few resources (i.e.,
light, temperature, and a few mineral nutrients)? Since then, explaining the
plankton paradox has become one of the favorite activities among theoretically inclined ecologists. Most explanations that have been offered point
out that the simple n species-n resources relationship has been proven only
for species coexisting at constant densities in a constant environment, and
that either environmental variability or internally generated density fluctuations could promote the coexistence of more species.