Depth of the Biomass Maximum Affects the
Rules of Resource Competition in a Water Column
Alexei B. Ryabov and Bernd Blasius
The
American Naturalist
Vol. 184, No. 5 (November
2014) (pp. E132-E146)
Abstract:
The theory of resource competition in
spatially extended systems with resources and biomass fluxes is far
from trivial. Here, we analyze the competition between two
phytoplankton species for light and a nutrient in a weakly mixed water
column. We develop a general framework for such an analysis and show
that the competition outcome can be largely understood from a single
parameter, the slope of the invasion threshold in the plane of
resources. Using
this approach, we show that the competition outcome crucially depends
on the depth of the biomass maximum. Under eutrophic conditions, when
the phytoplankton production peaks on the surface, species composition
depends on the ratio of resource supplies, and the competition outcome
follows the “classic” rule: coexistence is possible if each competitor
has the greatest effect on its most limiting resource. By contrast, in
oligotrophic systems, characterized by deep biomass maxima, the
absolute level of resource supplies drives species composition, and
coexistence becomes more feasible if each competitor mostly consumes
its least limiting resource. Finally, when the production peaks in the
subsurface, good nutrient competitors are favored. Our findings are
supported by empirical data.
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