Resource Competition Under Phosphorus Limitation
49
1.6
-...
-
I
"C
-- V
~ 1.2
' "'
.fl
~
e 0.8
bO
0
I+::
....
0
V
c.. 0.4
til
0.0~------~--------4--------4--------4-------~
o
2
4
6
8
10
Dissolved inorganic phosphorus ([J.1g P] liter-I)
Fig. 3.6. Monod curves (numbered solid lines) relating steady state growth rate to equilibrium
DIP concentration for the three model species in Table 3.2. Dashed horizontal lines bound the
range of steady-state growth rates where a given species is competitively superior
From the parameters in Table 3.2 we can construct Monod curves
[Eq. (3.10)], describing the relationship between specific growth rate and
the equilibrium concentration of dissolved inorganic phosphorus when
phosphorus uptake and growth are in balance. The relative positions of the
Monod curves determine the competitive ability of phytoplankton species that
are subject to a constant loss rate [which in the absence of grazing and sedimentation will be equal to the dilution rate (D; dati) of the system]. The equilibrium inorganic P level for a single phytoplankton species growing at equilibrium with dilution losses is given by substituting}l = D in the Monod equation
[Eq. (3.10)] and solving for S. The species with the lowest equilibrium resource
level will be able to invade any community dominated by inferior competitors
to the extent of competitive exclusion, while the new equilibrium will be uninvadable to the inferior competitors (Hsu et al. 1977; Tilman 1982). For the set of
the model species (Fig. 3.6), this means that equilibria of species 1 will be uninvadable at low loss rates, while in a gradient of increasing loss rates, species 1
will be successively replaced by species 2, which again will be replaced by
species 3.
49
1.6
-...
-
I
"C
-- V
~ 1.2
' "'
.fl
~
e 0.8
bO
0
I+::
....
0
V
c.. 0.4
til
0.0~------~--------4--------4--------4-------~
o
2
4
6
8
10
Dissolved inorganic phosphorus ([J.1g P] liter-I)
Fig. 3.6. Monod curves (numbered solid lines) relating steady state growth rate to equilibrium
DIP concentration for the three model species in Table 3.2. Dashed horizontal lines bound the
range of steady-state growth rates where a given species is competitively superior
From the parameters in Table 3.2 we can construct Monod curves
[Eq. (3.10)], describing the relationship between specific growth rate and
the equilibrium concentration of dissolved inorganic phosphorus when
phosphorus uptake and growth are in balance. The relative positions of the
Monod curves determine the competitive ability of phytoplankton species that
are subject to a constant loss rate [which in the absence of grazing and sedimentation will be equal to the dilution rate (D; dati) of the system]. The equilibrium inorganic P level for a single phytoplankton species growing at equilibrium with dilution losses is given by substituting}l = D in the Monod equation
[Eq. (3.10)] and solving for S. The species with the lowest equilibrium resource
level will be able to invade any community dominated by inferior competitors
to the extent of competitive exclusion, while the new equilibrium will be uninvadable to the inferior competitors (Hsu et al. 1977; Tilman 1982). For the set of
the model species (Fig. 3.6), this means that equilibria of species 1 will be uninvadable at low loss rates, while in a gradient of increasing loss rates, species 1
will be successively replaced by species 2, which again will be replaced by
species 3.