Agriculture Reference
In-Depth Information
Fig. 10.6
Relationship between growth and investment for defense. Each
curve
represents a
hypothetical species;
arrows
indicate the maximum realized growth rate. The optimal defense
differs depending on the growth rate of the plant species. For plants that have a high potential
growth rate, it is advantageous to invest in growth by reducing the investments for defense, but
plants with a lower potential growth rate should invest for defense. (From Coley et al. 1985)
The first possibility is the resource availability theory for plant defense (Coley
et al. 1985; Agrawal 2006). This theory is predicated on the assumption that the
resource environment in which a plant grows will condition its defensive invest-
ments. The theory is developed with reference to herbivores but in principle should
also apply to defense against pathogens. The logic of the predictions rests on the
following mathematical model (Coley et al. 1985) generating the series of growth
curves shown in Fig.
10.6
:
( ) ( )
g G
= − −−
1
kD
a
H mD
b
(10.3)
where
g
is the realized growth rate and
G
the potential growth rate, which represents
the rate without loss by herbivory or without any defense against herbivory.
D
is
investment for defense,
H
the potential herbivory, and
k
,
m
,
a
, and
b
are constants.
The first term of the right-hand side of (10.2) is the growth rate, indicating that the
potential growth rate (
G
) is reduced by the investment for defense (
D
). The second
term is the level of leaf damage from herbivory, suggesting potential herbivory (
H
)
is reduced by the defense. The subtraction of herbivory losses from growth gives
