Food Supply Regimes and Individual Growth Histories
4.4 Food Supply Regimes and Individual Growth
Histories
79
Rigler (1961) noticed that at low food levels the feeding rate of Daphnia
seem to be limited by the amounts of water the animal can filter, while at
high food levels it is limited by some other factor. As a result, the ingestion
rate increases with food concentration until the "incipient limiting level"
(McMahon and Rigler 1965) is reached, after which the ingestion rate levels
out and becomes independent of the food level. Both reduced filtering rate
through lowered appendage beating frequency, and increased rejection rate
through more frequent clearing of the food groove by the abdominal claw
are probably important mechanisms in determining the functional
response in Daphnia (Porter et al. 1982).
An optimal foraging model presented by Lehman (1976) predicts that
animals should stop feeding at very low food levels in order to save energy.
Experimental evidence so far indicates that such a threshold must indeed
be very low [at most a few (Jig C) rl; Muck and Lampert 1980; Porter et al.
1982], indicating that the feeding response in Daphnia is probably a
monotonic increasing function.
The Functional Response. Due to the conspicuous increase in experimental
scatter at high food levels in typical Daphnia feeding experiments, several different functions can be fitted with almost equal goodness-of-fit (Lampert 1977;
Porter et al. 1982). There is some evidence that the transition to saturated ingestion often is more abrupt than would be predicted from the common rectangular hyperbola (the Michaelis-Menten curve of enzyme kinetics), and that a
piecewise linear function generally is more appropriate (Condrey and Fuller1985).
With the notation used so far, the dependence of the specific ingestion
rate on food concentration [C; (mg C) rl] can be written as
{
C
-,-, CsC' I'
1= 1 C
= - min(C,c')'
I'
C>C' C'
(4.11)
where C' is the incipient limiting food level [(mg C) rl) and fis the maximum
ingestion rate at a given body size[Eq. (4.10»).
The functional response [Eq. (4.11») contains the implicit assumption that C'
is independent of body size. The available experimental data seem to be both
limited and ambiguous; McMahon (1965) reported changes in C' with body
size, while Lampert (1977) presented feeding curves indicating a constant C' for
different size groups of D. pulex grazing on Stichococcus. Most workers have
found the incipient limiting food level to be in the range 0.2-Q.5 (mg C) r l for
Daphnia feeding on readily ingestible algae (Lampert 1987), although
Thompson et al. (1982) have reported values below 0.2 (mg C) r l for Daphnia
feeding on natural seston.
4.4 Food Supply Regimes and Individual Growth
Histories
79
Rigler (1961) noticed that at low food levels the feeding rate of Daphnia
seem to be limited by the amounts of water the animal can filter, while at
high food levels it is limited by some other factor. As a result, the ingestion
rate increases with food concentration until the "incipient limiting level"
(McMahon and Rigler 1965) is reached, after which the ingestion rate levels
out and becomes independent of the food level. Both reduced filtering rate
through lowered appendage beating frequency, and increased rejection rate
through more frequent clearing of the food groove by the abdominal claw
are probably important mechanisms in determining the functional
response in Daphnia (Porter et al. 1982).
An optimal foraging model presented by Lehman (1976) predicts that
animals should stop feeding at very low food levels in order to save energy.
Experimental evidence so far indicates that such a threshold must indeed
be very low [at most a few (Jig C) rl; Muck and Lampert 1980; Porter et al.
1982], indicating that the feeding response in Daphnia is probably a
monotonic increasing function.
The Functional Response. Due to the conspicuous increase in experimental
scatter at high food levels in typical Daphnia feeding experiments, several different functions can be fitted with almost equal goodness-of-fit (Lampert 1977;
Porter et al. 1982). There is some evidence that the transition to saturated ingestion often is more abrupt than would be predicted from the common rectangular hyperbola (the Michaelis-Menten curve of enzyme kinetics), and that a
piecewise linear function generally is more appropriate (Condrey and Fuller1985).
With the notation used so far, the dependence of the specific ingestion
rate on food concentration [C; (mg C) rl] can be written as
{
C
-,-, CsC' I'
1= 1 C
= - min(C,c')'
I'
C>C' C'
(4.11)
where C' is the incipient limiting food level [(mg C) rl) and fis the maximum
ingestion rate at a given body size[Eq. (4.10»).
The functional response [Eq. (4.11») contains the implicit assumption that C'
is independent of body size. The available experimental data seem to be both
limited and ambiguous; McMahon (1965) reported changes in C' with body
size, while Lampert (1977) presented feeding curves indicating a constant C' for
different size groups of D. pulex grazing on Stichococcus. Most workers have
found the incipient limiting food level to be in the range 0.2-Q.5 (mg C) r l for
Daphnia feeding on readily ingestible algae (Lampert 1987), although
Thompson et al. (1982) have reported values below 0.2 (mg C) r l for Daphnia
feeding on natural seston.