70
Herbivores and Algae: Food Utilization, Growth and Reproduction ...
Lynch (1989) found a significant variation in egg size with food conditions,
but the effect was so small «10%) that it can in practice be assumed that egg
carbon content in Daphnia pulex is a constant Bo = 1.1 J.l8 C, which is not
significantly different from the neonate body mass (B I ; Ilg C) reported by the
same author. Goulden et al. (1984) also found only a slight and insignificant
difference in dry weight between eggs and neonates in D. galeata and
D. magna. The small mass decrease during egg development is supported by
the results of Bohrer and Lampert (1988), who found very low respiration
rates in D. magna eggs « 20% of the rates found in juveniles of the same
species). It can therefore be assumed that the initial body mass in the first
instar is equal to the mass of a fresh egg (Bo = B I ) •
0.6 •
----.
-
•
I
"0
' - '
0
•
...
cd
0.4
I-<
c::
0
.- ...
cd
- ·S
.- en en 0.2
~
...
0
Z
0
0
20
40
60
Body size (~g C)
Fig. 4.2. Specific net assimilation rate [estimated from Eq. (A2.7») as function of body size in
Daphnia pulex [pooled data from food levels> I (mg C) 1' 1 from Lynch 1989). Solid line is
given by the model given by Eq. (4.7)