LAKE DWELLING TRICLADS
35
construct any sort of picture. This problem has been tackled in three
main ways :
(a) by examination of squashes of triclads recently collected from the
field for the remains of prey. This method has the disadvantage that
results may be biased in certain directions, especially towards oligochaetes, which are more likely to be detected on account of their setae.
(b) laboratory experiments in which selected prey were exposed to
triclads starved for a uniform period (Holling, 1963). This approach has
two obvious disadvantages, the range of prey is restricted compared
with natural conditions, and the normal behaviour of either prey or
predator may be interfered with. The latter was probably reduced in
the experiments by the provision of cover for both organisms.
(c) the use of a serological technique for detecting prey in squashes
of field specimens. This is the most reliable approach but it has only
been used to a limited extent so far.
The results from the examination of field specimens, both young and
adult, are shown in Table VII. The main conclusions are that various
TABLE VII
Food Organisms Found in the Guts of Triclads Collected from the Field.
(Reproduced with permission from Reynoldson and Young, 1963.)
Expressed as percentage of total identifications
Polycelis .
Dugesia
Deiadrocoelum
ri igrc,
I’ dermis
lugubris
lacteuin,
Oligochaot,a
Lumbriculus
variegatus
Naididae
TubXicidac *
Lumbricidae
Arthropoda
Insecta
Asellus
Others
Mollusoa t
Lym.naeu sp.
Hydrobia jenkimi
Ancylus lacustris
Others
Total
. . . . . .- - -
28 -6
31.4
5.7
2.8
14.3
Nil
11.4
X il
Nil
Nil
5 *7
Adult
40.0
2 -8
31.4
8 -6
2 a 8
2 -8
5.7
Nil
Nil
Nil
5 *7
35.0
14.3
4 0 4
Nil
70-6
11.6
21.4
20.0
78-6
29.4
46.5
10.0
Nil
3.6
Nil
Nil
5.7
Nil
Nil
Nil
Nil
1.4
Nil
3.6
Nil
18.6
Nil
Nil
Nil
Nil
2.3
1.4
5.0
10.7
Nil
Nil
15-7
Nil
Nil
Nil
Nil
11-4
35.0
Nil
Nil
Nil
1.4
Nil
Nil
Nil
Nil
1.4
Nil
3.6
Nil
* May include Enhy!meidae.
t Based on radulae only.