HABITAT SELECTION BY AQUATIC INVERTEBRATES
349
and so leave a more ragged leaf than those left by the type I1 larvae. The
comparative behaviour of colonies of the two types in the field is also
noteworthy. Type I colonies construct several tents in a short time,
and they space these and their feeding sites over distances of several
metres, while type I1 colonies construct one tent and remain feeding on
one leaf sometimes for more than 10 days. Following metamorphosis
the type I larvae give rise to active adults, whereas adults from type I1
larvae are sluggish. Wellington’s detailed study is interesting in its
own right, but quite clearly has broader implications for the study
of behavioural differences between individuals of species living in the
sea and fresh water, a field that has received very little attention.
Putting aside the possibility of observer or experimental error,
it is at f i s t sight difficult to understand what function these behavioural
differentiations might have, and we are not even certain whether our
classification has any meaning apart from bringing order to scattered
observations. Neither is it clear whether most of the recorded instances
of individual variation are phenotypic or genotypic. However we do
feel that some unusual behaviour patterns may be the means whereby
in certain circumstances new environments are colonized, and thus
may also play a part in speciation. These points will be discussed in
detail below.
Although the behaviour of individuals within a species may vary in
rather unexpected ways, in general species have recognizable behaviour
patterns that they use to select their habitats. We should now turn to
consider how these recognizable behaviour patterns differ between
taxonomically closely related species occupying the same or different
habitats. Reference will only be made to papers in which species within
the same genus have been investigated. The studies of Powers (1914)
on four species of freshwater crayfish (Cambarus), of Gowanloch and
Hayes (1927) on three intertidal species of Littorina, of Meadows ( 1 9 6 4 ~ )
and Gamble (1971) on two Corophium species, of Williams (1958) and
Aldrich et al. (1968) on three marine shrimps (Penaeius), of Jones
(1970) on two species of intertidal isopod (Eurydice), and of Phillips
(1971) on two species of Callianassa, demonstrate species differences in
preferences mirroring the species’ ecological distribution, and in the
same way there are differences in substrate preferences between the
settling larvae of various Spirorbis species (Garbarini, 1936; de Silva,
1962), differences in the reaction to current of the settling larvae of
Balanus species (Smith, 1946), and in fresh water, differences in the
habitat preferences of the nymphs of two closely related mayfly species
(Heptagenia) which are often found in the same part of a stream (Madsen,
1968). Other examples come from commensal relationships such as the
349
and so leave a more ragged leaf than those left by the type I1 larvae. The
comparative behaviour of colonies of the two types in the field is also
noteworthy. Type I colonies construct several tents in a short time,
and they space these and their feeding sites over distances of several
metres, while type I1 colonies construct one tent and remain feeding on
one leaf sometimes for more than 10 days. Following metamorphosis
the type I larvae give rise to active adults, whereas adults from type I1
larvae are sluggish. Wellington’s detailed study is interesting in its
own right, but quite clearly has broader implications for the study
of behavioural differences between individuals of species living in the
sea and fresh water, a field that has received very little attention.
Putting aside the possibility of observer or experimental error,
it is at f i s t sight difficult to understand what function these behavioural
differentiations might have, and we are not even certain whether our
classification has any meaning apart from bringing order to scattered
observations. Neither is it clear whether most of the recorded instances
of individual variation are phenotypic or genotypic. However we do
feel that some unusual behaviour patterns may be the means whereby
in certain circumstances new environments are colonized, and thus
may also play a part in speciation. These points will be discussed in
detail below.
Although the behaviour of individuals within a species may vary in
rather unexpected ways, in general species have recognizable behaviour
patterns that they use to select their habitats. We should now turn to
consider how these recognizable behaviour patterns differ between
taxonomically closely related species occupying the same or different
habitats. Reference will only be made to papers in which species within
the same genus have been investigated. The studies of Powers (1914)
on four species of freshwater crayfish (Cambarus), of Gowanloch and
Hayes (1927) on three intertidal species of Littorina, of Meadows ( 1 9 6 4 ~ )
and Gamble (1971) on two Corophium species, of Williams (1958) and
Aldrich et al. (1968) on three marine shrimps (Penaeius), of Jones
(1970) on two species of intertidal isopod (Eurydice), and of Phillips
(1971) on two species of Callianassa, demonstrate species differences in
preferences mirroring the species’ ecological distribution, and in the
same way there are differences in substrate preferences between the
settling larvae of various Spirorbis species (Garbarini, 1936; de Silva,
1962), differences in the reaction to current of the settling larvae of
Balanus species (Smith, 1946), and in fresh water, differences in the
habitat preferences of the nymphs of two closely related mayfly species
(Heptagenia) which are often found in the same part of a stream (Madsen,
1968). Other examples come from commensal relationships such as the