HABITAT SELECTION BY AQUATIC INVERTEBRATES
363
by each and every species present. New habitats may suddenly become
available to a species by changes induced by man-new wharfs, buoys,
lighthouses, or by natural changes such as the shifting of a sand bank,
the gradual silting up of an estuary, or the appearance of new sources of
food. The ecological consequences of changes of this sort in aquatic
environments have been followed by Kitching (1937), Pyefinch (1943),
Holme (1949), Boaden (1962) and Landenberger (1967) but have not
been analysed experimentally. What really amounts to a recolonization
of old habitats can also occur after short periods of environmental
catastrophe, such as the 1962163 cold winter in Britain, and again the
consequences have been described (Bradley and Cooke, 1958 ; Webb,
1968a ; Crisp, 1964). Members of a species are sometimes forced to move
out to new habitats by population pressure and the phenomenon is well
known in the terrestrial environment, but has not been systematically
investigated in the sea or fresh water except by Bovbjerg (1964).
New habitats may also be colonized in aquatic environments by a
process akin to olfactory conditioning in insects (see above) : a group
of animals might not for one reason or another be able to find their
normal habitat or host, and might then make do with something less
suitable. Once in the less suitable habitat the animals might then
become conditioned to it in preference to their original habitat, and so
remain (Meadows and Campbell, 1972). Obviously this sequence of
events is a matter of some speculation, but enough is known of conditioning in insects to make the speculation feasible.
Spontaneously occurring mutations changing a pattern of behaviour
will almost certainly influence the responses of a species to its environment, and probably to a great enough extent to allow colonization of
new habitats that might then become the permanent home of the
mutant. There is enough evidence from the terrestrial environment
at least, to support this hypothesis. A number of Drosophila mutants
respond differently to light intensity and wavelength (McEwen, 1918;
Brown and Hall, 1936; Volpe et al., 1967) and also to a combination
of light and humidity (Waddington et al., 1954). The only aquatic
example is of the behaviour of mutant Gammarus chevreuxi Sexton
towards light (Wolsky and Huxley, 1932). These are all responses to
the physical environment ; however there are also instances where
mutation appears to change the behaviour of an animal to its biological
environment. We consider that the changed activity and mating
behaviour of Drosophila mutants (Bastock, 1956), and of the mutants
of the moth Panaxia dominula (L.) (Sheppard, 1952) fall into this
category. Studies on behavioural mutants of aquatic invertebrates
would be rewarding. It would be very interesting, for instance, to find
363
by each and every species present. New habitats may suddenly become
available to a species by changes induced by man-new wharfs, buoys,
lighthouses, or by natural changes such as the shifting of a sand bank,
the gradual silting up of an estuary, or the appearance of new sources of
food. The ecological consequences of changes of this sort in aquatic
environments have been followed by Kitching (1937), Pyefinch (1943),
Holme (1949), Boaden (1962) and Landenberger (1967) but have not
been analysed experimentally. What really amounts to a recolonization
of old habitats can also occur after short periods of environmental
catastrophe, such as the 1962163 cold winter in Britain, and again the
consequences have been described (Bradley and Cooke, 1958 ; Webb,
1968a ; Crisp, 1964). Members of a species are sometimes forced to move
out to new habitats by population pressure and the phenomenon is well
known in the terrestrial environment, but has not been systematically
investigated in the sea or fresh water except by Bovbjerg (1964).
New habitats may also be colonized in aquatic environments by a
process akin to olfactory conditioning in insects (see above) : a group
of animals might not for one reason or another be able to find their
normal habitat or host, and might then make do with something less
suitable. Once in the less suitable habitat the animals might then
become conditioned to it in preference to their original habitat, and so
remain (Meadows and Campbell, 1972). Obviously this sequence of
events is a matter of some speculation, but enough is known of conditioning in insects to make the speculation feasible.
Spontaneously occurring mutations changing a pattern of behaviour
will almost certainly influence the responses of a species to its environment, and probably to a great enough extent to allow colonization of
new habitats that might then become the permanent home of the
mutant. There is enough evidence from the terrestrial environment
at least, to support this hypothesis. A number of Drosophila mutants
respond differently to light intensity and wavelength (McEwen, 1918;
Brown and Hall, 1936; Volpe et al., 1967) and also to a combination
of light and humidity (Waddington et al., 1954). The only aquatic
example is of the behaviour of mutant Gammarus chevreuxi Sexton
towards light (Wolsky and Huxley, 1932). These are all responses to
the physical environment ; however there are also instances where
mutation appears to change the behaviour of an animal to its biological
environment. We consider that the changed activity and mating
behaviour of Drosophila mutants (Bastock, 1956), and of the mutants
of the moth Panaxia dominula (L.) (Sheppard, 1952) fall into this
category. Studies on behavioural mutants of aquatic invertebrates
would be rewarding. It would be very interesting, for instance, to find