346
P. 9. MEADOWS AND J. I. UAMPBELL
temperature reductions (often to 12OC) caused by atmospheric cold
fronts. Thus the postlarvae of P . uztecus are exposed to considerably
lower and more changeable estuarine temperatures than those encountered by P . setiferus. Aldrich et al. suggest that burrowing by
P . azteczcs postlarvae could extenuate the influence upon them of the
temperature changes to which they are exposed and could also protect
them from predators when their escape responses are slowed by the
fall in temperature. They go on to consider circumstantial evidence
which suggests that the postlarvae of P . uztecus may also burrow offshore during part of the winter, before entering shallower water.
Many intertidal animals behave differently in and out of water and
will therefore show alterations in behaviour as they are continually
covered and then uncovered by the tide. The molluscs Nussurius
Ob8OletUS and Lepidochitonu cinerea are geonegative under water and
geopositive out of water (Evans, 1951 ; Crisp, 1969), and Corophiurn
volutator is geopositive and photonegative when crawling over surfaces
out of water and photopositive when swimming in water (Barnes et ul.,
1969; Meadows and Reid, 1966). Analogous behaviour changes have
been noted for the amphipod Hawtoriw arenarim (Slabber) which is
photopositive while swimming and photonegative when burrowing
(Dennell, 1933) and for Littorina neritoides which, when under water,
crawls towards light on the under surface of a rock but away from light
on the upper surface (Fraenkel, 1927). These are all animals living
in the sea or on the shore and it would be interesting to know of instances
from the freshwater environment. Furthermore, the whole concept of
invertebrates being able to switch their behaviour in contrasting
situations is one that has not received the attention it deserves.
We have presented in this section clear evidence that aquatic
invertebrates can learn, and have suggested how this might influence
their selection of suitable habitats. Habitat selection is also influenced
by the age, physiological state, previous experience, and the past
and present environment of an animal although in some cases so little
is known of aquatic invertebrates that one can only quote terrestrial
parallels. As yet it is not possible to state how important or common
these factors might be in the general processes of habitat selection
in fresh waters and the sea ; however their listing should at least draw
them to the attention of those planning or executing experiments.
VIII. INDIVIDUAL VARUTION, THE COLOMZATION OF
NEW HABITATS, AND THE ORIGYX OF NEW SPECIES
The previous section emphasizes how variable many aspects of
habitat selection are, and how previous experience, learning, and the
P. 9. MEADOWS AND J. I. UAMPBELL
temperature reductions (often to 12OC) caused by atmospheric cold
fronts. Thus the postlarvae of P . uztecus are exposed to considerably
lower and more changeable estuarine temperatures than those encountered by P . setiferus. Aldrich et al. suggest that burrowing by
P . azteczcs postlarvae could extenuate the influence upon them of the
temperature changes to which they are exposed and could also protect
them from predators when their escape responses are slowed by the
fall in temperature. They go on to consider circumstantial evidence
which suggests that the postlarvae of P . uztecus may also burrow offshore during part of the winter, before entering shallower water.
Many intertidal animals behave differently in and out of water and
will therefore show alterations in behaviour as they are continually
covered and then uncovered by the tide. The molluscs Nussurius
Ob8OletUS and Lepidochitonu cinerea are geonegative under water and
geopositive out of water (Evans, 1951 ; Crisp, 1969), and Corophiurn
volutator is geopositive and photonegative when crawling over surfaces
out of water and photopositive when swimming in water (Barnes et ul.,
1969; Meadows and Reid, 1966). Analogous behaviour changes have
been noted for the amphipod Hawtoriw arenarim (Slabber) which is
photopositive while swimming and photonegative when burrowing
(Dennell, 1933) and for Littorina neritoides which, when under water,
crawls towards light on the under surface of a rock but away from light
on the upper surface (Fraenkel, 1927). These are all animals living
in the sea or on the shore and it would be interesting to know of instances
from the freshwater environment. Furthermore, the whole concept of
invertebrates being able to switch their behaviour in contrasting
situations is one that has not received the attention it deserves.
We have presented in this section clear evidence that aquatic
invertebrates can learn, and have suggested how this might influence
their selection of suitable habitats. Habitat selection is also influenced
by the age, physiological state, previous experience, and the past
and present environment of an animal although in some cases so little
is known of aquatic invertebrates that one can only quote terrestrial
parallels. As yet it is not possible to state how important or common
these factors might be in the general processes of habitat selection
in fresh waters and the sea ; however their listing should at least draw
them to the attention of those planning or executing experiments.
VIII. INDIVIDUAL VARUTION, THE COLOMZATION OF
NEW HABITATS, AND THE ORIGYX OF NEW SPECIES
The previous section emphasizes how variable many aspects of
habitat selection are, and how previous experience, learning, and the