HABITAT SELECTION BY AQTJATIU INVERTEBBATES
355
when two incipient species are separating in the same environment
(Hinde, 1959) and so, allopatric origin of new species, where
separation takes place by the development of geographic barriers over
long periods of time, need not concern us.
Perhaps the most probable way habitat selection may initiate or
assist sympatric speciation is by leading animals to new local habitats
which might then result in the formation of new breeding populations
(Meadows and Campbell, 1972). However the individuals in the new
colony must be prevented from periodically returning to the parent
population if they are to have a reasonable chance of evolving into a
new species. Now this could conceivably take place by an alteration in
the local environment such as the isolation of a sand bank by shifting
sediments in an estuary, but environmental change of this sort when it
occurs may not be permanent. The effective isolation of a colony
would of course be straightforward if the colony had originated from a
mutant line whose behaviour and habitat selection had thus been
genetically altered, and we have given examples of mutants that fall
into this category. If the new colony came from some of the aberrant
individuals known to occur in populations of certain species, effective
isolation would be more difficult, although once set in motion the
process could be reinforced by something analogous to olfactory conditioning in insects. But more than this is likely to be needed since
there would still be very little to prevent individuals from the new
colony returning to the parent population. A genetic change in behaviour would on the other hand prevent the return, and this is exactly
what has been described by Dobzhansky and his co-workers as occurring in populations of Drosophila selected for particular behaviour traits
over a number of generations.
IX. CONCLUSION
The evidence we have presented in this review shows that the local
distribution of most aquatic invertebrates is determined by their
behavioural reactions to their environment. Animals respond to a
wide range of physical and chemical variables such as temperature,
light and salinity as well as to their biological environment which
includes encounters with their own and other species, with plants and
micro-organisms, with their food, and with predators or prey.
Upon this background of the interplay between behaviour and
environment is superimposed variation caused by age , previous experience, physiology, individual variation, and so on. Animals therefore test and select their habitats according to a complex set of rules.
An explanation of animal distribution in terms of animal behaviour
355
when two incipient species are separating in the same environment
(Hinde, 1959) and so, allopatric origin of new species, where
separation takes place by the development of geographic barriers over
long periods of time, need not concern us.
Perhaps the most probable way habitat selection may initiate or
assist sympatric speciation is by leading animals to new local habitats
which might then result in the formation of new breeding populations
(Meadows and Campbell, 1972). However the individuals in the new
colony must be prevented from periodically returning to the parent
population if they are to have a reasonable chance of evolving into a
new species. Now this could conceivably take place by an alteration in
the local environment such as the isolation of a sand bank by shifting
sediments in an estuary, but environmental change of this sort when it
occurs may not be permanent. The effective isolation of a colony
would of course be straightforward if the colony had originated from a
mutant line whose behaviour and habitat selection had thus been
genetically altered, and we have given examples of mutants that fall
into this category. If the new colony came from some of the aberrant
individuals known to occur in populations of certain species, effective
isolation would be more difficult, although once set in motion the
process could be reinforced by something analogous to olfactory conditioning in insects. But more than this is likely to be needed since
there would still be very little to prevent individuals from the new
colony returning to the parent population. A genetic change in behaviour would on the other hand prevent the return, and this is exactly
what has been described by Dobzhansky and his co-workers as occurring in populations of Drosophila selected for particular behaviour traits
over a number of generations.
IX. CONCLUSION
The evidence we have presented in this review shows that the local
distribution of most aquatic invertebrates is determined by their
behavioural reactions to their environment. Animals respond to a
wide range of physical and chemical variables such as temperature,
light and salinity as well as to their biological environment which
includes encounters with their own and other species, with plants and
micro-organisms, with their food, and with predators or prey.
Upon this background of the interplay between behaviour and
environment is superimposed variation caused by age , previous experience, physiology, individual variation, and so on. Animals therefore test and select their habitats according to a complex set of rules.
An explanation of animal distribution in terms of animal behaviour