ASPECTS OF STRESS IN THE TROPICAL MAKINE ENVIRONMENT
257
there being tropic-adapted species, behaving in many ways more as
cool-water species do at their lower temperatures. Along with such
tropic-adaptation, though, is inability to range into cooler waters as
many of the unadapted ones can do. It could, of course, equally well be
said that these are the typical inhabitants of the tropics and that it
was necessary, for example, to increase growth rates before a species
could spread into cooler waters. Since metabolic processes would be
reduced at the lower temperature, a rate equal to that of the tropicadapted species could then be maintained. The graph of the relation of
intertidal zonation to temperature suggests that there is tropic adaptation also to whatever factors limit vertical spread on the shore. A
similar adaptation is found in ability to grow to large size; in fact, all
aspects in which there is an increased coefficient of variation in the
tropics suggest such adaptation. It would be most interesting to know
whether adaptation for one character tends to accompany adaptation
for another also. The available data though are quite inadequate and
there are few species for which we have information on more than one
of the aspects we have considered.
There is abundant documentation for the increase in number of
species in the tropics, for example Fischer (1960) and Stehli (1968).
These include marine as well as land forms. Stehli et al. (1967) and
Stehli (1968) provide data which show that, while numbers of both
genera and families also increase towards the tropics, the number of
species per genus and the number of genera per family are higher in
the tropics than in temperate waters.
In some works data are given in the form of the relation of numbers
of species to latitude, but it is clear that the basic relation is with
temperature rather than latitude. For example, in Stehli’a charts of the
distribution of numbers of genera of hermatypic corals, calculation of
the partial correlations show that the relation of numbers to temperature
is significant while that to latitude is not. Fischer (1960) considered
that the distribution of number of species along the American coasts
showed the expected trend, the correlation with temperature, either
minimum, mean or maximum, was not close and suggested that seasonal
range of temperature was, perhaps, more important. However, when
temperatures from the Coast and Geodetic source used previously are
compared with the species distribution, the temperature relationship
shows upon both Atlantic and Pacific coasts whereas the temperature
range relationship is very doubtful. The data given by Wells (1 955) for
the distribution of corals on the Great Barrier Reef shows a good relation
of numbers of genera to mean temperature, but not to temperature range.
There seems little doubt, then, that speciation is related to temperature
257
there being tropic-adapted species, behaving in many ways more as
cool-water species do at their lower temperatures. Along with such
tropic-adaptation, though, is inability to range into cooler waters as
many of the unadapted ones can do. It could, of course, equally well be
said that these are the typical inhabitants of the tropics and that it
was necessary, for example, to increase growth rates before a species
could spread into cooler waters. Since metabolic processes would be
reduced at the lower temperature, a rate equal to that of the tropicadapted species could then be maintained. The graph of the relation of
intertidal zonation to temperature suggests that there is tropic adaptation also to whatever factors limit vertical spread on the shore. A
similar adaptation is found in ability to grow to large size; in fact, all
aspects in which there is an increased coefficient of variation in the
tropics suggest such adaptation. It would be most interesting to know
whether adaptation for one character tends to accompany adaptation
for another also. The available data though are quite inadequate and
there are few species for which we have information on more than one
of the aspects we have considered.
There is abundant documentation for the increase in number of
species in the tropics, for example Fischer (1960) and Stehli (1968).
These include marine as well as land forms. Stehli et al. (1967) and
Stehli (1968) provide data which show that, while numbers of both
genera and families also increase towards the tropics, the number of
species per genus and the number of genera per family are higher in
the tropics than in temperate waters.
In some works data are given in the form of the relation of numbers
of species to latitude, but it is clear that the basic relation is with
temperature rather than latitude. For example, in Stehli’a charts of the
distribution of numbers of genera of hermatypic corals, calculation of
the partial correlations show that the relation of numbers to temperature
is significant while that to latitude is not. Fischer (1960) considered
that the distribution of number of species along the American coasts
showed the expected trend, the correlation with temperature, either
minimum, mean or maximum, was not close and suggested that seasonal
range of temperature was, perhaps, more important. However, when
temperatures from the Coast and Geodetic source used previously are
compared with the species distribution, the temperature relationship
shows upon both Atlantic and Pacific coasts whereas the temperature
range relationship is very doubtful. The data given by Wells (1 955) for
the distribution of corals on the Great Barrier Reef shows a good relation
of numbers of genera to mean temperature, but not to temperature range.
There seems little doubt, then, that speciation is related to temperature