ASPEUTS OF STRESS IN THE TROPIUAL MARINE ENVIRONMENT
231
the cooler series. This lower ecotone may perhaps be displaced somewhat downwards in the warm series, but the upper one undoubtedly
shows considerable displacement. The zone between the two neap
ecotones also seems to show some downward displacement in the warm
series.
It would seem to be consistent with the hypothesis that the tropics
are a region of stress that the zones would be displaced towards wetter
conditions where such stress exists, and that such displacement would
be more apparent on the upper part of the shore than on the lower part.
There are several possible sources of error to consider in interpreting
these results. The first is the effect of wave action. It is unlikely that
there is a systematic difference in wave action through the series.
However, tidal ranges tend to be less in the tropics, and any wave action
would therefore cause a greater relative displacement there. In practice,
wave action tends t o move upper limits upwards and lower limits
either upwards or downwards. Any wave error might therefore be
expected to move the upper ecotone upwards in the tropics, which would
reduce, not produce, the observed shift. Varying degrees of wave
action at the different localities would also result in a tendency to
smooth out the observed peaks.
For lack of complete tidal data for all localities, we were forced to
assume a constant neap : spring ratio for all localities. We know,
however, that this ratio is higher in the tropics than in temperate
waters. This would result in some shift in the two neap ecotones
towards mid-tide level in the tropics. Even if we took spring:neap
ratios for our two temperature groups as the extremes shown in Fig. 6,
this should not produce more than a 30% shift, whereas we observed a
60% shift, and the figure of 30% is based on a much bigger difference
than was actually the case for the averages of all localities in the two
groups. It seems, then, that the observed shift is real.
D. Growth rates and temperature
There have been many attempts to formulate an equation of universal application describing growth. None of them suits our needs.
To begin with, at sexual maturity many animals either cease growing
or reduce their rate more or less sharply. We have therefore considered
growth up to sexual maturity as distinct from that after maturity ; the
two are probably controlled by different factors. Unfortunately, much
data on growth has had to be disregarded for lack of information on
maturation. The many references from which we have drawn data are
included in the bibliography.
In comparing species, growth needs to be expressed in terms of
231
the cooler series. This lower ecotone may perhaps be displaced somewhat downwards in the warm series, but the upper one undoubtedly
shows considerable displacement. The zone between the two neap
ecotones also seems to show some downward displacement in the warm
series.
It would seem to be consistent with the hypothesis that the tropics
are a region of stress that the zones would be displaced towards wetter
conditions where such stress exists, and that such displacement would
be more apparent on the upper part of the shore than on the lower part.
There are several possible sources of error to consider in interpreting
these results. The first is the effect of wave action. It is unlikely that
there is a systematic difference in wave action through the series.
However, tidal ranges tend to be less in the tropics, and any wave action
would therefore cause a greater relative displacement there. In practice,
wave action tends t o move upper limits upwards and lower limits
either upwards or downwards. Any wave error might therefore be
expected to move the upper ecotone upwards in the tropics, which would
reduce, not produce, the observed shift. Varying degrees of wave
action at the different localities would also result in a tendency to
smooth out the observed peaks.
For lack of complete tidal data for all localities, we were forced to
assume a constant neap : spring ratio for all localities. We know,
however, that this ratio is higher in the tropics than in temperate
waters. This would result in some shift in the two neap ecotones
towards mid-tide level in the tropics. Even if we took spring:neap
ratios for our two temperature groups as the extremes shown in Fig. 6,
this should not produce more than a 30% shift, whereas we observed a
60% shift, and the figure of 30% is based on a much bigger difference
than was actually the case for the averages of all localities in the two
groups. It seems, then, that the observed shift is real.
D. Growth rates and temperature
There have been many attempts to formulate an equation of universal application describing growth. None of them suits our needs.
To begin with, at sexual maturity many animals either cease growing
or reduce their rate more or less sharply. We have therefore considered
growth up to sexual maturity as distinct from that after maturity ; the
two are probably controlled by different factors. Unfortunately, much
data on growth has had to be disregarded for lack of information on
maturation. The many references from which we have drawn data are
included in the bibliography.
In comparing species, growth needs to be expressed in terms of