A preliminary study is presented of the temperature factor (temperature sensitivity) among twelve species of oceanic copepods. The temperature factor decreases downwards through the population except at night and among the shallower living species. This is the opposite of the relationship
of the illumination factor. The effects of possible variations in the pressure factor are discussed. Shallow living species tend to be most sensitive to temperature changes and least sensitive to illumination changes. Interspecific relationships of the factors at night are more closely
associated with day than with night conditions. Vertical spread, previously shown to increase with depth, is now shown to do so only to a point and then decrease again. The day-night range of depth and factors is found to be more closely associated with day than with night conditions.
The day and night vertical distribution of a typical copepod have been calculated from known behavior constants. The effect of varying these shows greater sensitivity to changes in the illumination factor than in the temperature factor.
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