Habitat profitability in pelagic environments

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Abstract
Habitat profitability is analysed with a set of simple equations comprising predation risk, food availability, sex ratio, number of offspring per survivor, generation time and expected reproductive outcome. We show that organisms with fixed generation time should prefer hunger instead of increased feeding if the increase in feeding is associated with the same relative increase in predation risk. On the contrary, feeding is of higher reproductive value for organisms that may canalize increased feeding to a shortening of the generation time. These are more likely to tolerate increased predation risk associated with increased feeding possibilities. Generation times are often temperature dependent. The analysis indicates that an increase in environmental temperature may be more beneficial than the same relative decrease in predation risk. The theory is illustrated with data on the copepods Calanus finmarchicus and Paracalanus parvus.