IMPLICATIONS OF NONLINEAR DENSITY-DEPENDENCE

Ranges of the ratio of maximum net productivity level (MNPL) to carryi ng capacity (K) are explored in general models for pinnipeds and odont ocetes. MNPL/K is used in management of marine mammals but no empirica l evidence exists to limit the range of values expected. Density depen dent changes in age-specific birth and death rates have been used to i nfer MNPL/K. Non-linearities in these rates do not translate directly to population growth curves. The simple models demonstrate: (1) densit y dependence is likely to involve more than a single parameter (such a s birth rate), (2) MNPL/K can be greatly reduced from that inferred fr om one strongly non-linear parameter when changes in other parameters are linear, (3) ranges of MNPL/K depend on biological limits on ranges of fecundity and survival rates, and (4) the magnitude and sign of bi as incurred by inferring MNPL/K from functional forms of single parame ters cannot be determined. Given current empirical evidence the range of MNPL/K for marine mammals as a group is large. Although MNPL/K shou ld not be inferred from single parameter non-linearities, distribution s oe MNPL/K values can be generated through models which account for s ingle species ranges for birth and death rates and maximum population growth rate.