IDEAL FREE DISTRIBUTION OF COPEPODS UNDER PREDATION RISK

Optimal vertical distribution of a copepod population of equal competi tors under predation hazard is modelled by ideal free distribution (IF D). The foragers may be limited by both depletable (food) and non-depl etable (temperature) resources. Individuals are assumed to maximize gr owth rate per mortality risk (g/M). Mortality risk is assumed density- dependent whenever the copepod concentration is high enough to satiate predators. The growth rate depends upon temperature or food concentra tion in absence of competition, and is density-dependent under competi tion. These relationships may yield peaked habitat profitability curve s. For L depths with peaked profitability curves, the computational co mplexity scales to 3(l). Simplifying restrictions to allow numerical s olutions when a large number of depths are available are presented and discussed. At moderate and high copepod stock size, the restrictions find the optimal distribution much faster, but at low stock sizes they may predict suboptimal distributions. The model predicts that individ uals shall be more sensitive to predation risk at low and moderate com petitor abundance and more sensitive to resource input rate at higher competitor abundances. Deviations from a food-based IFD are therefore most pronounced at low copepod population size. The IFDs are compared with predictions from a dynamic programming model with state- and time -resolved motivation of the copepods. (C) 1997 Elsevier Science B.V.