A copepod in a seasonal environment continuously faces the trade-offs
among allocating surplus growth to a storage compartment (lipids), to
somatic growth or to reproduction. By building up lipids, it can survi
ve periods with low food, and gain reproductive success the following
season by transforming fat to eggs. Also, copepods face a trade-off be
tween survival and growth, as surface waters generally are more risky
and productive than the dark refuges at greater depths, both in the di
el and annual temporal scale. Implicit in these trade-offs are the num
bers of generations, population dynamics and productive potential of t
he copepod. The authors develop a model which is used to investigate (
1) how optimal diel and ontogenetic vertical migration might vary with
season, individual state (size and lipid reserves) and growth conditi
ons; (2) whether fat is mainly used for overwintering or for fueling r
eproduction in early spring; and (3) the adaptive value of behavioural
flexibility in migration patterns. The model suggests an explanation
for observations of absence of vertical migration during spring bloom
and before descent to overwintering, and it suggests 1-2 successful ge
nerations per year in its basic version. It shows that migratory strat
egies are not similar between stages and strongly depend on the level
of accumulated reserves, that the risk of predation can affect growth,
distribution and number of generations and that one should expect phe
notypic plasticity in DVM patterns. The model is very sensitive to the
rate of metabolism during dormancy.