progress and mortality under varying habitat conditions (temperature, food
availability, time of day, ...). An initial set of vector animals is best established from
field data about a particular ocean place and season. When vectors reproduce, the
“eggs” are assigned new vectors.
(^) In a population-dynamical IBM for Calanus finmarchicus moving in the flow of the
Gulf of Maine (Miller et al. 1998), some model elements were added to each
individual’s development vector representing its spatial address in a site-specific
circulation model. The model was initiated at the winter solstice, December 21, by
defining a set of 1000 vectors, each representing a single, resting fifth copepodite
(C5), the G 0 generation. At suitable time steps, the vector animals emerge from rest,
move to the surface layer and, as they mature, are advected along by applying current
velocities specified at each one’s spatial address by the Quoddy model of regional
flow (Lynch et al. 1996). They are also given random moves representing mixing
dispersion. (For nekton, changes in position could also be applied to represent
swimming.)
(^) As the G 0 C5s mature, they are assigned new vectors appropriate for spawning
females, and as eggs are produced they are assigned to larval vectors. Each vector has
six elements (Table 4.3). The probability that any given C5 will emerge from diapause
and mature at a time step starts from zero at the winter solstice (Day 1), then rises.
Progressively, all individuals mature and are assigned to a female vector. Clutch-
readiness fraction (CR) at maturation is set to a random number, 0 to 1.0, to force
spreading of spawning time around the day, which may not be realistic but smooths
the shifting of stage abundances. After activation (vector assignment), 7 days (age as
) are allowed to pass before reproduction begins, then CR is incremented at each
hourly time step by 1/24th of the inverse of the clutch-to-clutch interval in days
predicted by a Blehrádek function (Fig. 4.15a) fitted to some data for clutch interval
as a function of temperature. This inverse is the fraction of clutch development
occurring in the one-hour time step. When CR reaches 1.0, a clutch of 50 eggs is
produced and each is assigned to an egg-C4 vector, and CR is zeroed. Temperature for
this and other purposes in the model is drawn from a seasonal function developed
from a long set of field data. Each day, each female and larval vector is subjected to a
random chance of death (e.g. female daily survivorship = 0.975). One of the main
problems with such modeling is that we have only weak clues about the stage-wise
mortality rates (see Chapter 8).
Table 4.3 Vector values and meanings for three distinctive life stages as modeled by
Miller et al. (1998). Pixel number refers to a spatial element in the physical model.
CR is a female’s clutch readiness variable that increases as oocytes mature, leading to
spawning when CR = 1.0. MCF is a larva’s molt-cycle fraction that increases as it
grows; it molts (and “stage” is incremented) when MCF = 1.0. When “stage” reaches