(^) That would lend selective advantage for any genetics producing males over genetics
producing females (Fisher 1930). That effect should operate up to the point at which
an overabundance of males left most of them to die without issue (as the saying goes).
The balance usually lies at about 50% males, which evolution has fixed in many
species by rigid, chromosomal sex determination. For copepods to sustain variable
sex ratios and ESD, there must be some mechanism by which a variable aspect of the
habitat informs an individual before it matures about its reproductive odds as male or
female, directing the choice. This, too, could be modeled with a multigenerational
IBM, which would be more complex to program but equally simple in conception.
“Adaptive” models are indeed applied in testing at least the logic, though not the
reality, of evolutionary theories. For an example, see the model by Fiksen and Giske
(1995) of the adaptive advantage of diel vertical migration (it is not an IBM, per se).
Developing Individuals Embedded in Flow Regimes
(^) Individual-based models are good tools for simulating the effects on individual
organisms of growth conditions and advection. An early representation of habitat
effects on reproductive and development timing in plankton populations is Batchelder
and Miller’s (1989) life-history model of Metridia pacifica (a copepod). The basic
idea is that a stock of individual animals can be represented in a computation by a
large number of vectors (up to >10^6 ) whose elements represent their developmental
and reproductive status. Elements can include alive-vs.-dead (1 or 0), age, stage, age-
within-stage, nutrition, readiness of the ovary for spawning, and anything else
necessary to represent the likely contribution of the individual to the status and
dynamics of the population. Vector elements are changed at successive time steps
according to functions based on biological information describing developmental