Dissertation - HQ

28 Behaviour in models
Using mean population performance in models is not appropriate
when only a small portion of the performance distribution may constitute
the survivors. Therefore, variance around the mean has to be
derived from observations 63 or estimated from published accounts and
incorporated into the model to provide a realistic range of individual
results. Such a probabilistic approach can be accomplished through
individual based models where traits of individual particles can be assigned
following a probability density function. In addition, maximum
values should also be considered because successful recruits may be
the very few “best” individuals of each cohort (Figure 1.1).
1.2.2 Ontogeny of behaviour
Just like morphology, behaviour develops during the pelagic larval stage
from essentially planktonic at its start to nektonic at its end, and the
passive portion of it is likely to be short. In addition to ontogenetic
changes in behavioural ability (e.g. swimming speed), there are frequently
ontogenetic changes in the use of those abilities (e.g. age-related
changes in depth or in swimming direction). The methods for modelling
behaviour need to be adjusted according to the state of knowledge of
physical-biological interactions that result in larval growth. Indeed, most
studies indicate that size (or stage of development) is a better predictor
of behavioural ability than is age 64 .
Ontogeny of behaviour
is best described by size
• When growth is explicitly included in the model, behaviour can
be formulated as a function of size. In addition, as mentioned
above, this relation should not be deterministic and should not
consider only the mean value for the population; associated variation
should be included. In this case, as larvae are subjected
to differential growth, in a model with spatially heterogeneous
resources for example, they will display differential performance
for a given behaviour.
• When larval growth is not resolved in the model or when not
enough information is available to predict a continuous relationship
between size and behavioural performance, either age
or developmental milestones can be used to model behaviours,
possibly in a simplified, step-wise manner. Age and ontogenetic
stages can be expressed by a dimensionless metric such as an
developmental age 65 or ontogenetic index 64 .
1.2.3 Taxonomic resolution of behaviour
Ideally, the behaviour of larvae of the species to be modelled should be
incorporated into the model. Nevertheless, it is important to know the
degree to which the behaviour of a particular species can be generalised
to other taxa, because it is unlikely that we will ever have even partial
information on the behaviour of all fish species. At present, the amount