Environmental Engineering Reference
In-Depth Information
Fig. 4.5 Results from the fish model of H
olker and Breckling (2002, 2005). (a) Increase in
biomass and size dependent diet of roaches (
Rutilus rutilus
). Large individuals are capable of
exploiting bigger food items (molluscs) thus providing a higher nutritional value [Figure adapted
from H
€
olker and Breckling (2005)]. (b) Simulation results of the length development of a second
year roach cohort. The length frequency illustrates the differentiation in size. Most roaches are
below 13 cm and only a few are 0.5-1 cm longer
€
with an explicit behavioural repertoire to react to its environment and comprises, e.g.
food searching, movement and biomass and season dependent reproduction. Bio-
energetic processes were implemented in detail to represent a realistic food depen-
dent growth and reproduction, which includes a size dependent exploitation of
resources. The model was parameterized for the roach (
Rutilus rutilus
) and simula-
tions were carried out for the abiotic conditions of a Northern German lake of about
1.1 km
2
surface.
The analysis of model results revealed changes in structural relationships.
Depending on size the fish were able to exploit further resources (molluscs)
providing a higher nutritional value (Fig.
4.5a
). Heterogeneities in size structure
thus were amplified (Fig.
4.5b
) allowing the larger individuals to reproduce 1 year
before the rest of the cohort. The model thus allowed to analyze causes for the
empirically determined cohort structure and potential reactions to changing envi-
ronmental conditions.
4.5 System Types and Modelling Approaches:
A Modern Diversity
For model development, a structural overview of the relevant relations to be
included or left out of consideration is essential. Formulating this overview in an
explicit way is the primary step of model development. If there are shortcomings in
