Environmental Engineering Reference
In-Depth Information
that allows both vegetation forms to coexist - and why disturbance pattern can have
long lasting influences.
Statistics are applied to data, while models are used to interpret systems states
and processes, representing the dynamic developed and often applying an iterative
procedure. However, models and statistical applications cannot be strictly and
consistently delimited, though specific domains of application can be defined -
with a minor overlap.
Furthermore, modelling allows to test the coherence and degree of completeness
of the understanding of distinct ecological processes. For instance, for a long period
it was not clear what kind of behavioural modes would be sufficient to lead to highly
aligned fish schools. With an individual-based modelling approach to represent
different behavioural patterns of individual fish it was possible to test the existing
assumptions (Fig
2.3
). Results revealed that, depending on distances between
neighbouring fish, attraction, adjustment of direction and swimming speed and
repulsion were sufficient to produce schools. Modelling also revealed, that it was
only necessary to consider a limited number of nearest neighbours to keep a school
together (Huth and Wissel 1994). For aggregation of a school, weighting of neigh-
bours according to distance turned out to be a more efficient model assumption
(Reuter and Breckling 1994). Thus models may help to check if knowledge on
partial processes is sufficient to represent observed system behaviour.
Fig. 2.3 Schooling in fish.
Left
: Traces of a fish school in a heterogeneous environment: the gray
shaded area is a part of the environment with higher food density where individuals move more
slowly. Coming from the upper right some individuals are outside the food patch and accelerate.
To stay within the school these individuals change direction (turn right). As a result the whole
school stays on the food patch.
Right
: This phenomenon occurs as an emergent property if the
speed difference between preferred and non-preferred parts of the habitat is sufficiently large.
Simulated schooling fish stay considerably longer on food patches than do solitary fish. (rel.
location indicates how much longer a fish stays on food patches in relation to their coverages;
speed difference to normal cruising speed of 25 units/timestep)
