Environmental Engineering Reference
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movement pattern
recorded position
source
forest
hedge
row
forest
island
500 m
step length a 1
turning angle
a 1
target
0.01
0.02
0.03
0.04
0.06
0.08
0.02
0.05
0.1
0.15
0.2
0.4
Fig. 2.6 The construction of Move Steps distributions and Model output from a model on beetle
dispersal (Jopp and Reuter 2005). Upper Left and Middle : Derivation of movement rules from
empirical data. Upper Right : Simulation set-up for the analysis of connectivity effects of hedge-
rows and stepping stones. The width of the hedgerows and the number of stepping stones are
varied in the scenarios. Lower Left and Right : Resulting long term pattern of dispersal for a model
population from a source habitat ( top ) to a sink habitat ( bottom ) which are connected by six
habitats functioning as stepping stones. Dispersal success and densities result from a combination
of movement speed, mortality on hostile lands and probability to cross habitat boundaries. Abax
parallelepipedus , a slow disperser with high habitat fidelity, has to colonize all stepping stone
habitats before reaching the sink habitat (lower right). In contrast, Carabus hortensis , which easily
crosses borders between habitats, does not colonize the stepping stones, but reaches the sink
habitat in a fraction of time (lower left)
result. Nonlinearities frequently are not so easy to extrapolate. Here models are
often the only promising way to expand ecological knowledge. For instance, this is
frequently the case on grid-based processes (see Chap. 8 on Cellular Automata).
A pattern studied on the basis of grid-based processes are forest fires. The final
pattern can be well observed on the regional scale. The overall transition-rules on
the small-scale, however, can only be estimated. Model assumptions can be tested
to determine whether they lead to patterns that are in line with the observed findings
(e.g. Ratz 1995).
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