Environmental Engineering Reference
In-Depth Information
Table 8.1 Matrix of displacement probabilities that were used in the model
Displacing species
i
Resident species
j
Phalaris
Bituminaria
Hordeum
Hirschfeldia
Lagoecia
Phalaris
-
0.2
0.6
0.15
0.3
Bituminaria
0.1
-
0.01
0.03
0.04
Hordeum
0
0
-
0.01
0.01
Hirschfeldia
0.03
0.01
0.01
-
0.02
Lagoecia
0.1
0.01
0
0.01
-
investigate diversity-productivity relationships in natural grasslands. Experimen-
tal plots consisting of 2, 4, 8, 18, and 32 native species were established and
maintained since 1997 in seven European countries. For the parametrization of
our model we chose the two-species configurations, extracting relative biomass
changes and estimating competition strength to simulate the interactions between
five plant species:
Phalaris coerulescens
,
Hordeum geniculatum
,
Hirschfeldia
incana
,
Lagoecia cuminoides
,and
Bituminaria bituminosa
.Amongthefivespe-
cies, pair experiments have shown their competitive hierarchy and biomass
changes in the plots yielded information on the competitive strength. This was
assumed to translate into displacement probabilities in the model (Table
8.1
).
Results showed that longer distance dispersing plants have a competitive advan-
tage in colonization success as compared to better competitors, especially in the
cases of disturbance-mediated creation of gaps in coverage. An increase in species
number led to more resilient communities and a higher percent cover of the
landscape. A further model adaptation therefore incorporated
l
A scale-related neighbourhood structure
l
Asymmetrical hierarchy in competition
l
Invasion processes
The neighbourhood structure in the model was based on the dispersal attributes
of the different species, and showed significant change in final assemblage
patterns where short-distance dispersers were found to decrease in abundance.
Asymmetrical hierarchy (in terms of competition) was modelled as a stochastic
process, and showed to alter the composition of steady-state communities signifi-
cantly, favouring assemblages with low overall diversity. Invasion was shown to
interfere and alter the overall pattern of abundance. The effect of disturbances was
studied as well, examining whether the community is resilient to disturbances or
tends to change subsequent to disturbances (e.g. Fig.
8.8
). The approach high-
lighted the emergence of complex community patterns from simple local inter-
actions. A great amount of information is necessary for the parametrization of
such a model, yet the outputs of the model provide a broader understanding of
patterns that are far too complex to grasp with any other tool. Therefore, despite
the relative complexity of the model, it provides the means to gain understanding
of complex patterns in nature, the underlying mechanisms of which are otherwise
poorly understood.
