Environmental Engineering Reference
In-Depth Information
Fig. 5.1 Simulation of flow between available (
V
i
) and unavailable (
B
i
-
V
i
) prey biomass in
Ecosim.
a
i
is the predator search rate for prey
i
,
v
is the exchange rate between the vulnerable
and un-vulnerable state. Fast equilibrium between the two prey states implies
V
i
¼
vB
i
/(2
v
þ
aB
j
)
(based on Walters et al. 1997)
life histories, to trace nutrients and pollutants through the food web and several
others (for more details see Christensen and Walters
2004
).
5.3 Application Examples
5.3.1 Ecopath Approach
The following example is based on Wolff (2006), who compared Ecopath II models
of two mangrove fringed estuaries in Costa Rica (Gulf of Nicoya, at the Pacific
shore) and Brazil (Caet
´
estuary, NE of Belem) with respect to biomass and energy
flow distributions, productivity and fisheries potential, with the added objective to
obtain guidelines for conservation and management of these systems.
Figure
5.2
shows the flow charts of the two models derived from the ECOPATH
programme.
Figure
5.3
shows a routine of ECOPATH, which allows the visualization of
flows that enter (as food) and leave (to the predators and the fishery) a compartment.
In the example below the central mangrove consumers in both systems (land crab in
the Caet´ system and shrimps in the Nicoya Gulf) are shown. A biomass pyramid of
both systems is also included.
The input data matrix (see additional material at
http://www.mced-ecology.org
)
needs three input parameters for each compartment: biomass (B), turnover rate
(P/B) and consumption rate (Q/B). The trophic level of each group is calculated by
the program based on the diet matrix, which connects the model compartments.
Differences in biotic structure, energy flow and resource productivity's between
both systems proved to be substantial as seen by the summary statistics of the model
calculated (but not included here). These are largely due to differences in topography,
