Environmental Engineering Reference
In-Depth Information
Table 5.1 Ecosystem indices given in the EwE software
Name of index
Meaning
Cycling index
Fraction of an ecosystem's throughput that is recycled
Predatory cycling index
Corresponds to the cycling index but is excluding detritus groups
Cycles and pathways
A routine that presents the numerous cycles and pathways that are
defined by the food web representing an ecosystem based approach
suggested by Ulanowicz (
1986
)
Connectance index
The ratio of the number of actual links to the number of possible links.
Feeding on detritus (by detritivores) is included in the count, but the
opposite links (i.e. detritus “feeding” on other groups) are
disregarded
System omnivory index
The average omnivory index of all consumers weighted by the
logarithm of each consumer's food intake. It is a measure of how
the feeding interactions are distributed between trophic levels. An
omnivory index is also calculated for each consumer group, which
is a measure of the variance of the trophic level estimate for the
group
Trophic level
decomposition
Aggregates the system into discrete trophic levels
sensu
Lindeman.
The routine reverses the routine for calculation of fractional trophic
levels.
Trophic transfer
efficiencies
Calculated for a given trophic level as the ratio between the sum of the
exports plus the flow that is transferred from one trophic level to the
next, and the throughput on the trophic level. The transfer
efficiencies are used for construction of trophic pyramids, and
others
Primary production
required (PPR)
To estimate the PPR to sustain the catches and the consumption by the
trophic groups in an ecosystem the following procedure is used: all
cycles are removed from the diet compositions, and all pathways in
the flow network are identified using the method suggested by
Ulanowicz (1995). For each pathway the flows are then raised to
primary production equivalents using the product of the catch, the
consumption/production ratio of each path element times the
proportion the next element of the path contributes to the diet of the
given path element
Mixed trophic impact
(MTI)
Leontief (1951) developed a method for input-output analysis to assess
the direct and indirect interactions in the economy of the USA,
using what has since been called the “Leontief matrix”. A modified
input-output analysis based on the procedure described by
Ulanowicz and Puccia (1990) is implemented in EwE. The MTI
describes how any group (including fishing fleets) impacts all other
groups in an ecosystem trophically. It includes both direct and
indirect impact, i.e. both predatory and competitive interactions.
Ascendency
EwE includes a number of indices related to the ascendency measure
described in detail by Ulanowicz (
1986
). Ascendency is seen as a
measure of ecosystem growth and development
vulnerabilities expressing the rate with which prey move between being vulnerable
and not vulnerable, prey biomass, predator abundance. The model as implemented
implies that “top-down versus bottom-up” control is in fact a continuum, where
low
v
's implies bottom-up and high
v
'stop-down control. EwE has incorporated
numerous further computational routines; to force time series, to handle complex
