Ecosystem Flow Analysis - Ecological Systems - page 76

ecosystem development, have also been formulated as ecological goal functions -
which describe observable macroscopic patterns over time. They are not strict goal
functions in the sense of mathematical optimization models (neither is economic
utility although it is used as such), but indicate the tendency for ecosystems to follow
during development, for example, during succession from early r-selected species
and r-selecting environments to late K-selected species and K-selecting
environments. Some of the more common goal functions employed include:
maximum power [ 13 ], maximum dissipation [ 14 ], maximum cycling [ 15 ], maxi-
mum residence time [ 16 ], minimum specific dissipation [ 17 , 18 ], maximum energy
[ 19 ], and maximum ascendency [ 20 ] (see [ 9 ], for a detailed description of these).
The idea is that the ecological network self-organizes itself in a way that leads to
directional change in the property of these values. For example, maximum power,
interpreted to mean the maximum throughflow in the network is given by: TST = f (0)
+ f (1) + f (2) . Therefore, TST increases when there is more boundary flow (mode 0),
more first passage flow (mode 1), or more cycled flow (mode 2). The mechanisms for
this to increase practically relate to the system's ability to capture more boundary
flow by increasing the uptake. Both first passage flow and cycled flow also depend on
the second stage of growth exemplified by the structure of the network and the
efficiency of flows along each connection. Similar rationale can be made for the
other goal functions listed above, and in fact it has been shown that the goal functions
are complementary and mutually reinforcing in that the realization of one generally
promotes the others. Together they provide a holistic view of ecosystem develop-
ment through different thermodynamic perspectives. Again, the value of this eco-
system knowledge is obvious for application to design and to manage human
systems sustainably. If ecosystem services are required, then the inherent dynamics
of the systems used should be better understood. Human activities in line with these
directions will be supported by natural processes, those that do not will experience
additional resistance and therefore additional cost and difficulty. Humans are better
off working with nature than against it if possible.
Conclusions and Future Directions
Ecosystem flow analysis clearly shows that the distribution of energy flow in
a network is not simple. Some significant fraction of the energy remains in the
system and cycles before exiting the system. This insight was evident in R.
Lindeman's [ 21 ] seminal work on Cedar Bog Lake in which he referred to his
eight-compartment ecosystem as a “food-cycle.” Unfortunately, he did not have
the quantitative tools at his disposal, like flow analysis, and to simplify the
calculations, proceeded to analyze the system according to two distinct “food-
chains,” although in reality they are linked and contain cycles. Further work in this
area also neglected the presence and significance of food cycles until research in
the mid-1970s (such as [ 22 - 25 ], and others) when network analysis techniques
developed sufficiently to provide a holistic investigation of the ecosystem