Ecosystem Network Analysis

Network analysis depicts the ecosystem as a collection of nodes (species or trophospecies) connected by arrowhead arcs portraying trophic relations (exiting the prey items and entering the predator).

Trophic exchanges are measured as energy flows (i.e., kcal m~2 yr-1) or nutrient transfers of different currencies (i.e., carbon - mgCm~2yr_1; nitrogen - mgNm-2 day-1; phosphorus - gPm-2 yr1).

Figure 1 depicts the Cone Spring ecosystem with five compartments (n = 5) and eighteen flows distinguished in two imports from outside (to plants and detritus), three exports to outside (from plants, bacteria, and detritus), five respirations (a ground symbol on each node), and eight intercompartmental exchanges.

A graphical scheme can likewise be represented as an (n + 3) x (n + 3) square matrix of transfers [T], with tj elements describing outflows from row compartment i to column node j (see Figure 2). First row stands for imports from outside to the column compartments, and the last two columns list exports and respirations from any row compartment. The internal n x n submatrix reports internal exchanges.

11 184

8881

2309

Detritus

->

Plants

->

Detritus

* 300

200

feeders

2003

860

635 3109

1814

167

370

Carnivores

203

Figure 1 Cone Spring ecosystem is composed of five compartments (plants, bacteria, detritus feeders, carnivores, and detritus) and it shows: two imports (green), three exports (red), five dissipations (blue), and eight intercompartmental exchanges (black). Flows are expressed in kcalm~2yr~1.

Imports

Intercompartmental exchanges n elements

n + 3 elements

Figure 2 Graphical example of T matrix for a generic n-compartment ecosystem, with size = (n + 3) x (n + 3). Imports to system nodes are summarized in the first row, exports and dissipations are set in the last two columns, and the internal n x n matrix shows transfers between system compartments. This model of T matrix is adopted for Cone Spring.

T =

0 11184

0

0

0

635 0 0

0 0

0

0

0

8881 300 2003

00

0

75

0

1600 255 3275

00

0

0

370

200 0 1814

00

0

0

0

167 0 203

00

5205 2309

0

0 860 3109

0 0

0

0

0

0 0 0

0 0

0

0

0

0 0 0

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