Indicators Thermodynamically Oriented or Based on Network Analysis

In the last two decades, several functions have been proposed as holistic ecological indicators, to account for suitable system-oriented characteristics, expressing natural tendencies of ecosystem development. In general, these proposals resulted from a wider application of theoretical concepts, following the assumption that it is possible to develop a theoretical framework able to explain ecological observations, rules, and correlations on the basis of an accepted pattern of ecosystem theories.

Eco-exergy.

Table 6 Expected trends of the metrics included in the EBI as a response anthropogenic stress (direction of change)

Metrics

Expected trend

Total number of species

Decrease

% Abundance of the dominant species

Increase

Fish abundance

Decrease

Number of nursery

Decrease

Number of estuarine spawning species

Decrease

Number of resident species

Decrease

Proportion of benthic associated species

Decrease

Proportion of abnormal or diseased fishes

Increase

where R is the gas constant, Tis the absolute temperature, C¡ is the concentration in the ecosystem of component i (e.g., biomass of a given taxonomic group or functional group), Pi is a factor able to express roughly the quantity of information embedded in the organism's biomass, namely accounting for the genome size. Detritus was chosen as reference level, that is, P¡ = 1 and eco-exergy in biomass of different types of organisms is expressed in detritus energy equivalents.

If the total biomass in the system remains constant, then eco-exergy variations will rely upon its structural complexity. Specific eco-exergy is defined as eco-exergy/ biomass. Both eco-exergy and specific eco-exergy may be used as indicators in environmental management, being advisable to apply them complementarily.

This formulation of eco-exergy does not correspond to the strict thermodynamic definition of the concept, but provides nevertheless an approximation of exergy values. In this sense, it was proposed to call it exergy index. This formulation allows us to estimate empirically the eco-exergy index from normal sets of ecological data, for example, organism's biomass, provided that P¡ value for the different types of organisms is known. The estimation of correct P values constitutes one of the major difficulties involved in applying the eco-exergy concept in ecology, and requires further research. Eco-exergy has been applied as an indicator of the state of ecosystems in European lakes, estuaries, and coastal lagoons, and related with natural or human induced changes, such as eutrophication and biomanipulation. Results suggest that exergy-based indices are able to provide useful information regarding the state of the systems.

This index is extensively treated in Eco-Exergy as an Ecosystem Health Indicator.

Ascendency. The ascendency, A, expressed in terms of trophic exchanges, Tj, from taxon i to taxon j is calculated as

A dot as a subscript indicates summation over that index. The application of this indicator to a few estuarine data sets shows that network analysis appears to provide a systematic approach to apprehending what is happening at the whole-system level. A major inconvenience regarding its use is the considerable time and labor needed to collect all the data necessary to perform network analysis. This index is extensively treated in Ascendency.

See a/so: Abundance Biomass Comparison Method; Benthic Response Index; Berger-Parker Index; Biological Integrity; Eco-Exergy as an Ecosystem Health Indicator; k-Dominance Curves; Margalef's Index; Pollution Indices; Polychaetes/Amphipode Index; Shannon-Wiener Index; Simpson Index.

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