Identification of the Lagoon Ecosystems - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 18

Typical temporal and spatial scales on which a trophic unit operates and the
relationship to the network is the meaning of spatio-temporal organization of the
biocoenose underlying a lagoon HGMU. The biocoenose is subject to continuous
change because any unit, like a population or a group of populations, can have only
a finite lifetime and a finite spatial distribution, as described in Chapter 5.
The basic unit for the network describing the spatio-temporal organization of a
lagoon biocoenose is a trophic dynamic module (TDM), first introduced by Pahl-
Wostl. The modules are defined for both dynamic and trophic function. According

to Pahl-Wostl,

26

a trophic dynamic module comprises all populations that have the
same dynamic characteristics and the same functional niche in the trophic web and
that coexist over the same finite period in time and space. Thus, having reliable data
and estimates concerning the variables listed earlier for a given biocoenose, we can
identify the homomorph or structural model by applying the following stepwise
procedures.

26

1. Based on the dynamic characteristics of the identified dominant popula-
tions, or cohorts ( τ ), the dynamic classes C are established.

i

2. By locating these Classes ( C ) in time and space, the dynamic modules

i

) are established.
3. By taking into consideration the functional characteristics of populations
or cohorts, as expressed by their functional niches (

(MD

ikr

C ), the trophic-

ik

dynamic modules are established (MTD ).

ikra

The following definitions apply:
• Cohort—Embodies a group of individuals that are part of the structure
of a given population that have the same or similar age and share the same
functional niche.
• Dynamic Class ( C )—Includes all populations or cohorts whose biomass

i

turnover time ( τ ) is in a range where τ remains a constant value on a

logarithmic scale.
• Dynamic Module (MD )—Comprises all dominant populations and

cohorts belonging to the same dynamic class (

ikr

C ) that co-exist within the

i

same time and space interval.
• Trophic-Dynamic Module (MTD

)—Comprises all dominant popula-
tions and cohorts belonging to a dynamic module (MD

ikra

) that have the

ikr

same functional niche ( C ).

ia

• Functional Niche ( )—Indicates the position occupied by dominant

populations and cohorts within the trophic connection network, or their
position within the network as matter and energy carriers. Primary pro-
ducers ( Figure 2.5) are taken as the reference position for establishing the
position within the network of the other functional niches.

C

ia

• i = dynamic class ( i = 1, … , n )

k = time interval by units τ

i

r = space indicated by units S

i

a = functional niche

τ = biomass turnover time (B/P)