Ecofunzionalità in ambienti acquatici artificiali: dinamiche di sistemi donor-controllati in condizioni di stress
Author(s)
Novelli, Claudia
Date Issued
February 10, 2011
Type
Doctoral Thesis
Abstract
The study of the structural complexity of an ecological community is important to better understand
the complexity-stability relationship, so long emphasized in ecology. Generally, the measures of
structural complexity describe the organization and the relationship between the components of an
ecological community: the problem is to find metrics that are able to describe the system dynamics,
with the aim to predict the behaviour under stress conditions. The focus of this thesis is on how the
macrodetritivorous invertebrate assemblages responds to varying conditions of salinity both in
structural (taxa assemblages and food webs) and functional (detritus consumption rates) terms,
according with the current developments in network analysis and information theory. The study
area is the Tarquinia saltern, an artificial transitional water ecosystem in Latium (central Italy). The
site is characterized by an extreme variability of physical-chemical parameters (i.e. salinity),
establishing an excellent artificial laboratory to test the stress effect at community level. We
performed the study of the macrobenthonic community by using metrics derived from information
theory, as well as measures of centrality, derived from network analysis. In particular, the
information theory is used to identify and quantify the variation of community structure in several
sampling stations subject to salinity fluctuations. The network analysis is used to identify and
quantify the effects of environmental conditions on the structure of the network in terms of
organization of the potential links along nodes. The results emphasized that the two adopted
approaches seem useful in highlighting the different characteristics of how the community structure
answers to the environmental conditions. To obtain a measure of the structural complexity, the two
approaches have been integrated to formulate a synthetic index using (i) the number of taxa, (ii) the
total complexity (sensu Anand and Orloci, 1996) and (iii) the diversity of flows within the network,
the latter weighted on the different positional importance of nodes in the network.
To complete the previous studies, the structure-function relationship is analysed integrating also the
process of consumption of the detritus of Phragmites australis (Cav.) Trin. ex Steud, by
macrodetritivory under salinity stress. According to literature data, the experimental results
emphasise that the salinity variation seems to influence (i) the leaching of detritus of P. australis
and (ii) the structuring of the macrodetritivore community (i.e. taxa abundance, composition and
inter-taxa links). Integrating network analysis, informative theory and function measures, the
structural indices that seem to better correlate with the observed functionality variations are the
ascendency and the synthetic index of structural complexity. Finally, the metrics and methodologies
employed for better understanding the structure-function of the macrodetritivore community are
also used to formalise a theoretical model where the structural organization of the community is a
variable, dependent on the quality and quantity of trophic resource availability. The preliminary
model allows to simulate, dynamically, the effects of constant and pulse inputs of trophic resources.
The analytical solution of the model has highlighted the importance of transient dynamics by
disturbance furnishing useful indications to active conservation management of transitional water
ecosystems. My thesis provides both a theoretical preliminary contribution to understand, in detail,
the structuring and functional processes of macrodetritivore communities of the transitional water
ecosystems and some suggestions to better manage planning measures of active nature
conservation.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
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