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Publication year : 0
Thematic : Biodiversity
Language : English
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Keystones are defined as relatively low biomass species with a structuring role in their food
webs. Thus, identifying keystone species in a given ecosystemmay be formulated as: (1) estimating
the impact on the different elements of an ecosystem resulting froma small change
to the biomass of the species to be evaluated for its ‘keystoneness’; and (2) deciding on the
keystoneness of a given species as a function of both the impact estimated in (1) and its
own biomass. Experimental quantification of interaction strength necessarily focus on few
species, and require a priori assumptions on the importance of the interactions, which can
bias the identification of keystone species. Moreover, empirical measurements, although
very important, are expensive and time consuming and, owing to the spatio-temporal heterogeneity
of habitats, physical conditions, and densities of organisms, published results
tend to be case-specific and context-dependent.
Although models can only represent but a caricature of the complexity of the real world,
the modelling approach can be helpful since it allows overcoming some of the difficulties
mentioned. Here we present an approach for estimating the keystoneness of the functional
groups (species or group of species) of food web models. Network mixed trophic
impact analysis, based on Leontief’s economic input–output analysis, allows to express
the relative change of biomasses in the food web that would result from an infinitesimal
increase of the biomass of the observed group, thus identifying its total impact. The
analysis of the mixed trophic impacts presented here was applied to a suite of massbalance
models, and the results allow us to rank functional groups by their keystoneness.
Overall, we concluded that the straightforward methodology proposed here and
the broad use of Ecopath with Ecosim (where mixed trophic impact analysis is implemented)
together give a solid empirical basis for identification of keystone functional
groups.
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Keywords : Parascaptor leucura
Encoded by : Pauline Carmel Joy Eje
