Abstract

MILESI, Fernando A et al. Management guilds as indicators of environmental conditions: a case study with birds and habitat disturbances in the central Monte desert, Argentina. Ecol. austral [online]. 2002, vol.12, n.2, pp.149-161. ISSN 1667-782X.

Different supra-specific groupings (e.g., guilds, functional groups) are used as management tools to obtain simple or economical indicators of the state of resources or "health" of local communities. One proposed approach was to use "management guilds", grouping those species that respond in a similar manner to the impacts in their environment. According to the a priori proposed technique, we classified the species of birds at the central Monte Desert (Biosphere Reserve of Ñacuñán, Argentina) into foraging and nesting guilds, using our own local data of diet, foraging behavior and nesting substrate, emphasizing microhabitat use. We estimated the richness of the bird assemblage, the density of each guild and the structure of the vegetation (cover of vegetation strata) in protected open forest ("control") habitats and in habitats affected by the two most common disturbances in this system: fire and grazing. Both perturbations were associated with long-standing important changes in the structure of vegetation, particularly the fire: a reduction of the cover of grasses and woody plants. The number of bird species followed the same trend than the structure of vegetation, but the densities of only some of the foraging and nesting guilds were correlated with these modifications. Obtaining management guilds by grouping species according to the common use of resources is a plausible hypothesis, but not a property established by definition. For example, granivores did not present an homogeneous intra-guild response, and the only guilds that showed a consistent outcome to these disturbances were those whose resources, by definition, were drastically altered (e.g., if there are no shrubs, the birds that forage searching in the shrubs disappear). The a posteriori grouping of species that respond in a similar way to the disturbance may produce a useful tool, but not without problems (circularity, unknown extrapolative power, plausible but fallacious reasoning). In these cases, in which two observable variables are been associated, it is easier and more direct to measure the affected resource rather than the indicator, being the latter unnecessary.

Keywords : Birds; Disturbances; Fire; Grazing; Indicators; Management guilds.

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