Seasonal dynamics of guild structure in a bird assemblage of the central Monte desert.

LÓPEZ DE CASENAVE, J., V.R. CUETO & L. MARONE

BASIC AND APPLIED ECOLOGY

Elsevier

Año: 2008 vol. 9 p. 78 - 90

1439-1791

Most studies of ecological guilds consider guild membership as a fixed attribute of species, and the guild structure as a fixed attribute of a community. Consequently, almost no study tackled the examination of temporal changes in the guild structure of a particular assemblage. We used data on foraging patterns of central Monte desert birds to assess seasonal differences in resource use by resident species, and to examine seasonal changes in the guild structure of the assemblage. From 1993 until 1999 we quantified the use of foraging substrates, manoeuvres, and height strata, and the utilization of plants by 18 bird species. Resident species showed different kinds of seasonal dynamics, from no noticeable (e.g., Rhinocrypta lanceolata, most foliage foragers) to drastic changes (e.g., Asthenes baeri, Poospiza torquata) in their foraging patterns. Seasonal changes in guild structure were remarkable. Only two guilds were present all year round (ground foragers and foliage foragers), although they suffered important species turnover. Other three guilds had a seasonal occurrence: graminivores (during the non-breeding season), arboreal herbivores and aerial feeders (breeding season). Two species changed from a guild to another between seasons. Both presence-absence of migrant species, and changes in the feeding ecology of resident species had an influence on the temporal dynamics of guild structure. These factors appeared to be related with changing resource availability and with the birds’ ability for facing lean conditions through migration and with the opportunistic use of seasonally superabundant resources. Our results undermine the trust on studies in which guild membership was assessed irrespective of temporal variations. We show also that guild membership is not a fixed attribute of species: we should evaluate the individual’s resource use in a given moment in order to assign them to a guild, instead of obtaining a single measure purporting to represent a species’ fixed attribute.