INVESTIGADORES
LOPEZ DE CASENAVE Javier Nestor
artículos
Título:
Can seed-eating birds exert top-down effects on grasses of the Monte desert?
Autor/es:
L. MARONE; J. LOPEZ DE CASENAVE; F. A. MILESI; V. R. CUETO
Revista:
OIKOS
Editorial:
Blackwell
Referencias:
Año: 2008 vol. 117 p. 611 - 619
ISSN:
0030-1299
Resumen:
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Granivorous animals can exert major effects on the abundance
and diversity of plants when they are selective as well as efficient consumers.
However, even under such conditions granivore impact will ultimately depend on
whether environmental stress obscures plant-animal interactions. We studied
diet and seed selection patterns of seed-eating birds to corroborate whether
they are selective consumers in the central Monte desert of Argentina. Overall,
83% of seeds in bird stomachs were grass seeds, whereas only 30% of available
seeds were from grass species. Therefore, we conclude that avian granivory is
highly selective. We developed a set of a priori expectations to test whether
birds are efficient consumers (i.e. whether they reduce seed reserves
significantly), through short-term mechanism-explicit enclosure experiments.
Birds decreased the number of selected grass seeds by 50%, and also reduced the
amount of non-selected grasses and selected forbs when selected grass seeds
were scarce in the habitat. Thus, consumption was context-dependent, varying
with the composition of background seed reserves. The corroboration of foraging
plasticity through mechanism-explicit trials seems to be crucial to correctly
assign direct and indirect effects of seed predation in long-term enclosure
experiments. The comparison of average grass seed reduction caused by bird
predation with mean declines of grass seedlings caused by senescence (ca 95%)
allowed us assess top-down (e.g. seed availability) vs bottom-up control (e.g.
rainfall) on grass recruitment. Despite moderate to high seed predation, the
number of grass seeds that remains in the soil in spring would not limit seed
germination and seedling recruitment. By contrast, safe-site availability and
drought may be important factors limiting grass recruitment, at least in the
undisturbed habitats of the Biosphere Reserve of Nacunan.