IFEVA   02662
INSTITUTO DE INVESTIGACIONES FISIOLOGICAS Y ECOLOGICAS VINCULADAS A LA AGRICULTURA
Unidad Ejecutora - UE
artículos
Título:
Herbivory resistance traits in populations of Poa ligularis subjected to historically different sheep grazing pressure in Patagonia
Autor/es:
ROTUNDO, J.L. Y AGUIAR, M.R.
Revista:
PLANT ECOLOGY
Referencias:
Año: 2008 vol. 194 p. 121 - 133
ISSN:
1385-0237
Resumen:
INSTRUCTIVO PRESENTACIN SOLICITUDES DE PROMOCION AO 2009
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Seeding
selected populations with high grazing resistance may foster recovery of plant
populations threatened by overgrazing. Resistance to grazing depends on grazing
avoidance (escape from grazers) and grazing tolerance (ability to growth after
defoliation). Many studies of grazing tolerance defoliate plants at fixed
height instead of removing the same proportion of biomass and therefore
confound tolerance with avoidance. For this reason, the information on
evolution of tolerance to defoliation at the intraspecific level is remarkably
scarce despite the abundance of papers published that evaluate responses to
defoliation. The estimation of the cost of tolerance is also troublesome because
current methods usually include spurious correlations due to correlation
between variables that share common terms. The objectives of this paper were to
assess the intraspecific variation in tolerance and in traits associated with
avoidance and growth in populations with different sheep grazing histories. We also
estimated the percentage of biomass removed when the defoliation treatment was
imposed at fixed height in order to separate tolerance and avoidance. Finally,
we estimated the cost of tolerance using a new method proposed for spurious
correlations. Results of a greenhouse experiment indicated no difference in
tolerance among the three compared populations. However, the populations from
overgrazed fields had more prostrate growth form, higher specific leaf area,
and higher tillering rate (when no defoliated) than populations from
exclosures. We confirmed that fixed height defoliation would have removed a
higher proportion of shoot biomass from taller than from shorter individual
plants, confounding grazing tolerance and avoidance. Regarding the cost of
tolerance, we found no differences from a null model of no cost, indicating
that the evolution (or future breeding) of more tolerant genotypes would not be
constrained by this cost.