Seasonal Diets of Sheep in the Steppe Region of Tierra del Fuego, Argentina

Abstract

Sheep diets were determined seasonally for large flocks grazing year-round in 2 landscape types of the Magellanic steppe of Argentina. A tussock-grass steppe of Festuca gracillima Hooker f. dominates the uplands of the whole area. On acid soils (Quaternary landscape), woody variants of the steppe prevail; on neutral soils (Tertiary landscape), woody plants are almost ahsent and short grasses and forbs are abundant. Principal tasa consumed throughout the year were: Poa L., Deschampsia P.Beauv., and "sedges & rushes". Consumption of woody species and of the dominant tussock-grass Festuca gracillima increased notably in winter. Despite the large proportion of species in common, diets differed significantly between landscapes. In the Quaternary landscape, which has a higher botanical diversity, diets were more dissimilar among seasons and had a higher annual diversity indes. Because of their different composition of forage types the 2 landscapes differed in their overall grazing value. The Tertiary landscape, with a low floristic diversity but richer in highly preferred species as Poa spp. would be a more risky grazing area in winter, when an ice sheet or a snow cover limits harvesting of the lower layer of short grasses and forbs.

Use of food availability by guanacos (Lama guanicoe) and livestock in Northern Patagonia (Mendoza, Argentina)

“…Evidence of this could be: (1) the lower grass proportion in the horses diet in rocky habitats, where herbaceous stratum was less available than in sandy habitats; (2) the increase of dietary diversity for guanaco, horses and sheep in early summer, due to the inclusion of phanerophytes buds and several forbs whose appearance was seasonal. A similar increase in the niche breadth of sheep in response to an increase in food diversity was detected in Tierra del Fuego, Argentina (Posse et al, 1996). Point (2) above agrees with the selective quality hypothesis (Weckerly & Kennedy, 1992), also identified as forced selectivity (Quintana et al, 1994), defined as an alternative hypothesis within the optimal foraging theory.…”

Do domestic herbivores retard Polylepis australis Bitt. woodland recovery in the mountains of Córdoba, Argentina?

“…Considering that most nutritious forage grasses became almost unavailable in winter due to frosts and drought, animals increase the consumption of P. australis as the cold and dry season advances (Teich et al, unpublished data). Frequently, woody species are an alternative forage resource in winter, especially in highly seasonal systems (Posse et al, 1996;Rao et al, 2003).…”

Conditional outcomes in plant–herbivore interactions: neighbours matter

“…The herbaceous cover could constitute a secondary attraction to herbivores, as suggested by the negative relationship between the percentage of herbaceous cover and the intensity of herbivory in maple saplings. In most cases, a grazing herbivore attracted to the shrub by the herbaceous cover beneath does not consume the sapling, but during the summer drought, with most of the grasses already dry, the probability of damage to the woody plants increases (Posse et al 1996, Bartolomé et al 1998). Thus, plot 1 in Sierra Nevada showed a net increase in herbivore attack for sapling under shrubs (both maple and pine) from the beginning to the end of drought.…”