Large-scale movements of large herbivores: livestock following changes in seasonal forage supply
AbstractLarge-scale movements allow large herbivores to cope with changes in seasonal forage supply. Pastoralists use mobility to convert low-value ephemeral forage into high-value livestock. Transhumant pastoralists may move livestock less than ten to hundreds of kilometres. In semi-arid tropical sites, water and forage shortages in the dry season cause pastoral livestock to move to water or key resource areas. In temperate summers, livestock may be moved to higher-elevation snow-free meadows. In winters, animals may be moved lower to warmer sites, or to mountain valleys protected from steppe winds. Despite the recognised value of mobility, pastoral mobility is being reduced around the world. Changes in the mobility of three pastoral groups are reviewed, the Aymara of the South-American highlands, Mongolians, and the Maasai of Kenya and Tanzania, for which quantitative results are given. The Maasai of Kajiado District, Kenya are subdividing some group ranches into individually owned parcels. In subdivided Osilalei Group Ranch, herders moved an average of 5.6 km per day, whereas in undivided northern Imbirikani, herders moved 12.5 km per day. Residents of northern Imbirikani accessed more green vegetation the more they moved, whereas those in subdivided southern Imbirikani did not. Maasai selected areas with more heterogeneous vegetation during the dry season than found at their permanent households. In modelling, subdividing to 100-ha parcels allowed Eselengei Group Ranch to support 25% fewer livestock by mass, even though the area remained the same. For any pastoralist, the costs of mobility must be weighed against benefits, but pastoralists have demonstrated flexibility in their mobility, if constraints such as human population growth and limitations in land access are not too great. We show that pastoralists have successfully evolved methods of herding livestock to access adequate forage in areas of variable climate
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