9 - Plant Selection in Grazing

Abstract

Diet selection affects not only the grazing animal's nutrient status but also the successional processes in plant communities. Selecting some plant species against others, large herbivores have a profound effect on the competitive relationships of plants growing in mixed plant communities. The impact of livestock on rangelands occurs primarily because they selectively defoliate the available herbage, rather than indiscriminately consuming herbage according to its availability. Restricting the term “palatability” to plant characteristics or conditions and the term “preference” to the reactions of the animal to these differences provides a proper basis for evaluating the extent and causes of selectivity. Palatability refers to that combination of plant characteristics that stimulates animals to prefer one forage over another, or can be extended to any feedstuff. Preference refers to the selective response made by the animal to plant differences and is essentially behavioral. Selectivity by an animal may be influenced by the presence, either concurrently or previously, of one or more other animal species in the area, either by changing the short-term relative availability of the different plant species or differentially affecting the palatability of the remaining forage; even rodents and insects may affect food preference by the grazing animal.