Effects Of Plant Spatial Distribution On Foraging Behavior Of Sheep

The food resources of large herbivore are typically patchily distributed. Research on foraging behavior has often focused on diet selection but has rarely taken into account the influence of the spatial distribution of different food patches in multiple plant species foraging environments. However, especially when traveling costs become significant, the pattern of food resources spatial distribution is likely to be a major factor in determining foraging behavior.The effects of spatial distribution patterns (random distribution and aggregated distribution) of the food resources on foraging behavior of sheep were examined. 72 patches (bowls) of food which contain 24 Leymus chinensis patches, 24 Phragmitis australis patches and 24 Lathyrus quinquenervius patches were laid out in a 60 m×30 m vegetation-free field. Five different food presentation treatments were created by configuring different spatial distribution with random and aggregation for the three species. Groups of three sheep were allowed to feed from the patches for 30 min.The results of experiment showed as follows:(1) Plant spatial distribution patterns have significant effects on gross intake of sheep. It is advantageous for sheep to forage on patchy resources when food resources are aggregated. When low quality species are aggregated and when diets are diversity on small scale, it is advantageous for sheep to forage preferred species. Plant spatial distribution patterns do not affect sheep to forage low quality species.(2) Plant spatial distribution patterns have not significant effects on the results of diet selection. For sheep what to forage is mainly determined by food quality, most commonly nitrogen. However, plant spatial distribution patterns have influences on the degree of diet preference.(3) Traveling time is altered by different plant spatial distribution patterns. Traveling time of sheep is lower when preferred species are aggregated than dispersed, so foraging costs are lower in this circumstance.(4) Plant spatial distribution patterns have significant influences on foraging efficiency of sheep. Sheep have higher foraging efficiency when food resources are aggregated and when diets are diversity on small scale, so it is advantageous for sheep to maximize net energy gain.(5) Plant spatial distribution patterns have significant effects on diet switching frequency of sheep. Switching of sheep becomes more frequent when food resources are dispersed than aggregated. Also, the distance of between aggregations affects diet switching frequency of sheep. Switching of sheep is lower when the distance of between aggregations is far. Overall, the results demonstrate, when offered food patches in aggregated or dispersed patterns, it is more advantages for sheep to forage on patchy resources when the food resources are aggregated than dispersed. This corroborates the prediction that foraging costs associated with patch distribution are involved in determining diet selection in patchy grasslands. The use of spatial memory, area concentrated searching and social facilitation has been demonstrated to explain the foraging success when food resources are aggregated. The study also suggests that plant spatial distribution patterns may change foraging tactics of sheep. Sheep will make good use of spatial memory to aid foraging in lower heterogeneous foraging environments. However, as the environments become more variable, spatial memory will be replaced by sampling behavior. With respect to grazing management the important implication is that, aside from the relevance of foraging quality and abundance, the spatial distribution of food resources is another factors determining grazing distribution of large herbivore and, hence, their impact on the vegetation.