Effects of feces on spatial distribution patterns of grazed grassland communities.

Animals excrete feces during grazing. The uneven distribution of feces causes a spatial heterogeneity in grassland communities. In this study, we attempted to clarify the effects of feces on spatial distribution patterns of plant species. A field study was conducted on four grasslands each grazed by a single cow. These four grasslands were defined as Poa pratensis (Kentucky bluegrass) dominated grassland without feces (PoF-), Poa pratensis dominated grassland with feces (PoF+), Zoysia japonica Steud. (Japanese lawngrass) dominated grassland without feces (ZyF-), and Zoysia japonica Steud. dominated grassland with feces (ZyF+). A 50 m line that transects 100 equally spaced quadrats (L-quadrats) was drawn on each of the four grasslands. Each quadrat was 0.50 m ×0.50 m in size and consisted of four equal-area cells of 0.25 m × 0.25 m (S-quadrats). The occurrences of all plant species were recorded in each S-quadrat. The binomial distribution (BD) and beta-binomial distribution (BBD) were used to represent the variation in spatial patterns. The BBD provided a significant description of the frequency distribution of plants per quadrat. A power law was used to calculate the spatial heterogeneity of each species together with the community heterogeneity. The results revealed that the plants on each of the four grasslands were aggregatively distributed. The ZyF+ exhibited greater spatial heterogeneity than the ZyF- due to the uneven deposition of feces by cows grazing on the grasslands. Additionally we also found that the feces had effect on the heterogeneity inZyF+ and did not have effect in PoF+.