Seasonal patterns of endozoochory by cattle in subtropical grassland in southern Brazil

Abstract

AbstractSeed dispersal influences plant community dynamics and regeneration. Zoochory by cattle is a particularly important type of dispersal in grasslands, but still poorly understood in subtropical grasslands. We studied endozoochory in a native grassland area with different grazing intensities, defined by distinct forage allowance levels. On one day in each of the four seasons of the year, dung samples were collected and kept in a greenhouse for germination over one full year. At each dung collection date, a survey of reproducing plants was conducted to relate the species composition of seed within dung to the community in dispersal phase. We used randomisation tests to compare grazing intensities and seasons in terms of dung community richness, abundance and composition. We recorded 93 species in the dung samples, with 65 species in the spring samples, 61 in summer samples, 45 in the autumn samples and 37 in the winter samples. Of the 90 species identified in the vegetation, almost 50% (43 species) also occurred in dung samples. Graminoid herbs presented the largest number of species in all samples. Grazing had no effect on overall seed and species number, but was related to compositional differences in the cattle dung communities. Grazing also influenced the species composition in relation to life cycle, by the increase of annual species at the extremes of our grazing gradient (very high or very low grazing intensities). We conclude that endozoochory by cattle is an important process for the dispersal of native species in the studied system, with potential applications in grassland management and restoration. A better understanding of the strategies involved in seed dispersal is essential to improve knowledge about grassland vegetation regeneration and maintenance.