PARENT SESSION
Poster Session 7: Grasslands
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Grazing by cattle causes bottom-up effects on the arthropods of grassland.
Imura, Osamu*,1, 1 National Institute of Livestock and Grassland Science, Nasushiobara, Tochigi, Japan
ABSTRACT- To conserve biodiversity on grasslands, we studied interactions among organisms influenced by cattle grazing on a semi-natural grassland dominated by Zoisia japonica. We tested four hypotheses, intermediate disturbance, vegetation diversity, vegetation architecture and plant defense, to explain the interactions related to arthropods. A rotational grazing by a herd of cattle was carried out on the grassland from May to October for three years (2002 - 2004). The rotation period was one week and the rotation interval was three weeks. The herd rotated on pastures five or six times in a grazing season in each year. Four grazing levels, no grazing, grazing twice a year (in total two weeks), three times (three weeks) and five or six times (five or six weeks), were set in a pasture by covering or uncovering experimental plots using a protection cage (120cm x 120cm x 120cm) when the herd entered the pasture. We surveyed the experimental plots for vegetation and arthropods in May, July and September. Grazing levels significantly influenced the biomass, architecture, chemical composition and diversity of the vegetation, and the abundance and diversity of predators but the influence was weak on herbivores. The diversity of herbivores changed following the change in the diversity of vegetation, suggesting a possible hypothesis of the vegetation diversity to explain the cause. Abundance of herbivores of gramineous plants increased as N content of the plants increased, indicating that the hypothesis of relative shortage but not the plant defense was more appropriate to explain the interaction. The abundance of predators was explained by the vegetation architecture hypothesis and their diversity might be explained by the vegetation architecture or intermediate disturbance hypothesis. We conclude that cattle grazing cause bottom-up effects on the grassland arthropods through altering diversity, chemical composition and architecture of vegetation.
Key words: cattle grazing, arthropods, interactions, bottom-up effects