Ants and Spiders in Grassland Food Webs: Top-down Control and Intraguild Interactions

A challenge in ecology is to uncover the link betweenfood web interactions and ecosystem function. Recentstudies have shown that top-down forces byinvertebrate predators on their prey and cascadeeffects on plants play an important role instructuring terrestrial communities. The strength ofsuch trophic cascades is hypothesised to be affectedby habitat structure, predator diversity and predatoridentity. Ants and spiders are among the Earth?s mostabundant terrestrial arthropod predators and most aregeneralists, feeding on a wide variety of prey,including other predators. To study the role ofpredation by ants and spiders in six fieldexperiments the density and diversity of predatorgroups, the habitat structure and habitatfragmentation were manipulated. These experiments demonstrate that predators caninteract positive and negative, depending strongly onhabitat structure, the predator identity anddiversity, and that these interactions change thestrength of top-down forces.