In “The Wolf’s Tooth: Trophic Cascades, Keystone Predators and Biodiversity,” just published by Island Press, Cristina Eisenberg outlines the many research findings in recent decades about “trophic cascades,” or the string of problems that can be created when keystone predators – ranging from wolves to sharks or even spiders – are removed from an ecosystem, allowing other species to disproportionately flourish and cause havoc.