In a food web, all the organisms are related to each other and a change in population of one organism will affect the population of others. In a food web, wolves eat herbivorous animals, such as rabbits, deer, etc. These herbivores, in turn, eat plants and grass. Wolves may, themselves, be food for higher carnivores. Thus, if a disease kills 85% of the wolf population, their prey (rabbits, deer, etc.) will have very few predators and hence will grow in numbers. This herbivore population increase means more consumption of grass and plants. And hence, the population and concentration of grass and plants will go down. Near absence of wolves will also mean that any carnivore who was competing with wolves, will now have less competition and more food (from increased herbivore population) and will grow in numbers. Ultimately, this increase in population of competing carnivores, prey herbivores and decreased population of plants and grass, will force a new equilibrium in the food web. Extra herbivores, that cannot be supported by decreasing food levels, will die or be consumed by higher carnivores, thus bringing their population in check. This will, automatically, ensure a growth of plant and grassy material, thus bringing in a new equilibrium.
Hope this helps.