What would happen to the grass population if the population of wolves in the ecosystem decreased? why ?

Wolves are a predator, meaning they keep the cattle population down. Take away wolves and you end up with more cattle. More cattle eats more grass, too much grass. The grass is eaten faster than it can grow back. Cattle are being born more quickly than being eaten by wolves. The region would ultimately become uninhabitable and nothing could live there. 

The investiture controversy began as a power struggle between pope gregory vii (1072–85) and henry iv, holy roman emperor (1056–1106).[2] a brief but significant struggle over investiture also occurred between henry i of england and pope paschal ii in the years 1103 to 1107, and the issue played a minor role in the struggles between church and state in france, as well.by undercutting the imperial power established by the salian emperors, the controversy led to nearly 50 years of civil war in germany, and the triumph of the great dukes and abbots. imperial power was finally re-established under the hohenstaufen dynasty. historian norman cantor: