I believe you have a rabbit problem. Rabbits are herbivores that feed on grass and other plant life. They will also leave blighted areas where they have eaten selectively - especially if clover is available. The rabbit does leave small round pelletized feces and in fact they actually pass two types of feces. One of these is reingested or "eaten again" to help process the food even further. Some rabbits den in holes and others above ground. Voles will eat grass as well and will zone in on Hostas and other ornamental plants when available. They leave little furrows or tunnels through the grass and create numerous holes about the size of a silver dollar. They like to inhabit moles tunnels and break through at intervals. Since I saw no sign of mole tunnels or vole holes in the pics I'm confident that it's a rabbit issue. A bittering agent may help train them to stay away from certain areas but trapping and physically removing them or "legally dispatching with lead projectiles" are the other options. Good luck!