The article by Olff and Ritchie (1998) explores the complex effects of herbivores on grassland plant diversity. While herbivores are generally thought to enhance plant diversity through their consumption of dominant species and indirect impacts on competition, the effects can be either positive or negative, depending on the type and abundance of herbivores, as well as the spatial and temporal scales at which these effects are measured. Large grazing mammals and domesticated grazers at low stocking rates can increase plant diversity, but high stocking rates can decrease it. In contrast, insect herbivores often have weak or negative effects, although outbreaks of specialist herbivores can increase diversity. Intermediate-sized herbivores, such as prairie dogs and rabbits, create soil disturbances that enhance plant diversity. The authors highlight that the effects of herbivores on plant diversity vary across different environments, with grazing mammals in more productive grasslands increasing diversity, while those in arid or saline environments can decrease it. Recent research suggests that these effects are influenced by the balance between local colonization and extinction rates, the body size of herbivores, and the supply of plant resources. The spatial and temporal scales of herbivore effects are also crucial, as short-term increases in diversity from herbivory can be followed by long-term declines due to succession to tolerant plant species. The article concludes by emphasizing the need to consider the type and scale of herbivores, as well as environmental characteristics, to understand why similar herbivores can have both positive and negative impacts on plant diversity. This framework can help guide biodiversity management and resolve conflicts arising from conflicting individual studies.The article by Olff and Ritchie (1998) explores the complex effects of herbivores on grassland plant diversity. While herbivores are generally thought to enhance plant diversity through their consumption of dominant species and indirect impacts on competition, the effects can be either positive or negative, depending on the type and abundance of herbivores, as well as the spatial and temporal scales at which these effects are measured. Large grazing mammals and domesticated grazers at low stocking rates can increase plant diversity, but high stocking rates can decrease it. In contrast, insect herbivores often have weak or negative effects, although outbreaks of specialist herbivores can increase diversity. Intermediate-sized herbivores, such as prairie dogs and rabbits, create soil disturbances that enhance plant diversity. The authors highlight that the effects of herbivores on plant diversity vary across different environments, with grazing mammals in more productive grasslands increasing diversity, while those in arid or saline environments can decrease it. Recent research suggests that these effects are influenced by the balance between local colonization and extinction rates, the body size of herbivores, and the supply of plant resources. The spatial and temporal scales of herbivore effects are also crucial, as short-term increases in diversity from herbivory can be followed by long-term declines due to succession to tolerant plant species. The article concludes by emphasizing the need to consider the type and scale of herbivores, as well as environmental characteristics, to understand why similar herbivores can have both positive and negative impacts on plant diversity. This framework can help guide biodiversity management and resolve conflicts arising from conflicting individual studies.