This chapter discusses attributes of vertebrate and invertebrate biology that might influence their impact plant recruitment and mortality are compared, and the effects on different aspects of plant performance by the two kinds of herbivore. The indicators of plant performance considered here are flower production, fruit production, seed production, seed size, seed predation, seedling survival, rate of growth and vegetative spread, and death rate of mature plants. Perhaps the most conspicuous difference between the vertebrate and invertebrate herbivores is their size. In order to estimate the net impact of different kinds of herbivores on plant performance, their per capita feeding rates are multiplied by their population densities. There is little difference between vertebrate and invertebrate herbivores in terms of their lifetime mobility. Comparison of fencng and insecticide-exclusion experiments leaves little room for doubt that in most ecosystems, vertebrate herbivores have a substantially greater impact on plant population dynamics and community structure than invertebrates.