What density-dependent growth limiting factors kept the human population relatively low prior to the advent of agriculture?

Limited food supply and competition

Explanation:

Density dependent factors are those which in general lead to reduction of growth rate of population when the population density increases. One of such factor is availability of food and competition.

Whenever the density increased to an extent where the resources or available food becomes scarce or limited,then the growth rate of population decrease.  These factors generally lead to logistic growth pattern of population.  

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.