A limiting factor is a factor in the environment that will cause the population to decrease. The population in a given area is limited to its surroundings. Things like water, food shelter and space will limit how many individuals can thrive in an area. If there is only enough water, food shelter or space for a certain number of individuals the population will continue to grow until the maximum population is reached. After that the food, water, shelter or space would run out and the area could not support any more individuals. At this point individuals would either die or emmigrate out of the area to a place less populated.
The number of frogs that can survive in an area is dependent on the resources available to them.