Limited resources cause growth in a population because there is less competition in the population so kangaroos won't conflict with each other. A smaller population due to less food supply will survive longer.
Immigration makes the Kangaroo population larger. Kangaroo's immigrate to more successful kangaroo herds because their food supply and living space is more plentiful. Kangaroo birth rates also increase population sizes. Mothers are more likely to survive due to a plentiful food supply and low predation.
Populations decrease because of high death rates and high emigration. Populations die more because of high predation, and low food supply. Populations emigrate because of low food and there are more successful conditions else ware.
Disease and competition in a large population effect the size because kangaroo's will compete for more resources. Due to a large population, disease will spread faster due to a large amount of red kangaroos in one area.
Habitat destruction and drought disrupt population size. The lack of a habitat will cause Kangaroos to die because mother kangaroos do not have a place to reproduce. Drought will cause death because the lack of food.