Answer:
Predators
Parasites
Competition
Waste accumulation
Step-by-step explanation:
Competition- it comes about when organisms depend on the resources whose availability is limited. As population size increases these resources become limiting and competition sets in.
Predators- predators feed on other animals called the prey. When these predators feed on prey, they decrease their numbers but may increase their own.
Parasites- parasites live temporarily or permanently in the host or on the host deriving benefit from it and causing harm. Most parasites cause diseases which result in deaths when more individuals are living together in the same place. Parasites are also more likely to spread under these conditions.
Waste accumulation from human activities. Some of their activities have resulted in environmental pollution. High population densities can lead to the accumulation of harmful waste products that reduce the population’s growth due to death.