Finch populations on the Galapagos fluctuate with rainfall and in response to severe storms. Storm events are an abiotic factor that reduces the food supply, a biotic factor. Human population growth and age distribution Human populations worldwide are currently growing exponentially. Ecologists have never found a species that can grow indefinitely at an exponential rate, but the human carrying capacity of the earth is unknown, and much debated. Population growth and population density are not evenly distribution worldwide.
Age distributions vary dramatically as well.
Dispersal is the movement of individuals beyond their birthplace and between their normal movements on territory or during migration. Larvae of barnacles, although adult barnacles are stationary Many young mammals and birds disperse away from their parents. Young male mammals, in particular, often move great distances. Range Expansion Dispersal happens regardless of whether a range is expanding or contracting. Range expansion occurs when individuals not only disperse but are able to establish populations beyond their old range limits.