Population viability is the ability of a population to persist and avoid extinction. It increases and decreases depending on changes with the birth, death and growth rates of individuals. Population viability analysis refers to methods that use mathematical models to predict population dynamics. The abundance of natural resources can either aide or diminish the population viability of a species.
Sources:
http://www.eoearth.org/view/article/51cbedc57896bb431f693ccb/
http://encyclopedia2.thefreedictionary.com/Population+viability
Picture:
http://www.eoearth.org/files/116501_116600/116545/250px-Yellowstone_Grizzly_Bear_PVA.jpg