Henderson's Dictionary of Biological Terms, by Eleanor Lawrence. 10th Ed.
Evolutionary Ecology, by Eric R. Pianka, 3rd Ed.
Population growth is due to two factors, importation of individuals from nearby populations, and reproduction. In this section, I will discuss reproductive strategies that affect population growth.
Generally speaking, species my utilize one of two reproductive strategies, high fecundity at young ages, or delaying reproduction, and having high fecundity at older ages. These strategies re referred to as r-selection and K-selection respectively. Species, such as weeds, undergo r-selection. They are reproductively mature at young ages, and they produce large numbers of offspring. But these species tend to die young, within 1 to 2 yrs. Species, like elephants, undergo K-selection. They are reproductively mature much later in life, and they produce only a few offspring. Such species also care for their young, protecting them against predators and other dangers in the environment. Species utilizing K-selection tend to live longer.