Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In biology and demography, fecundity is the potential reproductive capacity of an organism or population, measured by the number of gametes (eggs), seed set or asexual propagules. Fecundity is under both genetic and environmental control, and is the major measure of fitness. Fecundation is another term for fertilisation.
Fecundity is important and well studied in the field of population ecology. Fecundity can increase or decrease in a population according to current conditions and certain regulating factors. For instance, in times of hardship for a population such as a lack of food, juvenile and eventually adult fecundity has been shown to decrease.
Fecundity has also been shown to increase in ungulates with relation to warmer weather.