is no inherent reason why fecundity should be restricted to females. Regardless, ecologists have defaulted to using the gender-general term of 'reproductive success' to describe the reproductive output of both males and females. We adhere to these traditions and restrict our definition of fecundity to apply to females only. However, reproductive success is not equivalent to fecundity because the former is a measure of an individual's genetic contribution to subsequent generations. As such, reproductive success can vary among individuals due to the effects of maternal age, fitness of progeny from clutches of different size, and other life-history characteristics. Fecundity is therefore a genetical and developmental trait that evolves within a particular selective framework. The term 'fertility' differs from fecundity in that it describes the actual (or current) reproductive performance of (typically) a female, and it is a generalization of the terms 'maternity', 'birth rate' and 'natality' which refer to the average number of offspring produced by an individual female of a particular age per unit time. 'Net reproductive rate' is defined as the average number of daughters produced by mothers over a lifetime. Fertility varies primarily as a function of environmental stochasti-city and demography, and generally fluctuates temporally and spatially among individuals and populations.
In this article we have chosen to discuss both fecundity and fertility given their obvious connection and importance to the discipline of ecology. Henceforth the usage of each term relates specifically to the developmental and evolutionary (fecundity) or environmental (fertility) contexts shaping these fundamental parameters of population biology.
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