Reproductive effort is defined as that proportion
of the total energy budget of an organism that is.
devoted to reproductive processes. Reproductive effort at a
given age within a species will be selected to maximize
reproductive value at that age. Reproductive effort is not
directly affected by changes in juvenile survivorship,
nor necessarily reduced by an increase in adult survivorship.
Selection for high levels of reproductive effort should
occur when extrinsic adult mortality is high, in environments
with constant juvenile survivorship, and in good
years for juvenile survivorship in a variable environment,
provided that the quality of the year is predictable by
adults. Data necessary to measure reproductive effort
and to understand how selection results in different levels
of effort between individuals and species are discussed.
We make several predictions about the effect of increased
resource availability on reproductive effort. The empirical
bases for testing these predictions are presently inadequate,
and we consider data on energy budgets of organisms
in nature to be essential for such tests. We also conclude
that variance in life table parameters must be known
in detail to understand the selective bases of levels of reproductive
effort.