Reproductive effort in variable environments, or environmental variation is for the birds

We analyze a model of life history evolution in which there is a temporally variable cost of reproduction. Analysis of the stochastic growth rate indicates that the optimal clutch size in a variable environment can be substantially increased or decreased relative to the optimal clutch size in a constant environment. This finding holds regardless of whether the cost of reproduction varies discretely or continuously. Our results also illustrate how two distinct optimal life histories can evolve in response to a given amount of environmental variability. One life history pays a cost of reproduction that is relatively fixed and small on average (by producing a small fixed clutch size); it can always produce an optimal clutch size but is unable to exploit highly favorable environments. The other pays a cost of reproduction that is variable and large on average (by producing a large fixed clutch size); it cannot always produce an optimal clutch size but is able to exploit highly favorable environments.