HOW TO KEEP FIT IN THE REAL-WORLD - ELASTICITY ANALYSES AND SELECTIONPRESSURES ON LIFE-HISTORIES LN A VARIABLE ENVIRONMENT

Most life-history theory assumes the environment is invariant. For the first time, analytical and numerical techniques were employed to inve stigate the impact of environmental variability on selection pressures (elasticities = proportional sensitivities) on a range of life histor ies. We find that the impact of variability is influenced significantl y by the amount of variability an organism experiences (more variabili ty affects selection pressures more), the correlations between variati ons among the vital rates (negative correlations are more likely to re lax selection on fecundities and increase it on survival rates), and t he life history in question (shorter life histories are more affected) . In addition, the impact of a variable environment on the elasticitie s of life histories is sensitive to the sampling distribution used to generate the variability, and it is particularly sensitive to extreme values, such as those caused by occasional catastrophic events. The el asticities of life histories in highly variable environments may bear little relationship to those in a constant environment. In detailed op timality or evolutionarily stable strategy (ESS) modeling, variability in vital rates as small as a standard deviation being 10%-15% of the mean may appreciably alter the conclusions. Thus, it may be very impor tant to consider the possible impact of environmental stochasticity an d not to assume that it has no effect.