DOES ENVIRONMENTAL STOCHASTICITY MATTER - ANALYSIS OF RED DEER LIFE-HISTORIES ON RUM

Most life-history theory assumes that short-term variation in an organ ism's environment does not affect the survivorships and fecundities of the organisms. This assumption is rarely met. Here we investigate the population and evolutionary biology of red deer, Cervus elephas, to s ee if relaxation of this assumption is likely to make significant diff erences to the predicted evolutionary biology of this species. To do t his we used 21 years of data from a population of deer on Rum, Western Isles, Scotland. Population growth rates in a stochastic environment were estimated using Tuljapurkar's small noise approximation, confirme d by bootstrap simulation. Numerical differentiation was used to see i f the selection pressures (i.e, sensitivities of population growth rat e to changes in the vital rates) differ between the stochastic and det erministic cases. The data also allow the costs of reproduction to be estimated. These costs, incorporated as trade-offs into the sensitivit y analysis, allow investigation of evolutionary benefits of different life-history tactics. Environmentally induced stochastic variation in the red deer vital rates causes a slight reduction (similar or equal t o 1%) in the predicted population growth rate and has little impact on the estimated selection pressures on the deer's life-history. We thus conclude that, even though density-independent stochastic effects on the population are marked, the deer's fitness is not markedly affected by these and they are adapted to the average conditions they experien ce. However, the selected life-history is sensitive to the trade-offs between current fecundity, survivorship and future fecundity and it is likely that the environmental variance will affect these trade-offs a nd, thus, affect the life-history favoured by selection. We also show that the current average life-history is non-optimal and suggest this is a result of selection pressures exerted by culling and predation, n ow much reduced. As the use of stochastic or deterministic methods pro vide similar estimates in this case, the use of the latter is justifie d. Thus, r (the annual per capita rate of population growth) is an app ropriate measure of fitness in a population with stochastic numerical fluctuations. In a population of constant size lifetime reproductive s uccess is the obvious measure of fitness to use.