All individuals experience environmental variation in one or the other way, either in abiotic or biotic conditions. Such environmental variation has a strong impact on the fitness of individuals and thus strongly influences the evolution of life-histories strategies. I am particularly interested in two major sources of environmental variation: the predictable variation in size within populations (see cannibalism and stage structure), and environmental uncertainty with focus on largely abiotic factors such as desiccation and climatic changes. The latter research focuses in particular on the selection pressure in such environments and how individuals use different strategy such as phenotypic plasticity of bet-hedging to cope with such uncertainty. Much of my past and present work uses empirical work (mostly in amphibian systems) and theoretical models to create a predictive framework for understanding how environmental variation shapes the evolution of life-history strategies.

The optimal timing of metamorphosis

Most organisms undergo some sort of metamorphosis during their life. This may either be a complete metamorphosis such as in amphibians and many insects, or maturity, or it might be a distinct chance in habitat use. In all cases the timing at which this shift occurs has significant consequences for an individuals fitness, and is thus under strong selection pressure. Using daily monitoring transects, laboratory experiments and a conceptual model we examined how different forms of environmental variation affect the reaction norms of age and size at metamorphosis. Results suggest that time constraints such as those imposed by desiccation and their predictability can result in three major types relationships of age and size at metamorphosis, ranging from a positive correlation, to no correlation, or a negative correlation between both traits. (Rudolf & Rödel 2006)

Iteroparity, delayed maturity and skipping of reproduction

There are a variety of strategies to deal with environmental uncertainty, including iteroparity, delaying maturity and potentially skipping reproduction. While previous have focused on those factors in isolation, most organisms show multiple strategies. Together with Henry Wilbur and Don Church, we use empirical data on different salamander species and mathematical models to examine how environmental variation affects the evolution of these different life-history strategies when they are present together, and how the evolution is affected by physiological trade-offs. Recent results show that environmental variation can select for both iteroparity and delayed maturity simultaneously, but the optimal strategy is strongly dependent on the presence of density-dependent processes and which life-history parameters are affected by trade-offs (Wilbur and Rudolf 2006). Current research focuses on the evolution of skipping reproduction in the face of environmental variation.

Relevant publications:

Wilbur, H.M. and Rudolf, V. H. W. 2006. Life History Evolution in uncertain environment: Bet-hedging in time. American Naturalist.

Rudolf, V. H. W. and Rödel 2006. Phenotypic plasticity and optimal timing of metamorphosis under uncertain time constraints. Evolutionary Ecology.