The influence of life‐history strategy on ecosystem sensitivity to resource fluctuations

Abstract

To cope with uncertainty and variability in their environment, plants evolve distinct life‐history strategies by allocating different fractions of energy to growth, survival and fecundity. These differences in life‐history strategies could potentially influence ecosystem‐level dynamics, such as the sensitivity of primary production to resource fluctuations. However, linkages between evolutionary and ecosystem dynamics are not well understood. We used an annual plant population model to ask, when might differences in plant life‐history strategies produce differences in the sensitivity of primary production to resource fluctuations? Consistent with existing theory, we found that a highly variable and unpredictable environment led to the evolution of a conservative strategy characterized by relatively low and invariant germination fractions, while a variable but predictable environment favoured a riskier strategy featuring more variable germination fractions. Unexpectedly, we found that the influence of life‐history strategy on the sensitivity of production to resource fluctuations depended on competitive interactions, specifically the rate at which production saturates with the number of competing individuals. Rapid saturation overwhelms the influence of life‐history strategy, but when production saturates more slowly, the risky strategy translated to high sensitivity, whereas the conservative strategy translated to low sensitivity. Empirical estimates from Sonoran Desert annual plant populations indicate that production saturates relatively rapidly with the number of individuals for most species, suggesting that life‐history differences are unlikely to alter sensitivity of production to resource fluctuations, at least in this community. Synthesis. Our modelling results imply that research to understand the sensitivity of primary production to resource fluctuations should focus more on the intraspecific competitive interactions shaping the density–yield relationship than on the life‐history strategies that determine temporal risk‐spreading.