COS 26-3: No growth/reproduction tradeoff in California oaks
Johannes (Jean) M. H. Knops, University of Nebraska, Walter D. Koenig, University of California, Berkeley, and William J. Carmen, Hastings NHR.
Tradeoffs between growth and reproduction are widely assumed and considered the fundamental paradigm for the understanding of life-history evolution. There are, however, relatively few studies unambiguously demonstrating such tradeoffs in plants, and tradeoffs have often been inferred from correlational studies. It is thus critical to determine the extent to which negative correlations between growth and reproduction reflect real tradeoffs rather than being incidental to other confounding factors. This is particularly true in perennial plants where a long lifespan makes manipulations difficult and where the expected tradeoff within years may be obscured for a variety of reasons, including that resources allocated to reproduction may be relatively small, seed production may be constrained by pollination, reproductive structures can supply a large part of the resources required, photosynthetic rates increase if the demand for carbon increases, and predator satiation might be driving annual variability in reproduction. Here we report a unique contrast among five California oak species demonstrating that the inverse correlation between growth and reproduction observed in three of the species is not causal, but rather a consequence of reproduction and growth depending in opposite ways on correlated weather conditions. These results indicate that growth and reproduction may be independent of each other, even when inverse correlations between these key life-history factors are observed. Thus, life-history evolution of reproduction and growth within these long lived plants are apparently independent of each other.