Dissecting components of population‐level variation in seed production and the evolution of masting behavior

Abstract

Dissecting components of population-level variation in seed production and the evolution of masting behavior. -Oikos 102: 581-591.Mast-fruiting or masting behavior is the cumulative result of the reproductive patterns of individuals within a population and thus involves components of individual variability, between-individual synchrony, and endogenous cycles of temporal autocorrelation. Extending prior work by Herrera, we explore the interrelationships of these components using data on individual seed production in 59 populations of plants from 24 species spanning a large range of annual variability, from species exhibiting strong masting to others with little annual variability in seed production. Estimates of population and individual variability were not biased by sample size or average overall seed production when based on untransformed seed production values, but these values declined as log-transformed seed production increased. Population variability was more strongly correlated with individual variability (r = 0.86) than individual synchrony (r = 0.73). These latter two components were also significantly correlated (r =0.45), but randomizations confirm that they need not covary closely. Thus, selection can act separately on inter-annual variability and between-individual synchrony. We illustrate the potential for such fine-tuned selection on seed production patterns by discussing several examples and by demonstrating significant differences in components of population-level variation in seed production among species related to their life-history.

Acorn production in Spanish holm oak woodlands

“…The great variability reported by all authors (Martín et al, 1998;Álvarez et al, 2002;Carbonero et al, 2002;Torres et al, 2004), both between individuals and within individuals between years, is common to most other woody species (Herrera et al, 1998;Koenig and Knops, 2000). From the previously discussed, we might expect the holm oak (as a wind pollinated species) to exhibit a high individual variability, with high population seed production synchrony, that would result in masting (Kelly and Sork, 2002;Koenig et al, 2003). We might also expect an effect of weather and soil nutrient availability, with more pronounced masting in less productive habitats (Kelly and Sork, 2002).…”

“…Therefore, the full fruit cycle spans two years: from the spring prior to flowering, when the staminate and pistillate floral buds are initiated, to the autumn of the year when flowers bloom (Abrahamson and Layne, 2003). The time required for the acorn to develop is important because whether flowers mature in 1 or more years influences the acorn production pattern and its relationship to climate Koenig et al, 2003). Detailed information on the reproductive morphology of the genus can be found in Kaul (1985).…”

“…Mast seeding of woody species is a complex phenomenon that has not yet been perfectly understood (e.g. Herrera et al, 1988;Kelly and Sork, 2002;Rees et al, 2002;Koenig et al, 2003). Two main explanations have been proposed: i) mast seeding is a direct response to environmental variability («resource matching»); ii) it is an evolved reproductive strategy, related to some economy of scale such as wind pollination or predator satiation.…”

The ecology of restoration: historical links, emerging issues and unexplored realms

“…First, it is well known that a number of species exhibit considerable interannual variation in seed production, and an ongoing goal of ecological research is to explain mast years of high production (c.f. Piovesan & Adams 2001;Abrahamson & Layne 2003;Kerkhoff & Ballantyne 2003;Koenig et al 2003). Of even greater interest to restoration, however, especially when seed must be gathered from natural populations, are years of total reproductive failure, compared with ÔnormalÕ years of merely low reproductive output (Hobbs & Young 2001).…”

Masting promotes individual‐ and population‐level reproduction by increasing pollination efficiency

“…Nonetheless, there may be other dynamics that constrain synchrony. In monoecious species (e.g., oaks and many conifers), where pollen and ovules are produced by different structures (Koenig et al 2003), relative allocation to male and female functions at the individual level might be influenced by trade-offs between the sexes (i.e., sex allocation constraints; Charnov 1982, Campbell 2000, Parachnowitsch and Elle 2004. Such constraints may influence sex ratios at both the individual and population level, which could in turn determine the degree of pollen limitation (e.g., Freeman et al 1980).…”