Contributions of economies of scale in pollination efficiency and predispersal predation to seed viability effects of masting

Abstract

Economies of scale (EoS), reduced individual costs when plant populations produce large numbers of seeds, are considered a central adaptive benefit of masting, the spatial synchronization of interannual variation in seed production. Throughout the development of seeds in wind-pollinated trees, multiple EoS mechanisms such as increased pollination efficiency and reduced predation rates have been identified. It is unclear, however, whether the same EoS mechanisms apply to co-occurring species and how sequential mechanisms interact to determine seed fate. Here, we use a long-term data set of seed production of beech (Fagus sylvatica), Norway spruce (Picea abies), and silver fir (Abies alba) in a primeval montane forest to investigate the relationship between seed production, pollination efficiency, and predispersal predation by insects. Our results show that the three species differed in presence and extent of EoS mechanisms. In silver fir, only pollination efficiency increased exponentially with seed density, while in Norway spruce only the rate of insect predation decreased with crop size. In beech, both EoS mechanisms had dramatic effects on seed quality and, importantly, our results suggest that pollination efficiency mediated the extent of predispersal predation. Furthermore, we found that both pollination and predation rates only increase strongly in the lower range of seed production, and that predation rates also depend on the extent of seed production the previous year. These findings illustrate that economy-of-scale effects are not universal and that multiple mechanisms in sequence can interact to shape seed fate.

Positive spatial and temporal density‐dependence drive early reproductive economy‐of‐scale effects of masting in a European old‐growth forest community

“…Seed production was monitored since 2003 on two 1-ha study plots (Mayer-Wegelin plot "MW", and Josef plot "JO") each equipped with 81 seed traps of 0.24 m 2 area, arranged in a geostatistical design (Gratzer et al, 2022;Pesendorfer et al, 2024). Starting in 2008, seeds collected in traps were sorted into "sound", "hollow" and "infested by insects", as evidenced by chewing marks and exit holes.…”