Prolonged diapause of specialist seed-feeders makes predator satiation unstable in masting of Quercus crispula

Abstract

Quercus crispula (= Q. mongolica var. grosseserrata) is the predominant tree species in cool temperate, mixed broadleaf/conifer forests in northern Japan. We compared 11 years of data on acorn production in a population of Q. crispula, with data on seed-insect populations, to try to answer the following questions: (1) Does Q. crispula show a regular pattern of masting? (2) How long do principal seed predators remain in diapause? (3) How do the seed predators affect the pattern of predator satiation? Q. crispula showed a tendency to alternate bearing, with significant synchrony between individual trees. The principal acorn-feeding insects ( Curculio spp. weevils), which infested 25%-70% of matured acorns, generally exhibited a prolonged diapause of 2 years. No significant negative relationship was found between the rate of injury by the weevils and the density of mature acorns, indicating that simple predator satiation fails due to the synchrony of the life-cycle of acorn-feeding insects and the periodical production of acorns. However, the rate of injury by the weevils was negatively correlated with the relative abundance of mature acorns to the number of weevil larvae that had matured 2 years previously. Thus, the proportion of sound acorns notably increased in a rich crop after a disturbance in alternate bearing. Prolonged diapause of specific seed predators is critical in determining the peak year of sound-seed production.

Advantages of masting in European beech: timing of granivore satiation and benefits of seed caching support the predator dispersal hypothesis

“…Simultaneous consideration of the two hypotheses provides a useful framework as it focuses attention on costs and benefits of masting that apply to interactions with different types of animals. For example, masting may both satiate invertebrate seed predators (Crawley and Long 1995;Maeto and Ozaki 2003;Espelta et al 2008) and ensure that some seeds are cached and left uneaten by rodents. From this perspective, these two hypotheses do not need to be treated as alternatives.…”

Acorn production in Spanish holm oak woodlands

“…The negative effect of insects can be very intense some years, with reductions in acorn yield up to 50% (Espárrago et al, 1993;Soria et al, 1996, Cañellas et al, submitted), however these figures are likely to increase some years attending to results in other European oak species (Crawley and Long, 1992). Some authors report an adjustment of some insect life-cycles to two or more year patterns, suggesting that insects would synchronize their diapause to fruit masting (Maeto and Ozaki, 2003). The exudation of sap in acorns, a phenomenon called «drippy nut disease» («melazo») possibly caused transmission of pathogens by insects, is another common source of acorn losses.…”

The effect of climate on masting in the European larch and on its specific seed predators

“…When several masting species are compared, cone production is more variable in plant species with specific seed predators able to endure prolonged diapause . The prolonged diapause of specific predators was shown to decrease the effectiveness of predator satiation in one species of oak (Quercus crispula) (Maeto and Ozaki 2003). Furthermore, the ability of seed predators to anticipate a year of masting through increasing reproduction the year before has been shown in tree squirrels (Boutin et al 2006), therefore allowing a fine adjustment of predator population size to the level of resources available in a given year.…”