Population and individual level of masting in a fleshy-fruited tree

Abstract

Masting is usually considered as a population phenomenon but it results from individuals' reproductive patterns. Studies of individual patterns of seed production and their synchrony are essential to an understanding of the mechanisms of masting. The aim of this study was to find the relationship between population and individual levels of masting. We examined individuals' contribution to masting, considering their endogenous cycles, interannual variability and associated weather cues, as well as interindividual synchrony of fruit production. We studied masting of Sorbus aucuparia L., which in Europe is one of the most common trees bearing fleshy fruits and is strongly affected by a specialized seed predator. The data are 11-year measurements of fruit production of 250 individuals distributed on a 27-ha area of subalpine forest in the Western Carpathians (Poland). Population-and individual-level interannual variability of fruit production was moderate. Synchrony among individuals was relatively high for all years, but the trees were much less synchronized in heavy crop years than in years of low fruit production. Weak synchrony among trees for heavy production years suggests that the predator satiation hypothesis does not explain the observed masting behavior. Fruit production, both at individual and at population level, was highly correlated with weather conditions. However, the presence of masting cannot be fully explained by the resource-matching hypothesis either. We suggest that adverse weather conditions effectively limit fruit production, causing high inter-individual synchrony in low crop years, whereas the unsynchronized heavy crop years seem to have been affected by individually available resources.

Reproductive success of individuals with different fruit production patterns. What does it mean for the predator satiation hypothesis?

“…Such extremely high levels of masting in response to extended diapause were found in Chinochloa (CV p range: 1.42–3.02; Kelly et al 2000). In our population, the variation of seed crops was not very high (CV p  = 1.07; Żywiec et al 2012), and it did not sufficiently reduce the A. conjugella population. For example, the relatively heavy crop year of 2005 followed five low crop years, and in that year, a 10-fold increase in fruit production was accompanied by nearly 40 % fruit infestation.…”

“…Fruit infestation was high even in some relatively heavy crop years. Seed loss in the population was probably considerable, not only for the seven studied years but also for the 12-year period of 2000–2011, as in the 5 years preceding the study of pre-dispersal seed predation (2000–2004), fruit production was low and without a year which could satiate predators (Żywiec et al 2012). Seed predator pressure on the population is apparently very high.…”

“…Five infructescences were randomly taken from each tree and all the fruits in them were counted. The fruit production of an individual tree was estimated as the product of the number of infructescences and the average number of fruits in five infructescences (see Żywiec et al 2012). Annual fruit production at population level was measured as mean fruit production per hectare.…”

“…Moreover, endogenous cycles of individual fruit production were not found. In consequence, rowan trees represent a range of fruit production patterns (Żywiec et al 2012). In this study, we determined the level of fruit infestation by A. conjugella and tested whether there are functional and numerical responses of predators to the variation of fruit production at the population level.…”

Interannual variation in tree seed production in a primeval temperate forest: does masting prevail?

“…As masting is the result of reproductive ''decisions'' of individual trees in a local population, one has to study patterns of seed production and their synchrony at the individual level as well Koenig et al 2003;Herrera et al 1998;_ Zywiec et al 2012) in order to have a mechanistic understanding. Therefore, we also tracked performance of individual trees across years and analysed patterns of variation in their reproductive output among years.…”